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Conservation of Historic Buildings

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Conservation of Historic Buildings

Frontispiece Ospizio di San Michele, Rome, Italy, before conservation

This state of affairs was due to lack of maintenance resulting from planningblight. The rainwater outlets were allowed to become blocked, so the guttersoverflowed causing rot in the ends of the main beams which in due coursecollapsed taking the roof structure with them

Conservationof Historic Buildings

Third edition

Bernard M. FeildenKt, CBE, D Univ, D Litt, FSA, FRSA, AA Dipl(Hons), FRIBA

Director Emeritus, International Centre for the Study of the Preservation and the Restoration of Cultural Property (ICCROM), Rome

Architectural PressAMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORDPARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO

Architectural PressAn imprint of ElsevierLinacre House, Jordan Hill, Oxford OX2 8DP200 Wheeler Road, Burlington, MA 01803

First published 1982Revised paperback edition 1994Third edition 2003

Copyright © Elsevier 1994, 2003. All rights reserved

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British Library Cataloguing in Publication DataFeilden, Bernard M.

Conservation of Historic Buildings. –New edI. Title363.69

ISBN 0 7506 5863 0

Typeset by Newgen Imaging Systems (P) Ltd., Chennai, IndiaPrinted in Great Britain

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Contents

Preface to third edition vii

Acknowledgements xiii

1 Introduction to architectural conservation 1

Part I Structural Aspects of Historic Buildings

2 Structural actions of historic buildings 25

3 Structural elements I: Beams, arches, vaults and domes 37

4 Structural elements II: Trusses and frames 51

5 Structural elements III: Walls, piers and columns 61

6 Structural elements IV: Foundations 79

Part II Causes of Decay in Materials and Structure

7 Climatic causes of decay 93

8 Historic buildings in seismic zones 119

9 Botanical, biological and microbiological causes of decay 133

10 Insects and other pests as causes of decay 139

11 Man-made causes of decay 157

12 Internal environment of historic buildings 173

Part III The Work of the Conservation Architect

13 Multi-disciplinary collaboration projects in the UK 189

14 Inspections and reports 203

15 Research, analysis and recording 221

16 Preventive maintenance of historic buildings 235

17 Fire 251

18 Presentation of historic buildings 261

19 Cost control of conservation projects 273

20 Rehabilitation of historic buildings 277

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Contents

vi

21 Special techniques of repair and structural consolidation 295

22 Conservation of modern buildings 327

Appendix I Historic buildings as structures by R.J. Mainstone 337

Appendix II Security in historic buildings 347

Appendix III Non-destructive survey techniques 353

Appendix IV Manifesto for the Society for the Protection of Ancient Buildings 359

Appendix V ICOMOS Charters 361

Bibliography 369

Index to buildings, persons and places 381

Subject index 383

‘It is important to understand why we are drawnto a good building of any age. First there is theintellectual achievement of creating an artefactof beauty and interest. Second, the humanachievement perceived by later generations inthe care of the craftsmen in its construction.This care can also be visible in later repairs andalterations. Thirdly, we are drawn by the senseof place created both by the designers andmany humans who have lived and worked inthe building.’

Alan Baxter—Journal of ArchitecturalConservation, no. 2, July 2001

Basically, all conservation consists of actions takento prevent decay, and within this objective it alsoincludes management of change and presentationof the object so that the objects’ messages are madecomprehensible without distortion. Architecturalconservation is more complex; first because abuilding must continue to stand up; secondly, eco-nomic factors usually dictate that it should remainin use; thirdly, it has to resist and use the effects ofclimate; and, lastly, a whole team of ‘professionals’have to collaborate. A professional can be definedas a person who contributes artistically, intellectu-ally or practically to a project. The principal profes-sions involved in architectural conservation arearchitects, archaeologists, building economists,structural, mechanical and electrical engineers, arthistorians, materials scientists, crafts persons foreach material, building contractors, surveyors, andtown planners. It should not be forgotten that thebuilding owner or his representative is also animportant collaborator. This list is incomplete,because a project may need other specialists in theteam such as biologists, geologists, hydrologists,seismologists and even vulcanologists. How doesone achieve aesthetic harmony with such a com-plex and disparate group of professionals?

The building conservation team should observecertain ethics:

1. the condition of the building must be fullyrecorded before any intervention is begun;

2. the materials and methods used during treatmentmust be documented;

3. historic evidence must not be destroyed, falsifiedor removed;

4. any intervention must be the minimum necessary.It should be reversible—or at least repeatable,and not prejudice possible future interventions;

5. any intervention must be governed by unswerv-ing respect for the aesthetic, historical and phys-ical integrity of cultural property.

These are stringent guidelines. Interventions mustnot hinder later access to all the evidence incorpo-rated in the building, and allow the maximumamount of existing material to be retained. Theymust also be harmonious in colour, tone and tex-ture, and if additions are needed, they should relatein form and scale, and also be less noticeable thanthe original material; but, at the same time, beingidentifiable by a skilled observer. Persons who haveinsufficient training or experience should notundertake the work. Some problems are, however,unique; and in this case, the conservation architectshould ask for a second opinion. He also has theright to ask for scientific advice. Due to the irre-placeable nature of cultural property, a conservationarchitect has a heavy load of responsibility. The doc-trine of conservation has been encapsulated by theInternational Council on Monuments and Sites(ICOMOS), in four Charters:

• The Venice Charter (1964) on the basis of allmodern conservation

• The Florence Charter (1981) on gardens andlandscapes

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Preface to third edition

• Charter for the Conservation of Historic Towns1987

• The International Charter for ArchaeologicalHeritage Management 1990

Mention should also be made of the Australia ICO-MOS Burra Charter—for Places of CulturalSignificance (revised 1999).

The first statement of principle, however, was con-tained in William Morris’ 1877 ‘Manifesto for theSociety for the Protection of Ancient Buildings’ (SPAB)(see Appendix IV), and this has been, and is still, mostinfluential in England. Architectural conservationdepends on a thorough study of the building as itstands, followed by any further analytical studiesdeemed necessary, in order to make a correct diag-nosis of the structural actions of the said building,and the causes of its decay. In this way, it is ratherlike the practice of medicine. It is then necessary toconsider alternative lines of action. With a multi-disciplinary team, it is difficult to obtain agreement,as each professional has different objectives, andoften his training has enclosed an expert’s mindwith too much specialization. A structural engineerconcentrates on stability and safety; an archaeologistconcentrates on retention of original material; an art historian is a specialist critic who is trained toobserve and interpret what is there, but is oftenunable to visualize alternatives to the status quo.Other members of the team may also have an undisclosed agenda, that of their particular profession.

The first step is to define the objective of a con-servation project. The next is to identify the ‘values’in the object, monument or site that is the culturalproperty in question, and to place these values inorder of priority. In this way, the essential messagesof the object will be respected and preserved. Thevalues can be classified under three main headings:‘emotional’, ‘cultural’ and ‘use’ values.

Emotional values• Wonder• Identity• Continuity• Respect and veneration• Symbolic and spiritual

Cultural values• Documentary• Historic• Archaeological and age• Aesthetic and architectural values• Townscape• Landscape and ecological• Technological and scientific

Use values• Functional• Economic (including tourism)• Social (also including identity and continuity)• Educational• Political

These values have to be analysed, and then synthesized in order to define the ‘significance’ ofthe historic artefact. Some of these values deserveamplification.

Symbolic and spiritual feelings depend on cul-tural awareness. In the West we have largely lost anunderstanding of symbolic decoration, and also thecontent of classical allusions in painting, nowunderstood mainly by art historians. Certain archi-tectural forms do, nevertheless, have a spiritualmessage—different forms for different cultures andreligions, and even in supreme cases, such as HagiaSophia in Istanbul, which has served as a church, amosque, and now a museum, a universal message.

Spiritual values can come from evidence of pastpiety, and from the present statement of the monu-ment and its site, such as a spire reaching toheaven, or an ancient temple set on a promontoryagainst the sea, each giving a message of some striv-ing with the infinite. When tourists enter a greatbuilding, one sees the hard lines on their faces relax,as the spiritual value of the place enters into theirsouls. It may be difficult to differentiate between thevarious emotional values, but they can be taken col-lectively and graded from the weak to the verystrong. Cultural values include aesthetic, art histori-cal, documentary, archaeological, architectural, tech-nological, scientific, landscape and urbanological,and are appreciated by educated persons, anddefined by specialists and scholars. There can, there-fore, be much debate about their relative order ofimportance in a specific case. It may be difficult toreach agreement on their order of precedence, yetthis is vital if any proposed intervention is to be exe-cuted successfully. Academics are not trained tocompromise, whereas professionals who work in thecontext of achieving acceptable solutions are moreused to compromising on non-essentials.

Aesthetic values vary with culture and fashion, yetgradually a consensus prevails. These values areestablished by the critical methods of art historians,and there is a time lag before the general public canaccept a revised view. Fifty years ago a changebegan, and now things Victorian or nineteenth cen-tury are enjoyed aesthetically. The graph of aestheticappreciation is generally lowest about thirty yearsafter a work of art was produced, and rises thereafter.

Artistic values are subjective. The more recent thework, the more subjective is the valuation. After the

Preface to third edition

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enthusiasm often generated artificially by the mediaat the birth of a new building, generally its artisticvalue is considered to decline rapidly in the nextgeneration, then, waiting to be rediscovered by anart historian, its values begin to be appreciated byspecialists, who will crusade for its recognition,which might reach official status after three genera-tions—that is, if it survives. Art objects may well sur-vive, but buildings are subject to all sorts of threatsin this process. First they must be able to stand up,then they are expected to be useable, whether agreat work or not. They may have been adapted twoor three times in the process of survival—each adap-tation potentially reducing its artistic value, althoughthe value may have been improved in some cases.

As suggested, artistic values change from genera-tion to generation. The forgeries of Vermeer’s workcreated by Van Meegeren deceived the experts,because they had all the attributes that the expertsassociated with Vermeer. A generation later, when wesee things differently, and scientific tests are moresophisticated, these forgeries do not seem too diffi-cult to detect. The older the work of art, however, themore consistent are the expert’s opinions as to its sig-nificance and artistic value. Ironically, art historiansfind it difficult to accept that ultimately, a work ofconservation must also be a work of art.

Architectural values are related to the participants’movement through spaces, to his sensations, whichare not purely visual in these spaces, to his interestin decorative plastic and sculptural treatment of sig-nificant forms and spaces. This, together with hispleasure in the colour and texture of the material,also in his appreciation of harmony, scale, propor-tion and rhythms, given by the elements of designwith their underlying geometry, contribute to thevalues. Because all the participants’ senses areinvolved, a building that functions badly has lowarchitectural value, although it may claim some aes-thetic or fashion value for a short time. In conserva-tion, in order to preserve architectural values,retention or reproduction of the design is important.

Architectural values were defined by Sir HenryWooten as ‘commodity, firmness and delight’.Delight covered the artistic element in architecture,such as the relationship of the building to the site,the massing and silhouette, the proportions of theelements as a whole, the size of the elements relat-ing to human dimensions, the appropriateness ofmaterials and decoration, and the significance of thebuilding in the hierarchy of its city’s or country’s her-itage. In buildings of the highest level in the civil orreligious hierarchy, sculptural values are also dis-played. In extreme cases, such as the Pyramids, thisexists as pure monumental sculpture. In certain peri-ods of great architecture, sculpture and architecture

have been integrated as, for example, in theParthenon in Greece, at the Sun Temple at Konarak inIndia, and Chartres Cathedral in France. Firmnessrelates to the building’s structure, which must resistthe loads imposed by various categories of use, aswell as wind, snow, earthquakes—in seismic zones,and its own weight. The foundations, resting on soilsand rocks of many different characteristics, carry thesecombined loads. Great engineering structures have anundeniable beauty. Firmness includes durability.

Commodity relates to the usefulness of the build-ing. If it cannot be used beneficially and becomesobsolete, it is subject to economic threats. It hasbeen found, however, that historic buildings areflexible in meeting a wide range of uses, if minorchanges can be accommodated. Refurbishing orrehabilitating domestic buildings in a city is gener-ally a better plan than demolition and rebuilding.

The supreme architectural values are, however,spatial and environmental. It is by walking throughan architectural ensemble that one senses its quality,using eyes, nose, ears and touch. Only by visiting abuilding or ensemble can one appreciate its true aes-thetic value. Townscape is an important element inurban conservation. Townscape values depend uponensembles of buildings, the spaces they stand in,with treatment of surface paving, roads and publicspaces. Often an unrelated clutter of wiring, lampstandards, telephone kiosks, transformers and adver-tisements spoil the townscape. Townscape alsoincludes views from significant reference points andvistas. Interest in townscape is found by walkingaround admiring fine buildings, going down narrowstreets into open spaces, which may have dramaticfeatures such as the Spanish Steps in Rome.

The urban setting of monuments is also vital totheir appreciation, as such buildings were designedfor their specific site, be it a street, a square or amarket place. Modern alterations can have a nega-tive effect, as instanced by the opening up of thewide avenue from the Tiber to the facade of SaintPeter’s in Rome. Analysis of the quality of a townincludes the compression and opening of space,formal spaces, surprises, drama and set pieces ofarchitecture. Often urban spaces interpenetrate in asubtle way the rich texture of historic cities. Thiscomes from their piecemeal renewal in which eachaddition has been carefully contrived, with anunderlying unity given by local materials and tradi-tional building technology, combining to give anenvironment with a human scale.

Functional and economic values are importantwhen considering rehabilitation or refurbishment of buildings, especially for modern structures. In this field, building surveyors can make a majorcontribution.

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Social values are largely covered by emotionalvalues, but are also related to the sense of belong-ing to a place and a group. Educational values areeasily recognized by the study of history, especiallyeconomic and social history, as historic buildingsprovide much of the evidence. One of the primemotivations in architectural conservation is to pro-vide educational opportunities.

Political values are not so difficult to define. His-torical buildings and archaeological sites can be usedto establish the history of a nation in people’s minds.This is quite important for relatively new nations,and accounts for many grandiose projects. Perhapsthe most important and rewarding scheme inspiredmainly by political motives was the re-building ofthe ruins of Warsaw, to help re-establish both thecultural and political identity of Poland after the ter-rible destruction of World War II. There are, indeed,political values in conservation; a minister can gaingreat publicity by some large restoration programme.

Unfortunately the thousands of minor acts thatconstitute a programme of preventative maintenancedo not win the same political mileage as one majoract, which often has disruptive side effects, disor-ganizing the labour force and diverting money frompreviously planned works. Due to the political pres-sures applied by religious and ethnic groups, con-servation work is often distorted, and such groupsoften wish to rewrite history by seeking to restoretoo much. Viollet-le-Duc succumbed to the politicalpressure of the Emperior Napoleon III in France,when he made his stylistic restoration of Pierrefondsnear Paris. Nations that have established themselvesrather recently are prone to use historic sites as anelement of their political programmes, in order toconfirm their identity.

I have dealt with some of the values in a culturalobject or historic building, because the success ofinterdisciplinary work depends upon recognizingthose values, in order to understand the signifi-cance of the historic resource.

Procedure for using value analysis

It is essential that consideration of the values in cul-tural property should be assessed as objectively aspossible and fairly. There is always a danger that theconservation programme will only reflect the bureau-cratic objectives of the department of Governmentthat is responsible. There is an old Zen saying, ‘Themadman runs to the east, his keeper runs to the east;they’re both running to the east, but their purposesdiffer!’ It is wise, therefore, to insist that an interdis-ciplinary, inter-departmental working group, whichincludes people genuinely interested in all values in

cultural property, establishes the goals and objectivesof the conservation programme. Their task is to rec-oncile their purposes, as well as the direction of theirmovement. As long as debate is fruitful and con-structive, it is valuable. I have found it best to get theconservation team to choose the ‘least bad’ alterna-tive, after having examined the practical possibilities.

An architect’s training focuses on design. His aimis to produce a well-designed building withinagreed cost, and at an agreed time. This is not easy,as these three objectives contain contradictions.Good design in fact, needs time and costs money,but good design is obtained by a consistency ofstyle from the concept down to the small details.The aim is to produce significant forms and spaceswith appropriate details and ornament. The archi-tect is trained to visualize solutions to complexproblems, and he thinks with his sketches. Being adesigner, he is sensitive to the design element inhistoric buildings, although these may have beenbuilt in widely different styles. Good design findssimple solutions to problems. As a conservationarchitect, I try to let each building in my care speakto me. Sometimes I have almost conversed with theoriginal builders, each of whom built in the style ofhis time. Evaluation of the merit of a building is adifficult task if the building is recent. Time helps toclarify the process as, if it has survived three gen-erations of beneficial use, one can assume it is agood building. As with people, a building’s charac-ter and quality become more discernible as theygrow older. The architect who is a creative designeris like the composer of music. The conservationarchitect is like the conductor of an orchestra; hehas a score that he cannot alter. He has to producea work of art, using the instrumentalists, and hispower of interpretation, based on his understand-ing of the messages in the music. When a conser-vation project is not an artistic success, it must bedeemed to be a failure.

The conservation of our historic buildingsdemands wise management of resources, soundjudgement and aesthetic sensitivity and a clear senseof proportion. Perhaps, above all, it demands thedesire and dedication to ensure that our culturalheritage is preserved. Modern long-term conserva-tion policy must concentrate on fighting the agentsof deterioration. Our industrial economy cannot andshould not be halted, but by combating waste,uncontrolled expansion and exploitation of naturalresources, and by reducing pollution of all types,this contributes to global sustainability, and damageto historic buildings can be minimized. Conservationis, therefore, primarily a process that leads to theprolongation of the life of cultural property for itsutilization now and in the future.

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Kenneth Frampton asks:

‘Have our standards become so exacting thatthey inhibit a more liberal approach to thereconstitution and appropriation of antique form?The world as a whole seems to be increasinglycaught in progressive beaurocratisation ofconservation . . . with architectural purity on oneside of the argument, and crass reconstructivismoperating with impunity on the other; the latterleading to a kind of Disney World that nobodyneeds or desires. Between these two poles, theresurely exists an intelligent sensitively calibrated“middle-ground”.’

Kenneth Frampton – Modernisation and LocalCulture in Architecture and the Islamic World,

Thames & Hudson 2001 Aga Khan Award.

Historic buildings have the qualities of low energyconsumption, loose fit and long life, so the lessonslearned from their study are relevant to modernarchitecture, which should aim at the same qualities.They teach us that buildings work as spatial environ-mental systems, and must be understood as a whole.There is no dichotomy between modern buildingsand historic buildings—they are both used andabused, and have to stand up. It is still not realized,however, how sophisticated traditional building tech-niques were. Since they have failed to understandbuildings as a whole, designers using modern tech-nology have now to relearn many lessons. It is anadvantage to every architect’s practice to have at leastone member of the design team knowledgeableabout the conservation of historic buildings.

‘The demands on those charged with the repairand conservation of our built heritage continueto expand in many and conflicting directions.On the one hand, there is this growing perception that all repair or intervention shouldbe kept to an absolute minimum. On the other,increased expectations of performance, safetyand longevity . . . coupled with cost restraintsand concerns over professional indemnity.’

Robert Demaus

This book is based mainly on my own experi-ence. It surveys the principles of conservation in their application to historic buildings, and pro-vides the basic information needed by architects,engineers and surveyors for the solution of archi-tectural conservation problems in almost every climate. There is a great overlap between the workof a conservation architect and that of a buildingsurveyor. Where I use the term ‘architect’, it can

often be deemed to include a suitably qualified surveyor.

This book is organized into three parts. In Part I,the structural elements of buildings are dealt within detail. Part II focuses on the causes of decay,which are systematically examined from the point ofview of the materials that they affect. Part III dealswith the role of the conservation architect, startingwith surveys, and including the organization of workand control of costs. Some special techniques are alsoreviewed. A new chapter (Chapter 13) on Multi-disciplinary collaboration has been added, in view ofthe importance of this subject, and a further chapter(Chapter 22) giving an introduction to conservationof modern buildings. There is a valuable appendix(Appendix I), by RJ Mainstone, which assesses his-toric buildings as structures. Further appendixes onnon-destructive investigation (Appendix III), as wellas one on security in historic buildings (Appendix II),have been included. The ICOMOS Charters have alsobeen given for ready reference (see Appendix V).

Although I have used the best sources known tome for recipes and specifications of chemical treat-ments, I must advise that these be tested on smallinconspicuous areas before wholesale use. Also, aswe have become more aware of the toxicity of chem-icals, and their effect on flora, fauna, and humanbeings we must be cautious in their application, sincethere may be risks in some of the chemical prepara-tions. Only qualified people should use chemicals.

To sum up, the methodology of conservationapplies to all workers in the field, and is based onvisual inspection, which leads to specific investigationsto the justified depth, before a diagnosis is made. As inmedicine, the needs of the patient must come first, andthe architect should not hesitate to obtain a secondopinion when necessary, and should have the right toreceive scientific support. All practical alternativesshould be explored, and then evaluated in the light oftheory in order to find the ‘least bad’ solution, whichmust respect the qualities in the historic building.

Conservation work is multi-disciplinary, involv-ing many skills that contribute to a balanced solution. The values of an historic building, and the messages contained therein, must be assessedand put in an agreed order of priority, before thearchitect undertakes any project. In executing aconservation project, the architect has a role similarto that of the conductor of an orchestra. The build-ing is his musical score—not a note may be altered;yet the artistic skill in presenting the buildingshould make its architectural music a joy to thebeholder.

Bernard Feilden (25.2.02)

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One difficulty of writing this book has been that Ihave been learning so much all the time from myworking experiences — so my first acknowledge-ment must be to those who have entrusted the conservation of the historic buildings in their careto me; in particular the Deans and Chapters of St.Paul’s Cathedral (London), York Minster, NorwichCathedral, the Minister of St. Giles (Edinburgh) andalso to all the numerous Parochial Church Councilsin the Diocese of Norwich who employed meunder the 1955 Inspection of Churches Measure,the application of which in England laid the foun-dations of an approach to the scientific conserva-tion of historic buildings. My other corporate clientsincluded the University of York, Trinity Hall,Cambridge, Magdalen College, Oxford, the ownersof historic houses and the Department of theEnvironment.

Clearly a book such as this depends on informa-tion, verbal and written, formal and informal, gathered from many sources. Inclusion in the Biblio-graphy is an indirect form of acknowledgement, butwhere long quotations are made, these are acknowl-edged in the text. Sometimes sources have been used,but the content has had to be altered or adapted tomake it relevant to historic buildings and for this reason cannot be directly acknowledged.

As author I owe a great debt to many persons withwhom I have had a professional contact, but it isimpossible to nominate all such persons. In particu-lar I would like to acknowledge the assistance andgenerous advice I have received over many yearsfrom Poul Beckmann who, together with DavidDowrick and Norman Ross of Ove Arup, RobertPotter, Patrick Faulkner, Frank Hall, Derek Philipsand ‘Steve’ Bailey, were my collaborators on the con-solidation of the foundations of York Minster, myinvolvement in which major conservation work pro-vided the impetus to write this book. This remarkableexperience of collaboration by a conservation team

of architects, archaeologists, art historians, engi-neers, quantity surveyors, builders and craftsmenworking together was stimulated by the urgent taskof preventing the Minster’s collapse, which couldnot have been carried out without the help of Messrs.Shepherds of York, whose manager Ken Stevensmade an invaluable contribution. Messrs. Shepherdshave kindly provided many of the technical photo-graphs, for which I am most grateful. No excuse ismade for referring to the work on York Minster, or toother historic buildings for which the author has hadresponsibility, for it is only by sharing experience thatwe can raise standards and improve judgement.

Rowland Mainstone has been most generous inhis time in giving advice on the presentation of thesection on the structural actions of historic buildingsand in reading and correcting the text. He has alsogiven permission to reproduce various diagramsfrom his classic book Development of StructuralForm (Allen Lane, London, 1975) and has con-tributed Appendix I, so completing the structuralsection by looking at buildings as a ‘whole’, whilemy treatment deals with parts or elements andcauses of decay of materials.

The content of this book has been considerablyrefined through further experience of lecturing atthe International Centre for Conservation in Rome.I am grateful to Giorgio Torraca, Laura and PaoloMora, Guglielmo De Angelis d’Ossat and GarryThomson for their help and permission to usematerial and quote from their respective works.

I owe a debt to the Chairman and Council ofICCROM for allowing me to use the material in PartIII which outlines the role of the conservationarchitect and which was prepared for lectures tothe ICCROM Architectural Conservation Courses. Inaddition, much of the substance of the Introductionwas taken out of a booklet entitled ‘An Introductionto Conservation’ which was prepared by me asDirector of ICCROM for UNESCO.

Acknowledgements

Acknowledgements

xiv

I am very grateful to Azar Soheil Jokilehto forredrawing my original diagrams, to CynthiaRockwell and Derek Linstrum for reading the text,to Alejandro Alva who provided Spanish terms inthe Glossary, and to Keith Parker, Former Librarianof the Institute of Advanced Architectural Studies, at the University of York, for his help with both theGlossary and the Bibliography.

Special mention must be made of the help andstimulus I have received from the late JamesMarston Fitch, Professor Emeritus of ConservationStudies at the University of Columbia, New YorkCity. He has pioneered conservation studies in theUSA and shown their value in aesthetic educationand given me help and encouragement over manyyears. Other individuals who have helped me withmaterial are O.P. Agrawal, H. Akai, John Ashurst, W. Brown Morton III, Freddie Charles, NormanDavey, David Dean, Roberto di Stefano, HarryFairhurst, Donald Insall, Maija Kairamo, BertrandMonnet, Wolfgang Preiss, ‘Donnie’ Seale, MarieChristie Uginet, Martin Weaver and Wilhelm Wolhert.

The profiles for Conservation Officer, LandscapeArchitect, Materials Scientist and Surveyor havebeen edited by Bob Chitham and drafted by JohnPreston, Peter Goodchild, Nigel Seely and JohnGleeson respectively, and helpful comments andrevisions have been made by Poul Beckmann,Deborah Carthy, Richard Davies, Gerald Dix,Francis Golding, Gersil Kay, David Lindford,Warwick Rodwell, TG Williams together with JohnFidler and Dr Brian Ridout. I am also grateful toJohn Allan for his help in Chapter 22 onConservation of Modern Buildings; to Dr DavidWatt for Appendix III on Non-Destructive SurveyTechniques, and lastly to John Warren for his pho-tographs and unfailling encouragement.

Institutions which have helped, besides theDeans and Chapters of St. Paul’s Cathedral, YorkMinster and Norwich Cathedral, are:

COSMOS UK; The Society for Protection of HistoricBuildings;

The Department of the Environment (UK) includingthe Building Research Establishment, BRE, andthe Princes Risborough Laboratory;

The Department of the Interior (USA);The Fire Protection Association, FPA (UK);The International Centre for the Study of the

Preservation and the Restoration of CulturalProperty, ICCROM;

English Heritage;

The United Nations Disaster Relief Organization,UNDRO;

The United Nations Educational, Scientific andCultural Organization, UNESCO.

Firms which have helped materially are:

Proprietors of The Architects’ Journal;Ove Arup & Partners;Feilden and Mawson;McGraw-Hill and Company;Allen Lane and Penguin Books;The Oxford University Press;Shepherds Construction Group Ltd.

Photographs are acknowledged in detail and I amespecially grateful to Ove Arup and Partners forproviding the diagrams relating to York Minster.

Lastly my gratitude and thanks are due to thosewho have typed and retyped the text and who hadthe patience to decipher my handwriting, my sec-retaries Dulcie Asker of Feilden & Mawson andElizabeth Ambrosi and Charlotte Acker of ICCROM,to Bob Pearson who has edited this production andto the staff of Butterworth-Heinemann.

As usual, the author takes full responsibility for what is written. Mistakes there may be, but Ihope they are not serious and that they will notmislead any practitioner of conservation of historicbuildings.

The book, took a long time to write, is dedicated tomy wife for her patience, support, encouragement andsacrifices in the cause of conservation.

Note on metrication

The question of metrication raises some difficulties,partly because the metre, being related to the earth’sdiameter, is a geographical dimension, whereas thefoot with all its historic variations is still a humanmeasurement. However, as metrication is the orderof the day, I have complied, but have added theImperial dimensions in parentheses.

As the dimensions themselves are often onlyapproximations, I have worked to the approximationof 300 mm to a foot rather than convert to the closerdegree of accuracy of 304.8 mm; likewise, an inchgenerally is considered to be 25 mm not 25.4. Theproblem is really conversion of one’s ability to visualize what the dimensions and stresses in onesystem mean in another.

1

What is an historic building?

Briefly, an historic building is one that gives us asense of wonder and makes us want to know moreabout the people and culture that produced it. Ithas architectural, aesthetic, historic, documentary,archaeological, economic, social and even politicaland spiritual or symbolic values; but the first impactis always emotional, for it is a symbol of our cul-tural identity and continuity—a part of our heritage.If it has survived the hazards of 100 years of use-fulness, it has a good claim to being called historic.

From the first act of its creation, through its longlife to the present day, an historic building has artis-tic and human ‘messages’ which will be revealed bya study of its history. A complexity of ideas and ofcultures may be said to encircle an historic buildingand be reflected in it. Any historical study of sucha building should include the client who commis-sioned it, together with his objectives which led tothe commissioning of the project and an assessmentof the success of its realization; the study shouldalso deal with the political, social and economicaspects of the period in which the structure wasbuilt and should give the chronological sequence ofevents in the life of the building. The names andcharacters of the actual creators should berecorded, if known, and the aesthetic principlesand concepts of composition and proportion relat-ing to the building should be analysed.

Its structural and material condition must also bestudied: the different phases of construction of thebuilding complex, later interventions, any internalor external peculiarities and the environmental context of the surroundings of the building are allrelevant matters. If the site is in an historic area,archaeological inspection or excavation may benecessary, in which case adequate time must heallowed for this activity when planning a conserva-tion programme.

Causes of decay

Of the causes of decay in an historic building, themost uniform and universal is gravity, followed bythe actions of man and then by diverse climatic

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Introduction to architectural conservation

Figure 1.1 Merchants’ houses, Stralsund, Germany

Inventories of all historic buildings in each town are essentialas a basis for their legal protection. Evaluation is generallybased on dating historical, archaeological and townscape values. Without inventories it is not possible to plan conservation activities at a national level

and environmental effects—botanical, biological,chemical and entomological. Human causes nowa-days probably produce the greatest damage.Structural actions resulting from gravity are dealtwith in Part I, Chapters 2–5, and the other causes inPart II, Chapters 7–11.

Only a small fraction of the objects and structurescreated in the past survives the ravages of time.That which does remain is our cultural patrimony.Cultural property deteriorates, and is ultimatelydestroyed through attack by natural and humanagents acting upon the various weaknesses inher-ent in the component materials of the object orstructure. One aspect of this phenomenon was suc-cinctly described as early as 25 B.C. by the Romanarchitect and historian Vitruvius, when consideringthe relative risks of building materials:

‘I wish that walls of wattlework had not beeninvented. For, however advantageous they are inspeed of erection and for increase of space, tothat extent they are a public misfortune, becausethey are like torches ready for kindling.

Therefore, it seems better to be at greatexpense by the cost of burnt brick than to be indanger by the inconvenience of the wattleworkwalls: for these also make cracks in the plastercovering owing to the arrangement of theuprights and the crosspieces. For when theplaster is applied, they take up the moistureand swell, then when they dry they contract,and so they are rendered thin, and break thesolidity of the plaster.’

Consequently, when analysing the causes ofdeterioration and loss in an historic building, thefollowing questions must be posed:

(1) What are the weaknesses and strengths inher-ent in the structural design and the componentmaterials of the object?

(2) What are the possible natural agents of deterio-ration that could affect the component materi-als? How rapid is their action?

(3) What are the possible human agents of deterioration that could affect the component

Introduction to architectural conservation

2

Figure 1.2 Trastevere, Rome, Italy

A sound structure has been neglected. The results are visible; a system of regular inspections and conservation planningcould prevent this sad state of affairs

materials or structure? How much of their effectcan be reduced at source.

Natural agents of deterioration and loss

Nature’s most destructive forces are categorized asnatural disasters, and include earthquakes, volcaniceruptions, hurricanes, floods, landslides, fires causedby lightning, and so forth. Throughout human his-tory, they have had a spectacularly destructive effecton cultural property. A recent, archetypal example isthe series of earthquakes that devastated the Friuliregion of Italy in 1976, virtually obliterating culturalproperty within a 30 km (19 mile) radius of the epicentres.

The United Nations Disaster Relief Organizationkeeps a record of disastrous events, a sample ofwhich, covering a period of two months, is given inTable 1.1.

After natural disasters, less drastic agents accountfor the normal and often prolonged attrition of cul-tural property. All these agents fall under the generalheading of climate. Climate is the consequence ofmany factors, such as radiation (especially short-waveradiation), temperature, moisture in its many forms—vapour clouds, rain, ice, snow and groundwater—wind and sunshine. Together, these environmentalelements make up the various climates of the worldwhich, in turn, are modified by local conditionssuch as mountains, valleys at relative altitudes,proximity to bodies of water or cities, to create agreat diversity of microclimates within the overallmacroclimates.

In general, climatic data as recorded in the formof averages does not really correspond to the pre-cise information needed by the conservation archi-tect, who is more interested in the extreme hazardsthat will have to be withstood by the building overa long period of time. However, if questions areproperly framed, answers that are relevant to theparticular site of the building in question can beprovided by an expert in applied climatology.

Human factors

Man-made causes of decay need careful assess-ment, as they are in general the by-product of theindustrial productivity that brings us wealth andenables us to press the claims of conservation. Theyare serious and can only be reduced by forethoughtand international co-operation. Neglect and ignor-ance are possibly the major causes of destructionby man, coupled with vandalism and fires, which

are largely dealt with in Chapter 17. It should benoted that the incidence of arson is increasing, put-ting historic buildings at even greater risk.

What is conservation?

Conservation is the action taken to prevent decayand manage change dynamically. It embraces all actsthat prolong the life of our cultural and natural her-itage, the object being to present to those who useand look at historic buildings with wonder the artis-tic and human messages that such buildings possess.The minimum effective action is always the best; ifpossible, the action should be reversible and notprejudice possible future interventions. The basis ofhistoric building conservation is established by legis-lation through listing and scheduling buildings andruins, through regular inspections and documenta-tion, and through town planning and conservativeaction. This book deals only with inspections andthose conservative actions which slow down theinevitable decay of historic buildings.

The scope of conservation of the built environ-ment, which consists mainly of historic buildings,ranges from town planning to the preservation orconsolidation of a crumbling artefact. This range ofactivity, with its interlocking facets, is shown laterin Figure 1.21. The required skills cover a widerange, including those of the town planner, land-scape architect, valuation surveyor/realtor, urbandesigner, conservation architect, engineers of sev-eral specializations, quantity surveyor, buildingcontractor, a craftsman related to each material,archaeologist, art historian and antiquary, sup-ported by the biologist, chemist, physicist, geologistand seismologist. To this incomplete list the historicbuildings officer should be included.

As the list shows, a great many disciplines areinvolved with building conservation, and workersin those areas should understand its principles andobjectives because unless their concepts are cor-rect, working together will be impossible and pro-ductive conservative action cannot result. For thisreason, this introductory chapter will deal brieflywith the principles and practice of conservation interms suitable for all disciplines.

Values in conservation

Conservation must preserve and if possibleenhance the messages and values of cultural prop-erty. These values help systematically to set overallpriorities in deciding proposed interventions, as

What is conservation?

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Introduction to architectural conservation

4

Table 1.1 Some Natural Disasters, over a Two-Month Period (Courtesy: UN Disaster Relief Organization)

Date (in brackets if date of report)

(1.2.80) Cyclone Dean swept across Australia with windsreaching up to 120 m.p.h. and damaging at least50 buildings along the north-west coast. About100 people were evacuated from their homes inPort Hedland. Violent thunderstorms occurredon the east coast near Sydney.

12.2.80 Earth tremor, measuring 4 on the 12-pointMedvedev Scale, in the Kamchatka peninsula inthe far east of the Soviet Union. No damage orcasualties were reported.

(12.2.80) Floods caused by heavy rain in the southern oil-producing province of Khuzestan in Iran. Thefloods claimed at least 250 lives and causedheavy damage to 75% of Khuzestan’s villages.

14.2.80 Earth tremors in parts of Jammu and KashmirState and in the Punjab in north-west India. Theepicentre of the quake was reported about 750 kmnorth of the capital near the border betweenChina and India’s remote and mountainousnorth-western Ladaka territory. It registered 6.5on the Richter Scale. No damage or casualtieswere reported.

(17.2.80) Flood waters swept through Phoenix, Arizona,USA and forced 10 000 people to leave theirhomes. About 100 houses were damaged in thefloods.

(19.2.80) Severe flooding caused by heavy rain insouthern California, USA, left giant mudslidesand debris in the area. More than 6000 personswere forced to flee as their homes werethreatened. Nearly 100 000 persons in northernCalifornia were without electricity. At least 36deaths have been attributed to the storms. Some110 houses have been destroyed and another 14 390 damaged by landslides. Cost of damagehas been estimated at more than $350 million.

22.2.80 Strong earthquake measuring 6.4 on the RichterScale in central Tibet, China. The epicentre waslocated about 160 km north of the city of Lhasa.No damage or casualties were reported.

(23.2.80) Severe seasonal rains caused widespreadflooding in seven northern and central states ofBrazil, killing about 50 people and leaving asmany as 270 000 homeless. Heavily affectedwere the States of Maranhao and Para where themajor Amazon Tributary Tocantins burst banksin several places, as at the State of Goias where100 000 people were left without shelter.Extensive damage was caused to crops, roadsand communication systems. The governmentreported in late February that 2.5 billioncruzeiros had already been spent on road repairsalone.

(26.2.80) Heavy rains brought fresh flooding to thesouthern oil-producing province of Khuzestan,Iran. At least 6 people were reported killed andhundreds of families made homeless by therenewed flooding.

27.2.80 Earthquake on Hokkaido Island in Japan. Thetremor registered a maximum intensity of 3 on

the Japanese Scale of 7. No damage or casualtieswere reported.

28.2.80 Several strong earth tremors in an area 110 kmnorth-east of Rome, Italy. The tremors, whichregistered up to 7 on the 12-point Mercalli Scale,were also felt in the towns of Perugia, Rieti andMacerata as well as in north-east Rome. Slightdamage to buildings was reported.

28.2.80 Earth tremor in the Greek province of Messiniain the south Peloponnisos, Greece. The tremor,which registered 3.5 points on the Richter Scale,damaged houses and schools.

7.3.80 An earthquake measuring 5 on the Richter Scalewas felt on Vancouver Island off the coast ofBritish Columbia, Canada. No damage orcasualties were reported.

(9.3.80) Heavy flooding in the southern provinces ofHelmand, Kandahar and Nimroz in Afghanistandamaged or destroyed 7000 houses andrendered over 30 000 people homeless.

9.3.80 Earth tremor in eastern parts of Yugoslavia,measuring 6.5 on the Mercalli Scale. Theepicentre was placed at 300 km south-east ofBelgrade. There were no reports of damage orcasualties.

(9.3.80) Persistent drought in central SriLanka wasreported to affect agricultural production and toruin 150 000 acres of prime tea plantations.Water and electricity supplies were restricted bythe government.

15.3.80 Heavy rains caused widespread flooding innorthwestern Argentina causing the deaths of 10 people, with 20 reported missing. Nearly 4000people were evacuated after the San Lorenzoriver overran its banks.

16.3.80 A volcanic eruption occurred in the Myvatnmountain region in northern Iceland. Nodamage or casualties were reported.

16.3.80 Earthquake on the island of Hokkaido, Japan.The tremor registered a maximum intensity of 3 on the Japanese Scale of 7. No damage orcasualties were reported.

19.3.80 Medium-strength earthquake in the central AsianRepublic of Kirghizia near Naryn, USSR. Nodamage or casualties were reported.

23.3.80 Medium-strength earthquake near the borderbetween Afghanistan and the USSR. Its epicentrewas located about 1120 km north-west of Delhi.No damage or casualties were reported.

24.3.80 Earthquake measuring 7 on the Richter Scale inthe Aleutian Islands off the Alaska peninsula,USA. Its epicentre was estimated just south ofUmnak Island.

28.3.80 Torrential rain and strong winds struck centraland southern areas of Anatolia, Turkey, cuttingroad and rail traffic. A landslide in the village ofAyvazhaci killed at least 40 people, while anadditional 30 villagers were reported missing.In Adana Province 12 000 houses were affectedby floods.

5

Figure 1.3 Merchant’shouse, Stralsund, Germany

Decay has gone so far that onlythe facade can be preserved andthe interior has to be rebuilt.Taking the city as a whole, thismay be justified. However, thereis a danger of deception whenonly townscape values are considered

Figure 1.4 Merchants’houses, Stralsund, Germany

Conservation work in progress.After a thorough study and re-evaluation it was found thatthese merchants’ houses could berehabilitated satisfactorily

well as to establish the extent and nature of the indi-vidual treatment. The assignment of priority valueswill inevitably reflect the cultural context of each his-toric building. For example, a small wooden domes-tic structure from the late eighteenth century inAustralia would be considered a national landmarkbecause it dates from the founding of the nation andbecause so little architecture has survived from thatperiod. In Italy, on the other hand, with its thou-sands of ancient monuments, a comparable structurewould have a relatively low priority in the overallconservation needs of the community.

The ‘values’ as already given in the Preface comeunder three major headings:

(1) Emotional values: (a) wonder; (b) identity; (c) continuity; (d) spiritual and symbolic.

(2) Cultural values: (a) documentary; (b) historic;(c) archaeological, age and scarcity; (d) aestheticand symbolic; (e) architectural; (f ) townscape,landscape and ecological; (g) technological andscientific.

(3) Use values: (a) functional; (b) economic; (c) social; (d) educational; (e) political and ethnic.

Having analysed these values they should be con-densed into a statement of the significance of thecultural property.

The cost of conservation may have to be allo-cated partially to each of the above separate valuesin order to justify the total to the community.Whereas for movable objects the problem of valuesis generally more straightforward, in architecturalconservation problems often arise because the utilization of the historic building, which is eco-nomically and functionally necessary, must alsorespect cultural values. Thus, conflicts can arisebetween cultural and economic values and evenwithin each group, for example between archaeo-logical and architectural values. Sound judgement,based upon wide cultural preparation and maturesensitivity, gives the ability to make correct valueassessments.

Ethics of conservation

The following standard of ethics must be rigorouslyobserved in conservation work:

(1) The condition of the building must be recordedbefore any intervention.

(2) Historic evidence must not be destroyed, falsi-fied or removed.

(3) Any intervention must be the minimum necessary.

(4) Any intervention must be governed by unswerv-ing respect for the aesthetic, historical andphysical integrity of cultural property.

(5) All methods and materials used during treat-ment must be fully documented.

Any proposed interventions should (a) bereversible or repeatable, if technically possible, or (b)at least not prejudice a future intervention wheneverthis may become necessary; (c) not hinder the possi-bility of later access to all evidence incorporated inthe object; (d) allow the maximum amount of exist-ing material to be retained; (e) be harmonious incolour, tone, texture, form and scale, if additions arenecessary, but should be less noticeable than originalmaterial, while at the same time being identifiable;(f ) not be undertaken by conservator/restorers whoare insufficiently trained or experienced, unless theyobtain competent advice. However, it must be recog-nized that some problems are unique and have to besolved from first principles on a trial-and-error basis.

It should be noted that there are several funda-mental differences between architectural and artsconservation, despite similarities of purpose andmethod. First, architectural work involves dealingwith materials in an open and virtually uncontrol-lable environment—the external climate. Whereasthe art conservator should be able to rely on goodenvironmental control to minimize deterioration,the architectural conservator cannot; he must allowfor the effects of time and weather. Secondly, thescale of architectural operations is much larger, andin many cases methods used by art conservatorsmay be found impracticable due to the size andcomplexity of the architectural fabric. Thirdly, andagain because of the size and complexity of archi-tecture, a variety of people such as contractors,technicians and craftsmen are actually involved inthe various conservation functions, whereas the artconservator may do most of the treatment himself.Therefore, understanding of objectives, communi-cation and supervision are most important aspectsof architectural conservation. Fourthly, there arethose differences which are due to the fact that thearchitectural fabric has to function as a structure,resisting dead and live loadings, and must providea suitable internal environment as well as be pro-tected against certain hazards such as fire and vandalism. Finally, there are further differencesbetween the practice of architectural conservationand the conservation of artistic and archaeologicalobjects in museums, for the architectural conserva-tion of a building also involves its site, setting andphysical environment.

Introduction to architectural conservation

6

Preparatory procedures for conservation

Inventories

At the national level, conservation procedures con-sist initially of making an inventory of all culturalproperty in the country. This is a major administra-tive task for the government, and involves estab-lishing appropriate categories of cultural propertyand recording them as thoroughly, both graphicallyand descriptively, as possible. Computers andmicrofilm records are valuable aids. Legislation pro-tects from demolition those historic buildings listedin inventories. The inventories also serve as a basisfor allocating grants or providing special tax relieffor those who must maintain historic buildings.

Initial inspections

A preliminary visual inspection and study of eachbuilding is necessary in order to know and define itas a ‘whole’. The present condition of the buildingmust be recorded methodically (see Chapter 14) andthen whatever further studies are required can bereported. Documentation of these studies must be

full and conscientious, which means a diligentsearch of records and archives. In some countries,reliance may have to be placed on oral traditions,which should be recorded verbatim and included inthe dossier created for each building.

When a country has a statistically significant number of reports, together with estimates given inrecognized categories of urgency, it can assess theprobable cost of its conservation policies and decidepriorities in accordance with its budgetary provi-sion. It can then plan its work-force in accordancewith its needs and allocate adequate resources.

All historic buildings should be inspected at reg-ular intervals, in order to establish maintenanceplans. The spacing of the intervals will be frequentin a hot, humid climate but in a zone climate fiveyear intervals are sufficient. Such preventive main-tenance should in most cases forestall the need formajor interventions, and it has been proved that itreduces the cost of conservation of a nation’s stockof historic buildings.

Continuing documentation

Complete recording is essential before, during andafter any intervention. In all works of preservation,

Preparatory procedures for conservation

7

Figure 1.5 A street afterconservation, Stralsund,Germany

repair or excavation of cultural property there mustalways he precise documentation in the form of ana-lytical and critical reports, illustrated with photographsand drawings. Every stage of the work of cleaning,consolidation, reassembly and integration, includingall materials and techniques used, must he recorded.Reports on technical and formal features identifiedduring the course of the work should be placed in thearchives of a public institution and made available toresearch workers. Finally, if the intervention can in anyway serve to broaden general knowledge, a reportmust be published. Often in large projects it may takeseveral years to write a scholarly report, so a prelimin-ary report or an annual series is desirable to keep thepublic informed and thus maintain popular support.

To ensure the maximum survival of cultural prop-erty, future conservators must know and understandwhat has occurred in the past. Consequently, docu-mentation is essential because it must be remem-bered that the building or work of art will outlive theindividuals who perform the interventions. Adequatebudgetary provision must be made for documenta-tion and this must be kept separate from that of theconservation works. Full documentation, includingphotographs before and after the intervention, isalso useful if the conservation architect has to refuteunjustified criticism.

Degrees of intervention

The minimum degree of intervention necessary andthe techniques used depend upon the conditions ofclimate to which cultural properly is likely to besubjected. Atmospheric pollution and traffic vibra-tion must be considered, and earthquake and floodhazards should be assessed.

Interventions practically always involve someloss of a ‘value’ in cultural property, but are justi-fied in order to preserve the objects for the future.Conservation involves making interventions at various scales and levels of intensity which aredetermined by the physical condition, causes ofdeterioration and anticipated future environment of the cultural property under treatment. Each casemust be considered as a whole, and individually,taking all factors into account.

Always bearing in mind the final aim and the prin-ciples and rules of conservation, particularly that theminimum effective intervention is always the best,seven ascending degrees of intervention can beidentified. In any major conservation project, severalof these degrees may take place simultaneously invarious parts of the ‘whole’. The seven degrees are:(1) prevention of deterioration; (2) preservation ofthe existing state; (3) consolidation of the fabric;

Introduction to architectural conservation

8

Figure 1.6 Doric temple, Silene, Sicily, Italy

Anastylosis can recreate the glories of the past, making thearchitectural values of space and mass more easily understood.Sometimes this is done at the expense of archaeological anddocumentary values. In this case the effect is spoiled by a plaster patch on one of the columns

Figure 1.7 Doric temple, Silene, Sicily, Italy

The column drums have been re-erected. Problems arise, however, as the stones have weathered differently while lying on the ground for centuries and it is this factor that gives thecolumns a rather strange appearance

(4) restoration; (5) rehabilitation; (6) reproduction;(7) reconstruction. These degrees of interventionare dealt with below.

Prevention of deterioration (or indirect conservation)

Prevention entails protecting cultural property bycontrolling its environment, thus preventing agentsof decay and damage from becoming active. Neglectmust also be prevented by sound maintenance pro-cedures based on regular inspections.

Therefore, prevention includes control of internalhumidity, temperature and light, as well as meas-ures to prevent fire, arson, theft and vandalism, andto provide for cleaning and good overall house-keeping. In an industrial environment, preventionincludes measures to reduce both atmospheric pol-lution and traffic vibrations. Ground subsidencemust also be controlled; it is due to many causes,particularly abstraction of water.

In summary, regular inspections of cultural prop-erty are the basis of prevention of deterioration.Maintenance, cleaning schedules, good housekeep-ing and proper management also aid prevention.Such inspections are the first step in preventivemaintenance and repair.

Preservation

Preservation deals directly with cultural property.Its object is to keep it in its existing state. Repairsmust be carried out when necessary to prevent further decay. Damage and destruction caused bywater in all its forms, by chemical agents and by alltypes of pests and micro-organisms must bestopped in order to preserve the structure.

Consolidation (or direct conservation)

Consolidation is the physical addition or applica-tion of adhesive or supportive materials into theactual fabric of cultural property, in order to ensureits continued durability or structural integrity. In thecase of immovable cultural property, consolidationmay for example entail the injection of adhesives tosecure a detached mural painting to the wall andlikewise grouting of the structure.

With historic buildings, when the strength ofstructural elements has been so reduced that it is nolonger sufficient to meet future hazards, consolida-tion of the existing material may have to be carriedout. However, the integrity of the structural systemmust be respected and its form preserved. No

historical evidence should be destroyed. Only byfirst understanding how an historic building acts asa whole as a ‘spatial environmental system’ is itpossible to introduce new techniques satisfactorily,or provide a suitable environment for objects of art,or make adjustments in favour of a new use.

The utilization of traditional skills and materials isof essential importance. However, where traditionalmethods are inadequate the conservation of culturalproperty may be achieved by the use of moderntechniques which should be reversible, proven byexperience, and applicable to the scale of the projectand its climatic environment. This sensible approachto conservation uses appropriate technology.

With short-lived materials, including reeds, mud,rammed earth, unbaked bricks and wood, suchmaterials and traditional skills should be used for therepair or restoration of worn or decayed parts.Preservation of the design is just as important a func-tion of conservation as preservation of original ma-terials. Finally, in many cases it is wise to buy timewith temporary measures in the hope that some better technique will be evolved, especially if consoli-dation may prejudice future works of conservation.

Restoration

The object of restoration is to revive the originalconcept or legibility of the object. Restoration andre-integration of details and features occurs fre-quently and is based upon respect for originalmaterial, archaeological evidence, original designand authentic documents. Replacement of missingor decayed parts must integrate harmoniously withthe whole, but must be distinguishable on closeinspection from the original so that the restorationdoes not falsify archaeological or historical evi-dence. In a sense, the cleaning of buildings is alsoa form of restoration, and the replacement of miss-ing decorative elements is another.

Contributions from all periods must be respected.Any later addition that can be considered as an ‘his-toric document’, rather than just a previous restora-tion, must be preserved. When a building includessuperimposed work of different periods, the reveal-ing of the underlying state can only be justified inexceptional circumstances. That is, when the part tobe removed is widely agreed to be of little interestor when it is certain that the material brought tolight will be of great historical or archaeologicalvalue; and when it is probable also that the state ofpreservation of the building is good enough to jus-tify the action. These are difficult conditions to sat-isfy, and unfortunately they may be brushed asideby unscrupulous archaeological curiosity.

Degrees of intervention

9

Restoration by anastylosis, using original mater-ial, is justified when supported by firm archaeolog-ical evidence and when it makes a ruin morecomprehensible, allowing the spatial volumes to bevisualized more easily. If taken too far, it can makean historic site look like a film set and devalue themessage of the site. This and the problem of patinaand lacunae are dealt with in Chapter 18.

Rehabilitation

The best way of preserving buildings as opposed toobjects is to keep them in use—a practice whichmay involve what the French call ‘mise en valeur ’, ormodernization with or without adaptive alteration.The original use is generally the best for conserva-tion of the fabric, as it means fewer changes.

Adaptive use of buildings, such as utilizing amediaeval convent in Venice to house a school and

10

Figure 1.8 Doric temple,Silene, Sicily, Italy

Forming individual bases forthe first six columns destroysthe original design in an arbitrary manner. Anastylosisshould at least be correct

Figure 1.9 Doric temple, Silene, Sicily, Italy

This plasterwork was probably unnecessary and detracts from thepresentation of the temple. Certainly, Vitruvius’ specification wasnot followed, for Portland cement was used with the inevitableresultant cracking

laboratory for stone conservation, or turning aneighteenth-century barn into a domestic dwelling,is often the only way that historic and aesthetic val-ues can be saved economically and historic build-ings brought up to contemporary standards.

Reproduction

Reproduction entails copying an extant artefact,often in order to replace some missing or decayedparts, generally decorative, to maintain its aestheticharmony. If valuable cultural property is beingdamaged irretrievably or is threatened by its envir-onment, it may have to be moved to a more suit-able environment and a reproduction substituted inorder to maintain the unity of a site or building. Forexample, Michelangelo’s ‘David’ was removed fromthe Piazza della Signoria, Florence, into a museumto protect it from the weather, and a good repro-duction took its place. Similar substitutions havebeen undertaken for the sculpture of the cathedralsof Strasbourg and Wells.

11

Figure 1.10 Temple of Zeus,Jerash, Jordan

Should the Temple of Zeus be subject to anastylosis? Most peopleknow what a Roman templeusing the Corinthian ordershould look like. The stones asthey lie bear eloquent testimonyto the force of the earthquakewhich destroyed the city in A.D. 794—a fact of historical significance

Figure 1.11 Temple of Zeus, Jerash, Jordan

The fallen stones give archaeological evidence sufficient tomake a model to demonstrate the original design

Reconstruction

Reconstruction of historic buildings and historic cen-tres using new materials may he necessitated by dis-asters such as fire, earthquake or war. Reconstructioncannot have the patina of age. As in restoration,reconstruction must be based upon accurate docu-mentation and evidence, never upon conjecture.

The moving of entire buildings to new sites isanother form of reconstruction justified only byover-riding national interest. Nevertheless, it entailsthe loss of essential cultural values and the genera-tion of new environmental risks. The classic exam-ple is the temple complex of Abu Simbel (XIXDynasty), Egypt, which was moved to prevent itsinundation following the construction of the AswanHigh Dam, but is now exposed to wind erosion.

Avoiding ‘planning blight’

In the sphere of economics and town planning thedemands of conflicting interests have to beresolved. ‘Planning blight’, an economic diseasecaused by lack of decision or by attempting tooambitious schemes, must be avoided. The lessonsof conservation are that minimum interventions atkey points are best for the community.

No proposed conservative action should be putinto effect until it has been analysed and evaluatedin the light of an objective clearly defined inadvance. Possible contradictions in values must beresolved and the ‘least bad’ or minimum interven-tion decided upon; then the conservation architectcan prepare his scheme for approval.

In all conservation of historic buildings, continu-ity of policy and consistency of artistic treatment isdesirable; this is best obtained by nominating anarchitect or surveyor who must be given overallresponsibility for the project but who is also subjectto multidisciplinary advice. His is the inescapableresponsibility for making history or destroying it.

The conservation architect and his team of co-workers

The conservation or historical architect, in additionto his (or her) basic and practical experience as ageneral architect, must have a knowledge andunderstanding of early building technology and mustbe able to identify the original fabric and later addi-tions, and interpret his findings to a client. To exe-cute any scheme he must co-ordinate the work ofarchaeologists, engineers, planners, landscape archi-tects, contractors, suppliers, conservation craftsmen

Introduction to architectural conservation

12

Figure 1.12 Salerno Cathedral, Italy

Contrary to the Venice Charter, the baroque work has beenunpicked to satisfy archaeological curiosity and expose earlyChristian arcading. How will the situation be resolved? Will thebaroque be reinstated for the benefit of the whole or will theearlier period take precedence. It is vital to decide on a clearpresentation policy in conservation

Figure 1.13 St Peter’s Palace, Leningrad, USSR

The remains after enemy bombardment and before restorationwork were daunting and grim. Cultural property must be fullydocumented to guard against disasters, thus making restorationpossible

and others who might be involved in an historicbuilding project.

The conservation architect is the generalist in thewhole building conservation process. His work isoutlined in Part III. He must have a good knowl-edge of all periods of architecture, combined with athorough understanding of modern building prac-tice; he must be able to preserve the artistic andhistorical value of the old structure, yet prepareschemes which are satisfactory in respect to modernrequirements. This latter includes complying withrelevant requirements laid down by codes of prac-tice and building regulations, or obtaining waiversto any inapplicable building codes regulationswhere justified by reference to fundamental princi-ples. He needs not only a knowledge of buildingtechnology but also an understanding of thepathology of buildings as evidenced by sinkingfoundations, crumbling walls and rotting timbers.This book is primarily written for just such a person.

Architectural conservators

The difficulty which the conservation architect has infinding, and communicating effectively to, those sci-entists who are able to appreciate his problems hasled the American National Conservation AdvisoryCouncil to recommend the recognition of a greaterdegree of specialization in architectural conservation.The person with these special responsibilities wouldbe called an ‘architectural conservator’, and he shouldhave a broad range of skills beyond those of eitherthe conservation architect or arts conservator.

The architectural conservator must be trained inthe new technology and in scientific laboratorymethods now being applied to the conservation ofartefacts in other fields; he must also be able to tapresources in such sub-specialities of chemistry asspectrographic analysis, radio-carbon dating andresistivity analysis. He should know how to use newarchaeological techniques for analysing site evidence,

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Figure 1.14 Palais de Rohan, Strasbourg, France(Courtesy: Klein-Franc Photo Publicité and B. Monnet)

The palace in 1945 after the bombing of 11 August, 1944

Figure 1.15 Palais de Rohan, Strasbourg, France(Courtesy: Photo Frantz and B. Monnet)

The synod chamber after reconstruction by Architect en Chef,Bertrand Monnet

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Figure 1.16 Palais de Rohan, Strasbourg, France(Courtesy: S. Norand and B. Monnet)

Aerial view of the palace after reconstruction following wardamage. The building is used by the Council of Europe

Figure 1.17 Church, Stralsund, Germany

This church has been turned into a maritime museum. The fabric is preserved and new spatial values created by insertionof a mezzanine floor. An interesting case of re-evaluation andadaptive use of an historic building, but purists might object

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Figure 1.18 Telc,Czechoslovakia(Courtesy: V. Uher and StatniUstav pro Rekonstrukse Pamat-kovych mest a Objektj v Praze)

A typological and volumetricstudy of the town in axiono-metric projection

Figure 1.19 Central Square, Telc, Czechoslovakia(Courtesy: V. Uher and Statni Ustav pro RekonstruksePamatkovych mest a Objektj v Praze)

View looking south-east from the castle

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Figure 1.20 Telc,Czechoslovakia(Courtesy: V. Uher and StatniUstav pro RekonstruksePamatkovych mest a Objektj v Praze)

View looking north-west fromcauseway of castle and principal church

Figure 1.21 Structure ofICCROM’s ArchitecturalConservation Course(Courtesy: Arch. J. Jokilehto,ICCROM)

The course, held in Rome, is forarchitects, art historians, townplanners, engineers and adminis-trators who have had at least fouryears’ professional experience andwho wish to specialize in conserva-tion. Within the overall structure,individual needs are met by varia-tions of emphasis and allocation oftime for research

computer technology for retrieval of recorded infor-mation and photogrammetry for producing accuratedimensional drawings and solving difficult problemsof recording. Very few such men exist at present.

Non-destructive investigation is covered inAppendix III. This is a field where specialistsshould be consulted in specific cases to advise onthe most useful technique.

The role of conservation crafts

The scope of building craft skills in conservationranges from the simple repair and maintenance ofdomestic properties to the most complicated workthat can be imagined, for which the highest skills arenecessary. The men to carry out the latter class ofwork should be classified as conservation craftsmenand have a status equal to that of other professionalsengaged in conservation. The clock cannot be putback and the extreme diversification of eighteenthand nineteenth century crafts cannot be recreatedartificially. However, a young but sufficiently experi-enced tradesman can acquire additional skills, andwith artistic guidance, skilled application and thehelp of science he can repair and reproduce thecraftsmanship of the past. The conservation craftsmantherefore has to understand the history or technologyof his craft and be able to analyse how historic workwas set out and produced. Samples of past work-manship should be collected and used for reference,as is done in Amsterdam and at Torun, Poland.

It is to be hoped that more building contractors willspecialize in repair and maintenance and that a newbreed of conservation craftsmen, well versed in thehistory of the technology of their craft, will emerge totake a place with equal status and wages alongsidethe architect.*

Good workmanship

When the Parthenon was being built, the architectand sculptor (Ictinus and Calicrates), the free men,the freed men and the slaves all received the samewage of one drachma a day, and produced a mas-terpiece. Good workmanship thus depends uponproper pay for a fair day’s work. Overtime and thebonusing of production have led to bad workman-ship and should not be used to obtain increasedoutput on historic buildings. Good workmanshipcomes from proper training, continuity of work andpublic appreciation and respect for the status of the

craftsman. The sad situation in the building indus-try now, is that the more skilled the craftsman, theless money he earns because he is put on to the dif-ficult, time-consuming tasks. The industry pays forquantity not quality, for muscle not skill.

Craftsmen are primarily responsible for the qualityof workmanship. The ability to evaluate quality ofworkmanship depends upon experience obtainedonly from inspecting many buildings of different peri-ods, but it is possible to generalize that a period whenquality of materials was at a premium would tend tobe a time of prosperity when building owners were

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*Operatives in the building industry in 1972 were earning asmuch as well-qualified architects, so this suggestion is not unrea-sonable, although it is likely to be resisted by vested interests.

Figure 1.22 Ethelbert Gateway, Norwich, England

The stone was so decayed that most of the evidence had dis-appeared. Research showed that an etching by J.S. Cotman, madein 1820, was a reliable basis for a reproduction by the sculptor

also prepared to pay for good work. However,generalizations are always dangerous and therecould be pronounced regional variations within thesame period. In England, the author has foundRomanesque and Early English workmanship to begenerally better than Decorated Gothic, but qualityimproved in the late Middle Ages only to deterioratein Tudor times and then gradually improve until theeconomic hardships imposed by the Napoleonicwars reduced standards. Some of the best work-manship was found in Victorian buildings, but sincethen there has been a gradual decline in standards,in spite of an increase in the standard of living.

To obtain good workmanship, materials and detail-ing must be suitable and skills must equal design.Possibly the highest qualities of workmanship wereachieved in the Baroque period, when it seems thatGothic freedom and adventure were given a furtherlease of life by the designer-craftsmen. Comparedwith Continental architects and builders, the Englishhave always been parsimonious with regard to mater-ials, to save which they were prepared to go to greatlengths. This attitude led to a smaller scale in Englisharchitecture, which can be seen in a study of the planand sections of St Peter’s, Rome, with walls 13 m(43 ft) thick and St Paul’s, London, with walls of less

than 3 m (10 ft). Designing to rather finer limits meantan ultimate sacrifice of durability.

It is interesting to note that of the part of theOspizio di San Michele, Rome, which was built hur-riedly and cheaply, a section fell down after abouttwo centuries, whereas the rest has been consoli-dated at much less expense. In earthquake zonesthe quality of workmanship is often the differencebetween collapse and stability. Although workman-ship is extremely difficult to assess, a study of allrepairs carried out previously is indicative of qual-ity. It can be said that any structure built withundue haste is liable to contain bad workmanship.

The context of inspecting historic buildings

In this book, great emphasis will be placed uponthe initial inspection of the historic building. This hasto embrace the whole problem as comprehensivelyand quickly as possible. Suggested norms for anexperienced conservation architect are five hourssitework for a small historic building, ten hours for amore complicated one and between 20 and 40 hoursfor a difficult or large one, although York Minstertook 2000 man-hours to inspect because of its archi-tectural complexity, and St Paul’s Cathedral about1200 man-hours because of its size.

The causes of decay are so complex, and indeedtwo or three causes may be operating simultane-ously, that it is usual for an architect to be unawareof all but the obvious ones when making his firstinspection. This must not deter him—his role is torecord facts and then seek the causes.

The work of survey, inspection and report shouldtake account of the building in its town planningcontext. Planners can be of great assistance in pre-venting traffic vibration by diverting heavy vehicles;in preventing or reducing atmospheric pollution bycorrect siting of industries and power stations in rela-tion to historic buildings; and in reducing fire hazardby considering access for fire-fighting vehicles.

How this book deals with the subject

Part I: Structural aspects of historic buildings(Chapters 2–6)

Gravity is both the force that keeps buildings stand-ing and the major cause of their destruction.Structural actions and analysis of the failure of ele-ments form the basis of this part of the book. Typicaldefects in various forms of structures are reviewedand examined in order to enable the architect to

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Figure 1.23 South Portico, St Paul’s Cathedral, London,England(Courtesy: Feilden & Mawson)

Atmospheric pollution had destroyed the carving of the urns bydissolving over 20 mm (0.8 in) of the stone in half a century.Before it was too late a reproduction was made of CaiusCibber’s early eighteenth century design. Here a master carverbreathes life into new stone

evaluate the structural condition of the historicbuilding for which he is responsible.

In dealing with structural analysis, the value ofR.J. Mainstone’s outstanding work The Developmentof Structural Form must be recognized. This classicbook is essential reading for architects, art historiansand archaeologists. It makes the structural problemsof historic buildings intelligible without the use ofcalculations. This statement may cause some won-der in certain quarters until it is remembered thatthe majority of major historic buildings were builtlong before mathematical analysis was developedby Poleni in 1742. The original builders had excel-lent correlation between hand and brain, and byusing acute observation were able to analyse—if notexactly quantify—the lines of thrust in buildings

which depend more upon the form of the structurethan on the strength of the rather weak (by modernstandards) materials of which it was made.

To quote Donald Insall: ‘Buildings are mortal.’ Itshould be stressed that there must be a point in timewhen a building will collapse if maintenance is neg-lected and the building is not repaired. This pointwas reached less than 24 hours after the author hadinspected the north portion of the Ospizio di SanMichele in Rome on 31 March, 1977. ‘Mortality’applies in nature as well as in the works of man, formountains erode, valleys fill in, the earth’s surface isaltered by earthquakes and the seas’ levels change.The pyramids of Gizeh, as structures, have immenseintrinsic strength, but even they have lost their outerskin and are gradually eroding due to the action of

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Figure 1.24 South-westtower, St Paul’s Cathedral,London, England(Courtesy: Feilden & Mawson)

The cornices of St Paul’s protectall the other masonry and soare the first line of defenseagainst the effects of atmos-pheric pollution which is dis-solved in rain water orcondensation. After over 250years many stones were defec-tive and had to be replaced. Alarge stone has been lifted 50 m(164 ft) and is then carefullylowered into place, then groutedand pointed and protected withlead. Handling such heavystones weighing up to a tonneeds great skill, the prerogativeof the mason, and also strongscaffolding

climate. Luckily, historic buildings were almost alloverdesigned and so have reserves of strength, butthis overdesign was not consistent. Some parts willtherefore be more highly stressed than others andcause strains to concentrate on one weak part, tothe point of its collapse. Any study of the strengthof a building must be at three levels and consider,first, the form of the whole structure; secondly, thestructural elements, i.e. roofs and walls, founda-tions and the soil they rest upon; thirdly, the mater-ials of which the component parts are made.

Before starting an investigation and certainlybefore undertaking any major intervention, theengineer and architect should have a clear idea ofthe objectives. What were the important character-istics of the building, which was it most desirable toconserve, and for what future use? Continued ‘use’,in the normal sense of the word, is always prefer-able to mere preservation, since it enables thebuilding to continue to play a full role and this pro-vides the best guarantee of continued attention andproper care. But there are also outstanding historicbuildings or ruins which have an important futureuse as physical embodiments of past cultures orexamples of supreme past achievements, withoutwhich we should be much poorer and whichshould be lovingly conserved for the real contribu-tion they make to the fulness of our lives.

In making investigations it is all too easy for theprofessional to find a defect which may give lay-men immediate alarm and concern, and for him topronounce a verdict, without proper investigation,that the structure is unsafe or beyond repair. Thisattitude is common among those without experi-ence of historic buildings, although they may beeminent in the field of conventional building, anddoes not take into account adequately the fact thatthe historic building has stood successfully for sev-eral centuries even though it may have quite seri-ous deformations and defects. Whereas facts mustbe faced and structural faults recorded, the goodpoints in the structure, however deformed, must beassessed and ingenuity used to find simple and ele-gant solutions which maximize the use of existingmaterial and knit together the historic structure insuch a way as to give it a further lease of life, whilenot prejudicing future interventions.

The best further safeguard for the future is toplace the building under the continuous care ofsomeone like a Dom Baumeister or a cathedral sur-veyor, preferably assisted by a permanent smallstaff of skilled craftsmen who learn to know thestructure intimately and can measure its movementsand monitor its structural health.

Whatever the objectives of its conservation, eachhistoric building presents unique problems. It is an

individual structure and its needs should be indi-vidually assessed, while keeping a proper sense ofproportion about the justifiable depth of investiga-tion. As has been said before, investigation of theneeds should take into account all relevant facts,including not only the future use but also the en-vironmental conditions, the foundation conditionsand the past history. This last information could bevery important in correctly interpreting apparentsigns of distress. Usually, the present condition ofthe structure provides some clues to it, but docu-mentary sources should also be consulted.

A qualitative structural assessment based uponvisual inspection should precede and guide quanti-tative analyses which may otherwise be based onmistaken assumptions or misleadingly concentrateon the more obvious aspects of the problem to theneglect of the real total situation. Analyses shouldalso start from first principles and not attempt totake short cuts by using rules from current codes ofpractice or other design procedures, since these arenever truly applicable. Architects and engineersworking on historic buildings need some qualitativeintuitive understanding on which to build, and abasic vocabulary with which to formulate and com-municate their insight. They should also be madefully aware of the need to have an adequate pictureof the structural action as a whole before attempt-ing detailed analysis of any part.

Where remedial interventions are considered to benecessary, they should respect, as far as possible, thecharacter and integrity of the original structure. Theyshould also, as far as possible, use materials similarto the original ones. Where different materials aresubstituted, their physical characteristics should har-monize with the original, particularly with regard toporosity and permeability, and care should be takennot to introduce elements of excessive strength orstiffness into a structure which will usually be lessstiff and more accommodating to long-term move-ments than contemporary structures. The finalchoice of the approach to be adopted should bemade only after a proper appraisal (consistent withthe scale of operations and the resources available)of alternatives, with some eye to the future.

Part II: Causes of decay in materials and structure (Chapters 7–12)

Climatic causes of decay vary immensely the worldover. The best techniques of conservation practiceare required wherever climatic extremes are met.Natural disasters are here included with the problemof climate. Generally, it may be said that sufficientthought has not been given to flood and earthquake

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hazards as these affect historic buildings. Lack ofmaintenance strategies has led to earthquakes beingblamed for much loss of life and destruction of cul-tural property which could have been avoided bypreventive maintenance. Climate also dictates whatbotanical, biological and entomological causes ofdecay may occur and to a large extent the strengthof their attacks. The chapters dealing with thesecauses are not meant to summarize or replace theextensive literature on these subjects, but rather totreat them from the point of view of the practisingarchitect, highlighting some of the preventive meas-ures that can be taken.

One comment arising from the study of the effectof climate on building design is that this phenomen-on is absolutely fundamental. What could be moreidiotic than putting an all-glass facade into a struc-ture in the Persian Gulf (or anywhere else perhaps),showing a complete disregard for the climate andthe lessons to be learned from the local buildings.

A chapter on the man-made causes of decay,which are complicated and widespread, discussesthe problems of vibration from heavy traffic andindustry, of water abstraction and of atmosphericpollution (Chapter 11).

Chapter 12, dealing with the internal environ-ment of historic buildings, is the corollary to that onclimate, as the primary purpose of buildings is tomodify the harsh or enervating external climate infavour of man, thus enabling him to pursue hisdomestic activities and his work, social, spiritualand leisure aims. It is important to understand abuilding as a spatial environmental system. Thischapter hopefully makes clear that there is a heatand moisture equation which must balance, andhow if you alter one factor in the equation, youmust also alter all the others.

Part III: The work of the conservation architect(Chapters 13–22)

Although this book considers all the causes ofdecay before dealing with inspections, in practicethe architect generally has to inspect a building andthen diagnose what is wrong and finally decidehow to cure it. However, by following a logicalplan it is possible to emphasize the wholeness ofthe building and the concept of its action as a struc-tural environmental spatial system. The chapter oninspections should be particularly useful to archae-ologists and conservator/restorers (Chapter 14).

Research, analysis and recording might be con-sidered before an inspection is made, yet in prac-tice until you have looked at the fabric in its totalityyou do not know what needs further study, what

sort of analysis should be made and what depth isjustified, nor do you know what recording is nec-essary. This chapter has therefore been placed afterthe one on inspections. The inspection should indi-cate what is necessary to be studied and used as thebasis of obtaining authority and funding for thenext stage of necessary investigations to be made indepth. For instance, in the case of York Minster, asoil mechanics investigation and structural analysis,together with exploration of the structure, wereshown to be essential as a result of an inspectionwhich had no preconceptions.

Inspections, followed by careful research, analysisand recording, are not an end in themselves. Actionmust follow. The first action should be to devise astrategic maintenance plan, so the chapter dealingwith this important matter comes next. When the mil-lennium comes, all historic buildings will have regularinspections and conservation will be based upon pre-ventive action, which, involving as it does minimumintervention, is the highest form of conservation.

Some 9000 historic buildings in the charge of theChurch of England, mostly mediaeval churches, havebeen cared for on this basis for 25 years and theamount of annual maintenance required has fallendramatically, so it can be proved that organizing theconservation of historic buildings on a preventivemaintenance basis saves money. Yet most ownersand administrators fail to understand this and arereluctant to commission regular inspections andorganize preventive maintenance, as they are unwill-ing to pay the fee for professional services, or in thecase of the government, to employ sufficient staff.

Passive and active fire protection form Chapter 17 ofthe book. It is a question of forethought and goodmanagement to prevent damage by fires, as well asloss of life. Security is also becoming increasinglyimportant as standards of public behaviour decline.Part of the philosophy is summed up by Murphy’s law:if it can happen it will happen—so we must preventthe thief and vandal and avoid the danger of fire.

Next, a chapter on the presentation of historicbuildings is included. Before any conservationaction is undertaken, both the objective and the waythe building is to be presented should be discussedand agreed. Difficult aesthetic and art historicalquestions and possible contradictions should beresolved before works are started. For example, willarchaeological excavations threaten the stability ofthe structure? The values of patina and problems ofdealing with lacunae and ruins also come under thesubject of presentation and so are discussed in thischapter.

To complete this part, chapters on cost control ofconservation projects and rehabilitation of historicbuildings are included. Much time and money is

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wasted and damage done to cultural buildings dueto lack of agreed concepts of conservation, leadingto expensive changes of mind due to lack of policyand of firm control in execution which must bedelegated to one competent person after the policyhas been decided by a multidisciplinary group ofexperienced experts. Conservation policy for anindividual building will be based on inspection, fur-ther studies and the objective of the presentation.The policy should not be made by one man, as theresponsibility is too great, but for consistent artisticinterpretation one man, like the conductor of anorchestra, must be in charge of the execution of theworks.

Special techniques of repair and reconstruction ofbuildings form the final subject, with scaffolding,shoring, jacking, drilling, grouting, together withconsolidation of stone, as topics. The young architectwho can use these techniques is useful, but if he canget outside his professional strait-jacket and managelabour, order materials and use a theodolite, hewould be invaluable in developing countries.

It is gratifying to find how useful and universalthe principles of prestressing are; this is becausemost traditional materials, except wood, are weakin tension and by applying prestressing one cangive old structures a new lease of life.

Summary

The conservation of historic buildings constitutes aninter-professional discipline co-ordinating a range ofaesthetic, historic, scientific and technical methods.Conservation is a rapidly developing field which, byits very nature, is a multidisciplinary activity withexperts respecting one another’s contribution andcombining to form an effective team.

The modern principles which govern the organi-zation and application of conservation interventionshave taken centuries of philosophical, aesthetic andtechnical progress to articulate. These principles areencapsulated in the charters produced by ICOMOSgiven in Appendix V. Certain national charters applymore directly to local circumstances. The problem ofconserving architecture and the fine and decorativearts is not simple. Even in a scientific age that hasdeveloped the technology of space travel andatomic power, the solution to local environmentalproblems and the prevention of decay still presenta major challenge. Only through understandingthe mechanisms of decay and deterioration can weincrease conservation skills for prolonging the lifeof cultural property for future generations, butwe must admit that decay is a law of Nature and wecan only slow the process down.

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Part I

STRUCTURAL ASPECTS OF HISTORIC BUILDINGS

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Loadings

The initial state of all the internal actions in a struc-ture was determined by its construction, whereas itssubsequent behaviour depends upon external cir-cumstances and its changed condition. A structuremust, however, have the capacity to resist in anacceptable manner all the loads that it is likely tohave to bear. Rapidly applied loads may have amuch greater effect than the same load appliedslowly, and when such loads are changed rapidlyand are rhythmically repeated they can have evenmore damaging dynamic effects if their repetitionscoincide with the resonance of the structure. Thecommonest dynamic load is wind, but earthquakesare essentially dynamic loads acting horizontally onall parts of the structure above ground as the resultof vibratory displacements of the foundations.Traffic, while producing comparatively smalldynamic loads, can have major long-term effects.Active loads such as the weight of people, furnitureand goods, vehicles on a bridge or water against adam have to be balanced by the resistance of thestructure and these, together with the dead weightof the structure, have to be passed on, and bal-anced by, the opposed resistance of the soil belowthe foundations. Whether there is an adequatereserve margin of strength and stiffening in all thestructural elements of an historic building and theirinterconnections to resist live and dead loadings isoften a matter of judgement.

Under applied loads each element tends to giveway to some extent and it is through this limited ‘giv-ing way’ or deformation that the necessary resistanceis developed. Moderate tensile loads are beneficial ontensile structures giving greater stiffness and stability.Excessive compressive loads may lead to bucklingand loss of stability through the harmful bendingactions they induce in slender structural elements.Chapter 2 of Mainstone’s The Development of

Structural Form amplifies these points. Changes intemperature and humidity or even the setting ofcement can produce expansions or contractionswhich, if restrained, produce large active loads.

The internal actions or forces inside a structure areknown as tension, compression, bending, torsionand shearing. A building must have the capacity toresist all of these forces simultaneously, as necessary,but to have this capacity depends in the first placeon the geometry of the structure together with thestrength and relative stiffnesses of the individual elements and their joints. Where the structure per-mits of only one pattern of equilibrium it is staticallydeterminate, but if more than one pattern is possiblethen the structure is statically indeterminate and theloads will take the path through the stiffer routes andby-pass those parts that give way more readily.

Determinate and indeterminate structures

Ancient structures tended to be massive and inde-terminate since they were built of relatively weakmaterials. With stronger materials and the applica-tion of mathematical analysis, modern structureshave tended to become much lighter, and in theprocess of paring away materials such structureshave tended to have less reserves of strength and tohave lost good thermal and acoustical qualities.

Examples of determinate structures are trusses,three-hinge frames, portal frames and catenariessuch as suspension cables. A determinate structurewill collapse if even one element fails, for it lacksthe ability to readjust itself.

An indeterminate structure has the possibilities ofmany readjustments within its form and can absorbnew loadings, settlements and distortions. In stati-cally indeterminate structures, deformations lead tothe establishment of one of many possible patterns

2

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Figure 2.1 Ospizio di SanMichele, Rome, Italy

This section collapsed less than24 hours after it was declaredunsafe by the author on 31 March, 1977. The basiccause was bad workmanship.The evidence of imminent col-lapse was a new bulge in thewall between two windows.The pattern of collapse tellsmuch about the condition ofthe structure

Figure 2.2 Types of loadings—(a) tension and (b) compression

Arrows indicate the direction of the applied force. Dotted linesindicate tension or pulling apart. Solid lines indicate compressionor pushing together. Tension requires positive joints

Figure 2.3 Types of loadings—(a) bending and (b) twisting

In bending, applied loads some distance from the end of abeam cause equal and opposite couples in their own plane.Twisting is caused by equal and opposite couples

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Figure 2.4 Types of loadings—(a) shear and (b) buckling(Based on R.J. Mainstone)

In shear, one part tends to slip over the other along the shearline (shown dotted). Buckling is a sign of overloading in members that are not sufficiently stiff

Figure 2.5 Determinate types of stability (Based on R.J. Mainstone)

(a) Suspension(b) End fixity(c) Cantilever(d) Beam on two supports

Figure 2.6 Examples of stable structures (Based on R.J. Mainstone)

(a) Two-hinge frame with ends fixed(b) Cracked arch with firm abutments and two fractures at

quarter-span(c) A three-hinge frame(d) A deformed arch having three cracks with one abutment

that has settled. Note that the line of thrust must gothrough the hinges

of equilibrium. Further deformations reduce thenumber of choices left to the structure, which tendsto become more and more nearly determinate inthe process of time. Each structural form has itsown characteristic faults, limitations and typical pat-terns of behaviour. The total deformation that anindeterminate structure can absorb is a matter ofjudgement which must depend upon considerationof analogous situations, while bearing in mind thatanalogies must not be pushed too far.

Calculation of stresses in historic buildings

The calculation of stresses in complex indeterminatestructures is an extremely difficult task. The masterbuilders of the Middle Ages and the architects of theRenaissance had only practical and empirical, not the-oretical, knowledge of the forces involved in theirbuildings; but a cathedral which survives severalhundreds of years is clearly the work of a goodbuilder. The typical Romanesque and Renaissancestructure is ‘cavernous’, i.e. a mass, as it were, hol-lowed out. Its aim was to disperse forces as much aspossible. Walls were pierced to admit light only withcaution, and vaulting and domes were designed so asto disperse rather than concentrate forces. The Gothicsystem conversely was to concentrate forces intoframes of stone, and a cathedral was required to be astall and light as possible. Viollet-le-Duc says that ‘fromthe moment that the flying buttress was clearlyexpressed in the building the structure of the (Gothic)cathedral developed’. Isostatic diagrams help one tovisualize stress distributions (see Figures 2.7 and 2.8).

Jacques Heyman (1966, 1969) and R. Mark(1972), who reviews Gaudet’s propositions of 1902,have made interesting analyses of the forces inGothic cathedrals showing how well the thrustsfrom the vaults were dealt with by flying buttresses.Mark has developed a method of photoelasticanalysis based on scale models made of cast epoxy-plastic plate 9 mm (0.3 in) thick and to a dimen-sional scale of 1:167. The models are subjected toloading in the same way as the original, but at anelevated temperature of 135�C (275�F); the stressesare then frozen and the model viewed in a polari-scope. The pattern of stresses can be seen by linesof colour and the stresses may be calculated fromthe visible patterns and colours. Jacques Heyman inhis paper ‘The Stone Skeleton’ deals with masonryarches, flying buttresses, vaults and domes. He con-siders that the stresses in Gothic structures are gen-erally light and that failures generally occurred fromother causes, often eccentric loads on foundations.Although Gothic structure is essentially one of

transverse arched frames, longitudinal wall linkshave some effect. This was confirmed by war dam-age to the cathedrals of Rouen and Cologne, inwhich parts of the structures remained standingdespite severe damage to buttresses and contra-forts,thus showing that when some flying buttresses aredamaged the horizontal forces can be carried for alimited time elsewhere.

The outward horizontal stresses resisted by theflying buttresses may be as low as 10.30 kN/m2

(1.5 lbf/in2) on single-arch buttresses and as high as150 kN/m2 (22 lbf/in2) on double-arch buttressessuch as those at Notre Dame in Paris. The horizon-tal stress is caused by thrust from the roof and vaultstructures and by wind loading, which is variable.Flying buttresses have minimum and maximumhorizontal loads imposed upon them, dependingupon the direction and intensity of the wind, butfunction as long as the lines of thrust are within themasonry arch. A graphical method of analysis isshown in Figure 2.9.

Ove Arup and Partners used a shear panel con-vention to simulate the structure of the central towerof York Minster, and by this means were able to cal-culate the loads of the lines of thrust with the helpof a computer (Figure 2.10). The lines of thrustshowed eccentric loading on the foundations; thiswas one of the main causes of subsidence and asso-ciated danger to the superstructure. Likewise, calcu-lations showed an eccentric line of thrust at the eastend which had to be rectified by insertion of newfoundations. The choir piers at York, which are ofsolid ashlar construction, were not rebuilt but onlyrefaced after the fire of 1829; the central tower pierhas an eleventh century rubble core with thirteenthcentury additions, all encased in a ring of rubblemasonry, with a thin skin of fine ashlar executed inthree or four phases in the fifteenth century anddamaged by fire in 1829 and 1840. With such vari-ables it is difficult to calculate the actual loadings onthe masonry, for who can tell how much load istaken on the core with up to 70% mortar contentand on the outer casing with about 3% mortar con-tent? However, the average loadings are 3900 kN/m2

(36 tonf/ft2) in these main piers. In the arcade piersof the nave and choir they are 4200 kN/m2

(39 tonf/ft2) and in the piers under the western towersthey are 6000 kN/m2 (56 tonf/ft2). Similar loadingsoccur at Milan Cathedral. Salisbury is reported tohave a loading of 4800 kN/m2 (45 tonf/ft2) under thecentral tower and spire, whereas loads at Beauvaisof 1300 kN/m2 (12 tonf/ft2) in the 6 m2 (65 ft2)piers and at Norwich Cathedral of 1400 kN/m2

(13 tonf/ft2) in the main tower pier are not quite soheavy. It may be helpful to keep in mind the figuresfor these loadings when making a visual inspection.

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In such inspections the structural actions of allthe elements should be visualized, but the struc-tural action of the building must be understood asa whole. As an example, let us take an EnglishGothic cathedral. The structural elements of such acathedral are clearly defined and consist of stonecross-frames, longitudinal arcades and walls, piers,arches, windows and doors, roofs and vaults, tow-ers and foundations—all made up of the individualstones and timbers. Towers at crossings and at theends of lines of arcades help to anchor these struc-tures which are, however, subject to ‘sway’ or ‘drift’in the joints of the masonry, mainly due to thermalmovements or vibrations in the presence of a direc-tional thrust. As the tower is heavier it will tend tosink, whereas the ends of the cruciform plan willmove outwards and the wall and arcades will tendto spread sideways in the course of time.

In comparing examples of seventeenth centuryconstruction at St Paul’s Cathedral, London, withGothic York Minster (13–15th centuries), both build-ings being similar in size and volume, one finds that

the latter weighs about one-third of the former andthat loadings in the piers are 8–12 times greater. Insuch highly stressed Gothic structures the lines ofthrust must be carefully analysed, with geometryand scale taken into consideration.

Deformations

Records of the speed and sequence of the buildingoperations should be studied for every major struc-ture, so as to assess the effect of settlements anddefects which arise during construction. Thesequence used to be carefully worked out accord-ing to Viollet-le-Duc, in order to give a type of pre-stressing to buttresses.

It is important to differentiate between the initialdeformations of a structure which may occur in up to20 years from its completion and those that occurlater. Considerable initial settlements usually occurredin arches using lime mortar when the centring wasstuck. Settlements of 50–100 mm (2–4 in) were

Deformations

29

Figure 2.7 Isostatics of a beam(Courtesy: R.J. Mainstone)

Isostatics are contour lines of tension (shown dotted) and com-pression (shown solid). The closeness of the contours indicatesthe intensity of stress. Where lines cross, shear occurs. It can beseen that tension is greatest in the bottom and compression inthe top of the beam at mid-span. Shear is greatest at the ends.

(a) Uniformly distributed loading(b) Two-point loads(c) One-point load(d) One-point load with crack

The occurrence of the cracks causes the beam to become anarch, only dealing with compressive stresses. Lateral thrusts arenow required to retain it in position. Local crushing may occur

Figure 2.8 Isostatics of a slab(Courtesy: R.J. Mainstone)

(a) A slab reinforced in one direction may be considered as aseries of parallel beams

(b) A slab reinforced in two directions set on four supports.For simplicity, only tensile stresses are shown, but compressive stresses are equal and opposite. The stress pattern is remarkably like the pattern made by the ribs of a Gothic vault which, by using arched forms, removesthe need for positive joints having tensile resistance butwhich generates outward thrusts

normal during the construction of large buildings (likeSt Paul’s Cathedral or the Capitol in Washington D.C.)and as much as 700 mm (28 in) was recorded for thepiers of one of Perronet’s large-span masonry bridges.

Deformations may not only result from taking uploads but from seasonal changes in temperature orinternal heating, from changes in moisture content ofmaterials and from differential settlements, move-ments of the ground or alterations to the structurethat introduce a new pattern of equilibrium. There iscontinual movement in the cracks of an historicbuilding which have a seasonal envelope. Whenmovement is cumulative in one direction it is mak-ing a significant deformation. Accordingly, the moreelastic materials are, the more likely they are to becompatible with the structure as a whole. This is oneof the advantages that lime mortars and plastershave over modern cement mixes.

Cracking, crushing and yielding of materials canbe looked upon as gross deformations with loss ofstiffness in the structure or as modifications in theinterconnections of the structural elements. In prac-tice, if it were possible to inspect closely enough,most historic buildings will be found to havecracked and yielded in numerous places. Somecracks may not be permanent and may close if aload is removed. Much cracking is part of a continu-ing process of adjustment to continually varyingloads and deformations due to thermal or moisturemovements and wind. Although it is not harmfulper se, the long-term consequences of such crack-ing may be the letting in of water, or if it becomesblocked with debris or dust shifted by vibrationsthe crack may get progressively wider.

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30

Figure 2.9 Graphical analysis of forcesin a Gothic flying buttress(Courtesy: Ove Arup & Partners)

The horizontal thrust must be known andthe weights of each section calculated. Theline of thrust can then be drawn from thediagram on the right. If the line comes out-side the masonry, tension is indicated andthis may lead to collapse

Figure 2.10 Shear panel computer analysis of YorkMinster’s central tower(Courtesy: Ove Arup & Partners)

Calculated deflections of the central tower and transept due togravity loads acting on an uncracked simulated structure werefound by computer analysis

In those structures made of brittle materials that areweak in tension, but much stronger in compression,and particularly in vaulted structures of masonry orconcrete, visible patterns of cracking can be a reveal-ing indication of the nature of internal action. Sincecracks in masonry occur more or less at right-anglesto the principal tensile stresses, these cracks indicatethe direction of the principal compressions, which areparallel to the cracks. This is a form of structuralanalysis by the building itself.

Apart from the above question of observation,analysis and diagnosis of weaknesses, the question ofabove-ground interventions rests chiefly on the choiceof materials suitable for consolidation or repair andthe treatment of the cracks inevitably found in build-ings constructed without preformed expansion orother movement joints. Thermal movements andmovements due to changes in moisture, as well as theconsequences of fire or the introduction of centralheating, can all induce cracking. Because, even in theabsence of extreme events, some cyclic movementsmust continue to take place, it is useless to attempt toeliminate all cracking. Necessary reinforcementshould be designed simply to keep it under control.

The great merits of traditional elastic, relativelyabsorbent and easily renewed lime mortars forpointing and rendering should be emphasized.Portland cement mortars are, on the other hand,stiffer, almost impermeable and excessively strong,so that repairs tend to break away in large sectionsor subsequent weathering destroys the original,weaker, brick or stone rather than the pointing. Itmust be recognized, however, that climatic condi-tions vary greatly and that the role of an externalwall as weather skin and environmental filter like-wise varies. The correct choice of materials in aparticular case can only be made in terms of thelocal conditions, considering the total function ofthe wall (which might, for instance, have an import-ant fresco on its other face) and the existing con-struction and materials, together with the availablematerials and skills.

The correct choice of materials for structural con-solidation is different. In any wall or pier it is desir-able that the core should be as strong and stiff as thefacings and should be well bonded to them. Exceptin the case of some solid brick walls, a few walls ofsolid ashlar masonry and most Roman concrete walls,this is rarely the case. Short of completely recon-structing such walls and piers with weak rubble coresand the like, grouting is the only available technique,possibly assisted by the introduction of a limitedamount of reinforcement. Stronger mortars for thispurpose are desirable, but Portland cement mortaragain must be criticized on the grounds of excessivehardness, lack of elasticity and impermeability.

With uniform loading on ground that offers uni-form support, a building should settle uniformly evenif the ground loading is excessive by modern stan-dards. In the case of an historic building, such settle-ment will usually have taken place long ago and nowmatters little. Even a linearly varying settlement, per-haps as a result of a continuous variation in the sup-port conditions over the length or breadth, matterslittle if the resulting bodily tilt of the building is not excessive in itself or in relation to its height. Inclinations of 1% are quite common. Differential set-tlements of a non-linear kind, such as a greater set-tlement in the centre of a building, are the ones thatmatter most, since they can be absorbed only byweakening deformations of the superstructure.Observations of comparable structures may help inassessing how much differential settlement a buildingcan accept, although it must be remembered that thistolerance is partly dependent on the original speedand sequence of construction. With a slow buildingprogramme in which construction is carried up fairlyuniformly over the whole extent of the building,much initial settlement is accommodated withoutstructural deformation, by built-in changes of level. Insuch cases, settlement histories over the centuriescan, and should, be constructed, as has been donefor the Leaning Tower of Pisa and for York Minster.

Usually, conditions below ground remain virtuallyunchanged through the centuries, whereas the struc-ture above ground suffers a progressive loss ofstrength due to weathering and decay of materials andthe disruptive effects of cyclic temperature changes,etc., interrupted from time to time by human inter-ventions. This situation should not, however, be takenfor granted. Water levels in particular may change asa result of drainage, pumping, obstruction of under-ground flows, or other interventions, and conditionsmay also be changed by adjacent works of otherkinds. The effects of a change in the water table maybe difficult to predict, but are usually undesirable.Preservation of the water table is therefore usuallyimportant. It was, for instance, reported that two-thirds of the present increase in the inclination of theLeaning Tower was due to water abstraction and thatthe earlier water table was now being reinstated bypumping in water. Local de-watering or pumpingconstitutes a similar danger, particularly if it leads tothe removal of silt. An example can be quotedwhere running water under a building leached sandfrom beneath it and led to a settlement of 300 mm(12 in). Stopping the flow stabilized the situation.

Where differential settlement is leading to exces-sive deformation of the superstructure, the situationshould be analysed in full in both its above-groundand below-ground aspects by architects, engineersand soil mechanic experts. The relative merits and

Deformations

31

costs of alternative schemes for strengthening thesuperstructure, underpinning it (i.e. carrying the foun-dation down to an existing firmer stratum), enlargingthe foundations or improving the soil conditionsshould then be weighed against one another to selectthe best course of action, which should involve theminimum intervention and maximum retention oforiginal material. Possible methods of improving thesoil condition, each having the advantage of leavingthe historic building untouched, include:

(1) Chemical stabilization by high-pressure injec-tion (difficult in built-up areas).

(2) Weighting the surroundings to prevent adjacentuplift (difficult in built-up areas).

(3) Local water extraction to cause local shrinkageand thereby a corrective differential settlement.

(4) Drainage or de-watering.

Adoption of these methods calls, however, forthorough prior investigation with an assessment ofthe advantages and disadvantages. It is better toseek the ‘least bad’ solution rather than whatappears the best. The least bad intervention is onethat should be assessed in terms of least damage tothe values of the historic structure and one thatkeeps most future options open. Cost efficiencyand how easily the solution meets the requirementsof statutory bodies are not prime considerations.

In all cases of possible hazard from groundmovements, it is desirable to investigate the generalgeological background to locate and identify, forinstance, a geological fault line or the presence offine laminations in a clay soil. In earthquake zonessuch investigations are of the utmost importance.However, despite sophisticated laboratory tests ofsoils, the writer has found that often an importantfactor has been missed. Much also depends oncareful and skilful control. Chemical stabilization,being irreversible, should be used with caution.

Three different possibilities exist in the way abuilding settles. (1) Equal settlement over the wholeextent of the building, resulting in it sinking as a rigidbody without rotation. Such settlements need notcause damage and if a building sinks evenly in fact itforms its own foundations by compressing the sub-soil and so increasing bearing capacity. This is fairlynormal with historic buildings and is accepted in theUSSR with modern buildings where 80–100 mm(3.2–4 in) settlement is accepted. (2) Settlement thatincreases uniformly from one extremity to another,resulting in sinking and rotation of the whole fabric,as in the case of the Leaning Tower of Pisa. Rotationsettlements may cause damage, especially whencolumns are tall and slender as in the case of MilanCathedral. In new buildings cracks occur when

rotation settlements exceed 1/500 of the span, but1/300 of the span is considered acceptable. In extremecases rotation settlements can lead to overturning. (3) Non-uniform settlements which cause local defor-mations and eccentric loads on foundations by thesinking of those parts that are most heavily loaded orthat stand on the weakest ground. Besides causingdamage the deformations may cause dangerouseccentric loadings on the soil below the foundation.The larger the building, the more vulnerable it is todefects due to foundation settlements and failure dueto unsatisfactory solutions of the static design and todeterioration of the materials, for the static and en-vironmental stresses are both greater. On the otherhand, smaller buildings are more liable to suffer fromneglect, carelessness and changes to unsuitable uses.Luckily, most historic buildings have withstood theabove-mentioned hazards, but it should be remem-bered that there have been many collapses and onlythe successful buildings are still standing.

Materials used in historic buildings

Let us consider the two main structural materialsfound in historic buildings—timber and masonry.Members of timber systems can resist tension aswell as compression, and the joints can resist ten-sion, but the strength of the total system is limitedby the strength of the joints. The span is limited bythe length of timber available. Known timber struc-tural systems include, for walls, solid timber treetrunks set vertically or horizontally, post and lintelsystems, box frames and cruck framing, and forroofs, simple beams, rafters and tie beams, trussedbeams, arch braced beams, hammerbeam trussesand framed trusses.

Masonry structural systems include simple postand lintel systems, as for timber, but the commonestsort of masonry system is mass construction withpierced openings; stone skeleton frames weredevised for sophisticated Gothic buildings withpointed arch and flying buttress, through which thelines of thrust were intended to flow within thephysical limits of the masonry. In contrast to timber,the total strength depends more on the compressivestrength of the materials rather than on the joints.

In the case of stone, its strength, quarrying facil-ities, lifting and transportation were also vital con-siderations. The longest stone beams known are inFukien, China. They are 23 m (75 ft) long, are ofgranite and were used to build a multi-span bridge.Calculations show that the tensile strength of thestone is just sufficient to support this length. Thelength of wooden beams is limited by the length ofavailable timbers.

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Primitive openings in masonry walls were formedby large inclined stones set in an inverted vee, as inthe Pyramid of Cheops or the Lion Gate at Mycenae.Arches may have developed out of the pseudo-archesfound in ancient Greek polygonal walls at Delphi orout of the sloping construction of a drainage culvertat Babylon or the tomb of Menteumhet El Assraf atThebes. In the bridge between Tiryns and Epidaurus,one of the oldest in the world, the arch effect may beaccidental as the large keystone only spans the twocantilevered projecting lower courses. Pseudo-archesbased on the cantilever principle were also used inthe domed Tomb of Agamemnon at Mycenae and inthe ‘Trullo’ dwellings of Apulia, as well as in similarhuts in Provence.

The prototype of the domical structure in com-pression was in all probability the radial frameworkof bent reeds, saplings or curved timbers meeting atthe apex and covered with turfs, thatch, skins or mat-ted materials. Innocent describes such a constructionbuilt by charcoal burners in England in 1900, andsimilar vernacular buildings are found all over theworld. Evidence of more or less conical domes ofmud or mud brick have survived from the sixth orfifth millennium B.C. in Iraq. The use of stone inconstructing domes followed that of the softer

materials and by 1300 B.C. had reached monumentalproportions with a span of 14.5 m (48 ft) in the Tombof Agamemnon at Mycenae. These early domes werein fact pseudodomes of conical shape as they werebuilt without centring, with each ring of stone can-tilevering inwards until capped by a large stone.

In the space of three centuries, Roman buildersusing pozzuolana cements achieved large archedspans—30 m (98 ft) was not unusual—that culminatedin the Baths of Caracalla in A.D. 211. Often, as in thecase of the Pont du Gard and Falerii Novi, arches werebuilt of well-fitting stones without mortar. The largestsurviving Roman bridge arches are those of the PontSt Martin near Aosta, which spans 35.5 m (117 ft). Suchspans were not surpassed until the development ofPortland cement and concrete with steel reinforcementin the latter half of the nineteenth century.

Three variations in arch construction were intro-duced by the Romans—first, the stepped pentago-nal voussoirs which bonded into the masonry andspandrels alongside, secondly the flat-topped archand thirdly joggled voussoirs. This joggling, whichreached extreme elaboration in Ottoman architec-ture, facilitated construction and reduced the dan-ger of collapse. The chain arch was a post-Romandevelopment, conceived as an answer to building

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Figure 2.11 (a) Strength, (b) density and (c) stiffness oftraditional and contemporarybuilding materials compared(Courtesy: Allen Lane and Penguin Books)

small bridges on very poor foundations which wereliable to tilt or spread. Examples are to be seen inVenice, but most are to be found on the YangtzeDelta of China where the type may have originated.

Like vaults, domes are generally built of brick orstone masonry. The earliest surviving concretedomes, dating from about 100 B.C., are in the frigi-daria of the Public Bath in Pompeii, which had a coni-cal form and span of only 6 m (20 ft). The so-calledTemple of Mercury at Baia, which was really anotherbath, was built a century later and had a larger spanof 21.5 m (71 ft). However, in the first and secondcenturies A.D. the development of the true dome wasrapid, culminating in A.D. 128 in the Pantheon, whichwith its internal diameter of 43.3 m (142 ft) remainedunequalled in size for 13 centuries and was notexceeded by more than a few centimetres for 19 centuries.

In the course of time, due to excessive consump-tion, as the supply of virgin wood was reduced,attempts were made to bolt and laminate timbers toform arches. The first major timber arches to berecorded were used in A.D. 104 by Apollodorus ofDamascus in a bridge across the Danube, consistingof 11 spans of over 30 m (98 ft). They are illustratedin carved relief in Trajan’s column.

Timber construction developed rapidly in Japan,where the reputedly oldest timber building, apagoda dated A.D. 670, still stands in Nara whichalso possesses the largest timber building—theToruji, dating from the thirteenth century whichalthough reduced in size by a fire in the seven-teenth century is still an immense structure.

The English hammerbeam roof, made of oak,was developed to span spaces without tie beams.It reached its supreme example in London’sWestminster Hall (A.D. 1402), having a clear span of20.5 m (67 ft) and length of 71.5 m (235 ft). Othernoteworthy roofs include the Basilica Vicenza, span20.5 m (67 ft), length 52 m (171 ft), using barrelvaults and steel ties, and the Hall of Justice inRouen, span 17.2 m (56 ft), length 40.6 m (133 ft).

To replace timber and in search of fire-resistingconstruction, cast-iron beams and columns wereintroduced by Bage in 1796, followed by Boultonand Watt in 1799 and developed by Tredgold in themid-nineteenth century.

Cast-iron arch forms initially followed timber: theIron Bridge at Coalbrookdale (England) in 1777,with a span of 30 m (98 ft), was followed by ThomasTelford’s bridges at Buildwas (England) andCraigellachie (Scotland). Eiffel developed wide-spansteel trussed arch bridges for railway loadings, as atGarabait in Portugal. The Forth Bridge (Scotland), byBaker, was an outstanding achievement of its time,with three pairs of trussed cantilevers reaching out

207 m (679 ft) and carrying a central span of 106 m(348 ft) to give a total clear span of 520 m (1706 ft).In welded steel, the gateway arch at St Louis,Missouri, USA, built in 1966, is now a pre-eminentarch with its span of 192 m (630 ft).

When it was found, after several failures, that castiron was weak in tension, a wrought iron substitutewas used by Fairburn; subsequently, steel beamswere developed in the later half of the nineteenthcentury and were exploited in steel-framed struc-tures, which are beyond the scope of this book.

The structural capabilities of buildings clearlydepend upon their materials, whose availability andcharacteristics determine the possibilities of spanand height.

The primitive mud wall may stand up to threestoreys, the rubble stone wall up to six or sevenstoreys. The stone arch may span 85 m (279 ft); themass concrete arch 25 m (82 ft), the mass concrete ormasonry dome 43.3 m (142 ft) (Pantheon); the Gothicstone skeleton and vault a span of 13 m (43 ft) spring-ing to 40 m (131 ft) in height. The steel-framed sky-scraper may reach 410 m (1345 ft); the reinforcedconcrete skyscraper 180 m (590 ft); the prestressedconcrete dome can span 120 m (394 ft) and the steelsuspension bridge 1020 m (3346 ft). With improve-ments in the technology of building, these figures willprobably be exceeded; however, they are interest-ing in that the possible size of a structure can becompared with the materials of which it is made, sogiving a basis of judgement. Nevertheless, the struc-tural actions of a building depend upon its form.

All the main materials now in use are derived fromthe same basic materials that have been used for thou-sands of years—earth, rock, timber and metals—buthave been improved in utilization and manufacture.Other new materials, such as plastics, synthetic resinsand aluminium, lack stiffness in practice, so play asecondary role in construction, because for most struc-tural purposes stiffness is as important as strength. Inthe context of historic buildings, reinforced concretemust be considered a new material.

If one compares the tensile and compressivestrength, density and stiffness of the main structuralmaterials used in historic buildings (stone, brick,mass concrete and timber) with cast iron andwrought iron, structural steel and aluminium alloy,striking differences are found. The historic materi-als except for timber are all very weak in tension,whereas the materials used in the nineteenth cen-tury and later, with the possible exception of castiron, are strong in tension and exceptionally so incompression; even wrought iron, the weakest ofthem, exceeds the best stone in compressivestrength. The comparative characteristics of ‘new’and old materials are set out in Figure 2.11.

Structural actions of historic buildings

34

Although the strength of materials is of interest inextreme cases, generally it is not of major significanceunless decay of the material affects the strength of astructural element; otherwise such decay is only ofsecondary importance. Most structural elements con-sist of one principal material. Historic buildings carrytheir loads by massive and stiff forms, differing fromlatter-day buildings which rely on relatively flexiblestructures having rigid joints and structural continuityand using both tension and compression equally.

Classification of historic structures inrelation to structural actions

Although a classification scheme based on materi-als could be developed further, difficulties arise onaccount of the very different ways in which particu-lar materials have been used. Further difficultiesarise where, as often happens, several materials areused in a single building.

In Mainstone’s classic study of the historical devel-opment of structural forms, mentioned in Chapter 1,classifications based primarily on the forms them-selves were preferred. Elements were discussed firstin several broad groups such as arches, vaults anddomes; beams and slabs; trusses; vertical supports andfoundations. Then different groups of complete build-ings were considered, ranging from the simplest earlyhuts to much more complex forms. These classifica-tions were probably ideal for following the intricatepattern of interrelated developments of elements andcomplete buildings and, at the same time, gaining aninsight into the essential characteristics of each form.

Where the historical pattern of development is ofsecondary interest in relation to the immediateproblems of understanding particular structures andassessing their present state of health, a slightlymodified approach may be adequate. In a paperwritten to introduce a symposium on Structures inHistoric Buildings, held at ICCROM in 1977 andreproduced as Appendix I, Mainstone offered hisown suggestions, concentrating on the principalfamilies of spanning elements. He emphasized,however, when presenting the paper, that eachbuilding must be considered as an individual, justas the doctor must consider each human patient asan individual if he is to care for him properly.Classifications and general understandings of theimportant characteristics and typical maladies ofdifferent structural families are a helpful basis forunderstanding the individual. But they should notbe regarded as more than a starting point.

Chapters 3–6 look further at Mainstone’s familiesof elements, although not in precisely the samesequence. Characteristic symptoms of structural dis-tress are considered, together with some possiblemethods of strengthening or repair. Foundationsare left to the end because the most accessible evi-dence of their condition is usually presented by theextent and nature of deformations and cracking ofthe superstructure. Although the approach is interms of elements, it must also be emphasized thateach structure must ultimately be considered as awhole before making a final assessment. Thus thereis little value in considering the stability of, say, anarch, without considering its supports and the firm-ness of the ground on which they rest.

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Beams

Post and lintel, column and beam and slabs madeof beams side by side, resting on continuous walls,are the most elementary form of building construc-tion in both timber and masonry. It is thought that,as in the development of the Greek Doric order,timber forms were generally carried on later instone. Disregarding catenary forms of nomad tents,houses, temples, public halls and palaces were con-structed this way until Roman times.

Just as a beam conceals within itself the action ofan arch, so slabs contain the actions of shells andmembranes. The directions of principal stresses, asshown earlier in Figure 2.7, of compression (thicklines) and tension (dotted lines) are known as iso-statics. These give a picture of typical situations thatwill enable visible evidence to be understood andinterpreted. A simply supported beam (free torotate about the supports at its ends and to expandor contract longitudinally) is an element acting inbending, compression and in shear. In carrying anyparticular sets of loads, a, b and c, it is equivalentto a family of arches (compression) associated withan orthogonal family of catenaries (tension). Theseinternal arches and catenaries adjust themselveswithin the beam to each change in the loads. Whenthe beam cracks due to weakness in tension, asoften happens with stone, the situation changesand the beam then acts mainly as an arch and pro-duces outward thrusts. The beam may also fail inshear and for this reason, in the Near East and Italy,masonry flat arches were often built with joggledjoints, to give greater earthquake resistance.

‘The natural state of the masonry flat arch or lintel isthe cracked state’, according to Professor J. Heyman,who has shown that a lintel built of masonry cannotact properly until it has cracked. Moreover, in thiscondition it is safe provided the abutments can resistthe lateral thrusts which the cracks generate. The

pressures due to these thrusts are generally low com-pared with the crushing strength of stone, but theymay be large enough to crush the soft decorativebrick often used in English eighteenth-century lintels.

The development of reinforced concrete and pre-stressed concrete beams was started by Pope in 1811with a beam made of prestressed blocks reminiscentof the reinforced masonry in the Place de la Concordeand Pantheon in Paris, but the first to recognize thecorrect disposition of the tensile forces in a beam wasWilkinson, with his patent of 1854. This was furtherdeveloped in 1897 by Hennebique and what was, ineffect, a new material—reinforced concrete—was cre-ated. When cast in situ, reinforced concrete has thegreat advantage of obtaining structural continuity.

Decay and repair

Decay in timber columns usually occurs as a resultof dampness and insect attack close to the ground.In oriental architecture the columns rest on a padstone set raised above the general ground level.This prevents or at least reduces rising damp andtermite attack. Decay in timber beams usuallyoccurs where they are embedded and subject tofungal and insect attack. Penetrating rain also cancause decay and a beam may collapse as a result.

Cracks in stone columns and beams can beinjected with epoxy resin and strengthened withdowels of stainless steel or bronze.

Steel columns or beams can have more materialadded in situ by riveting or welding, but satisfact-ory techniques of strengthening or repairing castiron have not been found. The most hopeful fieldis that of plating using epoxy resin glues.

In the diagnosis and cure of defects in reinforcedconcrete, considerable difficulties occur—first, ininvestigating the design, as the all important rein-forcement is not visible; secondly, in reinstating the

3

Structural elements I: Beams, arches, vaults and domes

strength of lost parts; and thirdly, in reinstating lostcontinuity. The structural conservation repair of his-toric skyscrapers will thus present problems theanswers to which have not yet been found. Smallcracks can be grouted with epoxy resins. Much themost difficult problem to deal with is the cure ofrusting in the reinforcement, due either to cracks orto insufficient covering material and inadequateprotection against the weather.

Arches

Arches must be considered in the context of the wallor arcade in which they are situated and of the thrustthey exert on their abutments. Pointed and parabolicarches are special cases. The hinging effect is mostrelevant when the depth of the voussoirs is small inrelation to the span. When voussoirs are deep in relation to span, arches are able to absorb deforma-tions generally by slipping, as in the case of theColosseum. In all cases the condition of the

abutments is vital to arches. If these supports aresliding, sinking or rotating, the stability of the architself is suspect; therefore, the abutments alwaysneed most careful consideration.

The sources of stress in arches come from theweight of the structure, dead loading and appliedloads. In long-span masonry arches the dead loadsometimes caused collapse when the shutteringwas removed. Stresses can be increased by the set-tlement of an abutment.

Loads can be calculated by graphical means andthen lines of thrust can be shown. Such diagramsare immensely helpful when investigating stressesin an arched construction (see Figure 3.3).

Assessment of strength of masonry arches

Assessing the condition and strength of masonryarches and vaults is one of the most difficult prob-lems facing the architect responsible for an historicbuilding. Calculations of their strength are rarely

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Figure 3.1 Transept arcade arch, York Minster, England(Courtesy: Shepherd Construction Ltd, York)

The thirteenth century arch has been severely damaged by thesettlement of the central tower. The top part had to be rebuilt,which work revealed an earlier eleventh century window opening

conclusive and, without the possibility of full-scaletests, experienced judgement must be the finalarbiter. One very important aid to assessing the con-dition of an arch is the full measuring of all move-ment, over a period of at least a year (much longer ifpossible), so that changes over all seasons can bestudied. There are various ways in which the strengthof an arch can be assessed by observation. The basicshape is of prime importance; parabolic and pointedarches are stronger than flat elliptical ones; archeswith a good rise are stronger than flat ones and

cause less thrust on the abutments. As a rule ofthumb, an arch is likely to be weak if its rise is lessthan a quarter of the span. The depth of the vous-soirs is also important—the deeper, the stronger, asthere will be a greater number of alternative lines ofthrust available to meet various loadings. The flatterthe arch, the more lateral thrust it produces; thus itdepends for its strength more upon the firmness ofits abutments, which should not be subject tomovement and should be carefully inspected.

The nature and condition of the masonry, thethickness of the joints and condition of the mortar,the degree and direction of any deformation from the true line of the arch, and the width, length andposition of any significant cracks must all be recorded.

Strength of bridge arches

Although they are not strictly historic buildings,ancient bridges have some special factors whichapply, in addition to the above general comments onarches. The average depth of fill above the crown ofthe arch is important in distributing point loads, andgood haunching at the abutments is essential for anybridge or arch. The impact of heavy vehicles is a frequent source of damage; this and the continuedlive loading to which all bridges are subject may giverise to longitudinal cracks running in the direction ofthe span near the edge of the arch, to bulging of thespandrels and to cracking of the wing walls.Longitudinal cracks may also be due to differentialsettlement of either abutment. Large cracks may indi-cate that the arch has broken up into narrower rings,each spanning independently, and this is a sign ofdanger. In some cases the insertion of pipes and otherpublic services may have caused local damage whichcan only be discounted if the structure is built of goodmaterials and workmanship, shown by good masonryset on its correct bed, or well-shaped, durable bricksin correct bonding with regular and narrow joints.

Cracks in arches

Arched architecture can absorb thermal movementsand excessive loadings by forming local cracks inthe arches which act as hinges. Three such hingesare theoretically permissible, but it must be remem-bered that with pointed arches the apex may act asa hinge, so only one hinge crack in each arc is safe.Thermal movements over long periods lead to‘drift’ or the lengthening of the upper parts of wallscaused by the sliding of the masonry in the arch’sjoints which tends to break up the mortar andweaken the abutments and spandrels.

Arches

39

Figure 3.2 Deformation in arches(Courtesy: Ove Arup & Partners)

(a) Intact arch(b) Arch cracked by spreading abutments(c) Arch cracked by differential settlement of one abutment

The voussoirs often compress the plastic lime mortar and areheld in position by friction, so that the cracking does not constitute the formation of hinges. In practice, both actions aregenerally combined

Approximately tangential diagonal cracks near thesides of the arch springing, which spread up towardsthe apex of the arch, are generally due to subsidenceof an abutment, and, if extensive, may indicate a dan-gerous state. Cracks in the spandrels near the quarter-points of the span indicate that the arch is acting as ahinged frame, but, other things being considered, donot indicate a dangerous state. Sometimes even if nosettlement or cracking is visible the face of masonryin an arch or vault is seen to be bulging outwards.This usually indicates poor internal condition of themasonry—it may originally have been badly builtwith rubble, re-used stone or poor mortar, or it mayhave deteriorated owing to water penetration, etc.The soundness of the masonry can be confirmed

by listening to the tapping of a hammer on the oppo-site side of the wall. Masonry and brickwork whichare consistently wet or where damp often penetratesare likely to be weaker than similar dry areas.

Repair of arches

Repointing and grouting masonry in arches can, ifapplied to the maximum depth possible, greatlystrengthen an arch. The repair of all types of archesmay involve taking down the arch and rebuilding it,using a traditional falsework of timber and shoringwith close-centred needles to carry the weightsabove the arch. On the other hand, if the arch iswide and the voussoirs are not of the full width itmay be possible to rebuild half at a time or to takeout defective stones or bricks and replace themindividually. This has the advantage of not affectingthe walling above to such an extent. Repair byrebuilding is rather drastic as it relieves compres-sive stresses, raising questions of prestressing thearch to avoid new deformations, which may requiregreat ingenuity. Such prestressing can well be car-ried out with hydraulic jacks, as described inChapter 21. Occasionally an arch can be freed bycutting out mortar joints and pushed back into posi-tion using hydraulic jacks.

Vaults

Vaults are usually constructed of stone or brickmasonry, as these are good materials when used incompression, but other materials such as timberand plaster can be used. The ceilings of YorkMinster are an interesting example of a stone vaultreproduced in laminated timber. Vaults such asNeumann used at Baroque Neresheim were con-structed of tufa reinforced with iron tie bars. Thecomplex cutting of stones with two curves to formvaults was avoided in Roman construction by theuse of mass concrete. Later, brick ribs were intro-duced into the groin, as in the Baths of Diocletianwhere clear spans of up to 20 m (66 ft) wereachieved. Such heavy construction demandedheavy centring, which was overcome by buildingthe ribs first and then filling in the webs virtuallyfreehand with a light curved centring. This pro-cedure, as developed in Islam in the tenth century,had far-reaching consequences when adopted inGothic buildings in the late twelfth and thirteenthcenturies. Ribs also facilitated construction in threeways—first, they served as cover strips to the groins;secondly, they simplified setting out and along withthe pointed arch gave freedom and flexibility in

Structural elements I: Beams, arches, vaults and domes

40

Figure 3.3 Diagram of thrusts and movements—eastend, York Minster, England(Courtesy: Ove Arup & Partners)

The diagram shows the line of thrust dangerously close to theoutside face of the wall and indicates eccentric loading on thefoundations. New reinforced concrete foundations weredesigned to give concentric loading

Vaults

41

Figure 3.4 Over Bridge,Gloucester, England

Because there were cracks atthe quarter-span and thebridge sagged at its apex,where there was also a horizontal crack, the roadauthorities had signed a contract to blow up this magnificent bridge of 45.5 m (150 ft) built byWilliam Telford. Due to earlysettlement of the east abutment the bridge had infact ‘binged’ at the quarter-spans. Examinationof the abutments showed thatthey were still perfectlysound. The authorities werepersuaded to keep the bridgeas an ancient monument

Figure 3.5 South face of tower,Norwich Cathedral, England

Due to aging, the c. A.D. 1120masonry of the tower has becomerather decrepit. Repairs of c. 1870 hadcovered the defects with rendering. A century later the tower had to beconsolidated by grouting andrefaced with new stone which wasbonded to the interior with bronzecramps

planning; and thirdly, they reduced the need forcentring. After the stone facing had been placed,vaults were frequently thickened with a backing ofbrick or lime concrete, in which case the rib lost itsstructural function and in time might fall away fromthe vault. Loose ribs are met fairly frequently inGothic construction. On the other hand, if thin, thevault itself might fall, leaving only the diagonal ribsand transverse arches standing. The care withwhich the masonry of vaults was designed is shownin Figures 3.7 and 3.8, taken from Viollet-le-Duc’sbook on construction.

Groined vaults form a naturally stiff shape and are,in effect, diagonal arches formed within the thicknessof the vault and therefore the maximum compressiveforces will occur at the springing of the arch. Cracksmight therefore form parallel to the groins.

The ribs in pointed arch buildings are the decora-tive expression of a constructional element, in thatthe ribs initially formed a permanent shuttering for the vault. Most early Gothic vaults are generallyquite thick, i.e. from 150 mm (6 in) to 450 mm (18 in),and may be considered as ribbed domes resting onfour points called the ‘tas de charge’. The walls maymove away from the vault and may leave a gap of30 mm (1.2 in) or more. In time, ribs may drop awayfrom the vault they are supposed to support, becom-ing a hazard should they fall, so in inspections greatcare must be taken to check that all ribs are safe. Tobe certain of this is difficult, and a detailed inspec-tion from scaffolding may be necessary.

There are outward thrusts in high vaults withpointed arches. To counteract these forces, deep but-tresses together with flying buttresses were devel-oped, with decorated pinnacles. The effectiveness ofthis buttressing depended upon the depth of its pro-jection and the top weight of pinnacles which couldhelp maintain the line of outward thrust within thesafe limits of the masonry. Buttressing was sometimesinadequate to counter the outward thrust from thevault and roof, so one often sees iron or steel ties thathave been placed across the vault at the springing.

Thin, continuous barrel vaults resting on parallelwalls or arcades may produce quite small thrustswhich are well distributed and can be countered bythe massive weight of the walling, which diverts thelines of thrust downwards.

The stresses on vaults covered by pitched roofscome mainly from their own weight and their inabil-ity to deform if their supports move. Ribs may formunstable mechanisms liable to collapse. Assessmentof damage and analysis will therefore depend firstupon correction of the causes of structural distress inthe supports. When these have been dealt with, thevault itself can be looked at; ribs will have to berebuilt together with damaged sections of the vault.

It is important that ribs, when rebuilt to a correctshape, are prestressed by use of wedges orhydraulic jacks which can be removed later. Vaultscan be consolidated with a penetrating grout. If thecracks are fine, an epoxy resin formulation is good,but if they are large, normal mortar grouts shouldbe used in the vault first, and then regrouted withthe epoxy resin. If such methods are not practica-ble, metal ties across the springing of the vault willhave to be inserted, as was common in the past.

Domes

The technological achievement of Roman architec-ture represented by the dome opened up a newarchitectural era with the potential of large, unen-cumbered interior spaces, but the design was ham-pered by the necessary heavy construction, as thethickness of the walls of the dome was 1/10 or 1/15of the radius. The great weight of early domes pro-duced tension in the perimeter, which was indi-cated by circumferential cracks in the lower partsuch as occurred in the Pantheon and later in St Peter’s, Rome. Lightness came only in the twentieth century, when with the use of materialslike reinforced concrete a ratio between thicknessand span of 1/200 was found to be practicable.

The dome of St Sophia (A.D. 532–537) in Istanbul,with its span of 31 m (102 ft) is one of the supremeexamples of this structural form. Built on penden-tives and flanked by two hemidomes, it gives abreathtaking sense of dematerialized floating spacewhich is enhanced by the flat surface treatment ofmosaics and marble. To resist tensile forces, thestones forming the cornice above the pendentiveswere cramped together with iron and, at the baseof the dome, wooden bonding timbers were builtinto the brickwork.

Lightness in dome construction was obtained bydivorcing the inner and outer shells. Such domes weredeveloped by Islamic architects to produce fascinatingexternal profiles with improved weather resistanceprovided by a durable and impervious surface ofglazed tiles of intense colour, or of gilded copper tiles.

So as to minimize cracking of domes, effortswere made to reduce the weight of the structure bycoffering and by using hollow pots to reduce theouter thrusts in the lower third of the dome.Tension rings of wood and stone were also insertedby Brunelleschi in the Dome in Florence and ofwrought iron by Wren at St Paul’s in London withthe same objective. Ribbed domes, such as those ofthe Grunbadi in Kharka, the Library of FridayMosque in Isphahan and San Lorenzo in Turin, areof particular architectural interest.

Structural elements I: Beams, arches, vaults and domes

42

Domes

43

Figure 3.6 Vault forms(Courtesy: R.J. Mainstone)

(a) Barrel vaults may be treated as a series of parallel arches.The outward thrusts are small if the spans are small andthe vault thin in relation to thick outer walls. Ties in tension may link the walls together to resist this thrust

(b) Domical masonry vault—isostatics. The compressive forcesare important, and meet together in the centre. Tensile forcesare resisted by the outer walls or the next domical vault

(c) Quadripartite Gothic vault. The ridges are held in positionby equal and opposite thrusts. All the compressive forces arebrought down to the ‘tas de charge’. The vault arches act inparallel to the side walls so cracks here do not matter

Figure 3.7 A ‘tas de charge’(After Viollet-le-Duc)

The setting out of such stones needs a master in solid geometryand was done full size on a tracing floor making templates foreach stone. Note that stones A, B and C are bonded integrallyinto the outer wall

Some outstanding recent examples include the‘small’ and ‘large’ sports palaces built by Nervi for theRome Olympic Games of 1960. Of reinforced con-crete precast voussoir construction, these domes arebuilt to such fine limits that regular and careful main-tenance will be the best way to ensure their preser-vation. Torroja with his Market Hall in Algeciras,Spain; Saarinen, Ammann and Whitney with theTWA terminal in New York and Utzon and Arupwith the Sydney Opera House have also made agreat contribution to the twentieth century art ofcovering large areas with the minimum of support.

Like arches and vaults, the dome depends uponthe firmness of its supports, so causes of distressmust be looked for there. The dome itself suffers

Structural elements I: Beams, arches, vaults and domes

44

Figure 3.8 A Gothic vault from above(After Viollet-le-Duc)

Note:(1) the form is curved in two directions, so giving great

stiffness(2) the heavy stones at the apex of the arches and in

particular the central boss which key the structure together(3) the filling above the ‘tas de charge’(4) often the vault is thickened by a covering of mortar or

bricks and mortar

Figure 3.9 North choir aisle vault, York Minster, England

A general view of the vault adjacent to the north-east pier of thecentral tower. Severe defects, resulting from the settlement of thetower, can be seen in the ribs and panels

from two major causes of stress—first, tension inthe lower part where the angle subtended at thecentre is greater than 51� 08� from the vertical,resulting in circumferential cracking; secondly, dueto thermal movement, as the shape of the domeand the rest of the building are different, leading toradial cracks.

Mainstone’s diagrammatic plans of the superstruc-ture of St Sophia analyse the principal compressionthrusts and show radial tensile cracking and the loca-tion of shear failure. These all contributed to the

spreading of the supports which, within about 20years of its completion, accentuated by an earth-quake, led to the partial collapse of the rather shal-low dome, which was completely rebuilt to agreater height. Brunelleschi’s masterpiece, theDome of Santa Maria del Fiori, Florence, has ribsand coffers which lighten the structure of the linkedshells. Wren’s solution for St Paul’s in London reliedupon an inner dome and a cone which supportsthe cupola, together with a timber structure to formthe outer dome.

Domes

45

Figure 3.10 North nave aisle vault, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Cosmetic repairs at intervals by generations of masons withoutprofessional supervision had obscured vital evidence. The failure to diagnose or record continuing settlements led to thiscritical situation

Structural elements I: Beams, arches, vaults and domes

46

Figure 3.11 North nave aislevault, York Minster, England(Courtesy: Shepherd BuildingGroup Ltd)

Recent cracking in the vaultwas caused by settlement of thenorth-west pier of the centraltower. However, most of thecracks had been mortared overpreviously without diagnosis oftheir cause

Figure 3.12 Vault over choirof Naples Cathedral, Italy(Courtesy: R. di Stephano)

After wartime bomb damage,the roofs had to be reconstructed. An elegantarched ribbed dome in weldedsteel was devised to support themetal deck on which the rooftiles rest

Repair of domes

Because domes may crack radially, repairs andstrengthening have generally consisted of insertingchains to act in tension. For the 1925–31 restorationat St Paul’s, the two drums of the dome were linkedtogether with forty-eight 100 mm (4 in) diameterdiagonal rods in tension and ninety-three 63 mm(2.5 in) diameter tie rods. Two additional steel chainswere inserted to encircle the base of the drum, beingrespectively 132 m (433 ft) and 180 m (591 ft) longand weighing a total of 58.5 t (57.5 ton). The fourquarter-domes had 100 mm (4 in) diameter ties andthe eight piers were each reinforced with 36 mm �30 mm (1.4 in � 1.2 in) oval deformed rods and had91.5 t (90 ton) of Portland cement grout injected. Inthis way the structure was united and the cause ofdifferential loading on the foundation removed.

Catenaries

Although these structures scarcely come within thescope of this book, a few random remarks may be ofinterest. The tensioned curve of a primitive nomad’stent was, of course, the prototype of the curved mem-brane structure. But this form had scarcely developedbeyond the large circus tent until the mid-twentiethcentury when fabrics with high tensile strength wereevolved from man-made fibres. In the USA, the saddle-shaped roof of the Raleigh arena with a spanof 100 m (328 ft) by Norwikci and Severad, theSaarinen and Severad hockey rink at Yale Universityand the Dulles Airport building by Saarinen, Ammannand Whitney are all examples of reinforced concretecarried on suspension cables. Again, meticulous main-tenance procedures are the key to their preservation.

Catenaries were developed in China from wovenbamboo cables. The very early iron tie rod suspen-sion bridges are also a type of catenary, the mostnotable being in Yunann which dates from A.D. 65and has a span of 75 m (246 ft). All suspensionbridges require continuous care and maintenance toensure their stability, as the failure of one cable cancause disaster. Indeed, a long suspension bridgeneeds as much maintenance as a large cathedral. Insome cases, suspension cables have had to bewelded in places where weaknesses have developed.

In 1940, the collapse in the USA of the TacomaNarrows suspension bridge, having a span of 850 m(2789 ft), led to a painstaking scientific inquiry into thecauses of the failure, which was found to be due tovibration caused by high winds. Freeman Fox’s Forth,Severn and Humber suspension bridges in Englandreflect developments to make the deck stiffer in orderto increase resistance to such dynamic loading.

Catenaries

47

Figure 3.13 Spherical domes(Courtesy: Allen Lane and Penguin Books)

(a) Geometry of a hemispherical dome. Early domes werethick because the action of tension in the lower part abbelow �� was not fully appreciated. Tension rings wereinserted in the lower parts

(b) The isostatic diagram shows the zone where tension occurs(c) In flat domes with no part below �� no tension occurs, but

much greater thrusts are imposed on the abutments

Structural elements I: Beams, arches, vaults and domes

48

Figure 3.14 Actions of hemidomes

A half-dome may be considered exerting compressive pressurein the upper part and tension in the lower part when an element in the whole structure

Figure 3.15 St Sophia, Istanbul, Turkey: part plans of the superstructure(Courtesy: Allen Lane and Penguin Books, and R.J. Mainstone)

Above—the dome and semidomes and main north arch shown with their outward thrusting actionscontained, ideally, by cramped string-courses at the springing levels acting as continuous ties.Below—the probable actual behaviour with associated tensile cracking, shear failures and majordeformations. Light continuous lines show the directions of the principal compressions (thrusts),heavy broken lines indicate ties, light broken lines indicate tensile cracking, and s—s denotes theapproximate location of a shear failure. For simplicity, no account is taken of the window openingsin the dome and semidomes, and the exedrae semidomes are omitted from the upper drawing, butthe representation of the probable actual behaviour does take into account the progressive nature ofthe deformations as construction proceeded

Catenaries

49

Figure 3.16 Isometric projection of St Paul’s Cathedral, London, England(Courtesy: The Dean and Chapter of St Paul’s and Feilden & Mawson)

The double dome resolves internal and external aesthetic problems. The cone supports the 813 t (800 ton)cupola, the cross of which is 112 m (365 ft) above ground. Tensile thrusts are resisted by some five chainsas well as the pillared buttressing round the drum. Two more chains of stainless steel were added in 1925

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Because trusses and frames require tensile strengthfor their function, masonry is excluded from thischapter which focuses on timber construction andits repair.

Development

What is reputed to be the oldest surviving timberroof truss, found in the church of St Catherine onMount Sinai, dates from the sixth century. It is prob-able that the early Roman basilicas, such as St Peter’sand St Paul’s Outside the Walls, had trussed roofs oftimber. The Pantheon anticipated structural develop-ment by some seventeen centuries by having a metaltruss of bronze; unfortunately, it was melted down.

In Japan a timber pagoda at Nara, dated A.D. 670,is the oldest complete timber building in the world.The same city has a Buddhist temple, the Toruji,that is the largest in the world, which is a rebuild ofan even bigger eighth century design. Both areframed structures using the tensile strength in tim-ber in order to cantilever the wide roof overhang-ings that are characteristic of oriental architecture.

Early mediaeval roofs consisted of couples ofrafters pinned together at the apex and having ashort collar about one-third of the way down.These rafters were covered with longitudinal bat-tens to which the roof covering was fixed. This typeof construction gave no resistance either to the lat-eral spread of the rafters, subjected to bendingmovements and deformation, or to longitudinal tilt-ing. Stability depended on three joints, one at theapex and two at the ends of the collar, so failure ofany one of them tended to allow the foot of therafter to push off the wall plate or move outwardson the supporting wall. It also induced consider-able thrust outwards on this supporting wall.

In late mediaeval times the roof came to be built using principal rafters with purlins supporting

common rafters. There might be two or even threepurlins in each roof pitch. The principal might havearch-braced wall posts together with a collar whichmight also follow the curve of an arch with its sof-fit. Above the centre of the collar a king post mightbe inserted and often this king post was linked with arch bracing in the longitudinal direction. Inaddition, further arched wind bracing might beintroduced into the panels formed by the principalsand purlins in the same plane as the roof andrafters. This type of framed roof construction wasextremely elegant and economical, and a fineexample may be seen in St Clement’s Church inNorwich, England.

Palladio’s sixteenth century bridge over the riverCisman near Barrano, Italy, was an importantachievement in truss design. Wren’s truss for theSheldonian Theatre, Oxford, was also a noteworthyexample of the seventeenth century, and from theeighteenth century we have examples of scientifictrusses such as at St Paul’s and St Martin-in-the-Fields, London.

The American timber trusses and bridges fromthe first half of the nineteenth century, using mag-nificent timber from the white pine, made a contri-bution to the development of this form. Because ofshortage of timber in Europe, wrought iron andsteel replaced timber for large-span roof construc-tion in the nineteenth century, early examples inEngland being Euston Station, London, in 1837, andLiverpool’s Lime Street Station, in 1849, with a spanof 46 m (151 ft). In London, in 1875, LiverpoolStreet Station by Fairburn and Hodgkinson is sig-nificant in that the principle of continuity is intro-duced into a multi-span steel-framed structure witharched trusses of graceful design, resting on tallcast-iron columns. This development led to portalframes that have truly rigid joints which are capableof execution by welded construction in steel orglued construction in wood. Mies Van der Rohe’s

4

Structural elements II: Trusses and frames

Crown Hall, built in 1956 at the Illinois Institute ofTechnology, with its clean detailing in welded steel,is likely to become an historic building.

Space frames—three-dimensional trusses withrigid joints—are a more recent development basedupon sophisticated structural analysis and weldingtechniques.

Analysis and assessment

The development of effective triangulation in tim-ber trusses was hampered by difficulties in jointing,as the joints themselves are generally the pointswhere trusses fail. Wood used for trusses creeps asa result of the tensile stresses imposed by the struc-ture and movements caused by variations ofhumidity. When subjected to bending stresses thelongitudinal fibres may be stretched by tension andsquashed by compression; if this process occursrepeatedly, the wood may deteriorate in a mannersimilar to fatigue in metal. Where subject to tensionthe timber may lengthen, and splits and cleftsformed during seasoning may widen. Likewise,metal nails may loosen their hold and as time goeson the wood fibres contract and leave a void intowhich atmospheric damp penetrates and condensa-tion occurs, causing corrosion of the nails. TheEnglish mediaeval practice of using woodentreenails and dowels avoided this possibility; whenmetal nails were used, the holes were frequentlycharred before driving the nails so as to reduce thecorrosive effect of the acids in the wood upon theiron. Putting varnish or grease into screw holes, asis done in boatbuilding, is the best practice.

The shrinkage and compression of timber alsoleads to the loosening of wooden structural joints;the resulting play between them, due to movementsinduced by wind, may quickly cause the wholestructure to become dangerous, especially with extraloadings caused by snow. Because joints offer ledgesand cracks where beetles can lay their eggs, thesevulnerable points are often attacked first and mostintensively. Joints are also vulnerable as they trapwater or condensation, thus starting the rot/beetleattack sequence. Pine buildings in Norway andSweden, with ventilated joints designed to be self-draining so as to minimize this source of trouble,have proved to be remarkably durable.

Joints may fail in tension (e.g. tenons may pullout or dowel pins fail) or may fail owing to distor-tion of the structure and to having to withstandforces never envisaged by the designers. Failure ina joint may set up a chain reaction. Typical of thisis the scissors-type truss, the thrust from the ends ofwhich can force a masonry wall outwards; this

Structural elements II: Trusses and frames

52

Figure 4.1 Roof trusses from the second to the nineteenth century(After R.J. Mainstone)

(a) Pantheon, Rome, Italy—second century(b) Notre Dame, Paris—thirteenth century(c) Theatro Olympico, Vicenza, Italy—sixteenth century(d) Sheldonian Theatre, Oxford, England—seventeenth

century(e) Royal Hospital, Greenwich, England—eighteenth century(f) Church at Steinbach, Federal German Republic—

eighteenth century(g) Lime Street Station, Liverpool, England—mid-nineteenth

century

Analysis and assessment

53

Figure 4.2 Baguley Hall, Manchester, England(Courtesy: W.J. Smith ATD, and DoE Ancient Monuments Dept)

The hall is an exceptional thirteenth century timber-framed structure of the greatest archaeological value. The joints in theframing were attacked by rot and insects so that it had to be heldtogether by ties, several of whose anchorages show. In addition,the slate roof was in poor repair. Attempts were made to repair thetimber in situ, but this was found to be impossible. It wasdecided to take the framing down, repair the joints and reconstruct the frames and roof

Figure 4.3 Baguley Hall, Manchester, England(Courtesy: W.J. Smith ATD, and DoE Ancient Monuments Dept)

The thirteenth century interior ‘screen wall’ frame seemsremarkably solid, yet behind this facade it has been ravaged bydeathwatch beetle attack and the integrity of the structure isimperilled

movement may be further aggravated by leakinggutters, leading to dry rot and beetle attack in therafter ends which in turn allows further movementthat breaks the joints higher up the truss.

The most common causes of failure in roof car-pentry construction are poor structural design, poorquality or lightweight timbers, alterations madeafter the initial construction such as cutting throughtie beams, loss of strength owing to aging of timber,breaking of joints, sagging and spread due to rot-ting of ends of beams, rafters and wall plates ormovement of supporting masonry. Purlin joints areoften found to be fractured.

To repair a timber-framed structure, first thestructural system must be studied, for example todetermine whether it is the early box-framed typeof construction (possibly with jetties and exposedtimbers) or the later balloon framing with hard-wood or softwood studs. Posts, girders, summers,principal rafters and braces should all be traced andthe timbers inspected to ensure that they are intactand the joints secure.

When the original frame has been discovered, itshould be surveyed and drawn in every detail. Oftenit is necessary to strip out parts of the building inorder to do this: wallpaper, plaster, brickwork,inserted floors, ceilings, partitions and fireplaces mayhave to be removed with caution, for what at firstmight appear to be rubbish can be some unexpectedoriginal feature. The inspection may show severed tie

Structural elements II: Trusses and frames

54

Figure 4.4 Baguley Hall,Manchester, England

Roof timber repairs. A roofrafter having the minimumamount of new oak insertedin order to make good atenon joint. Dismantling isnecessary for this work, butby restoring the joints thestructural integrity of thebuilding is maintained

Figure 4.5 Chester House, Knowle, Warwickshire,England(Courtesy: Architects’ Journal and F.W. Charles)

Drawing to be read in conjunction with the timber repairschedule for Truss 1, opposite (Architect: F.W. Charles)

beams, decay caused by leaking roofs and pipes, andfractured floors and walls without proper means ofsupport except loose bricks or plaster lath. Shakes inold timber may not matter, but where there are largeknots one may find indications of incipient breakingwhich must be repaired. Large shakes are oftenfound in old oak beams. Inspection must decidewhether these materially weaken the timber. Theseshakes can offer the female deathwatch beetle a con-venient crevice in which to lay her eggs; they alsoallow moisture to penetrate and reach the heart ofthe wood. It used to be the custom to fill theseshakes with putty mixed with hair, but such a fillinghas little ability to expand and contract with seasonalmovement of the timber, and caulking with tar andhemp as is done on ships’ decks has been suggested.The use of artificial rubber sealing compounds wouldappear to be more satisfactory, as these are adhesiveyet flexible, although their colour may be a problem.Large shakes can also be filled with pieces of match-ing timber cut to shape and slipped into position andthen ‘gunned’ with sealing compound.

F.W.B. Charles (1984) writes:

‘The replacement of original members by newtimber is clearly an even more exacting task thanframing the original building. Not only must thedimensions be dead accurate but the new com-ponents must be inserted into an existing frameinstead of assembled in a logical sequence ofoperations followed in the original constructionwhich would allow slight adjustments to bemade and the timbers fitted afterwards. Theproblem of shaped or curved timbers is evenmore difficult. In the original building the profilefor instance of a carved brace determined theexact location of mortices cut into the receivingmembers. In a replacement the member mustnot only fit the mortices, but its form must be asgrown, that is, in accordance with the naturalgrain rather than shaped by tools. It may alsohave to match a corresponding member whichsurvives in the original structure. Since no twobranches of a tree are ever exactly alike, this difficulty can be insuperable.

‘In restoration work, compromise is ofteninevitable. Jointing new timber on to old where,say, an end of a beam has decayed, combinesthese problems with the additional one of formingan exact and secure joint. This calls for an entirevocabulary of joints for a purpose seldom met inthe original construction. Yet the designs of these joints have all been acquired from actualexamples. Even the most sophisticated scissorscarf joint indispensable in replacing main posts,was found in a Middle Littleton tithe barn dated

Analysis and assessment

55

Timber repair schedule—Truss 1 (see Figure 4.5)Dimensions are given gross, allowing for tenons and cuttingto waste after checking dimensions on job. Mortices in members are not generally noted—refer to drawings. Newtimber only is given

Threshold 5 ft 6 in � 8 in � 3 in tenoned one end,morticed other

Sill beam 15 ft 0 in � 8 in � 8 in tenoned both endsMain post 7 ft 6 in � 8 in � 13 in rebated top,

2 tenons, bottom tenonDoor post 7 ft 0 in � 8 in � 8 in tenoned both endsStud 6 ft 0 in � 9 in � 4 in tenoned both endsStud 6 ft 0 in � 9 in � 4 in tenoned both endsStud 6 ft 0 in � 8 in � 4 in tenoned both endsStud 6 ft 0 in � 8 in � 4 in tenoned both endsMain post 7 ft 0 in � 8 in � 13 in as main postPlate Renew end 4 ft 6 in � 6 in � 6 in scarfed,

morticed to postBressummer 19 ft 6 in � 6 in � 7 in tenoned both endsMain post Renew end 2 ft 6 in � 10 in � 61

2 inscissor scarf, tenoned, patch2 ft 6 in � 5 in � 3 in

Brace as existingBrace stud Renew end 1 ft 9 in � 9 in � 31

2 intenoned

Brace (upper) as existingBrace stud Renew end 1 ft 9 in � 9 in � 31

2 intenoned

Stud Renew end 1 ft 9 in � 10 in � 3112 in

tenonedStud Renew end 1 ft 6 in � 9 in � 31

2 intenoned, patch 2 ft 3 in � 5 in � 311

2 inStud Renew end 1 ft 6 in � 9 in � 311

2 intenoned

Short stud 3 ft 0 in � 9 in � 312 in tenoned

Short stud Renew end 1 ft 6 in � 7 in � 3112 in

tenonedShort stud Renew end 1 ft 6 in � 9 in � 311

2 intenoned

Stud 6 ft 6 in � 10 in � 312 in tenoned both

endsBrace stud Renew end 1 ft 6 in � 8 in � 311

2 intenoned, patch 3 ft 3 in � 2 in � 2 in

Brace stud Renew end 1 ft 6 in � 812 in � 311

2 intenoned

Brace (upper) as existingBrace as existingMain post Renew end 2 ft 6 in � 10 in � 61

2 inscissor scarf, tenoned

Tie-beam Patch 9 ft 6 in � 1 ft 3 in � 7 in—seedrawing, patch 1 ft 6 in � 5 in � 7 in

Principal Renew end 5 ft 6 in � 12 in � 6 inrafter scarf, tenoned. Purlin blockedCollar beam Patch 5 ft 9 in � 15 in � 41

2 inStruts—below collar All as existing but allow for replacement

of 50% tenons and:1 new end 12 in � 8 in � 31

2 intenonedpatches 1 ft 6 in � 5 in � 311

2 in2 ft 9 in � 3 in � 311

2 in2 ft 9 in � 3 in � 311

2 in2 ft 3 in � 3 in � 311

2 inStruts—above collar 3 ft 0 in � 10 in � 311

2 in tenoned bothends, rest as existing

Yoke as existingPrincipal rafter as existing

circa 1250. The difference between repair jointsand construction joints is that modern powerfuladhesives can now be used for the former toensure the repaired member is as strong as the original. In construction joints the use ofadhesives would of course defeat the object of timber framing in permitting the slight movement necessary to prevent fracture.

‘The behaviour of new oak depends largelyon its method of conversion. Boxed heart andcleft timbers are less liable to shake or warpthan sawn timber. Cleaving is also the means ofavoiding knots, at any rate on the importantupper face or exposed surface. It seems that newtimber converted in the traditional way will notsuffer ill effects either when used as new components inserted into the existing frameworkor when jointed as a repair to an old timber.

‘Conversion by bandsaw is a different matter.When the timber is wholly dry, shakes appear,and while there is no reason to believe theyaffect impermeability or stability, their ultimateextent and depth is unforeseeable. Knots produce radial shakes and become loose. Lastly,the timber contracts and warps to an appreciablygreater extent than traditionally converted timber.

‘It is best to accept the distortions of age aspart of the maturity of the timber structure, forthe distortion itself is not necessarily a sign ofweakness. As an alternative to the repair of abroken joint, its strength can be restored bystrapping with metal. Dowels like stirrups in areinforced concrete beam can also be inserted soas to strengthen in situ cracked beams againstshear. No artificial strains should be put on thetimber work in an attempt to force it to do otherwise than it wishes. As warping stresses arevery severe, once a frame has been taken apartby knocking out the pins and pulling the jointsapart, it is by no means certain that it will gotogether again. Exposed timber members whichhave suffered from rot can be repaired by scarfing, and joints can be strapped or pinnedand bolted using fish plates to transmit tension.If the feet of posts or crucks have rotted, thesecan be repaired by bolting on stone or concretefeet, but no attempt should be made to jack upor straighten the old timber structure. When fixing unseasoned new oak, it should beremembered that the tannic acid therein candestroy steel nails. Bronze fixings should beused if possible, or else galvanized steel.’

The repair of timber-framed structures can beattempted by in situ scarfing, but this is often clumsyand unacceptable. The structure can be consolidated

Structural elements II: Trusses and frames

56

Figure 4.6 Chester House, Knowle, Warwickshire, England(Courtesy: Architects’ Journal and F.W. Charles)

Timber carpentry joint details used by the architect in repair work:

(a) Slip or fish tenon for studs, rods, etc.(b) Repair joint for studs only(c) Dovetailed tenon inset for collar or tie-beam(d) Sill beam joint(e) Face-splayed scarf for rafters(f) Post head—wallplate and tie-beam joint(g) Edge-halved scarf—vertical, horizontal or inclined mem-

ber, minimum length: depth � 3(h) Scarf for repairing horizontal members, minimum length:

depth � 2(i) Tabled scarf—beams and joists with both end fixed skew-

pegged, minimum length: depth � 2.5(j) Scissor scarf for repairing posts, minimum length: depth

� 2.5

Analysis and assessment

57

Figure 4.7 Gable of housein Weimar, Germany

Timber framing and varioustypes of infill including brickand wattle and daub used ina typical mediaeval house

Figure 4.8 Three houses,Christianshaven,Copenhagen, Denmark(Courtesy: Architects W. Wohlertand H. Laugberg and J. Fredstund)

Although condemned in 1960,these mid-eighteenth centurytimber-framed houses were economically conserved in 1975.Roofs had to be reconstructedand windows to a great extentrenewed, and external plasterhad to be removed and renewed

Structural elements II: Trusses and frames

58

Figure 4.9 One of the three houses at Christianshaven, Copenhagen, Denmark(Courtesy: Architects W. Wohlert and H. Laugberg and J. Fredstund)

Detail of timber framing and windows before conservation

as it is, by using fibreglass reinforcing rods andepoxy resins, but such work is chancy, messy andnot necessarily fire resistant—and also ignores theoriginal structural design whose integrity should bepreserved. It is therefore generally necessary to dis-mantle a timber-framed building section by section,recording every action archaeologically; then eachjoint can be reconstituted with the minimum use ofnew material and reassembled according to the origi-nal design, but with no attempt to eliminate distor-tions caused by time. Dismantling and reassemblingis practised in Japan, but distortions are eliminated,since the character of Japanese architecture, with itswalls all of light sliding screens, demands regularity ifthey are to function. Inevitably there is some loss ofmaterial in the infill panels but the integrity of thedesign and function of the timber frame is conserved.

The repair of timber frames has two furtheraspects—first, rot at or near ground level due to ris-ing damp and rain splash, and secondly, open jointsand attack by wood-boring beetle throughout theframe. To avoid damp penetration into the timbers,the tenons on the posts should be cut to faceupwards where possible and holes in the upper sur-face of horizontal members should be avoided or thejoints should be designed to drain; rot and beetleattack generally starts as a result of moisture stand-ing in these undrained joints. If the filling masonry isloose and the external plaster has been taken off,new sills may be inserted and posts can be repairedby splicing. Joints may be pulled together by irons;old oak dowels or treenails can be drilled out andrenewed, and faulty timbers can be replaced usingscarfed joints. Lastly, all sapwood and areas affectedby beetle attack should be cut back and a durablepreservative applied after any gluing.

Analysis and assessment

59

Figure 4.10 The three houses at Christianshaven,Copenhagen, Denmark, after conservation(Courtesy: Architects W. Wohlert and H. Laugberg and J. Fredstund)

After conservation, careful studies were made of the externalcolours

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61

Walls, piers and columns all form part of the samesystem of enclosure of space and support of theroof. Stone and brick masonry are consideredtogether as they are so similar, but mud brick hasspecial problems of its own, so is studied in a sep-arate chapter. Timber walls must not be forgotten,but here the problems are not so much structural asthe decay of the material itself, which will be dealtwith in the chapters on causes of decay, in Part IIof the book.

Walls—different types of mass construction

Each geographical region and period in history hashad its own characteristic way of building walls.Therefore, each type of wall has different preservationand repair problems dependent upon its constructionand the strength of the primary and secondary materials; for example, unbaked brick laid in mudmortar, unbonded stone blocks, closely fitted polygo-nal masonry laid dry and random rubble in lime mortar will age differently from, say, bonded masonrylaid in mortar or Roman mass concrete walls.

Ruins can often be informative about the natureof structural systems, as the collapse pattern of awall may show how it ultimately failed and thushow a similar type of wall should be reconstitutedand strengthened.

5

Structural elements III: Walls, piers and columns

Figure 5.2 Spalled facingstone, St Paul’s Cathedral,London, England(Courtesy: Feilden & Mawson)

To get a very thin joint at theouter face, the ashlar from St Paul’s was worked with ahollow bed. Unfortunately themortar has not always setproperly in the middle of thethick walls, and with compressive settlements excessive loads are thrown onthe outer edge, causingspalling like this along thejoint line

Figure 5.1 Split facing stone, St Paul’s Cathedral,London, England(Courtesy: Feilden & Mawson)

A detail of split facing stone on the west front of the catbedral(ground level). When under great pressure sedimentary stonewill laminate if it is laid incorrectly, as in this case where the bed is parallel to the face

Most stone-faced mediaeval and Renaissancewalls are filled with random stone rubble set in amass of mortar between the two outer faces ofstone ashlar or plaster. They were raised one courseat a time and then filled with a sort of mass con-crete. Such walls may appear to be more or lesshomogeneous but should the casing be defectivethe core will erode easily and may lead to runawayfailure. For strength and durability they dependmuch upon the quality of the mortar which repre-sents at least 30% of the volume.

To preserve the wall, its core must be protectedagainst internal erosion by penetrating rain whichcan, over centuries, wash out large internal voids;hence the primary importance of pointing masonryjoints for preventive maintenance. Then there isalso another danger, for when lime is used in thickwalls the lime may not carbonate and set properlyin the centre of the wall.

Many thousands of town buildings, particularly inEurope, were built of ordinary masonry in a rough,almost careless way with the walls coated with plas-ter. The solidity of such structures depends muchupon the binding capacity of lime mortar and thefrequent use of wood and iron bands or chains toprovide tensile strength. Dry rot and decay from bee-tle attack of these embedded timbers is a typical faultof such construction, except perhaps in drier con-tinental situations such as central Europe or Spain,where buildings are still constructed this way.

The load-bearing wall is probably the common-est type of building construction element. Load-bearing walls of masonry were used in buildingsranging from the Palace of Versailles to the countryvilla or farmhouse, including churches and castles,mosques and monasteries. Such buildings may suf-fer damage because of thrust from defective roofs,but overall damage is more likely to result fromdefects in foundations and thermal stresses (the largerthe building, the more vulnerable it is). Defects dueto disintegration of walls when the binding materialof lime or cement deteriorates, and defects due to moisture, decay and aging or rotting of woodreinforcements, are also inherent in this form ofconstruction.

The importance of soft thick mortar joints inallowing small movements to take place withoutconsequential damage may not be fully appreci-ated. It has been observed that many masonrystructures can settle up to 100 mm (4 in) or more,depending upon the quality of the mortar and thethickness of the joints, without showing the move-ment by cracking, for the movement is absorbed bycompression of the mortar. There may be a time lagof weeks or months between the actual movementand the showing of fresh cracks.

Structural elements III: Walls, piers and columns

62

Thin mortar joints may cause cracking and spallingof individual stones. This defect is very common in St Paul’s Cathedral, London, where the joints areabout 4 mm (0.2 in) in thickness on the face but widerbehind; the effect is that when the wall is loaded andthe lime mortar compresses, much greater stresses arethrown on to the face thus causing spalling. As thinmortar joints are surrounded by stone, the strength ofthe mortar is of less importance and the mortar isoften overstressed, when it may break up into powder and tend to fall out of the joints.

Shear and tensile cracks are quite common inmasonry walls, the former resulting most often fromsettlements and the latter from inherent designdefects. Diagonal cracks indicate shear, generallyresulting from unequal settlements. Local settlementsmay cause cracks soon after the building’s erection,possibly due to faults in the ground such as an oldtree, a midden or bog hole or well. Cracks may alsobe caused by the building having been initially putup over a ‘pipe’ (a hollow void) in chalk or in gravelsubsoil or by a local patch of sand or other materialunder the foundations. In some cases, archaeologicalremains have contributed to the cracking pattern bygiving the foundations unequal bearing capacities.

Compressive cracking consisting of close fine verti-cal cracks in an individual stone or brick is rare, as thewalls and piers of most historic buildings are gener-ally strong enough to resist this force. Sometimes,however, it occurs in the form of spalling along theouter edges of stones which have been bedded ontoo thin a mortar joint, or with a hollow bed, whichthrows all the weight on to the outside edges. Spallingmay also occur when vertical lengths of stone—detached columns for example—are built alongsidenormal coursed masonry, because the compression ofseveral mortar joints in the coursed masonry throws agreater loading on the long length of stone which hasonly one compressible joint. The fall of BeauvaisCathedral is attributed by Professor Heyman not toover-daring design but to slow shrinkage or compres-sion in the mortar joints of the clerestory wall, whichthen caused the overstressing of the monolithicdetached shafts whose failure in turn triggered off thewhole collapse some 20 years after initial completion.

Walls faced with ashlar and filled with rubblebecome fissured in time and liable to damage fromvibration. Also, if the joints in the external facingare fine and the blocks of stone are large there is adanger that the core will consolidate, leaving theskin to carry the loads in full with resulting pressurecracks, spalling and even bulging.

The low tensile resistance of masonry set in softelastic lime mortar leads to a particular formation ofcracks, as shown by records of structural movementsin York Minster, indicating that it takes several

months for movements and the readjustment ofstresses in one part of a building to affect those inanother. Due to the plastic nature of lime mortar, itwould appear that tensile forces tend to concen-trate slowly upon one course of stone which even-tually cracks; then the mortar adjusts itself and theprocess is repeated and the next course above orbelow cracks. Thus a quite small horizontal tensileforce can cause large cracks through a massivewall. For this reason masonry is suspect when it hasto take any horizontal tensile force, unless all thestones are cramped together. The dead weight ofthe superimposed masonry generally cancels outany tendency for vertical tensile forces to occurfrom wind loading, except in light structures suchas spires.

It has been said that the failure in timber systemsis not so likely to be due to structural causes somuch as to the decay of the material itself, particu-larly where it enters into or is close to the ground.This decay can lead to the failure of the masonrystructural elements by causing new stresses to beimposed upon the remainder of the structure; forexample, the rotting of embedded beams in foun-dations can cause cracking of the walls like anyother defect in the foundations. The rotting of tim-ber piles exposed to different conditions by thelowering of the water level is another example.

The effect of the decay of timber roofs on load-bearing walls below can be equally disastrous, par-ticularly where the walls are pushed outwards. The

rotting of one end of roof beams can cause multi-ple collapse, because the other end of the fallingbeam may lever sound masonry out of position.Likewise, if the walls themselves move because offoundation settlements, or for other reasons, theycan have an equally adverse effect on the roof con-struction. In mixed structures, the wooden elementsare liable to shrinkage in all dimensions and alsoare vulnerable to decay from fungi and insects. Ashas been said, the joints of the wooden elementsare the weakest parts and if these fail there is a dan-ger of thrusts developing on the walls, which theywere not designed to resist.

The investigation of defects in walls and theirappropriate repairs are topics dealt with after thenext section, as are the particular problems associ-ated with earth walls.

Piers and columns

Worn joints in masonry are caused by weathering,aging, vibration or excessive stresses. Their pres-ence can be determined by a test to see how easilywater penetrates through the masonry and joints.As symptoms of defects in piers and columns, wornjoints may be followed by the spalling or splittingof individual stones, disintegration of the mortarand slight displacements which may indicate exces-sive local pressure as well as the uneven beddingof stones or consolidation of the core. Cracked

Piers and columns

63

Figure 5.3 Lead jointunder column, St Paul’sCathedral, London,England(Courtesy: Feilden & Mawson)

Over two centuries of steadypressure has squeezed out thelead from this joint, below awest portico column, likecream from a bun. The leadhas saved the stone frombeing split by unequal pressures

stones are the result of such uneven bedding or tor-sion and shear resulting from settlement or evenvibration. If a visual inspection shows good reason,then cores must be taken to investigate more fullythe cause of decay.

Bulges in piers, often accompanied by fine verti-cal cracks, are very difficult to detect. They indicateoverloading and weak masonry which is bucklingand may well be dangerous, so shoring may be necessary before any further investigation is made.Before considering any repairs, the loadings on thecolumns or piers should be approximately calculated.Before repairs can be carried out on columns andpiers, temporary work consisting of strapping andcradling and shoring is necessary. A very sophisti-cated system of cradling has been developed for therepair of the piers in Milan Cathedral, which enablesindividual stones to be cut out and replaced, orwhole sections of the pier to be removed andreplaced. The inventor did not reveal the details ofthis process, but it must have involved prestressing.

After water tests have been made, the next step isto grout the masonry in a pier in order to consolidateit. The masonry is wetted and cracks are washed out.This preliminary washing generally indicates the sizeof voids to be met and the grout mix can be adjustedaccordingly. Grouting should be carried out in stagesfrom the ground upwards. When very fine cracks aremet in a pier, epoxy resin grout can be used, com-bined with stainless steel dowel pins.

The problem of all cutting out and replacementrepairs is that when the stone is taken out it is underpressure and the distribution of forces is altered.When the new stone is put back it cannot usually beprestressed and therefore some local readjustment ofthe stressing is bound to occur before the new stonewill carry its load. If the mortar joints are fairly widethis generally happens without difficulty, but if themortar joints are narrow and the stone brittle, thenfurther cracking may result from the repair.

Piers of composite construction or those built atdifferent times always present special problemsbecause later works are rarely found to have bondedsatisfactorily with earlier work. Furthermore, work ofdifferent periods often leads to the formation of a ver-tical joint which can get filled with dust, thus settingup a wedging action if there is any vibration.

The repair of the main piers of St Paul’s Cathedral,in London, is an interesting case study. Cracking wasdue to eccentric loading and differential settlementswhich this loading induced in the foundation. Thefoundations of the piers were suspected of beingoverloaded in 1913, but it was not until the crackingof the main piers that a commission was set up tocontrol the great restoration work of 1925–32. Thepiers were strengthened by the insertion of about

91.5 t (90 ton) of cement grouting and laced togetherwith 32 mm (1.25 in) diameter oval bars of deformed‘staybright’ stainless steel. Earlier wrought iron tiebars inserted by the architect Robert Mylne in 1750were replaced by 16 large stainless steel rods. Theremedy can be said to have succeeded when, afteralmost 50 years, further settlements have ceased. It isnow assumed that the foundation loadings haveequalized themselves. In this case, a symptom wascorrected rather than the cause, but the structurehelped cure itself, possibly at the expense of futurepossibilities of conservation.

Investigation of defects in walls

Cracks in wall elevations may be of three types.Those, over the point of settlement, sloping towardthe centre of gravity indicate a failure of the centreof the wall, and those opening outwards towards theextremities indicate settlement at the ends of thewall. Causes for such cracks should be investigatedin the foundations. A further type of crack is verticaland may be the result of weak material, shrinkage orthermal movements. Vertical cracks, wider at the top,can mean that a wall is moving outwards or rotatingon eccentrically loaded foundations.

Cracks may also result from the phasing of build-ing work and therefore it is highly desirable toknow the construction sequence of a building so asto assess the date of a crack and whether it is activeor static. Cracks and settlements due to initialdefects generally occur within the first 20 years ofthe building’s life.

Walls suffer from the same general defects as piersand columns, but are less vulnerable to eccentricloads in the plane of the wall as these can easily bedistributed along its length. Open joints due to ther-mal movement, aging and vibration damage are themost common defects. Spalling of stone is compara-tively rare, particularly if the bed joints are reasonablythick, as is most usual in ancient construction of or-dinary buildings. Cracked stones are due to local pres-sures or bad construction such as inadequate bondingor the junction of works executed at different periods.Bulges due to weak masonry or overloading are difficult to detect, although not uncommon. They canindicate that a wall is near collapse.

Bulges may occur in weakly bonded masonrybuildings, particularly if they have been refacedwith a different material. For example, a clay lumpbuilding may be faced with brick or a brick build-ing refaced with stone, and bulges may occur whenthe facing becomes separated from the core orbacking, due to disintegration of the building ma-terial or long-term vibration. Such bulging may be

Structural elements III: Walls, piers and columns

64

caused by the cumulative effect of thermal move-ments which causes the facing to expand, creep ordrift while the core remains more static. Ultimately,quite large bulges and cracks will form behind thefacing. Bulges up to 100 mm (4 in) occurred in theNorwich Cathedral spire, which is a 115 mm (4.5 in)brick structure faced with 75 mm (3 in) stone. Inthis case the bulges were aggravated by the ratchetaction prompted by wind vibration of dust andmortar which fell into the vertical cracks andwedged them open. Thermal action caused addi-tional movement and the dust gradually fell furtherdown, thus splitting the structure vertically.

Walls may have other defects besides cracks. Oneobvious flaw is an outward inclination; buttresseswere often added to arrest such a movement, butunless they were prestressed or built on rock, theywere generally of no value until the ground hadbeen compressed and the wall had moved a gooddeal further.

In Norfolk, England, it was the practice in thethirteenth century to build walls with an internalbatter, and the appearance of these walls can, atfirst sight, be alarming; however, inspection fol-lowed by taking accurate measurements andplumbing the outside face will usually allay thisalarm. In exceptional circumstances walls whichhave leant outwards may be pushed back into posi-tion, if this does not mean altering the design of thebuilding. If this course is taken, the cause of theprevious movement must be cured or compensatedfor in the repair works, for instance by putting in anew foundation concentric with the actual loads.

To carry out this rather drastic realignment pro-cedure, the wall is cradled on both sides in aframework of timbers that provides horizontalstrength and rigidity (steel joists with timber pack-ing may be used for greater strength). The verticaland horizontal timbers should be bolted togetherthrough openings in the masonry of the wall anddiagonal braces are necessary to keep all in posi-tion. When ready, a suitable cut is made at thebase—as in felling a tree—so that the wall willrotate into the correct new position with the wholewall in its cradling being pulled over by winches.The west front of Beverley Minster, England, wasreported to have been repaired by this method inthe eighteenth century. If it is in poor condition, thewall should be consolidated with grouting and rein-forcement before such a drastic treatment. A similarsort of cradling may be used to protect a buildingagainst mining subsidence, as the object of thecradling is to make the wall into a single rigid unit.

When working properly, buttresses exert a horizontal resistance to a wall moving outwards,their effectiveness depending upon the extent of

their projection and their own weight which actsvertically to deflect the resultant line of thrust.

Voids in stone walls

Although voids are often found in the walls of his-toric buildings, it is reasonable to assume that thewalls were originally solidly constructed. Thesevoids may have been formed by the mortar decay-ing and falling as dust downwards and outwardsthrough cracks or faulty joints, or alternatively thedecayed mortar may have been dissolved by acid-laden rain water and leached away, forming micro-caverns similar to the macro-caverns at Cheddarand the Gouffre de Padirac. Evidence of thisprocess has been found in the Norwich Cathedraltower and observed in the southwest tower of St Paul’s Cathedral and in the tower of York Minster.

The size of voids is unpredictable, but 0.1–0.3 m3

(4–11 ft3) is not uncommon and the total may wellamount to 5% of the volume of the structure. Theinitial crack and the subsequent void are both sig-nificant in terms of structural analysis.

Whereas cracks and slipping can be detected byvisual observation, suitable methods of detecting thesize or location of voids are problematical. Ultrasonicmethods may be successful in some cases. As for allwall defects, simply tapping with a hammer and lis-tening to the note can be helpful. Radiography canbe used to detect voids and cracks, but with masonrya powerful radiation source is required. Microwaveanalysis can detect discontinuities and acoustic test-ing can detect voids, cracks and cavities. The field ofnon-destructive investigation is constantly expand-ing, and a specialist should be consulted in eachspecific case (see Appendix III).

The condition of masonry can be investigated byusing a diamond drill to take cores say 75–100 mm(3–4 in) in diameter at not less than 75 mm (3 in)from the surfaces and in the centre of the wall.These cores should be inspected carefully, as howwell the sections hold together indicates the condi-tion of the mortar and stone. After taking the core,a lamp and mirror on a stem can be pushed downthe hole and large cracks and voids can be seenwith the aid of this apparatus, as it is rotated.

Water can be passed into the core hole througha sparge pipe. By limiting the outflow of water togroups of holes in the pipe, some indication of thepattern of fissuring can be obtained. Such a watertest is very useful in determining the general qual-ity of the masonry and should be used before majorgrouting work is proposed, but caution is advisedbecause with masonry in very poor condition suchtreatment might lead to an unfortunate collapse.

Investigtion of defects in walls

65

General repair of walls

Walls can be repaired by cutting out the defectiveparts piece by piece and so renewing the wall, but ifit is in very poor condition it is advantageous togrout it first. Grouting work cannot be guaranteed;all it can do is to consolidate work temporarily byfilling voids. Grouting cannot renew worn-out ma-terials. Indeed there is a danger that grouting mayaccentuate defects by filling vertical cracks with ahard material that does not bond to either face.

When repairing a very thick wall, it is often possi-ble by rebuilding a section to carry out the repair ahalf-thickness at a time, but care must be taken toensure that the two halves of repair are properlybonded or tied together. If this procedure is used, thewall need not be completely supported by needlingand shoring, although any opening will need tempor-ary struts. If a large area of wall has to be rebuilt, thenew work should be prestressed after the mortar hashardened sufficiently by using flat-jacks to ensure thatthe new wall carries its share of the total load. It issometimes advantageous to build a relieving archabove an arch that has to be repaired. Walls mayhave to be cradled with steel and timber bolted tighttogether wherever the opportunity presents itself, soas to make a rigid entity prior to structural works.

To prevent the crushing of the masonry by scaf-folding, packing pieces should be of hardwood,although there is a danger of damaging old walls fromraking and flying shores if the wedging is too tight. Ifneedling is necessary, seek out old putlog holes. Oneadvantage of tubular steel scaffolding is that it doesnot need putlog holes, but can be fixed to the face ofthe wall using stainless steel ties drilled into themasonry at inconspicuous spots. After serving its pur-pose, all shoring must be removed with great care.

Re-pointing masonry

Portland cement pointing should never be used forstone, as it is too hard, too rigid and too strong, andbeing too impervious it promotes frost damage. Thestrength and porosity of the mortar for stoneworkshould be related to the strength of the stone itself.For instance, for stone with a crushing strength of 55 500kN/m2 (8000 lbf/in2) a mortar with a crushingstrength of about one-third of the stone is ideal.Although the use of stone dust is often advocated bypractical masons, this may have dangers: first, thefines must be sieved out, as otherwise the surface ofthe pointing is too much like putty; secondly, in thecase of some stones the remaining coarse particlesmay decompose in time and thus spoil the mortar.On the whole, therefore, this practice is not to be

encouraged and reliance should be placed on get-ting the colour and texture of the sand right andadjusting the whiteness of the mortar by using whitePortland cement if necessary. A sharp crystallinesand with a little sparkle is desirable. The basic mixis 1 part of cementacious material to 3 of sand, butin exposed positions the mix may be 1 to 2 or 21

2.Ideally, the cementacious material should be awarm-coloured hydraulic lime. The aesthetic aimwith stone work is generally different from that withbrick or flint, as the pointing should be as close incolour and texture to the stone as possible andshould in no way interfere with the appearance ofthe stone. With brickwork, the final colour and tex-ture of the mortar is even more important as up to30% or 40% of the area of the wall is affected. In timethe colour and texture of the sand will dominate.

Buttressing

Repair by inserting buttresses is often ineffective, forthey may pull away from the wall they are supposedto support or, if well bonded, even pull the wall withthem. New buttresses should thus be designed toexert a positive horizontal thrust and be built on pre-stressed soil. Faults in old buttresses can be rectifiedby using needles and flat-jacks resting on en-largedfoundations. Inflation of these flat-jacks will prestressthe buttress together with the foundation and soapply a horizontal force to the wall.

The addition of buttresses, however, alters theappearance of an old building and should not beundertaken until all other methods have been con-sidered and rejected. The well-known invertedarches which strengthen the piers of the centraltower at Wells Cathedral are fine examples of tech-nical skill, but such virtuosity would be unneces-sary today with new techniques available thatenable repairs to be carried out in an invisible way.Buttressing of wall can be carried out using con-cealed cranked reinforced concrete columns, withhorizontal pressure applied by jacking the under-ground toe to prestress the virgin soil. Visible tiesto hold the tops of walls together are undesirable,and in some cases unthinkable, but if the ties areabove a vault and not visible, there can be noobjection on visual grounds. Ties of this sort can beanchored to a reinforced concrete ring beam inorder to restrict outward thrust from a roof or out-ward creep in a wall.

As an alternative to buttressing, where the vaultcrown comes above the line of the wall plate, apossible solution is to use ‘A’ frames of reinforcedconcrete. This was done in the re-roofing of theNorwich Cathedral nave and transepts where the

Structural elements III: Walls, piers and columns

66

fifteenth century vault rises well above the lowtwelfth century clerestory walls. These framesreplaced defective timber scissor trusses.

Repair of fractures

Vertical fractures in masonry walls are repaired byworking up from the bottom to the top and bondingboth sides together. In brickwork, bonders may beinserted across cracks, but as bricks are weak in ten-sile strength, indented stainless steel wire reinforce-ment in the thickness of the joint can give therequired resistance. If wall thickness allows, narrowprecast concrete bonding beams can be cut in andfaced within the thickness of a brick or stone wall.An example where this was found necessary was ina sixteenth century brick building with large mul-lioned windows, whose window sills were beingpressed upwards because the walls flanking the win-dows were settling more than the lightly loaded sills.Reinforced concrete beams were let in below thewindow sills to equalize the loading on the groundand allow walls including windows to settle as awhole. Cracks in brickwork or flintwork can berepaired by large dovetailed stitches of reinforcedconcrete up to 1.5 m (5 ft) long cut into the wall andused to hold the two sides of the crack together; thedovetails give sufficient anchorage in sound flint-work, while the shrinkage of the concrete is a formof prestressing that helps to close the crack.

Forming openings in walls

It is generally much more expensive to cut holes instone walls than in brick, because of the size of theblocks and the greater difficulty of needling andshoring stonework with large irregular coursing.With stone masonry the outer skin should, if pos-sible, be snapped off in say 80 mm (3 in) thicknessby using feathers, i.e. steel wedges. The surface canthen be reinstated exactly using the original facingstones when the works are completed. The diffi-culty of cutting holes for needles can be overcomeif a diamond coring drill is available, as thismachine can cut a neat circular hole of 150 mm(6 in) or 250 mm (10 in) diameter through mosttypes of wall without damage or vibration. Then asteel joist can be inserted as a needle, and con-creted into position. After the concrete has set,struts with hydraulic or screw jacks can take theload of the wall via the needles; then the openingcan be formed. In this way stress redistribution andsettlement by compression of the shoring areavoided and structural disturbance is minimized.

Openings in flintwork are difficult to form, forthere is a danger of local collapse, i.e. a run if themortar is weak or the material is badly bonded.Sometimes one meets clay lump walls with brickfacing; forming openings in this construction needsextra care, as the bearing capacity of clay lump isvery low.

In repair work, too much cutting out of stone,particularly if the stones are large, should not beundertaken as this may well shake the whole walland cause damage which will only show in the fab-ric many years later. Tools usually used in cuttingholes are the hammer, chisel, crowbar, Kango elec-tric hammer, and compressed-air drills and augerswith a variety of bits.

If new openings have to be formed in a wall dur-ing alteration work and the wall is thick enough, theexecution of the work in two halves using twinbeams or arches can be both kinder to the old fab-ric and more economical in cost, because needlingand shoring may be unnecessary. An alternativemethod is to insert, in a row, precast concrete blockswith preformed holes for reinforcement wires. When

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Figure 5.4 Barn gable, Oxnead Hall, Norfolk, England

The gable was leaning outwards and the central pier had settledsomewhat after a builder had formed two large garage doors

all the blocks have been inserted one by one thereinforcement is pulled through the holes, post-tensioned with hydraulic jacks and then groutedinto position. In this way a beam is put into thethickness of a wall without major structural redistri-bution of the forces and the wall below the beamcan be cut away safely without needling andshoring. Care must always be taken when cuttingopenings into old walls to ensure that the end bear-ing of the beams is sufficient, and if this is not thecase a reinforced frame should be inserted, sur-rounding the whole area being cut out. Wherethere is also a danger of adding a concentrated loadto a poor soil, an advantage of this method is that,by forming a complete four-sided frame, the load isspread much as before without the risk of alteringthe existing below-ground bearing.

As has been said, new work rarely bonds perfectlyto old, and therefore a mechanical key or the use ofnon-rusting metal dowels may be necessary. The oldwork should always be well wetted to encourageadhesion, for new mortar will not adhere to dry anddusty surfaces. Provided they are not subject todamp conditions, special resin-based bonding agentscan be used to improve the adhesion of new to old.All old material that can be re-used should be setaside and cleaned.

Concrete fill for restoration work is improved byusing crushed brick in the aggregate and, followingthe old practice, mortars may also have ground bricktogether with sand added to the mix. The final pin-ning up of new work in an opening needs great care,and is usually done by driving in two pieces of slateto act as wedges; then any voids should be grouted.A cement-based expanding grout can be used if it iskept back from the surface some 75 mm (3 in) andthe joint pointed with a lime mortar. Flat-jacksinflated by hydraulic pressure are a sophisticated wayof dealing with this problem.

Repair of rubble walls

Rubble is irregular random masonry with anundressed face. Before being grouted rubble wallsshould have their cavities washed out from top to bot-tom. Pointing should be carried out round each stonewith a flush joint and then finished with a dry brushso as to bring out the sandy texture. The primaryobject of pointing is to keep storm water from runninginto the building, but it will also contain the groutwhich is inserted as described elsewhere. Rubblewalls are weak at their angles and, to counter this,corners are often built of dressed freestone. Becausethis dressed stone might have been imported and thuswas expensive, quoins are often of inadequate size

or are poorly bonded and therefore come awayfrom the wall. In this case, they must be tied backto the rest of the rubble walling by drilling in tiesor dowels of non-rusting metal such as stainlesssteel or delta bronze.

The charm and interest of rubble masonry lies inthe ability of the observer to detect each individualstone, but the aim is not a rustic effect. In earlier cen-turies, rubble walls were generally limewashed* orcovered with very thin lime-rich plaster whichamounted to not much more than a skin of white-wash. Modern plaster technique raises a difficulty inthat it obscures the contours of the stones and is oftenapplied too thickly to be received by the projectingquoins. Old plaster techniques can be successfullyimitated by using very fine clean sand washed at leastsix times in distilled water and a 1:1 lime mix.

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Figure 5.5 Barn gable, Oxnead Hall, Norfolk, England

To stabilize the gable it was reinforced with stainless steel wire inthe horizontal joints and then re-pointed. Stranded steel cablewould have been better than the wire as the mortar has morebond or adhesion. Such cable is available from yacht chandlersin 2 mm, 2.5 mm, 3 mm, 4.5 mm and 6 mm diameters. The gablewas tied back at the same time into the side walls of the barn. Theexpense of rebuilding was avoided by this simple expedient

* See Ashurst (1983), Vol. 3, Mortars, Plasters and Renders inConservation, pp. 44–48.

Repair of ashlar walls

Ashlar walls generally consist of one or two faces ofsquared, finely fitted stones with the interspace filledin with odd pieces of random rubble mixed in mor-tar. When the mortar sets it loses its moisture anddecreases in volume. The thickness of the mortarjoints in the facework decreases very little in compar-ison with the decrease in the large amount of mortarin the core which can shrink considerably; thus theinternal core may subside leaving the upper part ofthe structure carried on two relatively thin faces. Inconstruction using lime mortar, much depends on thespeed of building, because the rate of hardening ofthe lime mortar is slow and the height of the lifts isconsequently limited. If the building proceeds tooquickly, the outer faces are likely to be overstressedand to bow outward, thus tearing away from theweak core. Indeed, Braun states that nearly all casesof failure in ashlar walls are due to this separation ofthe core from the face, and the problem of conserva-tion is how to tie it back.

Grouting would do nothing but fill the verticalcrack between the face under stress and the innercore, and although it might help stabilize the ashlarduring the repair work it is not an adequate methodof restoring the unity between the core and the face.Two methods for this can be used. The first is by theprovision of binders going right through the wall.These should be inserted where there are already bro-ken or decayed stones which will have to be replacedor where there are old putlog holes which can befilled in. A second method is by deep tying back,using rustproof cramps with dovetailed or fishtailedends. These can be cut into areas of sound rubble andbonded to the stone face. Alternatively, long dowelscan be embedded in epoxy resin glue anchors.

Rebuilding masonry walls

When any part of a masonry building has to betaken down for re-erection, a system should bedevised for marking each stone as it is removed.For simple cases a marked elevational photographwould suffice, but for a whole building, coursesshould be numbered from the foundations upwardsand stones numbered from left to right on each ele-vation and all openings lettered, with each of thestones forming the dressed surround numbered inassociation with the key letter, the drawings beingused as an index. This process is similar to thatused for the prefabrication of stones for a newbuilding in ashlar masonry.

Taking down a large area of rubble wall presentsspecial difficulties as it is virtually impossible to

employ a code. In this case a reference grid ofsmallish squares can be marked out in a removablepaint on the face of the wall, as has been done atMachu Pichu in Peru. What must be aimed at is torecord the character of the wall face by both blackand white and coloured photographs and, if pos-sible, a sample of the old work should be left toguide those concerned with reconstruction. Whenrepairs in stone work have to be concealed, the fac-ing stones should be snapped out as mentionedearlier.

Repair of window mullions and tracery in stone

Mullions and tracery can be repaired by halving andgluing sections on to existing masonry. Epoxy resinglues are especially made for this purpose. Cuspsand finials can be refixed by using stainless steel orbronze dowels and glue. Because these sections arevery exposed to weathering, they should only berepaired in a durable stone. For mullions, it is some-times necessary to use end bedding in order toobtain the necessary long, thin sections. Repairshould always ensure that the upper surfaces areproperly weathered, and for this purpose a mixtureof epoxy resin and stone dust is useful.

Substitutes for stone in repair

Reconstituted synthetic stone was formerly madewith white or coloured Portland cement andground stone dust, latterly with resin bindingagents instead of Portland cement. Unfortunately,synthetic stone on a large scale looks like syntheticstone and often weathers poorly and too uniformly,with surface cracking and crazing. Its life is limitedand in nearly every case that the author has exam-ined it has failed one way or another after some 30 years. It is inexpensive, however, and in limitedapplications—for small-scale dentistry, weatheringof concealed surfaces and making casts of decayingsculpture—it has valid uses. The problems to beovercome are the amount of cutting back and dove-tailing required, as in dentistry; the matching ofcolour and texture; and the question of porosity,which must be equal to or slightly greater than thatof the original material. Some architects, however,have more faith in reconstituted stone than theauthor. Optimistic supporters in some recent exper-iments in Germany and Switzerland say it is moredurable than natural stone, and they claim to havesolved the porosity problem. The material ismoulded on to a rustless armature which is pinnedsecurely to its base.

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Natural stone, when laminated, can be repairedby pinning and grouting with resin inserted by ahypodermic needle.

In treatment of damage to London’s WestminsterHall after a terrorist’s bomb, flaking stone was con-solidated with fine glass fibre pins pushed into anepoxy resin mortar which had been injected by amastic gun. The surface was protected by a latexcoating, which was later peeled off, and the jointswere finished with fine mortar, after which anycracks were filled with fine resin grout insertedthrough a hypodermic needle. Loose plaster canalso be consolidated by similar resin injections.

Repair of flint walls

Walls of knapped flint over six centuries old look inperfect condition today because flint itself, beingpure silica, is almost indestructible except by fire.The weakness of a flint wall lies in its mortar andin the bond between flint and mortar backing andbetween the face and backing.

If the mortar of a flint wall is too hard, capillarycracks occur; if too soft, the mortar ultimatelydecays because of all the rain the impermeable flintdiverts on to it. Flint walls should be lightly testedwith a 2 kg (4 lb) hammer to see if the flints arewell bedded and also to detect any of the possiblebulges which are a common defect due to the lackof internal bonding. When rebuilding flint walls it isdifficult to keep a true face, and shutter boards mayhave to be used and work carried out in 300 mm(12 in) lifts. Bricks or stones may be used as cross-binders in flint walls, and this mixture of materialscan be utilized to give attractive decorative effects.

To obtain good adhesion—for flint is a materialwith no suction—it is good practice to dip the backof the flint into a bucket of mixed lime cement groutbefore placing it in position. The mortar should bepressed into the joints before the initial set and thework brushed over. After the initial set the wallshould be lightly sprayed with water to expose theaggregate in the mortar, or cleaned with oil.

Repair of brickwork

The most common defect in brickwork is the agingand decay of the pointing; secondly, individual bricksmay have failed owing to frost action; thirdly, oneoften finds vertical cracks, particularly through thearches of windows and the walling above and belowsills, as well as diagonal cracks. As always, the causeof the defect must be rectified before cosmetic repairsare undertaken. Brick walls are often rendered and the rendering may be cracked owing either to

sulphates in the brick itself or to structural or thermalmovements. Cracked impervious rendering can col-lect and conduct large quantities of rain water intothe brickwork, trapping it and preventing evapora-tion. Before removing rendering it is wise to ask thequestion why the wall was not rainproof or whetherthe bricks were disintegrating generally under frostaction. Brick was often hacked and keyed beforebeing rendered and so after removal of rendering theexposed surface may not be satisfactory. A small testshould be made before committing oneself to acourse of action. Lime plaster renderings can beremoved quite easily, but some lime will be left in thepores of the brickwork and will add to the patina ofits age. Roman cement can be removed in great slabs,whereas cement rendering will, when prized off,generally pull away the face of the brickwork andleave a new face in a totally unsatisfactory condition.

Vertical cracks can be repaired by cutting in newmatching brickwork or, if the coursing is out of align-ment, can be made good with pieces of matching rooftile. If greater strength is required, special small pre-cast concrete beams of the same depth as one courseof brickwork can be cut in behind the outer face ofthe brickwork. Alternatively, 2.5 mm (0.1 in) diameterstranded stainless steel cable can be embedded in thebrickwork at a depth of about 40 mm (1.6 in). This isa very simple, economical and effective way of rein-forcing brickwork and can, if necessary, be usedround a whole building to tie it together.

It is very important that new bricks should matchthe old in colour and texture, and that the old formof bonding and jointing should be followed.Equally important is the colour of the mortar, aswell as the profile and texture of the pointing. Forre-pointing, brickwork should be raked out to aminimum depth of at least 30 mm (11

4 in) and thepointing inserted with a special trowel. Normallyeach brick should show and be given a slightlyrecessed or hollow joint, brushed to give texturewhile the mortar is still green. Smudgy edges topointings are undesirable. The effectiveness of abrick wall against rain penetration and its durabilitydepend upon the condition of its pointing.

The colour and texture of pointing have a majoreffect on the appearance of a brick wall, for point-ing may cover 30–40% of the area. If it is too light incolour it gives a recently re-pointed wall a garish andstark appearance. Darker colours of mortar bring outthe colour of the bricks, but the colour must not becold, as in the grey produced by Portland cement.Earth colours can be used to reduce the whiteness ofsome limes. If a natural darkish buff-colouredhydraulic lime can be obtained, this is the best. In the long run, however, the colour of pointingwill depend upon the sand used, and in the short run

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the sand will decide the texture of the mortar, sochoice of a well-graded sharp gritty sand is important.This is not the easiest sand to use, so bricklayers mayobject unless they are convinced as to the importanceof using a rather coarse sand, which when sprayedand washed down after the initial set will show goodtexture. The profile of the joint will also greatly affectthe appearance of the building. With old bricks hav-ing slightly eroded contours the mortar should beslightly recessed and given a slightly concave section,using the trowel handle or a radiused piece of wood.This should be offered up as a sample before finallyspecifying which should be done, as the factors ofcolour and texture and profile all interrelate.

It is worse than useless to try to cover up decayedbricks with coloured cement. If a face of a wall mustbe renewed, it is best to tie the new brickwork backto the old as in cavity wall construction and thenpossibly grout the gap between the new and the oldin order to prevent water seepage and frost action.

Repair of rubbed brick arches

Few brickyards still produce the soft, sandy bricksknown as rubbing bricks that may be found inarches. Rubbed brick arches can be salvaged inrestoration work by sawing through the joints, afterfirst removing the window frames. It will be foundthat a spoiled or damaged voussoir can often beturned round and the new face rubbed to match theold. A weakened rubbed brick arch can be made safeby using the brickwork as a permanent shuttering fora reinforced concrete lintel. The brick should bebonded to the concrete using stainless steel lugs andthe lintel can be cast in situ incorporating the lugs or,alternatively, the lugs can be fitted into a dovetailedslot in a precast lintel while the arch is being rebuilt.

Repair of half-timbered work

Brick panels in half-timbered work were often laiddiagonally or in chevron pattern to ensure a tightjoint between the brick and timber. Moisture move-ments in the timber cause cracking between theframe and whatever filling material is used, and windand rain find it easy to penetrate these cracks. For thisreason, in the eighteenth century it became the fash-ion to plaster over half-timbered work. A.R. Powys(1981) writes: ‘It is a mistake to assume that theplaster should be removed and the building shouldbe restored to its older form.’ He points out that theplaster probably covers previous alterations, particu-larly changes in window design. If brickwork has tobe renewed, a weather check in the mortar joint isessential to combat shrinkage and wind penetration.

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Figure 5.6 The Holy Shrine of Al Abbas, Kerbala, Iraq

The tiles have been stripped off and the parapet removed. Distressin the brick arch is due to two causes: first, pumping of groundwater which is removing silt, especially from the corners; secondly, the thermal expansion of the new reinforced concreteporch which expands and contracts quite violently each day withthe extremes of temperature. Unfortunately there is no expansionjoint between the concrete porch and the wall, so the weak brickarch suffers

Fortunately, with plaster-faced walls majorrepairs, even rebuilding, can be carried out in aes-thetic harmony because the whole surface is gen-erally repainted. This is quite different from repairsto weathered and textured masonry, where anyalterations are almost impossible to conceal.

Disadvantages of Portland cement inrepairs to historic buildings

Portland cement, in its various specifications, is amagnificent material for modern structures whichrequire its strength and quick-setting qualities. It isuseful in reinforced concrete, with suitable aggre-gates, to strengthen and consolidate the structure ofan historic building, under professional guidance.

On the other hand, Portland cement is not designedfor use in mortars or plaster on historic buildings,which do not require its specific good qualities, butwhich suffer from its defects and side effects on tradi-tional materials. Its disadvantages are as follows:

(1) Its use is not reversible. To remove it damagesall historic building materials, which cannotthen be recycled.

(2) It is too strong in compression, adhesion and ten-sion, so that it is not compatible with the weakmaterials of historic buildings. It is a paradoxthat such weak materials have the greatestdurability.

(3) Because of its high strength it lacks elasticityand plasticity when compared with lime mortar,thus throwing greater mechanical stresses onadjacent materials and hastening their decay.

(4) It is impermeable and has low porosity, so ittraps vapour as well as water and prevents evap-oration. Consequently it is no good for curingdamp walls. In fact, the reverse is true, for if usedit only drives moisture upwards. When used asmortar its impermeability accelerates frost dam-age and increases internal condensation.

(5) It shrinks on setting, leaving cracks for water toenter, and because it is impermeable suchwater has difficulty in getting out. Therefore, itincreases defects caused by moisture.

(6) It produces soluble salts on setting which maydissolve and damage porous materials andvaluable decoration.

(7) It has high thermal conductivity and may createcold bridges when used for injections to con-solidate walls.

(8) Its colour is ‘cold’ grey and rather dark. Thetexture is too often smooth and ‘steely’. Thesecharacteristics are generally judged aestheticallyincompatible with traditional materials.

Portland cement should not be used for mortarsor plasters in historic buildings, but as a last resorta small proportion of Portland cement, preferablywhite cement, although this costs more, should beadded to the lime, but not more than 10% of thevolume of the lime should be added without expertadvice.

The traditional methods of burning and slakinglime are best, but have been lost in many countries.Traditionally, lime mortars in the mix of 1 part limeto 3 parts of coarse sand were used. The sharperand more varied in size of its particles, the betterthe sand. Its colour determines the ultimate colourof the mortar. Its texture can be improved by scrap-ing with a small trowel.

In thick walls and to accelerate setting, somepozzuolanic material should be added. Some coun-tries like Italy and Germany have natural poz-zuolana; in others, it is possible to crush brokenbrick and tile to obtain this material, which is addedas part of the sand proportion to improve the set-ting characteristics of lime.

Because it is modern, efficiently marketed byadvertising and is readily available, and because itis indispensable to the modern building industry,many people think that Portland cement is ideal,but to sum up—unless it is correctly used, Portlandcement mortar is the enemy of historic buildings.

Earth buildings

Earth in brick form, clay lump or adobe, or rammedearth as cob or pisé or khesht, is probably one of theoldest and most-used building materials in the world. With local variations in technique, in themainly arid zones of Africa, Asia, North and SouthAmerica and the Middle East, earth has been usedfor buildings of every type—houses, tenements, fortsand palaces. Some ruins are impressive, such as theGreat Wall of China, others show advanced structuralskill in domes with pendentives, while houses of tenstories or more are found in Yemen and Morocco,but most impressive, perhaps, is the beauty of thedomestic architecture without architects, having aharmony dictated by the use of earth.

The oldest earth bricks are believed to come fromJericho, dated c. 8000 B.C. In desert conditions inPeru, earth structures are aged over three millennia,and in Egypt, arched earth brick storerooms from1600 B.C. still stand in Luxor. Earth construction wasparticularly efficient in military structures, because ofits ability to withstand artillery. There are magnificentruined forts, such as Bam in Iran, in India and inArabia. In China, city walls up to 20 m (66 ft) thick-ness are recorded by Needham.

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The merit of earthen construction, particularly inhot arid climates, is that it is comfortable due to itshigh thermal capacity and gives insulation, beingcool by day and warm by night. Earth also has lowcapillary attraction. Low cost and ready availability ofmaterials and the small amount of energy used inconstruction are also advantages which may con-vince builders that this material should not bedespised. Even so, the ancients knew fully well thatunless maintained regularly earth buildings couldnot be expected to last long. However, the materialof an obsolete or a decayed building is readily recy-cled into a new building. Before re-use, a sampleshould be tested to see if it has lost any of its bind-ing capacity, which can be improved by additives.

Further field tests can be readily undertaken todetermine the physical characteristics of samples, toevaluate comparative performance, including poros-ity, density and solubility analysis. These tests involvemaking up comparative samples of reconstituted orproposed new material, and these are best done astest cubes, formed in a simple mould. Techniquesand materials should be those that are used in thefield, and the samples should, therefore, be madeusing hand mixing methods and trowel application.

Mud brick is made up of clay silt and sand, thesand content generally being increased by additionso as to reduce shrinkage and cracking upon dry-ing. Mud mortar was often used but the bricks werealso laid dry. Fibrous material such as choppedstraw or reed, even animal hair, is added to the wet

mix. Blood and other additives may be used tostrengthen the mix and although bacteria arethought to destroy the cellulose of the fibrous ma-terials, it has been proved that stronger bricks aremade this way. It is thought that tannins, proteins,sugars or the products of their decomposition canstabilize mud bricks; certainly ancient recipes con-tain many suggestions of this nature. Ropes andmats of reed were often used to increase the tensileresistance and a surface protection was alwaysadded—in its simplest form this was a clay orclaylime plaster, but in ancient Iraq a baked-brickor terracotta surface was sometimes used.

Building in earth is a social activity in which thewhole community can be involved. The material isreadily available, but false economics and unrealland values coupled with the belief that it is a back-ward material led to its unwarranted rejection.

Decay of earth structures

Rain plays havoc with unprotected earth structures,especially if it comes in short torrential storms whichcause rapid erosion and deep furrows, for runningwater will quickly widen any cracks and may causepart of the structure to dissolve and collapse.

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Figure 5.7 Modern mud wall near Kerbala, Iraq

The destruction of the base by evaporation and salt crystallization shows clearly

Figure 5.8 Mud plaster wall, Mosul, Iraq

Mud plaster showing the amount of chaff used as bonder

Structures with reed layers are far more resistant.Rain splash or puddles at the lower level also erodethe base of the wall, particularly if water is allowedto collect and soften the earth.

Earth buildings will decay unless the walls are pro-tected by good roofs with overhanging eaves and arebuilt upon damp-proof foundations raised above thesurrounding ground, and the surfaces maintained ingood condition with an annual coat of mud lime plas-ter, being followed by coating of a more weather-resistant material such as limewash or tar, which caneasily be renewed without affecting the wall structure.

Maintenance and repair of earth structures

The capping of the wall and provision of rainwaterdrainage to sufficient channels or soakaways are thefirst priorities for preventive maintenance. The main-tenance of earth walls has to be at least an annualprocedure to make sure that the roof is sound or thatthe capping has no cracks and that rain water drains

away from the base with ample-sized drains to dealwith sudden exceptional storms.

An earth wall, providing it is capped, decays by asurface weathering process; probably rain reorien-tates the clay plates parallel to the surface of partiallydissolved bricks, so increasing their resistance. InIraq in the spring, climatic changes between 1400hours (2.00 p.m.) and after sunset can be as large as�75% RH and �25�C, and in the early morning condensation must take place. The surface of thebricks thus undergoes a daily cycle of swelling andcontraction which may result in fine superficialcracks and detachment of the weathered layer, butthis is a slow process compared with the action ofrain or groundwater.

The bottom 100–300 mm (4–12 in) of a structureis also vulnerable because of the effect of the cap-illary rise of moisture carrying soluble sulphates,chlorides and carbonates, which on evaporationshow white efflorescence, the crystallization disin-tegrating the surface inexorably. This action causesdeep erosion of the base of the wall at a rate far

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Figure 5.9 The Great Wall of China—the western end atGiau Guan. Famed as man’s largest historic construction,the Wall is an earth structure throughout its length,although stone-faced at its eastern end (CourtesyJohn Warren

Figure 5.10 Earth construction typical of Europe, theBalkans, through mountainous Turkey, Mesopotamia andthe Caucasus to the Himalayas. Here earth block is usedin the understorey with a light timber framing abovefilled with similar block. An outer skin of rendering—stripped from this example—may be used externally

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Figure 5.11 A palace at Birket Muz, Oman, rendered uninhabitable by air attack, demonstrating how man is one of themost potent forces of destruction (Courtesy John Warren)

Figure 5.12 Iran: medieval castle at Faraj. The collapse of a double-chambered tower demonstrates the slender cross-sections achievable with the use of squinches and secondary vaulting in the haunches of vaults. These techniques areapparent from the early Middle Ages and precede the structural magic of Persian brickwork (Courtesy John Warren)

more rapid than weathering of the surface. Miceand birds also cause damage, as well as the rootsof plants, which are difficult to eradicate.

Materials for capping and repair of earth struc-tures should meet the following requirements: (a) they should be fairly resistant to water; (b) theyshould not exhibit strength or thermal expansionmuch in excess of the mud brick walls; (c) theyshould not differ in colour, texture and porosityfrom the original material; (d) they should be inexpensive, as large quantities are usually needed.

A recommended procedure is as follows. A localclayey soil, as originally used for the manufactureof mud bricks, should be taken and mixed withabundant water and left covered with water to tem-per for at least a week. The wet soil is then mixed

to form a slurry consisting of 8 parts to 1 part ofsand and 1 part of Portland cement. Chopped strawis added to improve the mechanical properties ofthe mix, which is then set to dry in moulds restingon sand, which gives a rough texture. The bricksshould have a wet-mat covering for about a weekand be turned over after three days to ensure evendrying. After a week they can be allowed to dry inthe sun.

The tops of earth walls, if not roofed over, needspecial attention. A sloping rendering of mudcement mortar made like mud bricks but withoutthe addition of straw is not very satisfactory as itcracks after setting, even if executed in two coats.However, mud cement mortar is useful for groutingof cracks in walls, because it is not subjected torapid drying. A course of cement mud bricks over-sailing by about 10 mm (0.4 in) and set so as toshed the rain, is a better form of capping.Unfortunately, cement mud bricks are slightly dif-ferent in colour from those of simple earth.

Surface treatment of earth walls is best carriedout by using ethyl silicate 40, which is the cheapestmethod available and which is applied by sprayingwith hand-operated plastic pulverizers of commer-cial type. The solution is diluted by an equal part of96% commercial ethanol, no water being added asa sufficient amount is contained in the walls for theaction of hydrolysis. After being thoroughly mixed,the solution is left to stand for a short time until itheats up due to the chemical reaction. Two litresper square metre (3.5 pt/yd2) are required to forma weather-resistant layer of sufficient consistency.After some days the porosity of the earth isregained and a second treatment is beneficial. Thetreatment is only effective on vertical surfaces orsteep slopes, as on horizontal surfaces the thin crust is insufficient to resist the erosive action ofheavy rain.

If the surface layer is partially detached, adhesioncan be restored using polyvinyl acetate emulsionsdiluted with water and mixed with mud to form aliquid grout.

Earth walls can be repaired by removal of thedefective lumps and insertion of new bricks ofapproximately the same size and strength, whichare then plastered over and limewashed to matchthe old surface.

Repair of rammed earth

Rammed earth, known as cob or pisé or khesht, ismore difficult to repair than mud brick as the ma-terial is homogeneous, and since the repair iswetter it shrinks, making it difficult to obtain a

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Figure 5.13 A tower, now an isolated fragment of theGreat Wall of China, displaying vertical fissuring whichcauses the loss of segments in vertical slices. The loss oflateral restraint in the lowest zones effectively ‘unloads’the compression previously applied to the bottom strataby the mass of superimposed earth. The lateral stress-release causes the peripheral mass to form shearcracks parallel to the external surface. This phenomenonis unique to earths, among building materials, due to itscompressibility and low shear strength (Courtesy JohnWarren)

bond between old and new work. For this reason,the defective area should be cut out square anddried mud bricks set in mud lime mortar usedbefore applying a plaster coat and limewash.

Repair of wattle and daub

In Northern Europe, before bricks became common,mud in the form of wattle and daub was used as aninfill in half-timbered work, being fixed to the sill andhead of the space, and also for internal partitions.Sometimes the framing timbers were grooved to pro-vide a check to wind and rain. The hazel sticks outof which the wattle was woven are generally attrac-tive to wood-boring beetles and have often disinte-grated completely. Repair, if it is necessary, can bedone by copying the old methods. If no wind andwater check has been formed in the oak frame, onecan be planted on by screwing a tapered oak fillet tothe sides of the frame. Brick infill in half-timberedwork is generally evidence of later repairs.

Maintenance of archaeological excavations

Archaeological excavations present additional prob-lems of maintenance: due to the lowering of theground level, precautions must be taken to deal withrain which might destroy all the evidence beinglaboriously acquired. Exposure of previously buriedwalls subjects them to new static stresses as well aschanges in temperature and moisture content andcapillarity, which may be most serious due to dis-solved salts having penetrated the mud brick. If roofsare put over old walls they may well impose toogreat loads. Once recording has been done, oftenthe safest policy is to refill the archaeological siteusing sifted material from the excavation.

Another problem with upstanding ruined walls ofancient sites, is plant growth, which is expensiveand time-consuming to control. If the wall tops arerendered and made waterproof, this difficulty isreduced, but this may be objected to historicallyand aesthetically.

Maintenance of archaeological excavations

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The history and methods and materials of founda-tions are generally the same as the walls which theysupport, although in some cases new structureshave been built upon old foundations.

Foundations are that part of a building which dis-tributes the loads from roofs, floors and walls on tothe earth below. This is generally done by a widen-ing of the wall into a footing which bears on to thesoil under the building; however, in many earlybuildings no such widening was practised. Themajor factor in the permanence of a building is thesufficiency of its foundations and if this is lackingthere is no sense in spending large sums of moneyelsewhere on superficial restoration work.

Ground movement is not at all uncommon.Geologically it occurs continuously and in extremecases causes earthquakes. It can be induced by man-made activities such as mining and underdrainage.Heavy rain can also induce landslides, while under-ground streams, especially in chalk and gravel, cancause potholes and caves under buildings.Conversely, blocked underground watercourses maycause the water table to rise. The absolute move-ments of a building—with the exception of earthquakes—are of less concern than differential orrelative movements which may be caused by differ-ent types of ground under the building or unevenloading of different parts of the building.

The geology of the ground upon which a build-ing stands and which carries all the dead and super-imposed loads can have short- and long-term effects.Ground movements must be considered normal forall buildings with long life, but for important historicbuildings it is necessary to record these movements,as a time will come when preventive action must betaken. Abstraction of ground water is one of the prin-cipal reasons for ground movements, causing theshrinkage of clays and peats; mining subsidence isanother cause of such movements. Tunnelling anddrainage also cause ground changes. There are

gradual geological movements in most countrieswhich may affect the water table and undergrounddrainage patterns. Excessive reliance upon septictanks and local dispersal can cause a rise in theground water under a city, whereas irrigationschemes such as at Mohenjodaro in the IndusValley and the High Dam at Aswan can raise thewater table over whole provinces causing acuteproblems of humidity, dampness and crystallizationof salts.

Heavy buildings planted near an historic buildingcan alter the ground stresses and cause movement,and their foundations may block undergroundwater movement.

Ground failures do not always appear suddenly.The soil, particularly if of low permeability, maywell creep even when below its actual shear resist-ance. The structure above accelerates the effect ofground failure as this induces eccentric loadingsand turning movements. The rate of movementmay die away with time as soil resistance builds updue to its compression, or alternatively it mayaccelerate towards collapse.

With an architecture of thrust and counterthrust,loads are concentrated on to piers and buttressesenabling the windows to be large, and this means thatnot only are differential settlements likely unless theoriginal foundations took this into account, but alsothat they can within reason be accommodated. Thesesettlements may be aggravated by inconsistencies ofthe bearing capacity of the soil under the foundationswhich turn straightforward overall settlement into dif-ferential settlement, causing distortion and crackingof the superstructure. Very high loadings, up to800 kN/m2 (7 tonf/ft2) have been applied to founda-tion soils, and loads of 4000 kN/m2 (35 tonf/ft2) arenot unusual in piers. The ultimate stress of the soilhad in fact been reached under the central tower ofYork Minster before the 1967–72 restoration, so therewas a danger of the soil shearing.

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Structural elements IV: Foundations

Investigation of foundations

The scientific study of ground carrying foundationswas started over two centuries ago by Coulomb andis now a specialized study called soil mechanics,which depends upon the nature of the soils definedby the size of the particles and their geological origin.It should be borne in mind that peat soils and fine-grained plastic soils will compress and squeeze out-wards and fine sand combined with water will run.

Before carrying out major foundation works it isdesirable to monitor any movements by establishing asystem of measurements related to an accurate andreliable datum point, if this can be found not too faraway. Besides monitoring structural movements, it ishighly desirable to measure alterations in the level ofthe water table. With sufficient time for measuring,this movement can be estimated, according to E. Schultze.* Deep ground water is another factor notto be neglected. For example, abstraction of waterfrom the deeper layers of soil, as has occurred withthe underdrainage of London, which has sunk, likeVenice, a total of some 180 mm (7 in), causing waterto drain from the upper or perched water tablethrough fissures down to the lower water table. Thissituation, combined with dynamic influences such astraffic vibrations, deep construction and tunnelling,causes settlements. It must be remembered that manybuildings settle quite dramatically during construction,

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Figure 6.1 Hypothetical reconstruction of settlements since A.D. 1080, central tower, York Minster, England(Courtesy: Ove Arup & Partners)

Such a diagram combines history and soil mechanics and introduces the fourth dimension of time into structural engineering. After being in unstable equilibrium for nearly four centuries, the foundations of the centraltower began to settle again due to lowering of a perched water table

*In an unpublished paper given to a Symposium on EngineeringInterventions in Historic Buildings, organized by ICCROM inRome. Due acknowledgement is given for much of the materialon foundations.

Figure 6.2 Extreme settlement of a tower

(a) The weight acts through the centre of gravity(b) Wind forces add to the turning movement(c) The pressure on the toe of the foundation increases rapidly

as the tower leans(d) There is a danger of uplift

the Leaning Tower of Pisa being the historic case—corrections made during construction led to itsbanana-shaped form.

The success of a building’s foundations dependsupon the nature of the soil on which it is built. Assoils are infinitely variable, each problem of founda-tion failure must be individually examined. Thenature of the soil* depends upon its grain structureand the geological way the soil was laid down; thereare two general types—cohesive soils consisting ofclays and silts composed of fine particles and non-cohesive soils consisting of sands and gravels com-posed of larger particles. With non-cohesive soils,eccentric loads can decrease the factor of safety veryrapidly. The settlement of foundations can changethe direction and relative magnitude of thrusts fromroof and vaulting, setting up new stresses and thrustsin the fabric which the original scheme of counter-balancing of thrusts was not designed to meet.

Cracking and consequential damage are causedby differential settlements, which are largely due tounequal loading which can only be eliminated byenlarging those foundations that are overloaded.Ideally, in a building, all foundations should be

subject to the same pressures, provided they are onground which has the same load-bearing capacity.This was the objective in the restoration of YorkMinster.

If inspection reveals cracks and fractures that canbe attributed to ground settlement, or if the struc-ture is leaning, the probability is that stabilization ofthe foundations will be necessary. Such endan-gered structures are very sensitive, so great care isnecessary in the execution of the work. Thescheme for stabilization must be prepared after afull investigation; then the execution of the workmust be considered together with what temporaryworks are needed. Often these latter considerationswill modify the design proposals. Before finallychoosing measures for stabilization, these shouldbe the subject of in situ tests.

Defects in foundations may be indicated by a dropor sag in the line of the string course or plinth of abuilding that may be presumed to have been builthorizontal, or in more extreme cases by cracks andeven shattered stone. A.R. Powys writes that ‘exami-nation of suspected foundation trouble should bemade, as much to prove that no work is required, as

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Figure 6.3 Leaning Tower of Pisa, Italy(Courtesy: Bollettino Ingegneri)

Section showing pressure zones (in tonnes-forceper m2) and levels of recent sands and clayswhich have been compressed by the weight of the tower which is approximately 12 000 t(11 810 ton). The inclination of the tower hasbeen monitored accurately. The tower was closedto tourists because of concern over the condition of its masonry. Ground water levels have beencontrolled with beneficial results. In 1992 therewere proposals to maintain equilibrium by placing lead weights on the north side. In 2001,the tower was reopened to tourists, after its inclination to the south had been reduced byabout 50 cm (20 inches), by extracting soil underthe foundations on the north side. This simplesolution to a complex problem meets all the desirable theoretical criteria, and in itself isreversible.

*In Britain this information can be obtained from the Geological Survey.

to discover what should be done’. The presentauthor’s own experience endorses this advice.

First, the movements of the building should bemeasured and recorded. The inclination and defor-mation of the building should be studied for as longas possible. Inclinations are measured with plumbbobs, optical plumb bobs, theodolites and incli-nometers. Ground slopes should also be carefullyrecorded near leaning towers and walls. Groundwater variations at different geological levels shouldbe checked with piezometers.

All possible sources should be searched for plansand other relevant documents, and measured draw-ings should be made of the whole building recordingall cracks and deformations. The possibility that thefoundation walls may themselves have decayed due tothe chemical action of salts in the ground should not

be overlooked. If walls rest on wooden piles, thesemust also be checked, for often they have decayeddue to alteration—past or present—in the level of thewater table. Finally, the actual size and position of thefoundations must be discovered, together with anyarchaeological hazards that may affect them.

Lowering of the water table is generally causedby pumping either for building works or for min-ing, in which case it will probably affect a widearea. Percolation into deep drains can also affectthe water table.

A change in this level of the water table can alter thebearing capacity of the soil and may have other sideeffects, i.e. the raising of the water table may softenclay, or the lowering of the water table may cause drying and shrinkage of clay, or the washing away offines out of gravel and ballast subsoils.

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Figure 6.4 Central tower foundations, York Minster, England(Courtesy: Ove Arup & Partners)

Plan of north-west pier foundations showing stainless steel post-tensioned layout. The project was toenlarge the area of foundations making them symmetrical about the line of thrust a, so avoidingeccentric loads and dangerous pressures on the soil

If the lowering has been rapid, considerable dam-age can be caused to an historic building (cf. MilanCathedral). Prevention of this hazard is one of the pri-mary objectives of the St Paul’s Cathedral PreservationAct of 1935, which gives the cathedral authorities theright to intervene if the upper ground water levels arethreatened with change. Records show that the waterlevel varies slightly with annual rainfall.

Raising of the water table occurs gradually inriver valleys, particularly those that have silt-ladenfloods. Irrigation schemes such as in the IndusValley affecting Mohenjodaro and the Nile affectingCairo, have raised the ground water level consider-ably. Locally, increased sewage effluent from septictanks can raise the water table under certain hydro-logical conditions, as at Kerbala in Iraq. If the watertable land has been raised by some extrinsic causethis will show by dampness in cellars and increasedcapillarity and moisture content in walls. These areserious problems.

After the whole building, its site and setting,including adjacent buildings, have been inspected,then the soil and the underground environmentmust be studied. Simple methods of exploring foun-dations are in digging holes and/or measuring andprobing with augers at an inclined angle. Soil canalso be examined by taking cores with hand augers.General soil conditions can be obtained from gov-ernment agencies. Detailed information is obtainedby boring and retrieving cores for inspection and

undisturbed samples for laboratory analysis includ-ing standard soil mechanic tests such as triaxial testsfor different types of soil. The object is to find thebearing capacity of the soil and to understand itscharacteristics based upon its stratification. Thequality of the soil can be further explored andtested at great depth by driving heavy piles or pres-sure piles, which will indicate the load-bearingcapacity of the soil.

Structural interventions to improve foundations

From inspection of the building and its environ-ment and from the tests outlined above, it shouldbe possible to make an assessment of the causes ofstructural damage, and for a specialist to producecalculations of the earth statics and to devise pre-liminary proposals for conservation of the structurethrough correcting faults in the foundations.

Methods of consolidation of foundations dependnaturally on local conditions, and often severalalternatives can and should be considered. Theunderground soil may be improved by chemicalgrouting, modern methods having been developedusing boreholes 50 mm (2 in) diameter at 500 mm(20 in) centres involving pressures up to 200 atm tocreate piles with a bearing capacity of about 10.2 t(10 ton) each.

Structural interventions to improve foundations

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Figure 6.5 Central tower foundations, York Minster, England(Courtesy: Ove Arup & Partners)

Section through north-west pier foundation. The existing masonry was contained with the new concrete.The flat-jacks were slowly inflated to prestress the soil and equalize loads carried by old and new work

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84

Figure 6.6 North-east pierfoundation, central tower,York Minster, England(Courtesy: Shepherd BuildingGroup Ltd)

As fresh cracks were found in theshaft of the north-east pier, thiswas explored first. Severe shearcracks were exposed and glasstell-tales were fixed—thosebreaking within six months indicated active settlement of thefoundations, as suggested byfreshness of the upper cracks. Thelowest work is eleventh centuryfollowed by thirteenth century,and the upper work is fifteenthcentury. The eleventh centurymasons’ technique of diagonalaxe-cutting shows clearly

Figure 6.7 North-east pier foundation, central tower, YorkMinster, England(Courtesy: Shepherd Building GroupLtd)

Similar shear cracks were found onthe west side. The strength of the hori-zontal strutting should be noted, withthe screws and plates for applyingpressure to contain the masonry. Thepolythene pipes are for injection of liquid grout

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85

Figure 6.8 Investigationof foundations, YorkMinster, England(Courtesy: Shepherd BuildingGroup Ltd)

It was found that theNormans had used a grillageof oak beams to reinforcetheir foundations and that byand large this grillage, afragment of which can beseen being held, had rottedaway leaving voids

Figure 6.9 Investigationof foundations, YorkMinster, England (Courtesy: Shepherd BuildingGroup Ltd)

The photograph shows thatthe voids were continuousand in fact ran from belowthe high altar nearly to thewest end. Under the centraltower the masonry had bentwith the settlement, but luckily none of the voids hadcollapsed

Overloaded earth pressures may be reduced bysurface excavation, or uplift pressures may be bal-anced by a surcharge on the lightly loaded parts. Ifthe soil is thick and compressible, adjustment of theground water drainage will take a long time and isdifficult to control. Depending upon the nature ofthe soil, adjustment can cause shrinkage, whichmight help a leaning wall or tower to return to asafer position; or conversely, with different soils,replenishment of the ground water, or at leastmechanical control of its level, can assist in regain-ing or maintaining stability, as is practised in thecase of York Minster. Only an experienced expertin soil mechanics can advise upon such esotericmatters.

Foundations can be improved by enlargement, ordeepening, or the use of levers and anchorages andcontainment. Underpinning should be avoided inenlargement because of possible damage from localsettlement during execution. The most elegant wayto enlarge a foundation is to provide the increasedarea in reinforced concrete and then to needlethrough the wall and prestress the new foundationusing flat hydraulic jacks. The classic way of deep-ening foundations is by underpinning, but moremodern methods including pressure piles, verticalbored piles, root piles at an oblique angle andmany other types of pile give better results andimprove load-bearing capacity. When piling, it isimperative to choose a method that does not pro-duce vibrations, so bored piles are essential.

Levers can be constructed so as to apply a back-turning moment and so reduce the effects of foun-dation failure on the opposite side. The momentcan be applied by weights sliding inside a hollowcaisson, or by a hydraulic jack or by tensionanchorages fixed to piles. Tension rods which byprestressing can counteract the eccentric loadscaused by foundation settlements require counter-forts or anchorages sufficient to resist their tension.A suitable combination is a tension anchorage withmicro-draw piles. Containment by simple sheet pil-ing may be sufficient if the structure can withstandthe vibration resulting from such a driving process.

Before projects are begun, field tests on the siteshould be carried out using the favoured methodsof repair, all such tests being carefully monitored bymeasurements.

Temporary work relating to foundations

The question of whether temporary support is nec-essary must be carefully considered, bearing inmind that any works to foundations may cause fur-ther movements and induce increased danger until

the works are finally completed. Schemes whichare conceived in stages, so that results can beassessed step by step, have the advantage that theyallow a minimum intervention to be practised. Thesame measuring procedures that were used for the initial assessment should be retained during theworks and continued for some years afterwards inorder to monitor the effectiveness of the work.

A temporary support always looks unsightly andcreates its own foundation problems, particularly ifthe ground is poor. For such supports to be effectivethey should be set on hydraulic jacks which willensure that the correct amount of support is applied.Such hydraulic jacks can also be used to provide anactive back-turning moment to an inclined wall ortower. Temporary anchorages can be made usingmicro-pressure piles. Freezing of the ground mayalso provide temporary support but careful consider-ation must be given to the dangers of frost heave ifthis proposal is adopted. Schultze says that frostheave is generally not to be expected under existingfoundations. Cradling of the whole structure comeswithin the scope of temporary works when dealingwith foundations (it is also a technique used to pre-vent damage from mining subsidences). Besidescradling, elements can even be supported on cablesin order to enable works to be carried out.

Lowering of the ground water level for a short timeby local pumping is often permissible but sometimescofferdams or rings of well points are necessary. Suchcontinuous pumping must be watched carefully, aslowering of the water table may induce active springsand quite violent water movement which is danger-ous to the structure being repaired if any sand or siltis abstracted. In this case the work must be stoppedimmediately. Freezing the ground either wholly orinto blocks can overcome these difficult conditions,which of course should have been foreseen by initialsoil mechanic studies.

Excavation for foundation work must be properlyplanked and strutted and any underpinning must beneedled and shored. Strutting can be done usingscrew-type props or the newer hydraulic props,which are safer as they can share loads equally andhave less risk of individual failure. Timbers used fortemporary structures, such as planking and strutting,should be treated with preservative as a precautionagainst wet or dry rot. Where loads are heavy andnear the ultimate bearing capacity of the soil, and par-ticularly if these loads are eccentric and on a clay sub-soil, there may be a risk of some heave or uplift of theadjoining ground. This will place a restriction uponthe area which can be opened up for foundationworks at any one time. It may well be necessary toreplace the weight of the soil excavated by an equalweight of sand in rot-proof sandbags. In an area

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Temporary work relating to foundations

87

Figure 6.10 Archaeological sitework, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The photograph shows the archaeologists at work. One is taking levels and another is holdinga measuring rod, while the third is recording the measurements and sketching on a drawing. The remains of a post-Roman building on the Roman alignment at the west endare being recorded. In the distance three labourers are assisting an archaeologist in anexploratory dig. On the left is part of the main foundation of the south-west tower and thecollar above had been inserted previously. Continuity rods project outwards to bond the nextpiece of concrete firmly to the existing concrete, and the grooves in the reinforcement arealso to assist in securing a good joint. The necessary strutting has been left in position andthe concrete poured

that is critical, it is wise not to expose more thansay one-sixteenth of the total, but this will dependupon the circumstances.

Repair of foundations

If it is decided to enlarge the existing footings, thesenew foundations can be bonded to the old ones,using post-tensioned reinforcement. When newfoundations are added to the old, it is likely that thenew parts will not take up loadings until further set-tlements have taken place, but this problem can beovercome by the use of compression pads and inflat-able flat-jacks. The latter can be used to depress acompression pad into the earth, and if the pressureis controlled carefully the exact load on the newfoundation can be calculated and the stresses can beequalized with those on the old. Such a process mustbe carried out slowly by stages, with smaller incre-ments as the pressure increases. If the pressure isapplied too quickly, there is danger of punchingshear and not giving sufficient time for the subsoil toadjust itself to the new loadings. After prestressing,the jack space is filled with grout to give a perman-ent connection with the new compression pad; thejack can usually be salvaged for re-use.

The most traditional method of repair to founda-tions is underpinning, i.e. the removal of defectivefootings and their replacement by new andenlarged ones. In this method, short lengths ofwalling are cut out and propped up while the largerfoundations are inserted. The phasing of such workmust be arranged extremely carefully, bearing inmind the problem of shift of load from one part ofthe structure to another during the course of thework. Underpinning should also include the use offlat-jacks in order to prestress the loading. A deviceknown as the Pynford stool is most helpful forunderpinning. This consists of an upper and lowersteel plate of approximately 30–50 mm (1.2–2 in)thickness supported on tubular legs of approxi-mately 800 mm (31 in) length. Each of these iscapable of carrying loads of up to 102 t (100 ton)and they can be cut into position and grouted andwedged through the masonry, above and below,using an expanding grout to make sure the joint istight. The wall above can thus be carried temporar-ily while new foundations can be inserted by beingcast into position with the reinforcement passingthrough the four-legged stool. The success ofunderpinning depends however on the strength ofthe masonry above and if this is not sound, diffi-culties might occur. When underpinning founda-tions, the opportunity to insert a damp-proof courseshould be taken whenever possible.

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Figure 6.11 Archaeological finds, York Minster, England(Courtesy: Royal Commission on Historical Monuments,England)

A Roman column of the Headquarters Basilica lying where itfinally fell, before the Norman York Minster was built. Also, aNorseman’s tombstone. Interesting archaeological stratificationshows. Sufficient evidence was obtained to shed a little newlight on the Dark Ages in Britain

Figure 6.12 Tower, Bautzen, Germany(Courtesy: Ing. W. Preiss)

The tower was underpinned by W. Preiss of Dresden and thesequence of the operation was carefully worked out in 14 stages. The inclination of the tower was recorded and hadincreased by 21 mm (0.8 in) in three years. During the worksthis rate was somewhat exceeded, but on completion there wasevidence of less inclination and a cessation of movement

Repair of foundations

89

Figure 6.13 Tower foundations, Bautzen, Germany(Courtesy: Ing. W. Preiss)

(a) Plan showing sequence of underpinning(b) Record of movement of tower from May 1950 to October

1954

90

Figure 6.14 Underpinningwork, east end, York Minster,England(Courtesy: Shepherd BuildingGroup Ltd)

New foundations under theeast wall were required, so ithad to be underpinned instages of 1.2 m (4 ft). Thisshows the heavy strutting usedto enable the work to be done

Figure 6.15 Underpinning work,east end, York Minster, England(Courtesy: Shepherd Building GroupLtd)

The blocks are keyed together. The newfoundations were inserted in a carefulprogramme so as to control the settle-ments, which in this case were benefi-cial as they reduced previousdistortions. The precious stained glassabove and in the side walls was pro-tected by cutting out the perimeterjoints so as to allow for some movement

Part II

CAUSES OF DECAY IN MATERIALS AND STRUCTURE

92

CAUSES OF DECAY AND DAMAGE TO CULTURAL PROPERTY

Gravity causes buildings to fall downExternal Causes of Decay. The sun produces light with ultraviolet and heat radiation

Climatic causes Biological and botancial causes Natural disastersSeasonal temperature changes Animals TectonicsDaily temperature changes Birds Earthquakes Wind Insects Tidal wavesPrecipitation of rain and snow Trees and plants FloodsIce and frost Fungi, moulds, lichens LandslidesGround water and moisture in soil dust Bacteria AvalanchesDust Volcanic eruptions

Exceptional windsWild fire

Internal Causes of Decay (Note: the building modifies and protects)(Courtesy: Plenderleith, H.J. and Werner, A.E.A., 1971)

93

Introduction

Previous chapters have dealt with the effect of grav-ity, one of the principal causes of structural decay.This chapter deals mainly with geographical causes,i.e. with climate and its side effects. Earthquakesare given a separate chapter.

Climate, in all its aspects, is one of the funda-mental causes of the decay of buildings, throughfailure of their materials which in turn affects thestructure. To give a simple example, mud brick oradobe may last thousands of years in extremely dry,arid desert conditions such as found in North Peruor Nubia, but less than a decade in the hot, humidclimate of southern Nigeria. The resistance of build-ing materials to climatic agents of decay decreaseswith their exposure and age. Even in temperatezones, solar radiation is found to be more destruc-tive than frost. Water, in all its forms, is the agentthat promotes chemical actions and gradual deteri-oration of building materials and actively damagesbuildings when heavy rainfall overflows gutters andrivers rise in flood.

Whereas the macroclimate of the world has beenclassified according to the growth of different typesof vegetation or annual rainfall, this information isonly of indirect value to the architect examining anhistoric building. The active components of macro-climate that affect a building particularly are radia-tion from the sun, seasonal temperature changes,rainfall, particularly storms which may cause flood-ing on both a micro or macro scale, wind and thetransportation of ground moisture.

The siting of a building and the soil it stands onaffect its microclimate which can modify the macro-climate considerably and so increase climatic haz-ards. For example, the ruined Villa Jovis on the islandof Capri, built by the Emperor Tiberius c. A.D. 70,stands on a promontory rising about 300 m (1000 ft)from the Tyrrhenian Sea, exposed to the winds and

salt spray as well as being liable to attract lightningstrikes in an area noted for its thunderstorms. It hasbeen shown that cities modify the macroclimate,being warmer in winter and also much more liableto heavy concentrations of atmospheric pollution.Other examples of microclimatic effects are frost ponds, shading by hills or mountains, and theameliorating effects of water on temperatureextremes, as well as that of the moisture content ofthe soil.

The architectural form and structure of a buildingwill influence the microclimate of its parts.Indigenous or vernacular architecture shows howbuildings were used as ‘spatial environmental sys-tems’ to modify the external climate, one examplebeing the wind towers and water-cooling chambersused in Iran and the Gulf States. Courtyards withwater and fountains modify a hot, arid climate byproviding shade and evaporation, as do trees whengrowing around a building. Particularly in hothumid climates, air circulation is important both forcomfort and prevention of fungal attacks onorganic material which often precedes insect attack,and in such cases one finds that the vernaculararchitecture of the country responds to its climateby having light, open structures with roof shapesdesigned to encourage air movement. If an historicbuilding is to be used as a museum, both the exter-nal and internal climate will need careful considera-tion and the architect has a responsibility fordefining and assessing the climatic factors whichwill affect the exhibits.

Solar radiation

Solar radiation is the prime cause of climatic condi-tions, and its wavelengths range from the ultraviolet(0.2 �m), through the narrow band of visible spectrumof light (0.4–0.9 �m) to up to infrared (8 �m), which

7

Climatic causes of decay

94

Figure 7.1 Mean annual temperature—world(Courtesy: McGraw-Hill Book Co.; from Koeppe, C.E. and De Long, G.C.,Weather and Climate, 1958)

Figure 7.2 World temperature ranges(Courtesy: McGraw-Hill Book Co.; from Koeppe, C.E. and De Long, G.C.,Weather and Climate, 1958)

has the greatest energy input.* All terrestrial radia-tion is long wave, from 4 �m to 50 �m approx.Different materials vary in their ability to absorb dif-ferent wavelengths and only absorb a percentage ofthe radiant energy falling upon them. This percent-age is known as absorptivity and varies fromnought for a perfect reflector to one for a perfectabsorber. The term ‘albedo’ is used by climatolo-gists to define the percentage of incoming solarradiation that is reflected from a surface. Materialsthat absorb well at short wavelength are not neces-sarily good emitters at longer wavelengths. Shortwavelengths pass through glass which, however,does not transmit the returning long-wave radia-tion—a feature which is called solar gain.

Ozone, water vapour, clouds and dust restrict theamount of solar radiation which is receivable bybetween 30% and 60%. Maps showing mean dailysolar radiation averages for different months of theyear are available but these show radiation fallingon the ground, not on the vertical walls of a build-ing, so are not really relevant. Radiation can bemeasured by a climatologist using a radiometer.

Light, especially the ultraviolet component, is adestructive agent, particularly to organic materials

Solar radiation

95

Figure 7.3 Holy Shrine ofAl Hussein, Kerbala, Iraq

Thermal cracking in newcement mortar renderingaround base of dome due tolarge daily changes in temperature and use of aninflexible material

Figure 7.4 Palazzo at Fianello, Lazio, Italy

Note the destructive effect of ultraviolet light and other climaticelements upon untreated wood *1 �m = 1 micron = 0.001 mm; 25 �m = 0.001 in = 1 mil.

such as wood, textiles and pigments, and causesfading, embrittlement and loss of substance.Unprotected wood can erode at the rate of 5–6 mm(1–4 in) per century due to the combined attack of

ultraviolet light and rapid moisture exchange.

Temperature and thermal expansion

The cause of air temperature change is almostentirely the heating effect of the sun by day throughboth short- and long-wave radiation and the loss ofthis heat by long-wave radiation and convection atnight. Building materials are heated by solar radia-tion in three ways: by direct solar gain from externalradiation; by indirect internal solar gain through windows—the ‘greenhouse effect’; and by indirectheating via the external air whose ambient tempera-ture is raised by the sun. The shaded part of a build-ing stays relatively cool and immobile, being mainlyaffected by the seasonal average temperatures.

All building materials expand when heated andcontract again when cooled, this expansion and con-traction being called thermal movement which is amajor cause of decay in buildings. The colour andreflectivity of the material alters the radiant heat

input, which is the main factor inducing temperatureincrease. Dark, matt materials, for example, absorbmore heat than other materials. The extent of ther-mal movement depends upon the temperaturerange resulting from the heat input and modified bythe thermal capacity of the structure, the thickness,conductivity and coefficient of expansion of thematerial (Table 7.1). Building materials with highabsorptivity may reach temperatures much higherthan that of the ambient air. Thermal movement isreduced by the restraints the structure can impose.

The ranges of change in climatic temperatures varyconsiderably, being narrow in a humid tropical rainyequatorial climate, moderate in a maritime cool sum-mer climate, wide in continental steppe and polartundra conditions and extreme in arid desert climates,where daily and seasonal variations are at their great-est. The range of thermal movements tends to varycorrespondingly and, bearing in mind that a buildingof low thermal mass is most sensitive to daily varia-tions, it is not surprising to note that in hot desert climates the traditional permanent buildings are all ofheavy construction, having a high thermal mass tocompensate for the daily temperature changes.

A study of temperature ranges of stone surfacesshows that they reach temperatures much hotter than

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Table 7.1 Thermal Expansion Coefficients of Materials used in Buildings (unit m/m�C)(By courtesy of ICCROM)

Material Coefficient

Concrete 10 � 106

Concrete with gravel 9 12 � 106

Concrete with expanded clay 7 9 � 106

Cement mortar 10 11 � 106

Lime mortar 8 10 � 106

Limestone 7 � 106

Brick 5 � 106

Granite 8 � 106

Glass (10% alkali) 4.8 � 106

Iron 11.5 � 106

Steel 10 14 � 106

Copper 16.8 � 106

Aluminium 23.8 � 106

Lead 29.4 � 106

Pine, along fibres 5.4 � 106 across fibres 34.1 � 106

Oak, along fibres 3.4 � 106 across fibres 28.4 � 106

Fir across fibres 58.4 � 106

Wood laminates 10 40 � 106

Polyester resins 100 150 � 106

Glass–polyester laminates 35 45 � 106

Epoxy resins 60 � 106

Epoxy with silica filler (1 : 5) 20 � 106

Acrylic resins 70 80 � 106

PVC 70 80 � 106

Nylon 66 70 100 � 106

the atmosphere. Readings taken on these surfacesshow: (a) Borobudur (Indonesia), from 25 to 45�Cin 4 h (5�C/h); (b) Abu Simbel (Egyptian Nubia),from 15 to 41�C in less than 8 h (3.25�C/h); (c)Persepolis (Iran), from 2 to 34�C in 6 h with a max-imum rise of 16�C in half an hour. It takes time forheat to penetrate, and at a depth of 50 mm (2 in) orso the temperature of the stone is close to the aver-age. However, a repeatedly heated and cooled skincannot resist indefinitely. At Persepolis the lime-stone reliefs have lost their sharp outlines only 30 or 40 years after being uncovered from the soilthat preserved them for two and a half millennia.

The stresses induced in building materials bytemperature changes are dependent on the follow-ing five factors:

(1) The magnitude of absolute dimensional changein the material, which is the product of itsdimensions multiplied by the coefficient ofexpansion and temperature differential and theeffects of changes in relative humidity.

(2) The elasticity of the material.(3) The capacity of the material to creep or flow

under load.

(4) The degree of restraint to the movement of thematerial by its connection to other elements ofthe structure.

(5) The change in moisture content by evaporation.

The amount of solar heat gain in a structure isdetermined by the angle of incidence of the radia-tion to the receiving surface and by the thermalproperties of the receiving surface (some surfacesare reflective or are made so by being painted white,whereas others are absorbent). Heat gain is modifiedby evaporation of moisture in porous masonry andalso by the effect of exposure to wind. As well asaffecting the temperature of the material and internalair volume, solar gain can affect the internal tempera-ture of the building by radiation through windows(unexpectedly, in the months of March andSeptember, solar heat gain through windows can begreater in Scotland than in the Sahara).

Although thermal mass and conductivity must betaken into account, temperature differentials can beset up between various building elements of differingabsorption and with different angles of incidence; forinstance, between a lead roof which is subject to heatgain and has a much higher coefficient of expansion,

Temperature and thermal expansion

97

Figure 7.5 Seventeenth century monastery wall, Suzdal, USSR

Frost has destroyed poorly burnt or otherwise defective bricks

and a stone wall which, having great thermal massand being light in colour and therefore less absorbentof heat and at a more obtuse angle to the sun’s radi-ation, is little affected. Although traditional lead roofsare well designed to absorb comparatively largemovements, the fatigue caused by repeated move-ments is the main reason for their decay.

Thermal movements

Depending upon the nature and elasticity and plas-ticity of the mortar (hard cement mortar aggravatesthermal movement decay because of its lack ofresilience), thermal movements in masonry are notgenerally acute unless the building is longer than30–50 m (100–160 ft). Since the upper portions of abuilding are not shaded by its surroundings and arefurther away from the earth with its almost infinitethermal mass, they are liable to be subjected togreater solar gain and therefore to expand and con-tract more. The usual sign of thermal movement ina building as a whole is cracking of the upper por-tions or the loosening of the stones in their joints.As expansion of masonry is not necessarily fol-lowed by equal contraction, small annual thermalmovements can build up to a considerable exten-sion over a period of years. This is called creep ordrift. For example, the north and south arcadedwalls of the choir of York Minster are restrained atthe west by the central tower, whereas the eastwall, being without restraint and having founda-tions already eccentrically loaded, has moved atotal of 626 mm (25 in) in a temperate climateunder the influences of annual thermal movementsof 1–2 mm (0.04–0.08 in) during some 550 years.

Let us consider thermal movements under threesections: (a) the movement of a block of stone setin a wall; (b) the movement of the wall itself; (c) the movement of a building as a whole.

Thermal movement of a block of stone set in a wall

Considering a notional block of stone set in theexternal face of the wall, the structural forces whichare applied to the five embedded sides should be forpractical purposes constant, as wind loads and vari-ation in live floor loads have little effect on massiveconstruction. Foundation settlements may occurwhich would vary these forces, but these are dealtwith elsewhere. Here we will consider only thosethermal movements due to heat gain by day and lossby night on the sixth exposed face of the block.

Heat is transmitted through the stone by theprocess of conduction, but there is a considerable

time lag in the flow due to the thermal mass, lowconductivity and moisture content of the stone.This means that a steady state is never achievedwithin the block of stone. In temperate, humid cli-mates, such as that of England, the heat gain:lossequation is modified by evaporation of moisture inthe pores of the stone which tends to damp downthe heat gain or loss which would otherwise occurowing to daily temperature fluctuations. Dependingupon the season, there will be an inward or out-ward flow of heat through the stone. In late spring,summer and early autumn there is a net gain,whereas in late autumn, winter and early springthere is a net heat loss. Temperature differentialacross the block of stone is likely to be greatest inthe early afternoon of a hot day, but because of thetime lag the temperature gradient will not necessarilybe in a straight line.

In England, however, even assuming the mostextreme conditions, the stresses within the stonedue to temperature differential are unlikely to causecracking of sound building stone. If the restraint isgreater than the stresses engendered by thermalmovement, the stone will not move. If the beddingof the stone is imperfect, causing the outer edges tobe exposed to higher stresses, the edges may spallor crack at the arrises, especially if the joints are thinin relation to the dimensions of the stone, and moreespecially if the stone is large and heavily loaded. (Insome mediaeval buildings one will find that up to30–40% of the wall area is in fact mortar; at St Paul’sCathedral, in the outer facing of ashlar some225–450 mm (9–18 in) thick, this proportion isreduced to the order of 3% of the wall area.)Cracking may be aggravated if the stone is shaped soas to produce a fine narrow joint on the outside face,while behind the face it rests on a deeper mortarbed, for even without thermal movements such aconstruction throws a greater load on the outsideedges. There is a great deal of such spalling in thehorizontal joints of the lower pilasters of St Paul’s.

Thermal movement of a wall

The second aspect of study should be thermal move-ments in the wall of a large, heavy, stone structure.The outer and inner faces are generally of ashlarblocks, but the core is often of rubble material allbeing set in a lime mortar which is weak in relationto the strength of the stone. Each type of masonry willhave different physical characteristics, for as the corehas a greater proportion of soft mortar it is more com-pressible than the outer faces. A masonry wall canabsorb stresses to a remarkable degree, first by com-pressing the mortar, secondly by absorbing internal

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strains, thirdly by friction between the blocks of stone,and finally by the plastic nature of lime mortar.

Thermal movement of a whole building

As it takes a great deal of heat to raise the tempera-ture of a heavy building with thick walls by even1�C, so it takes time for the heat to flow through thestone and mortar. There is a tendency for the outerface to be heated up before the core can respondand long before the inner face is affected. This timelag would affect the theoretical temperature gradi-ent. Generally, conditions at the inner face are forpractical purposes nearly constant and almostdimensionally stable, whereas the outer face willexpand and contract. In a continuously heatedbuilding where winter and summer internal tem-peratures are almost the same, movements in theinner face of a wall will be minimal.

The degree of lateral restraint depends largely onthe plan of the building’s cross-walls, buttresses, etc.,along with the effect of the thermal mass of theground, the strength of end walls and their superim-posed weights, and the friction between the blocksof stone set in mortar. If walls are firmly restrained attheir extremities to cross-walls and to the remainder

of the structure, they will tend to bow outwards insummer and curve inwards in winter as the outerface lengthens or shortens. As mentioned previ-ously, the nearer one gets to the top of the build-ing, the more it is affected by temperature changes,and these changes will be more acutely felt becausethere is less restraint at higher levels.

Stresses set up by thermal expansion in a typicallimestone with a crushing strength of 21 000 kN/m2

(200 tonf/ft2) are about 330 kN/m2 (48 lbf/in2)per�C. In the worst conditions likely to be met inEngland, with the average daily air temperaturesvarying between 2�C (35.6�F) in winter and 16�C(60.8�F) in summer, the theoretical effect of tem-perature changes would be to induce a local maxi-mum stress of about 4000 kN/m2 (580 lbf/in2)which is much less than the compressive strengthof any building stone. In the vertical plane nomovement would occur until the upward thrust dueto the thermal expansion exceeded the downwardthrust due to self-weight. For example, in a wallloaded at 1600 kN/m2 (232 lbf/in2) no verticalmovement would occur until a 5.5�C (41.9�F) tem-perature had occurred across the whole sectionalarea. Even a large daily temperature change wouldbe acceptable because, since only a small thicknessof wall would be affected, the stresses could be

Thermal movements

99

Figure 7.6 Profiles of air and soil temperatures atSeabrook, N.J., USA(Courtesy: McGraw-Hill Book Co.; from Mather, J.R.,Climatology: Fundamentals and Applications, 1974)

absorbed within the stone and mortar. In arid con-tinental climates, stone structures have withstood adiurnal range of as much as 45�C (113�F).

Whereas rapid daily temperature fluctuations tendnot to penetrate more than a few centimetres, sea-sonal temperature movements create more noticeableeffects because the centre of the wall core warms upand the whole building tends to expand. However, aswith daily temperature changes, upward movementtends to be reduced by the compressive forces ofdead weight, and horizontal movement is thusrestrained. The expansion of the core of the wall hasless effect because of the large proportion of soft mortar, and there is in any case a lower range oftemperature movement in this region. Difference ofmovement between the outer face and the inner coremay cause vertical cracks to occur like the ones notedin the west front of the Capitol in Washington, D.C.

Thermal cracks in a building are not likely toshow in its horizontal joints, although there may besome crushing in the mortar joints. Movement inthe horizontal plane will show by a tendency forvertical cracks to form if mortar is compressedbeyond its limits or if the wall does not return to itsoriginal position. In such a case, the ends of thewall having expanded outwards, more so near thetop of the structure when the seasonal contractionoccurs, vertical cracks tend to open as there is notensile force to close them. The mortar turns topowder as it is crushed, and when contractionoccurs the fine particles tend to fall and fill thelower part of the crack. In addition, dust and gritfrom the atmosphere may also become lodged inthe open crack, forming a new bearing surface fornext season’s expansion; cracks thus tend to widengradually by the process called drift or sway, whichhas been noted by many observers.

Expansion of other materials

The above discussion of thermal movements in abuilding has dealt with stone masonry, as this illus-trates the problems most clearly. Brick and stonerubble or mass concrete structures such as Romanwalls and vaults react in the same way as stone, butif they have a larger proportion of soft mortar in thejoints they are rather more accommodating.

The importance of the mortar cannot be over-emphasized. One can compare a long boundary walllaid with lime mortar that shows no expansion prob-lems, with a short wall built with Portland cementmortar that needs to have expansion joints every 10 m(33 ft). In mass concrete and stone rubble construc-tion, the percentage of mortar to stone can vary from30% to 70%, in brick construction from 10% to 40%

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Figure 7.7 Hypothetical comparison of average air temperature and surface temperature of a thick masonry wall

The heavy line shows average seasonal air temperature; the dotted line shows the surface temperature of the walls of a heavyhistoric building with large thermal mass. In spring and summer the heavy fabric of an historic building is liable to becolder than the air temperature which is increasing, as shown bythe time lag ab which amounts to two or three months.Condensation is probable. In autumn and winter the fabric isliable to be warmer than the average air temperature, so condensation risks are reduced. The heavier the construction,the greater the area of ab and the longer the time lag

Figure 7.8 Theoretical temperature changes in a thickmasonry wall

(1) Temperatures may range through 55�C (99�F) or more onthe surface, falling below freezing on cold winter nights. Thiswide variation should be compared with a 12�C (22�F) sea-sonal variation in the centre of the wall and 2�C (3.6�F) inthe interior, which probably receives some heating in winter

(2) Daily variations of the surface temperature will be greater insummer, say 42�C (76�F), compared with winter, say 25�C(45�F)

(3) The dewpoint for interstitial condensation is near the outersurface and this may freeze in the outer layers

and in stone from 1% to 30%. Where the percent-age of mortar is small the joints are most liable toshow thermal distress. Often the external wall isplastered, and if this plaster has the same charac-teristics as the soft mortar then thermal movementwill cause only fine hairline cracks. As mud, brickand adobe are relatively weak, with low thermalexpansion and conductivity, they also have veryfew thermal movement problems.

Wood moves markedly and fairly quickly withchanges in the relative humidity of the air and thesemovements are far greater than thermal move-ments. Because of its nature, wood is generallyused in a framed structure which is able to absorbboth thermal and humidity movements.

The action of moisture*

The presence of water in any of its various formscauses or accelerates the decay of most building ma-terials. The access of water to porous masonry materi-als may be caused by rain. Water reaches a masonrysurface when the rain hits the surface directly; it mayalso reach the surface indirectly, falling somewhereelse on the building and gaining access through amore complicated path. The latter case often pro-duces the worst damage, because the rain water picksup soluble materials along its path, and destructivecrystallization processes occur when the water evap-orates. Faulty disposal of rain water is the most fre-quent cause of deterioration in ancient masonry.

Water also penetrates porous masonry materialsthrough capillary action; suction is exerted by ca-pillaries. The height of the capillary rise of water inporous masonry materials depends mainly on thepore size (the smaller the size, the higher the rise)and the rate of evaporation from the external sur-face (as evaporation increases, the rise is reduced).The capillary rise increases with time, as solublesalts are carried by water into the masonry andbecome concentrated there when the water thatcarries them evaporates from the side surfaces ofthe wall. The increased concentration of solublesalts causes in turn another force of attraction forwater, since it must diffuse from low salinity to highsalinity regions. The result is that an equilibrium isnever reached, and the capillary rise of waterincreases with the structure’s age. Old thickmasonry sometimes shows capillary rises as high as8–10 m (26–33 ft), 4–5 m (13–16 ft) being common.Sometimes the water drawn up by capillary actioninto the masonry is rain water that has been

discharged near the base of a wall by a faulty gutter system.

Finally, water can gain access to masonry materialsdirectly through the air, either by condensation or bythe deposition of aerosols, such as mist, fog or saltspray. Condensation occurs when the air is damp andthe masonry surface is colder than the dewpoint ofthe air. Condensation occurs on the coldest surfaceavailable; therefore, ‘cold’ materials, i.e. materialswith high density and high thermal conductivity, aremost affected by it. Metals and compact types ofstone are examples of such cold materials; concreteis colder than brick and lime mortars.

Condensation water is far more dangerous thanrain water because it sweeps a large volume of airin front of the cold surface (the Stefan effect),cleaning it completely of all suspended dirt orgaseous pollutants. Liquid solutions containing freesulphuric acid then form on masonry surfaces inpolluted atmospheres, and particles of carbonblack, iron oxides, calcium sulphate and other sub-stances are deposited.

Aerosols are liquid or solid particles suspendedin gases—in this case, air. Liquid droplets formedaround sodium chloride crystals, spread in the airby sea spray, can travel long distances over land,becoming progressively more acidic as they meetcity atmospheres or gases originating in swampyareas. Aerosols hit surfaces that are particularlyexposed to air currents and discharge their particleson them. They are also attracted by cold surfaces,where they produce effects similar to those of con-densation, even if the temperature on the surfacedoes not drop below the dewpoint. Thus, seasidebuildings are obviously exposed to aerosols.

The action of moisture

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*This section is by G. Torraca, Deputy Director of ICCROM.

Figure 7.9 Capillarity(Based on G. and I. Massari)

Capillarity increases as the size of the passage decreases. It canreach heights of 8–10 m (26–33 ft) above ground, Porousbuilding materials are a network of capillaries of varying diameter which draw water sideways as well as vertically

It is often not easy to decide by which mechan-isms water has gained access to a masonry material.Condensation, in particular, is often not sufficientlyconsidered, the ‘humidity’ it produces being attrib-uted to rising damp when it appears in the lowerregister of walls or to the penetration of rain whenit appears in ceilings and vaults. The consequencesof misjudgement are often ruinous. As a generalrule, in the case of cold, compact, low-porositymaterials, it would be wise to suspect condensationfirst, while the reverse attitude might be taken formore porous materials. Accurate temperature/relative humidity surveys should be made as oftenas possible.

A characteristic feature of water distributioninside hard porous masonry materials is the exist-ence of a critical water content that depends on thetype of porosity and the nature of the material.Above the critical content, water can move freely inthe liquid state inside the porous body, whereasbelow the critical value, water is held inside poresand can be removed only by evaporation. It is oftendifficult to dry a masonry structure because the criti-cal water content may be quite high. For instance,in walls containing hygroscopic soluble salts, as inVenice, the critical water content can be as high as18%, according to some authors.

Walls appear wet up to a certain height in a struc-ture where the water content is at the critical value.Above this point, walls appear dry, and the watercontent drops sharply to a low level.

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Figure 7.10 Thermohygrograph readings at Cloche, Iraq, Spring 1968(Courtesy: G. Torraca, Mesopotamia, 1968)

The readings show how relative humidity changes �75% with temperature �25�C between a hot noon and cool night with constant absolute moisture in the air. Even in desert conditions it ispossible for condensation to occur in the early hours of the morning

Figure 7.11 Excess moisture in a wall

(a) Difference between summer and winter evaporationzones. Decay due to crystallization within the surface iscritical

(b) Stone or brick are accepted as dry if their moisture contentis 3% of the volume or 5% of the weight. For tuff, 3% byvolume and 8% by weight is considered dry

(c) Constant evaporation from the surface only(d) Moisture is supplied from the water table or excessively

moist soils

Precipitation of moisture

Atmospheric moisture may occur in vapour or gasform, known as humidity, water in minute dropletform or as ice crystals, known as fog or clouds, oras liquid precipitation known as drizzle, rain, sleet,snow, soft hail (graupel), snow grains, hail, rime,glaze and dew.

Humidity is measured by hair hygrometers, psy-chrometers or lithium chloride meters, which give amore rapid and complete response to changes inhumidity than human hair. Moisture precipitation ismeasured by means of a rain gauge. A rainfall of 10 000 mm (400 in) over 12 months in the tropics maybe far less of a problem than exceptional downpourssuch as 31.2 mm (1.23 in) in 1 minute at Unionville,USA, on 4 July, 1956 or 126 mm (4.96 in) in 8 minutesat Fusseh, Bavaria, on 25 May, 1920. Rainfall aver-age intensity decreases rapidly with its duration, thegreatest amount recorded for a year being 26 461 mm(1042.6 in) in 1860–61 at Cherrapunji, India.

Rainfall data is generally presented in terms ofannual or monthly averages. For most localities inEurope, 80% of the total rainfall is due to intensities ofprecipitation below 50 mm/h (2 in/h). However, thepoint rainfall intensities in which we are interested forthe design of rainwater disposal systems that will beunlikely to flood, are much larger than averages.Heavy rainfalls are generally concentrated in durationand locality and if they are time averaged they can beconsiderably underestimated. Data for individualcountries (Table 7.2) shows variations of over 100%for different places, indicating that national designstandards should be taken with caution.

Using a graph of the cumulative distribution ofrainfall intensity (Figure 7.13), it will be seen that therate of 75 mm/h roughly corresponds to the 103

percentage of time (5 min) and gives the followingcorresponding values (which should be doubled fordesign purposes):

Curve 1. Tyrrhenian Coast of Italy(Genoa, Rome, Naples) andAdriatic Coast of Greece 230 mm/h

Curve 2. Central Italy, South ContinentalEurope 165 mm/h

Curve 3. North Continental Europe 100 mm/hCurve 4. Scandinavian Countries, UK,

Ireland 70 mm/hCurve 5. Norway, North Scandinavian

Countries 35 mm/h

The data is related to instantaneous values usedfor high-frequency radio transmissions which areaffected by rain. For architectural conservation, fur-ther research is necessary. The information gained

Precipitation of moisture

103

Figure 7.12 Aventino, Rome, Italy

A garden wall shows clearly the effect of rising capillary moisture and the evaporation zone where crystallization ofground salts destroys the planter and brickwork

Figure 7.13 Cumulative distribution of rainfall intensity(Courtesy: Fedi, F., 1979)

Percent of time a given rainfall is exceeded in one year, e.g.75 mm/h (3 in/h) is exceeded 5 minutes each year in the UK

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Table 7.2 Meteorological Stations for Rainfall Intensity Measurements (Courtesy: Fedi, F., 1979)

Country Locality Period Years Rain gauges P0* H † (mm)(%)

No. Type Area Sensitivity Int. Meas. Estim.funnel time(cm2) (sec)

Finland Helsinki 76–77 1 1 C 730 5 mm/h 15 2.1 260 —Sweden Stockholm 54–63 10 1 TB 750 0.2 mm 60 3.5 — 757Norway Arendal 67–75 7 1 TB 750 0.2 mm 60 3.5 647 —

Gardermoen 67–73 6 1 TB 750 0.2 mm 60 2.5 406 —Opstveit 68–75 8 1 TB 750 0.2 mm 50 6.8 1364 —Kjeller 75–76 2 1 TB 750 0.2 mm 60 2.9 338 —Trondheim 67–75 9 1 TB 750 0.2 mm 60 4.7 564 —Halden 74–75 2 1 TB 750 0.2 mm 60 3.5 489 —

U.K. Slough 70–74 5 1 DC 150 5 mm/h 10 4.3 — 700Mendlesham 73–75 3 3 DC 150 5 mm/h 10 3.5 — 338

Ireland Cork 70–75 6 1 S 648 0.2 mm 600 7.0 — 1145Germany, F.R. Darmstadt 75–76 2 10 DC 225 7 mm/h 10 3.0 — 485Netherlands Leidschendam 72–74 2 6 DC 284 7 mm/h 10 3.0 — 740Belgium Louvain 70–75 5 1 TB 1000 0.05 mm 60 3.5 — 970

La-NeuveFrance Paris 65–76 12 1 S 313 0.2 mm 60 5.0 646 —

Dijon 72–76 5 1 S 313 0.2 mm 60 5.0 — 796Switzerland Bern 74–75 2 8 TB 200 0.1 mm 60 4.0 960 —

Jungfrau 74–75 2 4 TB 200 0.1 mm 60 4.0 1133 —Valais 74–75 2 5 TB 200 0.1 mm 60 2.0 596 —

Austria Graz 75–77 1 1 TB 200 0.1 mm/h 360/R 3.2 — 493Portugal Lisbon 75–77 3 1 S 200 0.2 mm 300 4.0 — 950Italy Genoa 77–78 1 1 TB-C 1000 0.2 mm/h 720/R 6.4 1603 1602

Milan 67–70 2 10 TB 1000 0.2 mm 60 3.0 — 1190Udine 76–77 1 1 TB-C 1000 0.2 mm/h 720/R 6.5 1575 1594Rome 75–77 2 1 TB-C 730 0.27 mm/h 986/R 3.1 1143 1125Bologna 76–77 1 1 TB-C 1000 0.2 mm/h 720/R 3.0 631 628Fucino 75–77 2 1 TB-C 730 0.27 mm/h 986/R 4.8 1386 1328Bari 76–77 1 1 TB-C 1000 0.2 mm/h 720/R 2.2 520 498

Greece Kefellinia 74–75 1 1 C-S 730 5 mm/h 15 0.8 752 —Kerkyra 74–75 1 1 C-S 730 5 mm/h 15 3.1 734 —Aliartos 74–75 1 1 C-S 730 5 mm/h 15 0.67 522 —Milos 74–75 1 1 C-S 730 5 mm/h 15 0.82 374 —Hios 74–75 1 1 C-S 730 5 mm/h 15 0.32 543 —Athens 74–75 1 1 C-S 730 5 mm/h 15 1.6 264 —Hiraklion 74–75 1 1 C-S 730 5 mm/h 15 0.62 398 —Mikra 74–75 1 1 C-S 730 5 mm/h 15 1.7 421 —Kalamata 74–75 1 1 C-S 730 5 mm/h 15 0.29 640 —

*P0 is the average percentage of time in which rainfall exceeds 0.2 mm/h.†H is the actual or estimated annual rainfall (in mm).

Table 7.3 Recommended Parameters for the Design of Windows Exposed to Rain

Exposure pressure measured Windows watertight at: Leakage not excessive at:in water gauge (w.g.)

Normal bldgs. Historic bldgs. Normal bldgs. Historic bldgs.

Normal exposure 44 mm w.g. 6 mm w.g. 16 mm w.g. 24 mm w.g.(0.16 in) (0.24 in) (0.63 in) (0.95 in)

Moderately severe exposure 16 mm w.g. 24 mm w.g. 30 mm w.g. 45 mm w.g.(0.63 in) (0.95 in) (1.18 in) (1.77 in)

Severe exposure 30 mm w.g. 45 mm w.g. 60 mm w.g. 90 mm w.g.(1.18 in) (1.77 in) (2.36 in) (3.54 in)

from the high-frequency radio research is, however,helpful in establishing a picture of point rainfall andthe profile of a storm, as shown in Figure 7.14.

In such a storm, with gutters and down-pipesrunning full bore at a design level of 75 mm/h (3 in/h), it is clear that flooding would be liable tooccur for about 100 seconds, sufficient to causeserious trouble below parapet or valley gutters.

Rainfall records are the basis of rational design,but records of averages need interpretation. In theUK the rainfall probabilities can be predicted forany given site by a computer program. TheMetereological Office, London Road, Bracknell,Berkshire, England, will supply rainfall probabilitiesfor a given map grid reference, but the lesson ofthese figures is that rainwater disposal systems mustbe generously designed and should always haveoverflows to take care of exceptional downpours.

Backed up by high wind pressures, rain inexceptional circumstances can surmount checks of75–100 mm (3–4 in) in height. Wind exposure alsoaffects window design. Table 7.3 gives some recom-mended design parameters; it will be noted that50% higher standards are recommended for historicbuildings because over a longer period of time theymay have to withstand more severe conditions.

Both the rate of rain falling in a short period andthe direction in which it is driven are of crucialimportance in the maintenance and preservation ofa building. In Britain, exposure to driven rain isleast severe in the East Midlands, London and the

south-east; most driven rain comes from the south-west in the western half of the UK and from the direc-tion of the coast elsewhere. The ability of rainwaterdisposal systems to deal with the worst possiblestorms of short duration is vital. The short-term rate ofrun-off varies with the slope and friction of differentroofing materials, being greatest for sheet metals.

Rain can penetrate to the interior of a building andcause various kinds of decay. Absorbent surfacessuch as brick provide a very satisfactory answer tothe ‘damp dripping’ British climate, but it should beremembered that the absorption capacity is limitedand after 2–3 days of heavy driving rain a solid wall350 mm (14 in) thick, which is usually satisfactory,will become saturated and may well show signs ofrain penetration. The absorption capacity of stone ismuch less, for most types are nearly waterproof.Once the surface of stone or brick is saturated, largeamounts of water will stream down tall vertical sur-faces and, as mentioned previously, wind pressurewill force this through cracks or even through thematerial itself if it is sufficiently porous. Rain penetra-tion can cause internal decay in stone walls forminglarge internal voids, some of which may require 250 l(55 gal) or more of filling material such as grout.Voids totalling about one-twentieth of a wall’s vol-ume can be formed after five centuries or more.

The absorption capacity of a building material is animportant consideration. A permeable or absorbentmaterial must not be jointed or pointed with a moredense or impermeable mortar or else rain water will

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Figure 7.14 Example oftime behaviour of rainfallintensity, Rome, Italy(Courtesy: Fedi, F., 1979)

100 mm/h 14 in/h) isexceeded for about 80 secon this chart with a peak of400 mm/h (16 in/h) for ashort time

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Figure 7.15 St Paul’s Cathedral, London, England(Courtesy: Feilden & Mawson)

Weatherproofing faults have allowed severe recrystallization tooccur on the inner stone lining of the south-west tower. Thepointing of stone or brick masonry to prevent penetration ofmoisture is an elementary but most important action in preventive maintenance. The ladder is viewed from below

Figure 7.16 St Paul’sCathedral, London, England(Courtesy: Feilden & Mawson)

A general view of the northern-most chamber underthe west steps. Acid water penetration has dissolved stonewhich has recrystallized

be trapped in the pores of the material and whenthere is a frost will cause severe damage. In warmweather, a thin porous wall wetted by rain may be somuch cooled by rapid drying conditions as to induceinternal condensation if the internal air is humid.

Hard, impermeable materials throw greater strainon their joints and require harder mortars. Takingglazed terracotta or flintwork as an example: althoughthe material is almost indestructible by rain or frost itrequires more frequent repointing than brick, and tocounter this erosion a somewhat harder mortar is per-missible, but it must not be completely impermeable,for an impervious mortar such as Portland cement isliable to small cracks which will induce the inwardmovement of rain water by capillary attraction.

Dissolved salts

The composition of salts and their action by evap-oration are as follows:

(1) The salts that are potentially the most dangerousto the rendering and to the painted surface of awall are the sulphates of sodium, potassium, mag-nesium and calcium, because according to wherethey crystallize they cause serious disintegra-tion owing to the failure of cohesion of the materials. Calcium sulphate can form a white veilover the surface or it can be crystallized within therendering by the sulphation of calcium carbonateto which a polluted atmosphere contributes.

(2) The nitrates of sodium, potassium and calciumare soluble salts which normally give rise tothick efflorescences easy to eliminate and ofwhich the disintegrating action is inferior to thatof the sulphates.

(3) Calcium carbonate is a main component inconstruction in the form of limestone. Calciumcarbonate has not by itself a disintegratingeffect once it has crystallized, but it formsincrustations that are very hard and intractable.

(4) Sodium chloride is normally a surface deposit,having been transported by sea air, and in itselfdoes not cause disintegration. However, it isable by a process of hydration and dehydrationto promote the disintegration of surfaces by itsaction on other salts that may be present underthe effect of varying temperatures.

(5) Silica contained in certain rocks, in clays and incements is in a form that can be transportedvery slowly towards the surface by infiltratingwater. A long-term effect is the formation ofwhite incrustations of silicon dioxide (opal) orof silicate mixed with other substances, notablycalcium carbonate.

Frost and snow

The relative coldness of a climate is measured indegree days, i.e. the number of days when the tem-perature falls below 18�C (64.4�F), multiplied by thedegrees drop below that temperature. There is con-siderable variation in this figure throughout Britain—from 800 in the south to approximately 2000 in the farnorth. But it is not extreme cold that causes damageto buildings so much as frost changes—the actualprocess of freezing and resultant expansion of ice andsubsequent contraction on thawing, which may occurin the British climate on average between 1.5 and 2times per day in winter. In the case of foundationswhich may be affected by frost heave, the number offrost changes is rapidly reduced by increasing thedepth of the foundations. The following information,based on data from Potsdam, illustrates this point.Although it represents a colder continental climatethan Britain’s, it is one with fewer actual frost changes.

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Figure 7.17 Presbytery parapet, Norwich Cathedral, England

Fourteenth century masonry in an exposed position was badlyeroded. It was patched with Portland cement which acceleratedthe decay. Freezing expansion has opened up cracks

Depth in ground Number of frost mm (in) changes per year

0 (0) 11920 (0.8) 7850 (1.97) 47

100 (3.94) 24500 (19.7) 3.5

1000 (39.4) 0.3

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Figure 7.18 Presbytery parapet, Norwich Cathedral,England

The stone is crumbling due to freezing expansion. Again, patch-ing with Portland cement mortar has accelerated decay. Thedesign and shape of the mouldings is now in danger of being lost.The masonry was reproduced using the traditional techniques

Figure 7.19 North cloister arcade, Norwich Cathedral,England

Frost damage in winter of 1962–63. Some stones with poorerfrost resistance were disintegrated by severe freezing

Figure 7.20 No. 7 Warehouse, Hull, England

Neglect of rainwater downpipes led to saturated brickwork andthus consequential frost damage. The surface of the brick wasdisintegrated

Figure 7.21 No. 7 Warehouse, Hull, England

After years of neglect the rainwater downpipes became blocked andthen cracked due to freezing: they then flooded the walls behindthem, saturating the brickwork, which in turn was damaged by frost

Foundations should be deep enough to avoidfrost heave or expansion which can cause the sub-soil to move with consequent damage. This depthalso depends on the type of soil; in the UK it istaken as 455 mm (18 in) on sands and gravels and910 mm (3 ft) on clays. In Sweden the minimum is1500 mm (5 ft). The use of salt on roads has sideeffects in polluting ground water and causing watermains to be frozen at depths greater than 910 mm(3 ft), as happened in 1963 in Britain.

Ground temperatures also vary between summerand winter. At a depth of 1 mm (0.04 in) belowground, the variation at Potsdam can be between20�C (68�F) in July and 1�C (33.8�F) in February; at12 m (39.4 ft) depth there is much less variation,temperatures being 10�C (50�F) in February, andactually coldest in August at 9�C (48.2�F).

Freezing damages porous building materials suchas brick and stone, particularly if they are saturatedwith water. The resistance of these materials dependsupon the size of the pores and their hydrophilic orhydrophobic structure. If ice forms in the pores hav-ing a good structure it can expand on freezing with-out damage. In prolonged frost, however, ice mayactually build up inside the material because of con-densation of water vapour. Acceptable frost resistanceis specified in British and other national standards.

Snow falls in flakes and lies in thick blankets onroofs and over the ground. Driven snow can attachitself to near vertical faces and be blown in throughventilators and other openings and, having pene-trated, can cause stains on ceilings and floors whenit melts. There are many types of snow, the Finnishlanguage having nine words to express them. Snowis a good insulator and reflector of heat, and in thehands of the Eskimo it is a sophisticated buildingmaterial. If snow lasts during the winter, traditionaldesign, such as the Swiss chalet, takes account ofthis and uses it for insulation; but in countries wheresnow is more occasional, steep pitches on roofs areused to shed snow quickly before it can build up aheavy load. In England no allowance is made forsnow loads on pitched roofs, but an allowance for1.5 kN/m2 (30 lbf/ft2) is necessary for flat roofs.

Melting snow on a steeply sloping roof can formmini-avalanches which descend from the eaves, tear-ing down gutters if present and breaking conservatoryor other glass windows below. To prevent this, snowboards are sometimes provided at the eaves. If thereare parapets or valley gutters, melting snow can causeblockages, with melted water rising above the level ofthe waterproofing and so causing flooding. Packedsnow often has to be removed by hand, although in sophisticated installations embedded electricalheating can be used. For hand operations, a woodenshovel is recommended in order to avoid damage to

the roof covering. Duckboards reduce the hazard offlooding blockage in gutters and make roof mainten-ance easier. Snowboards and duckboards should bestrongly constructed of impregnated softwood, west-ern red cedar or durable hardwood (timbers like oakshould not be used on lead roofs as they may causeacid attack).

Wind

Wind is the result of different atmospheric pressuresin the weather system. Direction, speed, gustiness andfrequency of calms are important characteristics ofwind. Wind speeds vary at different heights and causeturbulence. Most published data on wind involves aconsiderable amount of averaging which reduces theusefulness of such data when considering historicbuildings. Wind-roses give a general picture of windconditions in a locality. Those given by Mather for theDelaware Valley in 1965 show how variable a quan-tity wind is from place to place (Figure 7.23).

Clearly the structure must be strong enough toresist wind pressures; it must also be able to resistthe associated suction on the lee side. It might wellbe assumed that because an historic building has suc-ceeded in resisting all probable strengths of windsduring its lifetime, it will be strong enough to resist allfuture wind forces, but this does not always follow, asthe structure may have deteriorated and there isalways the possibility of an exceptional wind. Forcesgenerated by wind can cause buildings such as bell-towers to sway. The 99 m (325 ft) high NorwichCathedral spire has been found to move about �76 mm (3 in) to and fro in a high wind. A sway ofeven 0.10 mm (1/250 in) can be noticeable, for manwith his cave-dweller ancestry is very conscious ofsway and quakes. It is theoretically possible for windpressure to cause tension in a windward face of a tall,thin structure. This becomes an actuality in tall, rela-tively light structures such as spires, where the upliftcan exceed the dead weight of the structure. InNorwich Cathedral this effect was countered by a ver-tical tie bar. It is said that Leonardo da Vinci recom-mended a pendulum, i.e. a tie bar tensioned by aheavy weight, to prevent uplift by such tension forces,and Wren appears to have used a similar idea in hisrepairs to the spire of Salisbury Cathedral.

Most coastal areas may expect winds of up to 97 km/h (60 m.p.h.) mean, with 162 km/h (100 m.p.h.) gusts. In Britain these will be exceededin Cornwall, Wales and the west coast of Scotland, butwill be somewhat less in the south-east. The BuildingResearch Station suggests that the wind speedshould be modified by a design factor for buildinglife; for an historic building, where risks cannot be

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Figure 7.22 The CathedralClose, Norwich, England

Bad frost damage hadoccurred to the base of agarden wall in combinationwith rising moisture.Variegated ivy was plantedto protect the wall againstfrost, thus rendering repairsunnecessary

Figure 7.23 Annual wind roses at selected stations in theDelaware Valley, USA, for 1965(Courtesy: McGraw-Hill Book Co.; from Mather, J.R.,Climatology: Fundamentals and Applications, 1974)

Figure 7.24 Spire, Norwich Cathedral, England

The W.N.W. buttress showing stone decay and multiple crack-ing and some previous repairs. The damage was caused bywind vibration and sway that got progressively greater as thestructure deteriorated

taken and a design life of 200 years is not exces-sive, it is recommended that this factor should be atleast 1.5 on the recommended design wind speedfor the locality. Tornadoes with their centrifugalvacuum effects are touched upon in the section onnatural disasters later in this chapter.

Because roof coverings such as tiles and even leadsheets can be lifted by lee-side suction, their fixingshould be carefully considered and detailed; looselyfixed slates can often be heard to ‘chatter’ in a highwind. (With prevailing westerly winds, the lee suc-tion eddy from a church tower normally falls on thenave roof and it is common for tiles to be lifted inthis area; extra nailing is the obvious remedy here.)

Wind exacerbates the general external erosion ofmost building materials. If a small piece of hard gritgets into a surface pocket, gusts can rotate it at highspeeds and thus drill quite a large hole in soft stone.After the reconstruction of the Temple of Abu Simbelin Egypt, a violent windstorm driving little stoneslifted from the ground in front of the temple severelydamaged the face of one of the figures on the facade.

Rapid evaporation by wind causes salt crystal-lization to take place within the wall rather than onthe surface. This breaks up the material of the walland causes cavitation, which intensifies evaporationand further crystallization—a phenomenon calledcavernous decay in stone. The eroding action ofwind combined with sand or dust can ultimatelydestroy massive buildings. Wind-borne sea saltsand rain can have similar effects, as may be seen atthe megalithic temple of Hagar Quin, Malta, whichwas built of globigerina limestone.

Indeed, the most serious effects of wind pressureare found in conjunction with rain. When com-bined with heavy rain, wind causes serious internaldecay after the surface reaches saturation point andthe rain, driven by wind pressure, penetratescracks, fissures and porous materials. Wind willalso blow rain sideways, a point often neglected indetailing, leading to unsightly streaks which occurwhere vertical upstands and joints check the side-ways movement of the rain water and thus causeconcentration of the flow downwards.

Particulates, smoke, dust and sand particles

Particulates or aerosols are solid particles thatremain suspended in the air. Particles that settle instill air are dust, sand or grit. Smoke is the result ofincomplete combustion of fuels.

The diameter of particulates is measured inmicrons (abbreviated �m) which are one thousandthof a millimetre or one millionth of a metre.

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Figure 7.25 Spire, Norwich Cathedral, England

The N.N.E. angle buttress with poorly bonded stone, repaired inat least four different periods, but the crack and bulge whichare due to wind vibration were serious

Figure 7.26 Spire, Norwich Cathedral, England

Note the decay of nineteenth century ‘plastic’ repairs. At theN.N.E. angle is a broken wrought iron strap of eighteenth century repair, but the fine crack to its left is more ominous. Itis caused by wind vibration and is repeated on each of theeight sides, heralding the failure of the structure

Particulates larger than 15–20 �m settle near theirsource of origin in still air, but winds can transportparticles of 100 �m to even 10 000 �m in size,depending on their speeds. In cities, particulates ariselargely from fuels burning in power stations and fromvehicles, so there is generally a lot of sooty tarry ma-terial in them. They are usually acidic from absorbedsulphur dioxide and often contain traces of metalssuch as iron, which can cause deterioration. Thiseffect is noticeable on some copper roofs inMelbourne—on buildings adjacent to trams, whosebrake blocks of cast iron give off dust which accel-erates the corrosion of the roofs.

The particles of matter that are transported bywinds at normal speeds range from about 100 �m toeven 10 mm. The minute particulates, which form athin smoke or haze, do not fall at all, due to theirinherent susceptibility to collisions with molecules ofair and water and the very feeble pull of gravity. Smallparticles are carried considerable distances beforethey fall to the ground; otherwise, their rate of fallincreases with the square of the logarithm of their size.

When the wind at ground level is sufficientlystrong to dislodge and propel stationary particles intothe air they may be lifted to a height of about 1500 m(5000 ft) or more, according to Kendrew, forming adust storm. Larger particles (sand) have a boundingmovement, with an average height of just over 1 m(3.3 ft), impinging at an angle between 10 and 16 degrees. If the ground surface is hard (pebbles orrocks), the sand grains may bounce to greaterheights; on the other hand if the surface consists ofloose grains of similar size, the vertical displacementis lessened by dissipation of frictional energy whichmay dislodge more grains of sand, so producing asurface cloud of sand with no increase in height.

A light breeze causes the slow and almost imper-ceptible movement of sand grains and it is by thismeans that vast quantities of material are movedover a period of time, such as the dunes of sand indeserts which can engulf a settlement or oasis.

On the lee side of a building or wall there is alow pressure zone which also occurs along theother sides to lesser extent. It is noteworthy that thetraditional central courtyard of not more than 6–7 m(19–23 ft) gives the best protection against dustdriven by wind from any direction. Perimeter court-yards of the same width give variable protectiondepending on the direction of the wind.

Historic buildings may be threatened by sand move-ment and wind-blown sand and pebbles. Local infor-mation should be obtained and traditional precautionsreviewed before any possible intervention into micro-climate control. For museums, dust is a major nuisanceand should be reduced and eliminated by filtered air supply, keeping a positive pressure inside the

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Figure 7.27 Spire, Norwich Cathedral, England

Major repairs to tower and spire, west face. An inspection in 1961showed that urgent work was needed to prevent the spire from collapsing. It was consolidated with grout and strengthened withreinforced concrete rings and stitches. A great deal of the brick lining had to be renewed and about one-quarter of the externalstone was replaced. The spire was reinforced with stainless steel inthe horizontal joints. Work on the spire took two years and wascompleted in 1963. In 1976 it withstood a 170 km/h (105 m.p.h.)gale

Figure 7.28 Holy Shrine of Al Hussein, Kerbala, Iraq

Vertical cracking at the base of the thirteenth century minaretbetween the minaret and main body, due to wind sway anddifferential settlement of two completely different structures. It isa sort of natural expansion joint and so should only be filledwith soft material

building and an air lock at the door. In order thatthe filters may be correctly designed, the size of theparticulates in the atmosphere must be measuredand graded.

Dust disfigures the exterior and interior of his-toric buildings. In Stockholm it may be remarkedthat the colour of the plaster finish of buildingsappears rather dark. Holmström (verbal communi-cation) states that research has shown that this isdue to the black dust from motor tyres and asphaltroads settling on the rough rendered surfaces of thebuildings, and suggests that a smooth finish to theplaster would reduce this effect. In St Paul’sCathedral, the dust was analysed and at least half ofthe material was human detritus—or a by-productof the millions of tourists who visit the cathedral. AtYork Minster, dust was 5–6 mm (0.2–0.24 in) deepon upper surfaces and generally obscured defectswhich became apparent when the interior wascleaned and washed down. Dust makes the archi-tect’s work of inspecting historic buildings bothdirty and more difficult.

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Figure 7.29 Furness Abbey, Lancashire, England

An example of combined action of wind erosion and risingdampness. The wind causes evaporation and the crystallizationof salts within the pores of the stone which breaks down the surface progressively

Figure 7.30 North-west tower, St Paul’s Cathedral, London,England(Courtesy: Feilden & Mawson)

A comparison between the moulded base of the column or theouter face of the building and inner face shows the enormouswear suffered by even a hard limestone from wind erosion andpollution

Figure 7.31 Carved ornament, St Paul’s Cathedral,London, England(Courtesy: Feilden & Mawson)

The central acorn feature was fractured and eroded by windand pollution. Note the reduction of size in comparison with thereplacement which is shown in two stages: the rough work prepared by the mason for the carver, and the process of carving

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Figure 7.32 Dust deposit,Cairo Museum, Cairo,Egypt

Dust is one of the most difficult environmental hazards to combat as it getsinto all unsealed spaces.Here it lies thickly on a roof light

Figure 7.33 Church, Scarperia, Italy

Damage by landslip. This Renaissance church was built on ageological fault. It is also vulnerable to earthquakes

Figure 7.34 Church, Scarperia, Italy

Details of cracking. Repairs always fail if the cause is not diagnosed: in this case a geological fault leading to a landslip

Natural disasters

Besides earthquakes, which are dealt with in Chapter 8, the main list of violent, unforeseen andcalamitous natural disasters which may affect historicbuildings includes seismic sea waves (tsunamis), tidalwaves, landslides and landslips and phenomenarelated to land movements and disruption, volcaniceruptions and gaseous exhalations, spontaneouscombustion, cyclones, hurricanes, tornadoes, whirl-winds, water spouts, typhoons, floods, avalanchesand snowslips, and even unexpected frost, for if thisoccurs only at infrequent intervals it can be all themore damaging for being unexpected.

An interesting example of a natural disaster is theSun Temple at Chauvim Huamtar in Peru, initiatedin 1600 B.C. and covered by a landslip of liquid mudin A.D. 1540. Only now is the temple being exca-vated and consolidated. A case of land movementdue to a geological fault is that of the Iron Bridge,in England, at the village of the same name, whichwas being crushed by a closing of the river Severn’sbanks. Insertion of a massive concrete strut underthe river bed has prevented this. At Scarperia, innorthern Tuscany, the mediaeval castle and aRenaissance church are badly cracked due to land-slipping along a geological fault.

Tornadoes consist of whirlwinds which move rap-idly and have the power to lift roofs off buildingsand throw cars about. At the centre of this whirlwindis a sudden vacuum which causes buildings toexpand outwards from their own internal air pres-sure. With the light timber construction of domesticand farm buildings in the USA, a tornado causes abuilding to disintegrate; the safest areas are centralhalls or bathrooms, which generally remain intact.

Floods

Floods have been recorded over a long time in manycountries, and certain levels can be predicted tooccur at intervals of 10, 50, 100, 200 and even 1000 years. The Nile is the classic case of recording,as the prosperity of Egypt depended upon the heightof the flood—that is, until the Aswan High Dam wasbuilt. Unfortunately one may not have to wait a hun-dred years for a 100-year flood, as it may come tomor-row. Besides tragic loss of life, floods mainly affecthistoric buildings, but if they submerge a city greatharm will be done to furniture, books, carpets andtapestries. When the Arno predictably floodedFlorence in 1966 it was found that heating oil floatingon the flood waters added materially to the damage.In the case of sea flooding, which may occur whenhigh winds add their impetus to high tides, the salt

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Figure 7.35 Church, Scarperia, Italy

Details of internal cracking due to the landslip

Figure 7.36 Record of flood levels, Ferrara, Italy

In the eighteenth century, flooding of the River Po up to first-floorlevel was usual. A record was kept on the Ducal Palace

water damages the building fabric and might leadto permanent dampness—such is the threat toVenice, which was also badly flooded at the sametime as Florence.

After such major disasters, massive first aid isneeded. Streets must be cleared, rubble removedand bodies recovered. Then conservators must bemobilized to save cultural property of all types fromfurther damage by over-hasty or wrong treatment.The International Centre for the Study of thePreservation and Restoration of Cultural Property(ICCROM), in Rome, has the task of mobilizing andco-ordinating help when it is needed.

The lesson one should learn from records of pastfloods is to put vulnerable cultural property, such asbooks, manuscripts, archives, water colours, oil paint-ings, and wooden objects and all ethnographical andorganic material, above any conceivable flood level.If this is not possible, then precautions must be takenby providing pumps and drainage sumps, togetherwith material ready for blocking up vulnerable open-ings such as basement windows. Polythene, sand-bags and even bricks and cement should be kept inreserve. Burst pipes also cause internal flooding ofbuildings, so no pipework should be allowedthrough storage areas for such cultural property.

Lightning

Perhaps the most frequent of natural causes of vio-lent damage is lightning, which is the natural meansof equalizing the electrical potentials of the earth andthe atmosphere. When, in certain atmospheric condi-tions, the potential difference builds up sufficiently, ahigh-voltage discharge will take place involving cur-rents of up to 160 000 amps for a few milliseconds.The discharge is usually in the form of a double flash,with 60% of the total energy dissipated in a flash fromatmosphere to earth and 40% in the reverse direction.

Lightning has a tendency to strike the tops of tallobjects (buildings and trees) standing up above thegeneral ground level. When there is substantialelectrical resistance in the path between the pointof striking and the mass of the earth, damage willgenerally be caused. This is because, by Ohm’s law,energy will be dissipated in a resistance when cur-rent flows through it. When the current is of themagnitude involved in a lightning discharge, thetotal energy can be many thousand megawatts; thisis nearly all dissipated as heat, with the result thatany moisture present is flashed into steam withexplosive force. This steam is what splits trees, shat-ters stones and causes most of the damage. Thenature of the damage is quite unpredictable; it isbasically as if a high-explosive detonating fuse were

running through a structure, the degree of disruptiondepending on variables such as differences inresistance and moisture content in materials in dif-ferent parts of a building.

Lightning can cause damage in other ways, mostseriously by setting fire to timbers, by melting andcracking metal objects and by causing overloadingof electrical wiring and devices through inductiveeffects. It can cause damage by indirect means,such as when displaced tower masonry fallsthrough a lower roof, and it can cause objects to bethrown about and damaged by magnetic effects.

If a lightning discharge, instead of passing suddenlyat random through the fabric of a building, can beconfined to low-resistance conductors passing directlyto earth, these ill-effects can be avoided; the principleof lightning protection is to provide such a conductor.A conductor also allows ground potential to moveupwards and so neutralize the threat of a strike.

Whether an historic building should be fittedwith a lightning conductor or not depends on thefollowing factors:

(1) The cultural and economic values of the build-ing and its contents.

(2) The size and height of the building.(3) The location and surroundings of the building.(4) The record of previous lightning strikes on the

building.(5) The general assessment of risk in the geo-

graphical location of the building.(6) Whether the lightning conductor can be main-

tained regularly.

There are belts of country and even individual siteswhere lightning strikes are more frequent than else-where, and if a domestic building has a record of twoor three strikes in 10 years a conductor is definitelyrequired. Information to help evaluate the risk is con-tained in BS 6651:1985. This new code greatlyincreased the requirements for lightning protectionwith more downtapes all to be bonded together atparapet level and ground level. As architects are notnecessarily informed when new codes are promul-gated they should ensure that the specialistinstructed, test the lightning protection installationand draw his attention to any deficiencies. Whetheror not there is a conductor, insurance cover againstlightning damage can be obtained without difficulty.

A tower with a flat top and parapet should have aring conductor around the top with four terminalspikes, as well as a single terminal if there is a tallcentral flagpole which can carry the terminal. If thereis a metal roof and no parapet, a single terminal willsuffice, provided it is bonded to the roof. Thereshould be two down tapes.

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Very few churches are entirely protected by a ter-minal on top of the tower. It is, however, rare for light-ning to strike churches anywhere else but on top ofthe tower, so unless the nave or chancel is very longor high or exceptionally valuable it is a justifiable riskto let the tower conductor suffice. In domestic build-ings, chimneys are especially vulnerable, as a columnof hot smoke especially during the summer months ismuch more conductive than the surrounding air anddoubles the effective height of the chimney as far aslightning is concerned. A single terminal on the chim-ney top will give the necessary protection.

In addition to the code of practice mentionedabove, which covers the installation of a conductorsystem in great detail, there are certain pointswhich apply particularly to historic buildings.Routes for tape conductors, for instance, can havedistinct aesthetic implications and must be plannedcarefully in conjunction with a specialist or consult-ant—but the architect must have final approval.

The main down-lead must go by the most directroute possible and avoid all sharp bends, particularlyloops such as might be needed around a cornice. It isbetter to drill through a cornice and line the hole witha lead or plastic sleeve. Otherwise lightning can leapacross a loop by the shortest path, at best punching ahole through a cornice on the way, at worst shatter-ing a length of stone that is difficult to repair.

When a tape has to pass from interior to exteriorit should do so through a hole of at least 150 mm(6 in) diameter, sloping downwards to keep outrain and wired to keep out birds. Metal roofs, struc-tural steelwork, bells and metal bell frames shouldbe connected to the conductor system; so tooshould minor metal items (flashings, gutters, etc.) if they are close to the down-lead or bonding tape and form a possible alternative route to earth.Gas and water pipes, electric conduit, metal sheath-ing and earth continuity conductors should be connected to the main down-lead if possible.

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Figure 7.37 Lightning conductors, St Peter’s, Rome, Italy

This massive building, with walls 13 m (43 ft) thick and superbly built with good travertine, needonly fear earthquakes and lightning. The ball is bronze gilded and well protected against strikes

The point in an installation most vulnerable toneglect is the connection between down-lead andearth terminal. If possible, this should be containedin a small chamber with a removable cover, so thatit is easy to inspect and repair. Earth terminals areusually sectional copper rods with the capability ofextension when necessary to improve earthing.

It is the moisture in the ground which provides theconductive path for lightning strikes, as the miner-als making up the soil—silica, alumina, lime, etc.—are poor conductors in themselves. In summer,sandy soils sometimes become so dry that resist-ance to earth is very high just when the conductorsystem is most needed. When this happens, matterscan be improved by putting rock salt in the termin-al box or in the soil and watering the ground witha hose. If there is a high resistance to earth from theterminal, the conductor will still operate—althoughless effectively than normally—but there will be arisk of great disturbance of the ground and pos-sible damage to the foundations.

Where protection is necessary and has beeninstalled, it is essential to maintain the original elec-trical performance. If joint continuity is lacking, forexample, the conductor can be more of a liabilitythan an asset, as the lightning discharge might leavethe conductor halfway down and possibly causemore damage than if it had struck directly. A con-tract should be arranged with a specialist firm toservice the system at one-year to, at the most, five-year intervals; some valuable high-risk build-ings need annual inspection. All connections on tapes and elevation rods should be remadeevery 20 years, however difficult access to themmay be (as on a tall spire). After a lightning strikehas taken place, it is wise to have the installationchecked.

Insurance against disasters

Insurance of historic buildings against fire and natural hazards poses difficult problems, particularly

as much of the fabric and contents is irreplaceable.Full documentation is an essential element of dis-aster preparedness. Record drawings of the build-ing should be made although this is rarely the case.The standard should be that required by the UnitedStates Historic Architectural Building Survey.

In the case of the contents, including furnitureand fittings, there should be a complete inventorywith record photographs and measured details withfurther details of acquisition and cost to substanti-ate a possible insurance claim. It is interesting tonote that the value of the contents of a historicbuilding may be several times that of the fabric. Allthese records should be duplicated and kept in asafe place in fire-proof cabinets.

Full insurance cover of historic buildings isexpensive, but the insurers will insist on uplift forinflation and unless agreed otherwise will reducethe claim by the percentage shortfall in cover. Withlarge buildings which are unlikely to be completelydestroyed by a disaster such as fire, insurance canbe for the largest single event, if the building isproperly compartmented.

After a disaster questions about insurance will beasked immediately. Was the property properlyinsured? Early contact with the insurance companyis essential and a loss adjuster will be appointed toact for them. The loss adjuster will review whetherthe full value was insured. If not, the value of theclaim will be reduced in proportion to the percent-age shortfall. Preparation and evaluation of insur-ance claims is time consuming and the cost of thistime is a legitimate part of the claim. If all the supporting documentation is available it will be atriumph of disaster planning. Full insurance claims,however, should not be made until reports havebeen obtained from all concerned, including policeand fire brigade if involved, and a meeting heldunder the chairmanship of a responsible person toestablish all the facts of a case. Frivolous or badlyframed claims only waste time and lead toincreased premiums. Detailed estimates of damageshould be obtained to substantiate the claim.

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Introduction

Earthquakes—the shifting of the earth’s crust—canresult in devastating destruction. While there is agrowing body of knowledge about the nature ofearthquakes, we cannot predict with confidenceeither their precise time of arrival or their intensity.We can predict only that they will eventually happen.

Even with our present knowledge of technologywe can do nothing to reduce either the frequency orthe intensity of earthquakes. The only thing we cando is to take precautions to mitigate potential devas-tation. Beyond the obvious need to protect humanlife, we must also take responsibility for protectinghistoric buildings and monuments. Already we havesuffered major losses of important structures.

Earthquakes are different from other disasters intheir capacity to destroy almost instantaneouslywithout warning, causing extensive, often irrepara-ble damage to cultural property. Preparing for andresponding to earthquakes involves local, provin-cial (state), and national (or federal) organizations.

Earthquake preparedness must incorporate plan-ning for contingencies common to most other types ofdisasters—especially fire, flood and looting. By plan-ning ahead vital time can be saved after the disasterhas struck. Fortunately the conservation of culturalproperty ultilizes different skills, techniques and mater-ials from those required to reconstruct modern build-ings. As a result, conserving our cultural heritage doesnot necessarily compete with other recovery opera-tions for scarce resources in the post-disaster situation.

Improvement of the seismic resistance of historicbuildings should be integrated into a regular main-tenance programme, based on periodic inspections by specially trained architects and engineers. Admin-istrators in seismic zones should ensure that theseinspections are carried out and that a full inventorywith detailed documentation is prepared before thenext earthquake. Disaster preparedness has to com-bat the natural inclination of the people to say, ‘Itwon’t happen here’, or ‘not in my lifetime’. The only

responsible policy is to work consistently and effec-tively to plan for the eventuality of an earthquake.

In seismic zones, the strengthening of valuablecultural property should be included in the generalprogramme of preventive maintenance and, wheneconomically possible, in conjunction with othermajor building repairs such as renewal of roofs orstrengthening of walls and foundations.

Well maintained historic buildings have a relativelyhigh degree of earthquake resistance. Bearing in mindthat earthquakes and the reaction of historic structuresto an earthquake are both unpredictable, the mostprofitable field of study is the analysis of previousearthquake damage in the locality. These case studiescan provide the basis for future applications of

8

Historic buildings in seismic zones

Figure 8.1 Quasr el Bint, Jordan

This remarkable second century A.D. building was given tensilereinforcement against earthquakes by insertion of lacing bandsof timber—most of which eventually rotted. However, it provedeffective in preserving the outer walls while the roof collapsed

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Table 8.1 Modified Mercalli Intensity Scale (Courtesy: Editor, Consulting Engineer, May 1978)

Number Descriptive Effects Acceleration term (cm/s2)

I Imperceptible Not felt. Registered only by seismographs �1

II Very slight Felt in upper storeys solely by persons at rest 1–2

III Slight Felt indoors. Vibrations like those caused by 2–5light trucks passing by

IV Moderate Hanging objects swing. Vibrations like those 5–10caused by heavy trucks or a jolt such as that occasioned by a heavy object striking the wall.Parked cars are set in seasaw motion. Windows, doors and crockery rattle

V Fairly strong Felt outdoors. Sleeping persons wakened. 10–20Small objects not anchored are displaced oroverturned. Doors open and close. Shutters and pictures are set in motion. Pendulum clocks stop and start or change their speed

VI Strong Walking is made difficult. Windows, crockery 20–50and glass break. Knick-knacks, books, etc.,fall off shelves; pictures fall from the walls.Furniture moves or is overturned. Cracks inweak plaster and materials of construction type D. Small bells ring (church, school)

VII Very strong Noticed by car drivers and passengers. 50–100Furniture breaks. Material of constructiontype D sustains serious damage. In somecases, cracks in material of constructiontype C. Weak chimneys break at roof level.Plaster, loose bricks, stones, tiles, shelvescollapse. Wave created on ponds

VIII Destructive Steering of cars made difficult. Very heavy 100–200damage to materials of construction type D and some damage to materials of type C. Partial collapse. Some damage to materials of type B. Stucco breaks away. Chimney,monuments, towers and raised tanks collapse. Loose panel walls thrown out. Branches torn from trees. Changes in flow or temperature of springs. Changes in water level of wells. Cracks in moist ground and on steep slopes

IX Highly General panic. Material of construction type 250–500destructive D completely destroyed. Serious damage to

material of type C, and frequent collapse. Serious damage also sustained by material of type B. Frame structures lifted from their foundations, or they collapse. Load-bearing members of reinforced concrete structures are cracked. Pipes laid below ground burst. Large cracks in the ground. In alluvial areas, water, sand and mud ejected

X Extremely Most masonry and wooden structures des- 500–destructive troyed. Reinforced steel buildings and 1000

bridges seriously damaged, some of them (�1 g)destroyed. Severe damage to dams, dikes and weirs. Large landslides. Water hurled onto the banks of canals, rivers and lakes. Rails bent

Construction method A:Good workmanship, mortar anddesign; reinforced, especially laterally,and bound together using steel,concrete, etc.; designed to resist lateral forces.

Construction method B:Good workmanship and mortar; reinforced but not designed to resist strong lateral forces

Construction method C:Ordinary workmanship and mortar; no extreme weaknesses such as failing to tie in at corners, butneither reinforced nor designed toresist horizontal forces

Construction method D:Weak materials such as a adobe; poor mortar, low standards of workmanship; horizontally weak.

strengthening measures as part of a general pro-gramme of building maintenance.

Nature of earthquakes

The surface of the earth consists of about twentyindependent tectonic plates floating on a softer innerlayer. These plates are in continuous motion relative toeach other because of currents in the internal liquidcore of the earth. Thus, elastic energy accumulatesalong the edges of the plates, and is eventuallyreleased with a sudden movement, which causesbrief, strong vibrations in the ground—an earth-quake. The place in the earth’s crust where thisenergy release occurs is the focus, or hypocentre.The vibrations propagate very quickly in all directions,but generally become weaker with distance.

Very often a major earthquake is preceded bysome foreshocks and is nearly always followed byaftershocks, some of which can be of comparablestrength. The intepretation of foreshocks is difficultand thus they arc seldom useful in predicting a majorearthquake. Aftershocks can be very dangerous, asthey will react upon already damaged structures.

Magnitude and intensity

The magnitude of an earthquake is expressed indegrees on the Richter scale. It indicates theabsolute strength or energy release of the earth-quake and is calculated on the basis of recordingsof the earthquake by accelerometers or seismo-graphs in different locations.

While magnitude characterizes the earthquakeitself, intensity indicates the effects of the earth-quake in a determined place. Intensity is most oftenexpressed in degrees (I to XII) on the Modified

Mercalli Scale, which classifies the observable damage to buildings and installations caused by theshaking ground. Damage caused by an earthquake ofa given magnitude and the intensity with which theearthquake is felt in a determined place, depends onmany factors: the distance from the epicentre, the

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Figure 8.2 Church of San Francisco, Antigua, Guatemala(Courtesy: Architect D. del Cid)

This church was damaged at the end of the eighteenth centuryin a great earthquake and left in a ruined state. It suffered further damage in the great earthquake of 1976

Table 8.1 continued

Number Descriptive Effects Acceleration term (cm/s2)

XI Disaster All structures collapse. Even large, well- 1–2 gconstructed bridges are destroyed or severely damaged. Only a few buildings remain standing. Rails greatly bent and Intensity scales:thrown out of position. Underground wires MM 1956 Modified Mercalliand pipes break apart MSK 1964 Medvedev-Sponheuer-

KarnikXII Major disaster Large-scale changes in the structure of the �2 g RF 1883 Rossi-Forel

ground. Overground and subterranean JMA 1951 Japan Meterological streams and rivers changed in many ways. AgencyWaterfalls are created, lakes and dammed up or burst their banks. Rivers alter their courses.

main direction, frequency, content, type of seismicwaves, the local ground conditions, the condition ofthe buildings affected (i.e. whether they have beenwell maintained and the quality of workmanship onprevious repairs), their form and design, etc.

Maximum ground acceleration is used to indicateintensity, but it is only one of the important factorsdetermining intensity; it is a directly measurablevalue that can be used easily in calculations. It isexpressed as a fraction of g, the gravity acceleration.

It is not surprising that the unfavourable groundconditions of the Friuli, Italy, earthquake (6.4Richter) produced a result (Modified Mercalli IXand X) as devastating as the 1976 Guatemala earth-quake of 7.6 Richter, one of the most severe everrecorded, with forty times the energy input of Friuli.In Friuli the second major shock followed a wholeseries of minor tremors and caused great havoc tobuildings already weakened.

Another significant example is the 1985 Mexicoearthquake, with a magnitude of 8.1 and an epicen-tre in the Pacific Ocean. In Zihuatanejo, on the coast,less than 100 kilometres from the epicentre, theearthquake registered an intensity of VII on theModified Mercalli Scale, but an intensity of IX insome parts of Mexico City, about 400 kilometresfrom the epicentre. This was due partly to the focus-ing effect in the wave propagation and partly to thegeological structure of the valley of Mexico City.Because of local variations in ground conditions, theintensity in Mexico City varied between VI and IX.

The secondary effects of earthquakes, such aslandslips (landslides), road fractures, bridge fail-ures, floods, and ground movements with changesof underground water levels and flow, can be dev-astating. The first effect is to disrupt communica-tions and make rescue difficult. In addition, anearthquake site is generally held in a pall of dust.

Knowing the risk

Inhabitants of seismic zones must realize that they livebetween two earthquakes. Barclay G. Jones, observesthat, even after administrators recognize the problemand take steps, their policies and preparations mustcontinually be updated and re-evaluated. ‘Institutionsand public bodies must face the problem and estab-lish policies’, to protect the cultural heritage.

Complete safety is unobtainable, so the issue ishow much safety is feasible to achieve, or con-versely how much danger is tolerable. Three concepts are involved in assessing dangers:

Hazard: The probability that a disastrous eventof given intensity will occur in a particular place.

Vulnerability: The degree of loss that will be sus-tained by an element from an earthquake of givenintensity.

Risk: The probable loss, combining the hazardsof location and the vulnerability of buildings andtheir contents. Risk can be removed, transferred,shared, accepted or accommodated.

A major earthquake may affect several adminis-trative zones, provinces, or even countries. It isnecessary to make not only a hazard assessment ofa country, but also very specific and technicalassessments of individual sites containing valuablecultural property.

Seismicity

The mean interval between two earthquakes of acertain intensity at a certain place is called the returnperiod of earthquakes with that intensity at thatplace. Return periods are of limited use for predic-tion, especially when the place is subject to earth-quakes from various independent foci, but theyprovide valuable statistical information. The returnperiods of earthquakes of various intensities enablethe risks to be assessed. In the ancient capital ofPagan in Burma, the acceleration is estimated at 0.2 gwith a return period of 100 years, but in 500 yearsthe estimate increases to 0.6 g. A large and recentearthquake indicates less probability of recurrence;thus, the hazard is lower, but increases with time.

In all estimates of acceleration and return periods,there is a large element of doubt. For safety rea-sons, the seismologist may overestimate and thismay lead to unnecessary interventions in historicbuildings. At present, it is thought wiser not to eval-uate intensities with return periods greater than onehundred years when designing strengthening measures for historic buildings, as this will avoidexcessive interventions that may not last the speci-fied return period. It is better to devise schemesthat do not prejudice future interventions and canbe strengthened if desired. Maximum accelerationsshould be given for specific sites so that alternativecourses of action can be studied and compared.

Seismic zones

Seismic zones correspond mainly to the edges ofthe tectonic plates that support the continents andoceans. Seismic maps are available in every coun-try and are periodically updated, although, as PierrePichard (1984) explains: ‘These maps are not as arule, distributed widely enough and in most cases

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are unknown, for example, to those responsible formonuments.’ However, these maps are invaluablein establishing a clear picture of the most threat-ened sites.

It is therefore recommended that national andinternal organizations responsible for the culturalheritage co-operate with scientific and governmentauthorities, to develop seismic maps that pinpointhistoric monuments, cities and quarters, archaeo-logical sites, and significant museums and libraries.This will provide a clear picture of the most valu-able sites and the priorities to be observed.

Building vulnerability

The vulnerability of cultural property, both build-ings and objects, varies widely. This vulnerabilityderives from differing characteristics of each partic-ular earthquake, the soil upon which the structurerests, and the characteristics of the structure itself:foundations, intrinsic faults due to design form, lackof bonding, poor workmanship, and extrinsic faultsdue to lack of maintenance and decay.

Vulnerability reduction plans must be devisedand instituted. The structure of vulnerability reduc-tion plans is consistent: inventory, recording anddocumentation, risk assessment, protection, emer-gency procedures, and restorative processes.

Vulnerability studies should be made for earth-quakes of different intensities, and the effects of dif-ferent degrees of proposed intervention should beassessed. Different types of earthquakes will havedifferent impacts on each individual historic struc-ture, but computer models can help assess poten-tial damage from each. These studies will show themost likely scenario and the range of variation fromthe median.

Most national or state codes for new buildingsare determined by the estimated thresholds of tol-erable risk. Unfortunately, it is rarely possible to dothis for historic buildings, especially the large numberof rural vernacular buildings or traditional dwellingsin historic centres.

The actions needed to prepare seismic safetyplans for historic buildings are:

(1) Estimate seismic hazards in terms of theexpected occurrence of earthquakes of variousintensities and their return period.

(2) Estimate seismic risk (loss of life, material damage, functional loss, building degradation).

(3) Identify structural systems and models foranalysis for historic properties. Prepare recorddrawings and seismic survey forms.

(4) Evaluate structural responses to earthquakes ofvarious intensities.

(5) Determine type and degree of damage for different predicted seismic intensities.

(6) Develop alternative upgrading (strengthening)methods and estimate costs, applying conserva-tion ethics to determine the minimum interven-tion necessary.

(7) Develop plan schedules and give approximateestimates of cost of alternative schemes for dif-ferent return periods.

(8) Prepare a management plan for a chosenscheme. Obtain budget allocations based onaccurate estimates. Execute desirable works toincrease seismic resistance.

Examination of earthquake damage shows that thedirection of the waves has a considerable effect onthe resistance of the building. The following is animagined scenario of earthquake damage. First, rooftiles begin to slip and fall, weak timber joints breakand the roof timbers batter the walls. Then cracksform in the corners of the walls and where stressesconcentrate around door and window openings andin vaults and arches. The centre portion of the vaultor arch may slip downwards wedging the structureapart. The roof falls in and portions of the vaults anddomes fall. Pinnacles and towers rotate, shift and fallcausing damage, and facades slip apart. The struc-ture disintegrates into large lumps if well built, andrubble if badly built. With simple vernacular build-ings the front walls fall out into the street and theroofs and floors crush the occupants.

The basic causes of damage are relative grounddisplacements and inertia loads that result fromground accelerations. The factors affecting the seis-mic performance of a historic building are its mass,stiffness, periods of vibration (all of which affectthe loading), damping capacity or the ability toabsorb energy, stability margins, structural geometry,structural continuities and distributions of mass and resistance. Historic buildings usually lack theductility and structural continuity which can bedesigned into new buildings. The compatibility ofthe various structural elements and the availability ofalternative structural actions, when some elementsfail, are important considerations.

Lastly, there is the general condition of the struc-ture—has it been well maintained and carefullyrepaired in the past? Earthquakes seek out the hiddenweaknesses in a building, so are often blamed forwhat was a faulty repair, bad workmanship or lackof preventive maintenance.

According to the Mercalli grading, most historicbuildings come within the lower strength classifica-tion being stiff structures made of brittle material.

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However, Mercalli quite rightly lays great emphasison the quality of workmanship. Perhaps he isunduly critical of adobe, which, if mixed with longstraw or tough grass, can achieve remarkablestrength and toughness.

Strengthening of historic buildings

For simplicity we should consider two main classesof historic buildings:

(1) The sophisticated (for its time) with high qualityworkmanship and materials.

(2) The vernacular which has evolved using materi-als available locally which meets climatic conditions as efficiently as possible.

In vernacular architecture improvements are pos-sible using modern materials to increase tensileresistance and bonding, but a blind use of reinforcedconcrete can be disastrous, so the nature of thebuilding needs understanding. The typical weak-nesses of South European vernacular buildings arefound in the construction of the door and windowopenings and in the tying of the roof structure and

floors into the walls; however these weaknessescan be rectified. Much can be learned from typicalfailure patterns in previous earthquakes, which willshow various degrees of damage.

Sophisticated buildings are much more complexso it is impossible to generalize as each is an indi-vidual. Strangely the original construction rarelyincludes anti-seismic elements except metal crampsin masonry and ties across arches openings andwide span vaults. Their vulnerability depends onthree main factors:

(1) Foundations. Is the soil homogeneous? What isits nature and likely seismic performance? Isthere ground water?

(2) Intrinsic faults due to form, design and lack ofbonding.

(3) Extrinsic faults due to lack of maintenance and decay (especially at the ends of embeddedtimbers).

A historic building may have already survivedseveral earthquakes. This shows its resistance but itmay also have been weakened.

The historic building can only be understoodthrough a study of its history, including sequence of

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Figure 8.3 Friuli, Italy(Courtesy: Architect G. Tampone)

Earthquake damage

construction, details of previous repairs and restora-tions and former earthquakes. Lack of maintenance,injudicious alterations and continual erosion of itsresistance by the combined causes of decay, includ-ing pollution and vibration, will also have causedweakening by cumulative effects. These can onlybe countered by regular inspections and a main-tenance and repair strategy. The maintenance strategy should aim at a gradual upgrading of theearthquake resistance of the building, in which wayeconomic results will be obtained gradually provid-ing that building owners recognize seismic risks.

The shock waves of earthquakes are various andthe seismic responses of historic buildings are infi-nitely variable. Seismic codes and standardized pro-cedures will not take into account the nature of aspecific historic building. Some of the so-calledstrengthening measures imposed incur damage andreduce the value in historic buildings. The upgrad-ing of seismic resistance needs understanding ofthe nature of historic buildings and the ability tomake difficult judgements. Such buildings are gen-erally stiff but built of weak materials; it is vital thatall means of strengthening should be compatible.

The role of the architect in seismic zones

After having researched the seismic history of thebuilding and having studied the relevant codes andseismological maps, the conservation architect hasan important role in initiating action to save historicbuildings.

In a specific case, the first step is to make a con-dition survey of the condition of the historic build-ing, noting all the visible defects and classifying theurgency of corrective actions. The causes of decayshould be diagnosed. The second step is to defineits significance and identify the values that give itthis significance so that all the specialists involvedat a later stage may understand and respect theauthenticity of the fabric.

The greatest danger to historic buildings comesfrom engineers who are unaware of their uniquevalues and apply the Codes literally, or who areunwilling to accept responsibility for making judge-ments. It can be said with some justice, that manya historic building has the options of beingdestroyed by the Codes or by the next earthquake.

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Figure 8.4 Friuli, Italy(Courtesy: Architect G. Tampone)

Earthquake damage

As the vast number of vernacular buildings areunlikely to be studied individually, the conservationarchitect may be involved in drafting practicalguidelines for their strengthening so that buildersand owners do not destroy the authenticity of theirbuildings.

Site investigation

The geology of the site greatly affects the risk, as wasshown in the 1987 earthquake which destroyed ten-storey modern buildings in Mexico City and left his-toric buildings scarcely damaged as their vibrationmode did not coincide with that of the earthquake.

The engineer will be jointly involved in researchinto the geology of the site, as this will affect the riskby several degrees. Microzoning will indicate localfaults that increase the risk and geological strata thatmay either decrease or increase the risk. The level ofthe ground water should be investigated as it may

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Figure 8.5 Ospedelletto di Germona, Friuli, Italy(Courtesy: C. Silver)

Private house with fresco on the facade. Attempts to save thisstructure were abandoned due to the severe earthquake damage. Collapse was judged to be imminent and conditionstoo dangerous to permit detachment of this fresco, which was a nineteenth century copy of a seventeenth century original. The house was demolished

Figure 8.6 S. Stefano, Antegna, Friuli, Italy(Courtesy: C. Silver)

Nineteenth century plaster hides the fine Lombard (c. A.D. 700)bas-reliefs and the frescoes. The keystone of the arch of the presbytery has been temporarily propped to prevent immediate collapse

induce liquefaction. The foundations should beinspected and the ground probed if necessary.

In addition to the direction of the shock wave,the predominant frequency of these waves and thenatural frequency of the building and ground arevital questions. The stiffness of the building in rela-tion to the properties of the subsoil should beassessed by a seismic engineer. The whole buildingmay vibrate at a certain frequency due to its formand stiffness, and if there is dynamic resonance thestructural damage will be much greater. Crackingand other disruption of the structure may acciden-tally increase or decrease this resonance. In asevere earthquake, badly bonded elements act likebattering rams oscillating in different modes. It hasbeen observed that a masonry building can survivea few shocks of great intensity, but that vibration oflong duration is damaging. In general stiff buildingssuffer less if the ground is soft and flexible, less ifsited on hard rock, but soft ground with sedimen-tary layers at depths down to two or three hundredfeet can amplify the shock. Sloping strata and varie-gated soils such as peat or clay, should be identi-fied as these increase the vulnerability.

Shock waves can be focused by the terrain andtend to concentrate in ridges. In order to assess therisk more accurately than is possible in a generalizedcode, it is desirable for the engineer to establish theseismic spectrum of the historic building.

Structural investigation

The form of the building will affect its resistance toseismic shocks; in descending order circular, octag-onal or square plans have good resistance, whereasa long building, or one with projecting wings, ismore vulnerable. Elements which have differentmodes of vibration are also vulnerable. In assessingthe seismic performance of a building the elementslikely to dissociate themselves should be identified;these include chimneys, gables, balconies, roofstructures and towers.

During an earthquake, stresses will tend to con-centrate wherever structure changes, as at openings,and where materials with different characteristicsare introduced. Corners are vulnerable becausestresses come from two directions. Previous repairsand the introduction of incompatible materials instrengthening programmes, often result in damage.

One of the great difficulties faced by engineers isto assess the strength of brick or stone masonry setin lime mortar. Cores should be taken from masonrywalls to ascertain the quality of the mortar and toestimate its strength. The mortar itself, may withtime, have lost its cohesion or have become as

strong as Portland cement mortar. Cracks and fis-sures will indicate loss of strength.

The structural system must be examined at threelevels; as a whole, as elements and as individualmaterials, to decide upon its action. The quality ofthe original workmanship is a material factor in theassessment of which the historic evidence is useful.

A change of use in a historic building can haveserious implications from a seismic point of view,especially if the dead weight is increased by furni-ture, office equipment, files and books. A use thatis sympathetic to the building and its authenticitymust be chosen.

A full investigation of the condition of the historicbuilding, should involve archaeologists, historians,geotechnicians, materials scientists besides archi-tects and engineers. The key experts should makejoint inspections in order to discuss the problems in situ and to use the evidence available in the fabric of the building itself.

Strengthening timber buildings

Provided their joints are sound, and the timbers arenot attacked by fungi, timber buildings are consideredto have good earthquake resistance. Unfortunatelythey are vulnerable to fires, which are often a by-product of an earthquake. If strengthening is neces-sary, elements can be strapped together and thestructure bolted to its foundations. Walls and roofscan be given additional strength by the addition ofplywood linings. Plaster and wattle-and-daub panelsin timber framing can be strengthened with galvan-ized expanded metal reinforcement nailed to theframing on both sides.

Strengthening masonry buildings

Possible methods of strengthening masonry wallsagainst seismic force loading are:

(1) Drilling and grouting in vertical steel reinforce-ment down the full height of the wall.

(2) Thickening the existing walls on the inside withsprayed concrete.

(3) Thickening the existing walls with cast-in-situreinforced concrete.

(4) Cutting away a layer of existing brickwork andreplacing with cast-in-situ reinforced concrete.

(5) Base isolation.

Thickening walls with sprayed or cast concrete isnot recommended. However, if internal walls are

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Figure 8.7 S. Stefano, Antegna, Friuli, Italy(Courtesy: C. Silver)

The interior of this small church contains important cycles of superimposed frescoes dating fromthe twelfth, fourteenth and fifteenth centuries under nineteenth century plaster. The altar in thepresbytery was found to be constructed from important Lombard bas-reliefs, also covered by nineteenth century plaster. Friuli has the highest level of rainfall in Italy. Therefore, the churchhas been covered with plastic sheeting to protect the cultural property inside. The proppings ofwood proved insufficient; thus two steel cables were locked about the exterior walls

Figure 8.8 S. Stefano, Antegna, Friuli, Italy(Courtesy: C. Silver)

Presbytery from outside. Note plastic-sheet waterproofing and two steel cables that encircle theexterior walls

plastered and of thick enough brickwork a layer of which can be cut away, it is possible to insertreinforced concrete to replace the brickwork andthen make good the plasterwork to the originaldesign.

Although it involves specialist skills and equip-ment drilling and grouting methods are to be pre-ferred, in spite of their greater expense, because theaddition of reinforcement does not seriously affectthe disposition of weights and is compatible withthe existing structural system.

Base isolation has been applied to historic build-ings, the most notable example being the City andCounty Building in Salt Lake City, Utah. Althoughthe insertion of base isolators reduces the need forstrengthening the historic fabric with consequentreduced loss of original material, it is difficult toinstall unless there is a basement and a gap of asmuch as 300 mm (12 in) all round the building toisolate it from the ground which will move duringan earthquake.

Vernacular masonry buildings

Examination of earthquake damage shows thatbonding of walls together at corners is vital,together with the tying of floors and roofs to walls.The insertion of tensile reinforcement with somedegree of prestressing to bond elements together,gives the masonry of historic buildings greaterearthquake resistance. Experiments have shownthat adobe or mud brick with diagonal prestressedcables anchored at top and bottom, have muchgreater resistance to dynamic forces. In existingadobe buildings, reinforcement, in the form of diag-onal galvanized steel wires, might be added underthe layer of mud plaster (stucco) that is normallyrenewed and anchored with small elements of rein-forced concrete at top and bottom.

For simple two storey masonry houses built oflime mortar, Kolaric recommends reinforcement inboth directions with 16 mm (0.6 in) steel ties fixedto the floor joists and anchored with 150 mm by150 mm (6 � 6 in) plates, 5 mm (0.2 in) thick,which are recessed into external walls and thencovered with plaster. Similar strengthening shouldbe done at roof level where the anchoring of wallplates and tying together of roof timbers should begiven special attention, as earthquake damage oftenstarts at this point. The falling of heavy roof tilesand collapse of roof and floor timbers are, perhaps,amongst the major causes of loss of life, generallypreceding or promoting the collapse of walls. Theroof structure should incorporate diagonal ties

which can be used to strut gable walls. Tiles shouldbe fixed with screws in holes drilled at the head.

A ring beam (bond beam) of reinforced concreteunder the wall plate is an obvious improvement tothe earthquake resistance of a masonry building;such a ring beam should be anchored securely tothe walls, tied across the vaults and extended roundthe base of the domes. The mix of reinforced con-crete should have strength characteristics similar tothose of the masonry, so should consist of weakaggregates and mixes.

Considerable strengthening of masonry buildingscan be obtained by grouting procedures of all typesusing hydraulic limes. In special cases the use ofexpensive polyester and expoy resin grouts will bemore than justified. Such grouts can be used fol-lowing the normal injections, thus exploiting theirpenetrating power to fill fissures and fine cracksand avoiding the necessity of filling large voids withexpensive materials. They are especially valuable asthey increase the tensile strength of masonry andconsolidate friable lime mortar, which weaknesswas reported to be one of the principal reasons forthe collapse of many historic buildings in theMontenegro earthquake in April 1979. Roughmasonry walls that are plastered can be strength-ened in the way suggested for mud brick or byapplying galvanized steel mesh on to both faces

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Figure 8.9 Tuscania, Lazio, Italy

Emergency shoring after an earthquake is vital, as often thegreater damage is caused by a second shock two or threemonths later. In this case, after some years the shoring has rotted where in contact with the ground. It often takes 10 yearsto rectify earthquake damage, so shoring should be rot-proof

and tying both faces together at about 1 m (3.3 ft)centres, and then replastering.

Cross walls and partitions must be securelyattached to the main walls. Lintels over doors andwindows should extend at least 400 mm (16 in)beyond the opening to give added protection. Ifdoors and windows are so placed as to cause aweakness in the wall, long reinforced concrete tiesmay have to be inserted in a concealed way, to dis-perse the concentration of dynamic stress whichoccurs at the corners.

Tall chimneys cause a hazard as they will have adifferent mode of vibration from the main buildingand are likely to collapse first, so causing damageand perhaps weakening a vital part of the structure.They should be strengthened, if possible, by verti-cal drilling and the insertion of prestressed ties or,if in poor condition, by being rebuilt at the sametime inserting vertical reinforcement anchoredsecurely to the mass of the wall below.

Earthquake shocks are transmitted to a buildingthrough its foundation. If the foundations fail theresults will be totally disastrous, so foundations shouldalways be investigated. If a building rests on a slop-ing stratum or variegated soils, such as peat andclay, special measures will be necessary, such aspiling of varying depth to support the whole build-ing on the same stratum, which must be sounditself and not liable to liquefaction when an earth-quake occurs. The pile caps must be linked withhorizontal beams and secured to the existing struc-ture carefully. In other cases it may be sufficient tounify the foundations with ground beams aroundthe perimeter.

To prevent mechanical plant from sliding, over-turning and jamming during an earthquake, from 20 mm to 40 mm (0.8 in to 1.6 in) clearances maybe necessary. There must be flexibility in the con-nections with pipes and wires and their fixingsmust be strong enough to withstand three dimen-sional movements. Electric mercury switches aredangerous, because vibration may activate them,and heating boilers with fire-brick linings are alsoliable to damage. Water and electric supplies tohospitals and fire-fighting services need specialprotection and should be examined by specialists.Also sculpture and landscape ornaments will needspecial fixings to prevent them from being thrownabout during an earthquake.

Administrative procedures

The responsible engineer should present two orthree practical alternatives to the multidisciplinaryteam for their review. The compatibility of the

proposals with the historic fabric together with anestimate for their effectiveness must be considered.If this can be tested so much the better. Finally the‘least bad’ solution should be chosen after assessinghow it affects the values in the historic building andits significance. The questions of whether the inter-vention is the minimum necessary and whether thescheme prejudices future interventions should beanswered.

When disaster strikes

The following actions are envisaged:

(1) Fight fires and prevent looting works of art.Prevent water damage from rupture of watersupply pipes or fire-fighting.

(2) Protect as much cultural property as possible.Label and transport all movable cultural prop-erty to previously designated warehouses,fumigate and give first aid.

(3) Obtain the co-operation of the local civil andmilitary authorities as soon as possible.

(4) Organize a quick inspection of damage andcoordinate the work of conservators, architectsand engineers. Grade damage to buildings.

(5) Set up multidisciplinary conservation teams andallocate labour to repairs, giving priority toimmediate protection against the weather.

(6) Seek international aid through disaster reliefagencies, requesting special equipment needed.

Emergency action

Following an earthquake, there is great humanshock. Obviously, priority must be given to savinglife and evacuating casualties. Fires have to befought and looting prevented. People must be fedand given shelter. In the emergency situation aftera major disaster, normal administrative channelsmay not be working and responsibilities may betaken over by relief organizations, the military orcivil defence. These organizations have communi-cations networks and other resources that mayoperate independently, bypassing existing institu-tional procedures. Disaster relief agencies and cul-tural property authorities do not yet have a traditionof co-operation. Thus, special guidelines for rescueactions in and around historic properties need to beincorporated into the plans of existing disaster reliefagencies.

The emergency plan for an institution should becompatible with the overall recovery operation.

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Specialized personnel, after attending to family andpersonal needs, should report to their institution toassist in recovery activities. These may includeinspecting and assessing damage, securing objectsfrom further damage from aftershocks, collectingbroken fragments, protecting against water damage,dealing with flooding from broken water pipes,moving precious objects in the event of approachingfires, etc.

Immediate action is necessary to protect valuablemovable property, which should be labelled, takento a previously designated safe place, and protectedfrom looting. Shelters should be erected over historicbuildings, especially those with valuable contents.

Part of the shock syndrome is to assist in thedestruction of what is left, arson is common, andwanton destruction of historic buildings that couldhave been saved is surprisingly frequent. In somecountries, conservation organizations have enlistedthe co-operation of military officers to organizesecurity and fire-fighting measures. Earthquake pro-tection could easily be added to these duties inseismic zones.

Emergency inspections

Following an earthquake, quick inspection of the damage is essential. Dangerous elements mustbe made safe. Historic buildings should havealready been marked with the Hague Conven-tion symbol. A system of documentation wasdeveloped for use in rescue operations followingthe Montenegro earthquake. Internationally recog-nized colour codes were superimposed on largescale maps to show categories of damage. Standardforms will enable all the information to be codedand analysed efficiently. This system is providedbelow:

Usable—Green:Grade 1—slight superficial damage, virtuallyintact.Grade 2—superficial damage, non-structural.Grade 3—superficial, light structural damage.

Temporarily usable—Yellow:Grade 1—structural damage, e.g. roofs and ceilings.Grade 2—serious structural damage to walls, etc.

Unusable—Red:Grade 1—severe structural damage, unsafe butcapable of repair.Grade 2—partial collapse, eg. roofs, floors, etc.Grade 3—total collapse, requiring reconstructionof walls, etc.

Emergency protection

After an earthquake temporary protection is vital.First aid will have to be given to buildings andobjects. There may be a delay of months or years,hence the importance of temporary measures.

The safety of working conditions will need con-stant monitoring. Helmets and dust masks shouldalways be worn. If perishable foods are left toolong in markets or cold stores, severe health hazardsarise due to decomposition, so much so that gasmasks and protective clothing become necessary.Rats and other vermin increase and make the diffi-cult work of cleaning much harder. A similar butmore unpleasant risk occurs when it is the localcustom to bury the dead in tombs above ground,for these disintegrate in an earthquake, scatteringtheir decaying contents.

It is essential that experts in architectural conser-vation be involved, to prevent unnecessary demoli-tion of cultural property and unthinking removal ofarchaeological material. They must have the authorityand means to make historic buildings safe by tem-porary strengthening and shoring.

Architects with sound engineering judgementand wide cultural knowledge are necessary for thiswork. Also, military engineers should receive specialtraining for earthquake duties. Particular emphasismust be given to structural first aid.

Glossary of earthquake terms*

Focus. The point within the earth’s crust at whichfirst rupture is estimated to have occurred. Earthmasses have long boundaries along which relativemovement occurs. Also the disturbance of theground at or near the surface may be more severeaway from the point immediately over the focus.The focus is typically about 20–30 km below theearth’s surface.

Hypocentre. An alternative word for focus.

Epicentre. The point on the earth’s surface immedi-ately above the focus.

Epicentral distance. The distance from an observa-tion station to the epicentre.

Hypocentral distance. The distance from an obser-vation station to the focus.

Tsunami. A tidal wave occurring as a result of a sub-ocean earthquake. The velocity of a tsunami is relatedto the depth of the water by the formula V = �(Dg)

Glossary of earthquake terms

131

*This glossary is reproduced by courtesy of the Editor of theConsulting Engineer (May 1978).

where V is the velocity and D is the depth. A typi-cal period for such waves is 1 h and for a depth ofsay 5.6 km the velocity would be 800 km/h. Thewave length therefore is about 800 km. At sea, thetsunami is almost unnoticed and its presence isonly noted when it reaches a landmass.

Seiches. A disturbance within a closed body of water.

Mode. A shape of oscillation which can be generatedin a given system of members and masses. Generallythere are as many modes as there are degrees of freedom of the masses in the system. In any givenmode the masses achieve the same proportion oftheir maximum displacement at the same time.

Normal mode. The first, or fundamental, mode inwhich greater displacements are observed furtherfrom the fixed base.

Modal response. The motion of all the masses in asystem at any instant can be expressed as the sum ofthe individually factored modes. On a time basis, thefactors applied to each mode vary so that the totalresponse is continually changing. Mathematical exam-ination of structures involves the assessment ofresponse of systems, mode by mode, and the motionof system in a given mode is called a ‘modal response’.

Period. The time taken for a system to move fromthe mean position and return but travelling in thesame direction, i.e. in passing through the meanposition twice. The fundamental period is that ofthe normal mode.

Critical damping. Damping can be applied to a system to slow down or reduce the amount of oscil-lation which takes place. Generally this is assumed tobe proportional to the velocities of the masses and isreferred to as viscous damping. Starting from zero thisdamping can be gradually increased until the massesreturn to the mean position at rest, having made oneoscillation. The minimum amount of dampingrequired to achieve this is the critical damping.

Damping. Any building system has some degree ofdamping. It is difficult to estimate damping due tothe elastic performance of the structure taking intoaccount joint slippage and damage to non-structuralcomponents, but whatever it is, it is normallyexpressed as a percentage of critical damping. Itvaries from 1% to about 10%.

Participation factor. At any given instant the contri-bution of a given mode to the total response can beassessed. The proportion of contribution of a singlemode is called the participation factor of that mode.

Base shear. When a system is vibrating laterally inresponse to a chaotic disturbance a lateral force atthe base of varying magnitude is required amongstother forces to maintain equilibrium. The probablemaximum value of this force in response to adesign disturbance is called the base shear. Certaincodes obtain this directly and indicate means of dis-tributing it throughout a system in order to obtain aseismic design loading pattern. By model analysisthe base shear is only relevant to the base andprobable loadings at other positions are obtaineddirectly.

Spectrum. In seismic terms a spectrum is a rela-tionship between the responses of systems in theform of acceleration, velocity and displacement andthe period for various values of damping.

Response spectrum. A family of curves of spectra inresponse to a given ground disturbance. A largenumber of response spectra may be combined togive a design spectrum.

Fourier spectrum. A ground motion trace of timeagainst acceleration, velocity or displacement canbe broken down into a Fourier series of functionsof period or frequency. A replot of these responsesagainst period for a given disturbance is called aFourier spectrum for that particular disturbance.

Strong motion accelerograph. This is a devicedesigned to measure the absolute acceleration/timerelationship of the ground on which the device isfounded. The various properties of the device are acompromise to obtain, as faithfully as possible, theground motion in spite of the variation of period ofthe ground vibrations.

Seismometer. This is a device designed to measurethe effect of a ground disturbance on a particularstructural system of given period and damping.

Seismograph. This is the normal seismologicalinstrument of great sensitivity designed to deter-mine the timing and nature of ground motion atpoints on the earth remote from the station. It is notcapable of measuring actual site ground motion.

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133

This chapter includes information on plants, bacterialichens, algae and mosses and fungi; because of thedamage they cause, fungi are given fuller treatment.

Botanical causes of decay

Ivy, creepers and other forms of plant life can causedamage if allowed to grow freely. Ivy drives a bullet-headed root into crumbling masonry and causes dis-integration. Fresh ivy tendrils can, when forciblyremoved, pull off a weak surface of brickwork orplaster, so the plant should be cut and killed and thenleft several weeks until it has lost its adhesivestrength. On the other hand, the rather familiar sightof a boundary wall covered with ivy should be stud-ied carefully because the ivy may in fact be holdingup the wall, and if it is removed the wall itself mayfall to pieces. On buildings proper, rather than gardenwalls, ivy must be kept in check to prevent its growthgetting out of control. When it is cut, the stem shouldbe treated with a strong weedkiller so as to poisonthe roots and prevent its sprouting again.

Stonecrop and wallflowers are pleasant, but theyusually indicate decay and poor maintenance. Indeedthe presence of growth often indicates that the point-ing has perished, in which case it should be renewedas soon as feasible, incorporating a toxic agent in themortar if plant growth is a constant nuisance.

Some kinds of wall-climbing plants do not dam-age masonry directly but must none the less bekept away from the eaves and gutters to avoidblockages. These include Ampelopsis veitchii, aform of Boston ivy with small ovate or trifoliatedleaves, which is often incorrectly referred to asVirginia creeper; Hydrangea petiolaris, a climbinghydrangea; and Hedera canariensis, Canary Islandivy. The last is evergreen and can be grown overunderburnt brickwork that is decaying due to frostas a form of protection.

The architect may well come into conflict with aclient who is a keen gardener and puts the life ofhis plants before the maintenance of his building—or the architect may himself think the building looksbetter covered up. In such cases it is good practiceto insert galvanized vine eyes and use stainless steelstraining wires. Alternatively, the plants can begrown on frames; an advantage of this is that whensuperficial maintenance of the wall is required theframe can be unfixed and the plants bent forwardintact on the frames.

The roots of trees and bushes can cause block-ages and local ground dampness by finding theirway into rainwater drains. In extreme cases, whenrainwater drains are broken by roots, the leakingwater can cause sandy types of soil to wash awayfrom below foundations. Conversely in clay soilsthere is the well-known fact that trees, particularlypoplars, can damage foundations by excessivewithdrawal of ground moisture in summer, result-ing in ground shrinkage and foundation movementwith subsequent cracking of walls and partitions.Trees and plant growths can overwhelm historicbuildings and sites in the tropics, where constantmaintenance is required to hold them back.

Biological and microbiological causes ofdecay

Bacteria and lichens can cause the decay of build-ing materials by producing acids which react chem-ically with the structural material. Examples of thisare sulphate-producing bacteria which grow onstone, and lichens and mosses which produce acidsthat attack lead and also low-silica glass. Algae,moss and lichens all grow on brick and stonemasonry and build up humus in which larger andmore damaging plants can grow. There is an added

9

Botanical, biological and microbiologicalcauses of decay

risk from dampness and clogging of pores if thematerial is not adequately frost resistant.

Some micro-organisms develop rapidly if the airhas a relative humidity of over 65%, and theyspread quickly if there is light. They may take theform of spotty staining of varied colour. A durablecure can only be effected if the source of dampnessis located and eliminated. After removal there issome surface loss in the form of tiny holes whichmay at first be almost invisible.

There are a great many varieties of algae; thosethat occur on most stone, brick or concrete surfacesare usually green, red or brown powders or fila-ments which may or may not be slimy according tomoisture conditions. They derive their energy largelyfrom sunlight, but need liquid water for survival.

Lichens are a combination of certain algae andfungi which can reproduce on moist external sur-faces. The grey-orange and blue-green lichens seenon limestones in country districts may seem veryattractive, but heavy growths of lichen and algaecan hasten the decay of stone by the production ofoxalic acids. They also slow down the drying-outprocess after rain, thus making frost damage morelikely. They are a major problem for conservationin the tropics.

Mosses need a rough, moist surface on whichsoil and dirt can collect; once established they tendto hold moisture in the supporting surface ofmasonry or wood.

Toxic washes are used to kill algae, lichens andmosses. Incipient lichen and algae can be softenedand removed by wiping with diluted ammonia, while

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heavier growths can be killed by spraying with for-malin. Large areas of masonry can be sprayed witha solution of 25 g/1 (4 oz/gal) of water of zinc silico-fluoride or sodium pentachlorphenate or vari-ous branded solutions. Horticultural tar wash willalso remove lichens and mosses, and as far as canbe seen does not seem to discolour the backgroundmaterial more than temporarily. After the growthhas died and shrivelled, it can be safely brushedaway or carefully scraped off. Plants growing injoints or pockets of masonry can be killed by spray-ing with an appropriate gardener’s weedkiller. It isimportant to kill the roots and remove any humuswhich may encourage future growths, and anypockets should be filled with mortar.

Fungi

Fungi, mildew, moulds and yeasts do not requiresunlight for growth; they depend upon organicmaterial such as plant life for their energy. Mouldsnormally appear as spots or patches that mayspread to form a grey-green, black or brown furrylayer on the surface. Any fungus has several basicrequirements for propagation and growth: ade-quate water and oxygen supply, suitable tempera-ture, a congenial substratum on which to grow, thespace for growth, and finally of course the sourceof infection. If any of these requirements is inade-quate, growth cannot take place. Water is a by-product of fungal growth; thus, if fungus hasestablished itself in a piece of wood and the rate of

Figure 9.1 A ruined templeat Sukothai, Thailand

Unrestricted plant growth posesgreat problems to archaeolo-gists and conservators. Takinginto account the climatic conditions, which favour rampant plant growth, in practice this ruined temple can only be dismantled andreconstructed

drying is less than the rate at which water is pro-duced by the breakdown of the wood substance,the attack will go on indefinitely with consequen-tial decay. This fact emphasizes the importance ofair movement and ventilation.

Certain minute fungi that attack wood can doimmense and irreparable damage in a short time,and the softening effect of this decay or rot canencourage subsequent beetle attack. It is importantto note, however, that fungal attack only occurs inwell-seasoned wood if damp conditions prevail, i.e. if the moisture content of the wood rises above20%. Thus, continuous heating and good air circu-lation, together with elimination of the entry of rainand moisture, prevent timber decay.

Detection of fungal decay in wood

The inspector should arm himself with a handytorch with a strong beam, a penknife and magnify-ing glass, and wear overalls or old clothes. Herequires a knowledge of the construction of historicbuildings.

Advanced stages of fungal decay are easily recog-nized because the structure of the wood is damaged,either crumbling or broken up into shrunken dis-torted cubes of lignin in extreme cases or with abowing inwards and outwards parallel to the grainor waviness and blistering effect. The colour may bechanged with a brownish or whitish discoloration,depending on the type of fungus, and this may showthrough paintwork, the brown colours coming fromfungi that destroy cellulose and whitish flecks on adarker background from those that destroy lignin. Inextreme cases the fruiting body is found in the mid-dle of a whitish mass of hyphae. It may be sterilizedimmediately to prevent the spread of spores, but itslocation as the centre of the attack is valuable evi-dence in planning eradication.

When inspecting historic buildings it is importantto look into corners and poorly ventilated cellars tocheck for fungal attack. Beams and joinery should betapped with a penknife and if they give a dull or hol-low ring, the point of the blade should be driveninto the wood in several places to see if it hasbecome relatively soft. Any timber that is embeddedin masonry may have too high a moisture contentand is therefore vulnerable to both fungal and beetle attack. Where appropriate, a further test ispossible in long-grained soft woods by inserting theblade and prising up a splinter; a long splinter cannever be prised up from decaying wood.

A musty smell may indicate extreme fungalattack, but in the author’s experience this has beenfound to be an unreliable guide.

‘Dry rot’ fungus

The most serious form of rot in Britain is Serpulalacrymans, generally known as ‘dry rot’ because itcan manufacture and carry its own moisture andthus attack dry wood as it moves away from its birth-place. It does not seem so serious elsewhere, eitherbecause of cold winters or lack of humidity in theclimate. This fungus grows from a spore or propa-gates itself from fine hairlike roots or strands calledhyphae, which may unite to form a snowy-whitegrowth. When well established this growth can pro-duce pencil-thick strands called rhizomorphs whichextend to 10 m (33 ft) or even 20 m (66 ft) distance,and then it will grow a fruiting body producing yetmore millions of spores. Hyphae strands can probethrough damp brick and stone, following the mortarjoints, or move behind plaster until they find morewood upon which to feed. They particularly likeunventilated voids such as linings to walls, andembedded timbers such as wood lintels. Attack isslowed down, although not prevented, by low tem-peratures; also, high temperatures of 42�C (108�F) orover will effectively sterilize the fungus.

As millions of spores are produced by a fruitingbody, amounting to 800 or 900 million per hour intropical conditions, the air must always containsome, so the possibility of infection must be con-sidered likely anywhere. The correct approach tothe prevention of dry rot is to avoid conditionsfavourable to the growth of the spore by keepingthe moisture content below 20%.

The cellulose in wood is the food source thatsupports the growth of the fungus, and so cuttingoff the source of supply is vital. Chairs, old booksleft in a damp basement or even carpenter’s shav-ings swept carelessly into a heating duct, canbecome causes of dry rot. Blocked gutters and rain-water down-pipes are perhaps the most frequentcauses as they provide the essential moisture forthe fungus spore to grow. Blocked under-floor ven-tilators and impervious floor coverings, whichreduce ventilation and so raise the moisture contentof the wood, are other frequent causes of attack.

Control of dry rot

The eradication of dry rot is not work for amateurs,who may inadvertently destroy valuable evidence asto the source and the extent of the attack. It must bedone by skilled specialists if the building owner is tobe assured that a further outbreak will not occur. Thetotal cost of rectification of dry rot damage to floors,joinery, plaster and decoration is often several timesthe cost of actual eradication of the fungus.

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In every case, the cause and starting point of theoutbreak must be identified and then the extent ofthe attack must be investigated to its limits.

Traditionally, when the extent had been estab-lished, affected wood throughout and beyond theaffected area had to be removed. This was painful,especially to the owner of the building and evenmore so when valuable historic joinery wasdestroyed. In ordinary cases it was thought ade-quate to go 600 mm (2 ft) beyond the last trace ofhyphae but to be additionally sure in historic build-ings 910 mm (3 ft) was recommended. All hyphaemust be killed or removed as otherwise the attackwill be renewed with increased intensity.

Eradication of all the dry rot hyphae requiresmeticulous care. Sterilization by chemicals hasreplaced attempts by blow lamp to heat the stoneor brick masonry until it is too hot to touch. Italways seemed doubtful that the heat would reachsufficient depth, and the time required was consid-erable. In addition, the fire risk to cultural propertywas not negligible.

However there is an alternative approach whichconsists of controlling the environment making it unfavourable to the Serpula lacrymans. Theattack can be inhibited with a spray of fungicideand, if ventilation can be increased and the causehas been removed, the dry rot will die in duecourse. Regular supervision is needed if thismethod is used.

‘Wet rot’ fungi

Wet rots are much less serious than dry rot as theydo not carry their moisture with them, so theirrange is localized. The most common form, cellarfungus (Coniophora cerebella), requires a moisturecontent of 25% before it will attack wood; it hasfine dark-brownish strands and a green, leatheryfruiting body and produces masses of whitehyphae. Pooria vaillantii has spreading string-likestrands. Phellinus megaloporus, which is hardlyever found in modern buildings, occurs in historicbuildings as it attacks hardwoods such as oak andchestnut where these are wet. Although wet rotsare treated with the same chemicals as dry rot, theextent of the area requiring treatment is usuallylocal and the hyphae are not dangerous. It is notnecessary to go beyond the affected area with sterilization.

The ends of timber beams, when enclosed inmasonry, are especially vulnerable to all types ofrot, and also termites. If possible, they should reston a metal damp proof course, and be surroundedby 25 mm (1 in) of air.

Osmophilic fungi

In Japan from the 1950s onwards synthetic resinshave been used to consolidate wooden sculpture.Mori and Arai report that a fungal growth wasnoticed some 15 years after parts had been treatedwith large amounts of resin. Examination showedthat these were osmophilic fungi feeding on a layerof sugar which was a by-product of an actionbetween the insect frass and the resin, drawn to thesurface by capillary action.

Wood-staining fungi

Wood-staining fungi grow on the surface of woodand so produce stains. They do not affect structuralstrength, but can cause painted surfaces to flake off.

Fungicides

Dr Brian Ridout writes:

‘The first important points to make are thatunder the Control of Pesticides Regulations(COPR, 1986) it is illegal to use anything otherthan an approved pesticide formulation, andthat formulation must only be used for thepurposes specified on the label. The on-sitemixing of fungicides is definitely prohibited.

‘It may also be worth noting that theregulations specify three categories of use forwood preservatives and masonry biocides.These are:

● amateur use● professional use● industrial use

‘A normal homeowner would not be able touse formulations that were only cleared forprofessional use. In practice, many formulationsare available for both purposes, but they areonly sold in 5 litre containers for amateur use.Popular active ingredients for wall sterilization tocombat dry rot are 3-iodo-2-propynyl-n-butylcarbamate, dodecylamine salts and boroncompounds. The surface spray treatment oftimbers to combat decay fungi is no longerconsidered to be particularly effective. Paste orgel formulations penetrate to a greater depth,and can be useful for targeted treatments. Gelscontaining boron compounds in ethylene orpropylene glycol can be particularly useful indamp timber.’

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Irrigation of the wall with fungicidal solutionsfrom reservoirs into holes drilled at spacings,depending on the porosity of the wall and flowcharacteristics of the fungicide, is an effectivemethod of sterilization. Care should be taken toensure that the salts thus introduced into the wallare not hygroscopic and do not aggravate capillar-ity. Irrigation is particularly useful to impose a pre-ventive cordon sanitaire between an outbreak andvaluable woodwork as yet unaffected. Such irriga-tion also protects timbers embedded in a wall,

which are most likely to be attacked because oflack of ventilation and high moisture content.

In damp cellars, the insertion of thin water-soluble rods of commercial preservative can beused as a preventive measure to sterilize the walls,exploiting the capillary effect of rising damp.Brushing or spraying all timbers with preservativemay also prevent a dry rot attack or stop it spread-ing rapidly. Wall plates and embedded timbers canbe drilled and infiltrated along their grain to avoidrot and beetle attack.

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Insects

Organic materials such as wood are all vulnerable toinsect attack. Insects cause a great amount of damageby weakening structural timbers and in many partsof the world they are a more likely threat to wood-work than fungi. The situation is becoming morecomplicated due to the fact that eggs and larvae oftropical pests may be imported with tropical woods.It is important that the architect be able to distinguishamong different types of beetle attack, so that he canmake an accurate assessment of the probable extentof damage. He is referred to the technical literaturerelating to the insects common in his own country,for without a detailed knowledge of the biology ofthe different groups of insects, effective measures forprevention of attack and repair cannot be taken.Eradication is much simplified by the fact that thedifferent species nearly all respond to the samechemical treatment.

Identification of insects

A summary of the diagnostic details of damage bywood-boring insects and marine borers is given in the‘Remarks’ column of Table 10.1. Identification roughlyfollows this procedure: what type of wood?—whatsize flight exit hole?—what sort of bore dust (calledfrass) is showing?—what sort of damage has occurred?Piles of bore dust and fresh clean-looking flight exitholes are usually symptoms of continuing activity.Live beetles may be found in the flight season whenthey emerge to mate and lay eggs. Larvae are rarelyfound on inspection, unless the affected wood isopened up to explore the extent of damage.

Incidence of beetle attack in the UK*

In the United Kingdom, about 80% of the reportedattacks are by the woodworm of the common

furniture beetle (Anobium punctatum). About 5–8%of attacks are by the deathwatch beetle (Xestobiumrufovillosum, about 4–5% by wood-boring weevils(Euophryum confine and Pentarthrum huttoni),about 2% by powder post beetle (Lyctus) and about0.5% by the house longhorn beetle (Hylotrupesbajulus). The incidence of woodworm attack ishighest in the south-western counties. The death-watch beetle, not found much in Scotland orNorthern Ireland, is most prevalent in the south and southwestern counties of Britain where rainfallis highest. Wood-boring weevils do not occur inScotland and are most common in the London area.The house longhorn beetle is most common inSurrey and Hampshire but is occasionally found else-where; outbreaks must be reported to the Ministry ofAgriculture in order that its spread may be stopped.

It is suspected that the incidence of woodwormattack is increasing and thus the number of preda-tors on this species is also tending to increase. Thepredators are important, particularly the CleridKorynetes caeruleus which is also a predator on thedeathwatch beetle. It is thus possible that theincrease in woodworm may be indirectly causing aslight decrease in the deathwatch beetle.

Woodworm can spread by flying; they attackonly sapwood in oak but will also attack the heart-wood in many other timbers, both hardwood andsoftwood. A large proportion of woodworm attackis found in roof spaces. If the attack is active, theflight holes are clean, sharp-edged and cream incolour. In inactive areas, the holes will be dirty andgreyish in colour. As larvae have been found inapparently inactive areas, any places that havebeen affected should be treated.

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Insects and other pests as causes of decay

*See BRE Digest 307:1986 Damage by wood boring insects,BRE Digest 327:1987 Insecticidal treatments against wood boringinsects,BRE Digest 371:1992 Remedial wood preservatives: use themsafely andBRE Report 98:1987 Recognising wood rot and insect damage inbuildings

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Table 10.1 Summary of Diagnostic Characters of Damage caused by the Commoner Wood-boring Insects andMarine Borers (from Bletchly, 1967, by courtesy of HMSO)

Type of timber Flight holes Tunnels Bore dust ( frass) Type of Remarksattacked insect or(sapwood and marine borerheartwood—exceptions givenunder Remarks)S = softwood H = hardwood

H, S Absent Sometimes enlarged Cemented Subterranean Tunnels connected tointo chambers. mixture of termites soil through mud(Separated by septa bore dust and galleries. Tunnel wallsof wood in case of wood chewings muddy. (Comparedamp wood termites) in mud carpenter ant)

H, S Absent Sometimes enlarged Ovoid pellets Dry wood Bore dust resemblesinto cavities with 6 longi- termites small poppy seeds

tudinal ridgesChiefly S Absent Separated by septa Large wet Damp wood In damp wood

of wood pellets termitesH, S Circular

312 to Circular. Diam. Sometimes Lymexylidae Active only in green

14

in diam.) (similar to flight absent from ambrosia timber. Compareholes) sometimes parts of tunnels beetles Platypodidae andvariable in same Scolytidaepiece of wood. Wallsunstained or slightlyso

H Almost Oval Longhorn type Clytinid long- Little feeding undercircular (about horn beetles bark before pene- 136 in diam.) trating into sapwood

S Perfectly Circular. Diam. as for Very tightly Siricid Live larvae present incircular (

18

to 34

fight holes. packed wood-wasps green and recentlyin diam.) Surrounding wood seasoned wood.

sometimes partly (Tunnels appear ovaldecayed in section if cut

obliquely)H, S Oval (size Oval, separate and Mixture of Forest longhorn Feed under bark

depending on scattered coarse pellets and Buprestid before penetratingspecies) and chips beetles into sapwood. Active

attack in trees, logsand sawn timberwhilst green. Attack bysome species con-tinues in seasonedwood. Compare houselonghorn beetle

S Oval (about Oval, tunnels coalesce Similar to some House longhorn Serious structural 38

� 136 in leading to breakdown other longhorns. beetle damage in undecayed

diam.) of walls. ‘Ripple’ Sausage-shaped (Hylotrupes sapwood of seasonedmarks on walls pellets bajulus) softwoods.

Characterized by a thin superficial skin ofwood concealinginternal disintegration

H, S Oval Oval enlarged into Damp agglo- Wharf-borer In damp decayedcavities meration of (Nacerdes sleepers, poles,

coarse pellets melanura) built-in timbersand shavings and harbour timbers

Mostly in Circular Circular 116 in diam. Fine very Ptilinus Active in seasoned

beech, elm, ( 116 in diam.) numerous densely packed pectinicornis wood. (Compare

maple and powder Lyctus powder postsycamore beetles)

Tunnel

s w

ith b

ore

dust

Insects

141

Table 10.1 continued

H contain- Circular ( 116 Circular

116 in diam. Copious fine Lyctus powder Active in partly and

ing starch in diam.) numerous loosely packed post beetles fully seasoned wood.powder Confined to sapwood

in timbers where theheartwood isdistinguishable.Wood disintegratedbeneath superficialskin in severe cases.Compare house long-horn beetle

Mainly H Circular (up As flight holes. As Lyctus Bostrychid See Lyctus. Mainly incontaining to

14

in diam.) Usually larger than powder post tropical timbers.starch Lyctus beetles Unseasoned wood

also attacked.Confined to sapwoodin timbers where theheartwood isdistinguishable

S Circular As flight holes Mostly brown Ernobius In timber yards and( 116 in daim.) (with a few mollis recently built houses.

white) bun- Often confused withshaped pellets Anobium but attack

limited to bark andadjacent sapwood

Mostly H Circular As flight holes Larger bun- Deathwatch Common in old build-( 18

in diam.) shaped pellets beetle ings especially in oak.(easily visible to (Xestobium Damage sometimesnaked eye) rufovillosum) internal in large

timbers and disinte-gration often severe

H, S (rare Circular As flight holes; Small ellipsoidal Common In wood usually morein most (

116 in diam.) convoluted shape. Pellets furniture beetle than 5 years old.

tropical H) Numerous (Anobium Birch plywood verypunctatum) susceptible

H, S Irregularly Circular (about 116 Similar to but Wood-boring In damp and decayed

oval to slit- in diam.). Mainly smaller than weevils, wood. Sometimesshaped with straight—compare Anobium Euophyrum and with Anobiumjagged edges Anobium Pentarthrum

Chiefly Absent or Partly concentric with — Carpenter ants Resembles termiteimported S irregular the annual rings (Camponotus damage but gallery

sometimes forming spp.) walls are cleanlarge cavities

H, S Absent Rapidly enlarge from — Shipworm Floated timber,minute size on surface (Teredo spp.) harbour fixtures andup to 1 in diam. boats attacked within. Chalky lining in salt wateroften present

H, S Absent Honeycomb of small — Gribble As for Teredo. Verticaldiam. (

210 in) short (Limnoria spp.) timbers become

( 18

in) surface tunnels eroded near water lineto form a ‘waist’

H, S Circular ( 510 to Frequently across the — Ambrosia beetles Wood surrounding

18

in diam.) grain. Diam. similar to (Platypodidae tunnels sometimesentry holes. Walls and Scolytidae) also stained. Activedarkly stained only in green timber

where bore dustejected through boreholes made by adults.Compare Lymexylidae

Tunnel

s w

ithout b

ore

dust

Tunnel

s w

ith b

ore

dust

142

Figure 10.1 Boreholes of the common furniture anddeathwatch beetles(Courtesy: Department of the Environment, BuildingResearch Establishment)

The boreholes of the common furniture beetle, Anobiumpunctatum, are about 1.5 mm (0.06 in) in diameter, whilethose of the deathwatch beetle, Xestobium rufovillosum, areabout 3 mm (0.12 in) in diameter. However, in the tropicseach species may be larger

Figure 10.2 Boreholes,frass and adults of the common furniture beetle(Courtesy: Department of theEnvironment, BuildingResearch Establishment)

Boreholes, frass pellets andadults of the common furniturebeetle, Anobium punctatum,are visible. This insect hasworldwide distribution

Figure 10.3 The deathwatch beetle(Courtesy: Department of the Environment, BuildingResearch Establishment)

The deathwatch beetle, Xestobium rufovillosum, islimited in its habitat. It is extremely difficult toeradicate from oak in mediaeval buildings

Insects

143

Figure 10.4 Deathwatch beetle attack in central tower roof beams, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Deathwatch beetle, Xestobium rufovillosum, attack in the main beams of the central tower roofhad continued for centuries. The cast-iron bracket on the right is part of the 1831 repairs bySmirke. The friable timber is structurally unsound, but modern techniques might have been usedto fumigate and kill the beetle and then vacuum impregnate the beam with a suitable epoxy resinformulation. These techniques were not, however, known in 1967. The beam proved to be structurally unsound after extensive exploration by drilling and had to be replaced

Figure 10.5 Powder post beetle, Lyctus(Courtesy: Department of the Environment,Building Research Establishment)

‘Lyctus’ forms circular holes 1.5 mm (0.06 in) indiameter, with copious fine powdered frass

Insects and other pests as causes of decay

144

Figure 10.6 Boreholes of thepowder post beetle, Lyctus(Courtesy: Department of theEnvironment, Building ResearchEstablishment)

This beetle confines its activities tosapwood of hardwoods wheresugar content is high, so is unlikelyto cause structural damage

Figure 10.7 The house longhorn beetle(Courtesy: Department of the Environment, Building ResearchEstablishment)

The house longhorn beetle, Hylotrupes bajulus, is rare inBritain except in the south, but more common in warmer temperate climates

Figure 10.8 Balcony of house in Trudos Mountains, Cyprus

The destruction of structural timber at joints is by the houselonghorn beetle, Hylotrupes bajulus in all probability. Note thecrushing of the affected timber

Deathwatch beetle

In England the deathwatch beetle is one of the majorenemies of historic buildings, as its favourite food isoak, the principal structural timber of old buildings,and it is extremely difficult to eradicate. Areas affectedby rot or dampness are generally those in which anattack is first established. Because the attack can onlybe detected by the holes formed by the emergingbeetle, it may be quite well established before evenbeing noticed. New holes are clean, sharp-edgedand clear of dust and dirt. Piles of frass may befound ejected from active holes. Old holes havecrumbled edges and are dark and dirty.

After emerging from her hole in the spring thefemale mates and soon lays some 400 eggs, choosingcracks and crevices where the wood has been soft-ened by rain or damp. The small larvae burrow intothe wood, where in order to mature they must obtainsufficient food by boring. This process takes sometime. In recently felled oak, five years may be longenough, but 10 or 20 years might be needed in hard,dry timber. The larvae bore up and down the grainof the oak in runs of about 1 m (3.3 ft) and each larvamust travel some 14 m (46 ft) in all, making a seriesof runs parallel to the grain. Each external exit holetherefore represents a considerable amount of inter-nal damage. The deathwatch beetle, once havingemerged, crawls around searching for its mate andemitting a sound which is believed to be its matingsignal; also, it may glide a short distance to other timbers and so initiate a new attack.

Control of deathwatch beetle

Eradication of the deathwatch beetle may take over20 years of constant attention, particularly if the attackis in hard timbers. Eradication by means of timber pre-servative applied by brush or spray has been tried, butit cannot reach the larvae that are causing destruction.Furthermore, manufacturers’ preservatives have a dis-appointingly short toxic life when applied externally.Drilling holes at 250 mm (10 in) intervals and fillingthem with liquid preservative is useful for protectingembedded timbers and vital areas such as beam bearings, but in hardwood the lateral spread of preservative is poor, as can be shown by using dyedpreservative in a sample and cutting long sections andcross-sections to inspect penetration.

Carpenter ants (Camponotus)

Generally the attack is on exposed timber and canbe noticed as soon as it starts, because the buzzingof the bees is very noisy. The attack may continue

for generations in the same timber and cause complete destruction.

The ants bore out large tunnels 30–40 mm(1.2–1.6 in) in diameter and up to 240 mm (9.5 in) inlength, in which they construct a series of cross-partitions made of wood dust and saliva to form cells.An egg is laid in each cell and provided with food inthe form of pollen or bee-bread; the larva hatches andfeeds on this and after about three weeks pupates inthe cell and after another three weeks emerges bygnawing its way out of the wood. With such a brieflife cycle severe damage can occur in a short time.

Control of carpenter ants

To prevent initial attack or reinfestation, timbersshould be either painted or coated with creosote,which must be renewed annually in tropical situa-tions. A thick coat of limewash applied twice a yearalso prevents attack.

Timber already subject to attack may be treatedby injecting the borer holes with a proprietary pre-servative or paradichlorobenzene in kerosene oil(paraffin) at the rate of 0.2–0.3 kg/l (2–3 lb/gal) andplugging the holes with wood.

Masonry bees (Osmia rufa)

Although damage to stone and brick caused by themasonry bee may be less widely spread than the better known causes, such as the crystallization of soluble salts, incorrect bedding, chemical attack, veg-etation growth and the use of inappropriate mortars,the decay to the material may nevertheless be consid-erable and could be more common than is realized.

There are about 12 000 species of bees, all ofwhich have four stages of development: eggs, larva,pupa and adult. The masonry bee is one of the soli-tary types that does not live in a colony but digs itsindividual burrow in the ground and occasionally insoft stone, particularly sandstone, weak bricks andcrumbling mortar joints. The female begins boring inspring and forms a series of galleries in which shedeposits her eggs. After providing honey and pollenfor the larva she seals the openings with mud anddeparts to make other cells. The young bees emergein summer but inhabit the galleries until the follow-ing spring when they, in turn, make further nests.Many of these holes become filled with water, whichexpands on freezing and causes the stone to flakeoff. Small flakes of newly broken off pieces of stonelying at the base of the wall suggest such action.

Raking out and repointing will probably not besufficient to eradicate bees that burrow in mortarjoints as it is likely that a new mortar mix for repair will

Insects

145

need to be weak to be compatible with the wallingmaterial and the bees will simply begin boring into thenew material; similarly if holes in the masonry or brick-work are stopped the bees will bore elsewhere in thesame wall. The only solution seems to be to spray thewall with an insecticide (approved under the PesticideSafety Precautions Scheme). The safest and most satis-factory time to do this is late summer or autumn but if this is not possible the liquid may be injected intothe gallery entrances in the spring. The spraying mayhave to be repeated annually for a few years.

Sprays based on synthetic pyrethroids are said to besuitable, such as ‘Permethrin’, an insecticide made bythe Wellcome Foundation. The powder is dissolved inwater and sprayed on the wall. When dry it leaves aslight powder deposit but should not cause any dis-coloration, unlike a copper sulphate solution, anotherremedy which will tint the wall blue/green. (FromAdela Wright, SPAB News, Vol. 4, no: 1, January 1983.)

Tropical insects

In many parts of the tropics, termites are commonlythought to be the main insect enemy but, apart fromcostal areas, if a building has been properly designed,constructed and reasonably maintained, the greaterdamage is reported to be inflicted by wood-boringbeetles mentioned above. Furthermore, when certaintropical hardwoods are used structurally, or wheresapwood is included in the hardwoods used forjoinery and flooring, the risk of attack by powderpost beetles is more likely than by termites. Whereassoftwoods (both indigenous and exotic) may beattacked by the longhorn beetle Oemidagahanispp., powder post beetles of the families Lyctidaeand Bostrychidae attack seasoned hardwoods only,reducing the sapwood to a fine flour-like powder.Although the damage is limited to the sapwood, thebeetles may emerge through the adjacent hardwood.Most hardwoods containing starch are attacked andthose with large pores such as antiaris and iroko aremore liable to infestation. The attack is usually initi-ated in the timberyard and may be difficult to detectin the early stages.

In tropical conditions, the life cycle of theseinsects is completed very quickly. It is quite commonfor beetles to emerge and then reinfect the wood,causing serious structural damage to a buildingwithin a few years or less. Their presence is readilyrecognizable from the fine flour-like frass, along withround tunnels and holes of 1–5 mm (0.04–0.2 in) indiameter, depending on the beetle concerned.Through the agency of imported woods, many trop-ical pests have now to be combated in temperatezones, for example Lyctus africanus.

Termites

General

Termites are dangerous and voracious, and willattack wood, fibres or keratin materials and destroyalmost anything, including synthetic material, that isnot too hard, repellent or toxic. They have evenbeen reported as attacking electrical insulation andplastic water pipes buried underground. Remarkabledifferences exist between the 2000 species, whichshould be identified by entomologists. As many as50–100 species may co-exist in a tropical area;indeed 147 species have been found in Guatemala,whereas only one or two will be found in areas insouthern France, Italy and central Europe. They aresocial insects and live in colonies with hundreds orthousands of individuals divided into large groupsof workers and soldiers, which do not reproduce,and a few, often only a pair known as the king and queen, which are reproductive and populatethe colony. The queen lays as many as 4000 eggsin a day.

The species of termite that attack timber will befrom one of two main groups—ground termites anddrywood termites. Naturally resistant timbers tendto be gnawed by termites, but the soft non-resistantspecies may be completely hollowed out, exceptfor an outside skin of wood, by drywood termites.Ground termites like to eat the soft spring and summer growth, leaving the late wood half-eaten,so they tend to form galleries of concentric circlesaround the annual rings in the cross-sections ofwood, working along the grain and leaving thinpaper-like pieces of wood as divisions. Contrary topopular statements, no timber is immune to groundtermite attack, although the range of resistance of dif-ferent timbers is appreciable: exposed to conditionsof equal intensity of attack one timber may last lessthan five years and another over 100 years, with othertimbers having a service life falling between theseextremes. It has been found that the natural resist-ance of hardwoods decreases with age and after 100 or 200 years such tropical woods as jacaranda in Brazil lose this inherent resistance. Moreover,resistance to fungal decay is not necessarily an indi-cation of resistance to ground termite attack. Suchnatural decay-resistant timber as heartwood oak doesnot show up well if exposed to termite attack.

It is said that termites are distributed in the trop-ical and temperate zones of the world within anisotherm of annual average 10�C (50�F), but H. Moriand H. Arai of Japan have found them in Hokkaidowhere the annual average is 7�C (44.6�F).

The termites given in Table 10.2 are of import-ance to architectural conservationists.

Insects and other pests as causes of decay

146

Ground termites

Ground termites live in large colonies in the earth,depending upon a source of moisture or water andthe retention of an unbroken covered earthwayfrom the soil to their sources of food; and theseearthways or tubes are the most obvious signs ofinfestation. Ground termites do not make tunnels intimber; they tend to feed in restricted zones thatbecome packed with mud as the attack progresses.

147

Table 10.2 Some Important Wood-eating Termites

Family Genus Climate

Ground termitesRhinotermitidae Heterotermes Tropics

Reticulitermes Subtropical and temperate zones; northern hemisphereCoptotermes Tropical rainforestSchedorhinotermes Tropics

Termitidae Microcerotermes Tropical rainforestMacrotermesOdomtotermes TropicsMicrotermesMasutitermes Tropical rainforest

Drywood termitesMastotermitidae Mastotermes WarmKalotermitidae Incisitermes

CryptotermesHumid coastal areas

}

}

Figure 10.9 Typical termites(Courtesy: O.P. Agrawal)

(a) King(b) Queen(c) Worker(d) Soldier

Figure 10.10 Holy Shrine of Al Hussein, Kerbala, Iraq

Embedded wood has been attacked by termites. Other defectsshown are sulphate attack in cement rendering (now crackingoff) and ground salt crystallization due to transport by capillary action of rising damp

Excluding ‘damp wood’ termites which are notfound in buildings, two main types of ground-dwelling wood-eating termites are of concern andthese are differentiated by the way they digest the cellulose in the wood. Using a simplified classifica-tion, as there is in fact a great deal of variation in thefood habits of termites which is not yet fully under-stood, the two types may be distinguished as follows.The first cultivates a fungus comb which is continuallybreaking down and being renewed. The comb is asponge-like body made of chewed wood and built tofit the chambers of the nest. Each species has a char-acteristic type of fungus comb in its nest. The secondtype does not make a fungus comb and these speciesprobably have protozoa in their gut which digest cel-lulose. How some termites digest wood is unknown,as they have neither protozoa nor fungus comb.

Ground termites will die if denied access to theirunderground home, which has a controlled envi-ronment. The nest is typically about 600 mm (2 ft)in diameter, is made of extremely strong cementedfaeces and is almost watertight. With a moist warm

atmosphere there is virtual climate control. Inside,the nest has a large number of cells with a sponge-like appearance. The cell for the queen is in thecentre and is thick walled.

Control of ground termites

Effective control of ground termites is secured byproper design and construction of buildings with bar-riers provided not less than 200 mm (8 in) aboveground level in all walls. Such termite shields shouldbe of 0.46 mm (0.018 in) (26 s.w.g.) copper sheet act-ing also as a damp-proof course under severe tropi-cal conditions, and in less severe conditions 0.50 mm(0.020 in) (24 s.w.g.) galvanized steel, or zinc sheetnot less than 0.60 mm (0.024 in) may be used withthe conventional bitumen damp-proof course belowit. The shields, which must be continuous irrespectiveof changes in level, should extend outward 50 mm(2 in) and then downwards at an angle of 135� foranother 50 mm. Joints in the sheet material shouldbe double-locked and sealed by soldering or brazing.Any holes cut for anchorage bolts should be sealedwith a hot-poured pitch-based sealing compound.With solid floors it is necessary to provide an imper-vious floor all over the site. At least 150 mm (6 in) ofconcrete laid on a base unlikely to settle or crack andextending under all walls is recommended.

It is desirable to poison the whole area of the exca-vation and hardcore beneath the building and, usinga stronger dosage, fill trenches around the footingwith poisoned soil. It is advisable to seek the adviceof forest entomologists before deciding upon a poi-soning technique. Gaps must be sealed with poisonedmortar or a coal tar pitch-base sealing compound.Woody or other debris containing cellulose will attractground termites (and incidentally induce dry rot); careshould therefore be taken to ensure that none dropsinto foundation trenches or is left under subfloors.

Where these barriers cannot be provided, forexample with timber such as railway sleepers, fenceposts and poles placed in contact with the ground,the choice is between naturally resistant timbers andthe less resistant ones adequately treated with woodpreservatives.

In existing buildings a precaution against groundtermites is for foundations to be exposed and theearth poisoned as it is replaced. In the bottom ofthis trench and elsewhere, holes can be drilled at300 mm (12 in) centres and poisoned. Any soil atthe foot of the cross-walls should also be poisonedso as to prevent termites climbing up the walls. Soilpoisoning is only the first line of defence againstground termite attack and may become ineffectiveafter some years. The most commonly used soil

Insects and other pests as causes of decay

148

Figure 10.11 Holy Shrine of Al Hussein, Kerbala, Iraq

A termite track runs across brickwork in the minaret and penetrates a thick brick wall crossing a structural crack. Thetrail leads back to the ground some 20 m (66 ft) below.Insecticidal dust can be introduced to such tunnels

termiticide at the present time is probably chlor-pyrifos (an organophosphate). Pyrethroids, includ-ing permethrin and cypermethrin, are also used,but these tend to be more easily broken down inthe soil. A new compound, imidacloprid is usefulbecause it does not repel the termites like the otherpoisons. The insects may continue to forage whenthe compound is present, and the colony may becontrolled by slow attrition.

Baits have become popular for termite monitor-ing and control. These are slow acting compoundsthat are incorporated into a food material, andoffered to the termites in bait stations set to inter-cept the termites foraging trails. The baits may bedirect poisons, or some form of growth inhibitor,they are carried around the colony by the insectsnatural social behaviour.

Where termites are a threat, at least two rigorousinspections should be carried out each year, one atthe beginning and the other at the end of the rainyseason (it is interesting to note that colonialWilliamsburg, USA, has one man engaged full time intermite prevention). If damage due to ground termitesis found, their contact with the soil and moisture must

be cut off, all soil runways from bricks or other partsof the structure must be cleaned off and the subsoilpoisoned by drilling holes at 300 mm (12 in) intervalsand infiltrating appropriate chemicals. Any cracksand crevices in masonry, brickwork or concrete andpipe runs where termites might gain access should bepoisoned and sealed. Any untreated and unprotectedtimber which may temporarily join the building to theground and through which termites could gain accessmust be removed.

Drywood termites

Drywood termites, which are indigenous to Asia,South America and the Caribbean and have nowbecome established in certain coastal regions ofAfrica, live in small colonies feeding on seasonedwood. They require no access to the soil. Theyinvariably feed just below the surface of the wood,and in most timbers attack is more or less confinedto the sapwood; they produce granular dust, appre-ciably coarser than that of furniture beetles, whichshowers out when the sound skin of the wood left

Tropical insects

149

Figure 10.12 Precautions against subterranean termites

(a) Soil poisoned under foundations(b) Holes at 300 mm (12 in) poisoned(c) Hardcore poisoned(d) Poisoned backfill(e) Coal tar or poisoned mortar seal in crack(f) Metal termite shield protects 50 mm (2 in)

Figure 10.13 Chapel in monastery of San Francisco, Lima,Peru

Active termite attack in an altar piece. Cleaners should beinstructed to report such events to the architects in charge of thefabric

on the surface of an attacked piece of timber is bro-ken. The feeding termites also push out granular dustthrough their exit holes, the mounds of dust oftenbeing the only evidence of attack in progress,although their presence may also be indicated byheaps of excreta pellets, resembling small, light-coloured seeds, appearing below infested timber.Flight holes resemble those of some furniture beetles.

The name ‘white ant’ which is applied to dry-wood termites is not strictly correct since thesecreatures, although insects, are not closely relatedto ants. Many of their habits are, however, similarto those of ants proper, with whom they competeand are therefore in enmity.

Drywood termites are all known to have protozoain their gut as otherwise they cannot directly digestthe cellulose in wood. They live on seasoned woodand are therefore an important pest. They live incompletely self-contained colonies and only leavethe wood to swarm and form a new colony, soexternal evidence of their presence is only the smallhard pellets which they excrete. Their activities maycontinue unsuspected until the timber is virtuallydestroyed. The colonies are much smaller than theground termites, so the process of destruction isslower. The next colony is started when a reproduc-tive pair, on entering a building, lodge in a crack ora crevice in something made of wood.

Feeding habits of drywood termites

When taking measures for control of termites, aknowledge of their feeding habits is necessary. Theyhave systems of mutual feeding with saliva, withregurgitated partly digested food and with ejectedfaeces, which may be repeatedly eaten until there isno nutrition left. They also eat the cast skins and deadbodies of other members of the colony and sicklyindividuals may be killed and eaten by the soldiers.Because of these habits, contact poisons carried intothe colony by a few individuals are spread rapidlyand kill many more termites than the quantity war-rants. Poisons in the wood which kill the protozoaultimately cause the death by starvation of the ter-mites which rely on this system of digestion.

Control of drywood termites

Drywood termites can be more troublesome thanground termites because of the difficulties of controlof these air-borne pests. Precautions for renderingbuildings safe from ground termites are ineffectiveagainst drywood termites; indeed, no economicmethods exist to prevent drywood termite activity.

The pest cannot be positively eliminated frombuilding timbers and other indoor woodwork byscreening buildings with fine metal gauze which, ofcourse, is extremely expensive and usually imprac-tical. Still, reasonable precautions can be adoptedthat will minimize the risk of drywood termiteattack, with dependence on curative measureswhen attack occurs. Ordinary painting of woodensurfaces is recommended as an effective method ofdenying drywood termites entry into such timber,and where this is practical the course should beadopted, e.g. for joinery. Planing has been sug-gested, but this is not an economical measure forcarcassing timber. It seems probable that the totalexclusion of sapwood may appreciably delay dry-wood termite attack.

Finding evidence of drywood termite attack isdifficult, even though they can be heard gnawingtimbers at night. A thorough inspection by tappingthe wooden members to find hollows is one la-borious method of detection; another is to keep aclose look out for frass or pellets of faeces whenthey fall from an opening.

Fumigation is a useful method of eradication, butit involves covering a whole building with a tent, asis done in the USA and Japan. Sheets with an over-lap of at least 150 mm (6 in) are fastened togetherwith strong clips to form the tent, which is held tothe ground by long bags filled with sand. If neces-sary, sealing tapes are used.

Before tent fumigation, all food must be removedand pets and humans must be evacuated. Severalemission points are used so that the gas is evenlydistributed. The fumigant generally used must bestable. Sulphuric fluoride, being colourless, odour-less, almost insoluble in water and only slightly sol-uble in some organic solvents, is favoured. Itshould be introduced slowly at the rate of 0.5 kg(1.1 lb) per 28 m3 (1000 ft3) and left for 24 hours tokill the termites. Methyl bromide, sulphuryl fluorideand carbonyl sulphide are available as fumigants,although methyl bromide is unlikely to be availablefor much longer because of fears regarding theozone layer. Fumigation must be carried out byproperly trained men. After eradication of the ter-mites by fumigation, unpainted wood should bebrush-treated with preservative to reduce the risk ofreinfestation.

The extent of the structural damage caused bydrywood termites is apt to be misjudged; at firstsight it appears devastating, but closer inspectionusually reveals the destruction to be less severethan was thought. In furniture, panelling and high-class joinery, even a small amount of damage maybe serious because the appearance is spoiled, butin carcassing timbers it is necessary for the damage

Insects and other pests as causes of decay

150

to be sufficiently serious to weaken the structurebefore alarm need arise. In practice, drywood ter-mite attack is localized. Some wooden members maybe attacked while adjacent ones are quite free.Moreover, it is usually only parts of such membersthat are infested and then often only to a depth ofabout 13 mm (0.5 in). If the infested zone is removedand the remainder of the timber is liberally dressedwith an oil-solvent wood preservative or even avolatile toxic substance like orthodichlorobenzene,attack will often cease and the reduced member isusually strong enough to continue carrying the loadrequired of it.

Marine borers

Marine borers fall into two distinct groups: the mol-luscan borers Teredo, Bankia and Martesia, whichare related to oysters and clams, and crustaceanborers Limnoria and Sphaeroma, which are relatedto lobsters and crabs. They cannot live out of con-tact with sea water for more than a short time. Thelarva of the molluscan borer enters the wood bymaking a tiny hole on the outside and then tunnelsalong the grain, gradually enlarging these tunnelsas it grows and emerges. Crustacean borers workmore slowly, usually at the waterline, and destroythe timber from outside, the effect being as if thetimber were eroded.

Marine borers attack wood and no timber isimmune, although some naturally durable speciesoffer resistance for a time. The attack leads to rapiddestruction even of wood previously treated withpreservatives, unless the amount for protectionused is double that for fungi and termites.

Control of marine borers

One method of preventing marine borer attack is todry the wood for a few days each month; altern-atively, the regular application of creosote or copper–chrome–arsenic preservatives is recom-mended. For vacuum impregnation before timber isused, loadings should be high, about 350 kg/m3

(22 lb/ft3) of creosote or 24–35 kg/m3 (1.5–2.2 lb/ft3)of the salts of the above preservatives.

Inspections for insect decay

The non-specialist who lives close to and cares foran historic building should be instructed in the dif-ferences between fungal and insect attack and be

able to take samples of insects for specialist identi-fication. Several samples should be put into a smallbottle containing alcohol or methylated spirits andsent in a tin, to prevent breakage, to the architector other person responsible for regular inspectionsof the building. Samples of bore dust and typicaldamage are valuable aids to identification andshould be supplied.

The specialist, architect or surveyor should makea detailed inspection, using his knowledge of therelevant points in design and maintenance of build-ings, including drainage and damp-proof coursesand the need for ventilation. He should have a gen-eral knowledge of timber so as to distinguishbetween commoner types of hardwoods and soft-woods and be able to differentiate between sap-wood and heartwood. He must also know the habitsof wood-boring insects, as this helps him to seekout the most likely areas of infestation. Identificationof the different types of wood-boring insects andsome knowledge of other insects found in flightholes or in crevices in wood, such as clothes mothsor carpet beetles, which cause little or no damageto wood is an important part of his skill, whichincludes an assessment of the present state of activ-ity and the probable extent of damage and risk offurther spread of attack. He must propose remedialmeasures, the most appropriate method of pre-ventive treatment and structural repairs if these arenecessary.

Flight holes about 1 mm (0.04 in) in diameter inhardwoods may be due to Lyctus, Anobium orAmbrosia beetles which have a world-wide distri-bution. In tropical areas, the holes may be larger,even 2–3 mm (0.08–0.12 in). Lyctus is usually activein freshly seasoned hardwoods, whereas Anobiumattack is normally slight in buildings, at least in tem-perate climates, less than 10 years old.

In softwood, flight holes of similar size probablyindicate Anobium ernobius or Ambrosia beetles.Where difficulty is experienced in making accurateidentification, samples should be taken and spe-cialist advice sought.

Piles of bore dust (frass) and fresh clean-lookingflight exit holes are the usual symptoms of contin-ued activity. Live beetles may be found in the flightseason when they emerge to mate and lay eggs.Dead beetles, usually furniture beetles, are often tobe found under roof lights or windows and death-watch beetles drop on to the floor below theinfested timbers, so giving a valuable indication ofthe position and, by their numbers, the extent ofthe attack. The cleaning staff of any building shouldbe alerted to collect dead beetles, noting the placethey are found, and to report the occurrence of anyfrass. The presence of predators or adult parasites

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is also indicative of continuing wood-boring activ-ity. A beetle containing moist internal organs indi-cates that it has recently emerged.

In historic buildings, wood-boring activity maysometimes have ceased, thus rendering remedialtreatment redundant but giving the architect the dif-ficult task of assessing the strength of the remainingelements. It is unfortunate that both fungal andinsect attack occur frequently at structurally impor-tant points such as the ends of beams, where thewood may obtain moisture from the wall and beinsufficiently ventilated and softened by fungalattack, or in joints where crevices exist convenientfor egg laying.

Special attention should be given to wall plateswhere these lie under gutters which may be defectiveor flood occasionally. Lack of damp-proof coursesat ground level, and in parapet walls and underwindow sills, gives rise to conditions favourable tobeetle attack. Sapwood, which generally ages to alighter colour than heartwood, is always most sus-ceptible to beetle attack, so particular attentionshould be paid to the edges of boards and struc-tural timbers.

Attack by the furniture beetle, deathwatch beetleand wood-boring weevil is more likely to occurwhere the wood has been wetted or subjected todampness. In roof spaces, furniture beetle infestationmay be found round the water tank due to wettingby condensation and may also be found in thecommunication hatch, dormer windows and venti-lators for the same reason.

All wooden articles in storage, especially in roofswhere they may be forgotten for years and particu-larly if they are made of birch, plywood or wicker-wood, should be carefully examined before storageand treated with preservative, as they may intro-duce infestation into structural timbers. During aninspection they should be carefully examined.

A powerful easily aimed torch with a strongbeam is essential for inspecting buildings for beetleand fungus attack. With this aid, the freshness ofthe flight exit holes can be judged and by anglingthe beam acutely the slight blistering effect, whichis evidence of the house longhorn beetle, isrevealed. Tapping the timber with a penknife, orfor heavier members a light hammer, will indicatethe general condition. Badly affected timbers havea hollow sound or dull resonance, while sound timbers ring true. The penknife can also be used toprod into the timber and comparisons of penetrationfor the same force are indicative of condition. Thepenknife and a small artist’s paintbrush are of valuein extracting samples of frass from bore holes, anda magnifying glass should be carried to examinethis dust. Test tubes, previously filled with alcohol

and corked, should be taken for collecting beetlesor larvae for subsequent inspection in a labor-atory by an entomologist, but matchboxes filled with cottonwool can also be used as temporarysubstitutes.

Termiticides and insecticides

Commercial contact insecticides would include anorganophosphate (chlorpyrifos) and a range of pyre-throids (permethrin, cypermethrin, deltamethrin,etc.). Other organophosphate compounds (e.g. lin-dane) will be available in some parts of the world.Different countries have different restrictions so thatit is impractical to draw up a world list.

Some compounds with strong insecticidal prop-erties such as disodium octaborate tetrahydrate maybe sprayed onto infested timber and will kill theinsects if the treated wood is ingested. These chem-icals may also be used to pre-treat the timber, but(theoretically) they may fail if the chemical isleached out by contact with water.

Compounds, like creosote, that are not water sol-uble, may be more stable. There are, however,increasing concerns regarding health risks if theycome into skin contact.

The third class of pre-treatment formulations con-tain mixtures of metallic salts or oxides like cop-per–chromium–arsenic, or copper–chromium–boron.These mixtures are stabilized by forming chemicalcomplexes with the wood. Perceived problems arehealth risks from the chromium and the arsenic if the mixtures are not fixed properly, and the dis-posal of a hazardous waste when buildings aredemolished.

Chemical preservative treatment against insects

A preservative is a substance which is applied toprotect cultural property from attack by pests,whereas a pesticide is used to eradicate an activeattack by pests, some only having a very short life.The ideal pesticide does not exist, but a given product should meet as many of the followingrequirements as possible:

It should: (a) be cheap; (b) be safe to user, i.e. beof low toxicity rating; (c) be effective in killing insectadults, larvae and eggs; (d) be fast working and easyto apply; (e) be able to retain its killing power.

It should not: (a) leave or form dangerousresidues; (b) break down or lose its effectiveness instorage; (c) be absorbed by and build up in animal

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or plant tissue; (d) injure non-target animals orplants; (e) corrode or damage building materials orequipment.

For most people, protection by treatment meansthe economical preservative treatment of wood toprevent insect attack and fungal decay, but alsounder this heading should be considered soil poi-soning and the surface treatments such as paint,varnish and textured finishes which have alreadybeen mentioned. In addition to their decorativepurposes, these surface treatments play an import-ant part in protecting wood from both weather andinsect attack. Experience has shown that protectivetreatments are often used in the wrong place, withthe wood in an inappropriate state, or used in thewrong way. The wood must have a sufficiently lowmoisture content to receive the treatment and havea suitable pore structure to accept the vehicle forthe chemicals proposed.

Assessment of the possible treatment should bemade from both the technical and aesthetic pointsof view. An analysis of the proposed treatmentshould be obtained and attached to the documen-tation of the historic building; failing this, a sampleshould be kept.

The supplier or manufacturer of the protectivemedium should be asked the following questions:

(1) How long will the protective effects last andwill it be simple to renew or supplement thetreatment during the life of the building?

(2) Can the treatment be properly carried out iflocal resources of trained men and facilities arelimited?

(3) Is the treatment offered appropriate to thewood to be used and its probable moisturecontent at the time of treatment?

(4) Is the protective medium or the method ofapplication hazardous to man, animals or birdsand if so is there an acceptable alternative?

(5) Does the protective medium have a bad smelland if so how long will it persist?

(6) Will the treatment have damaging effects onother materials, e.g. paintings on wood, gessowork, electrical insulation or fixing nails of dif-ferent metals, e.g. copper or Duralumin?

(7) Will other materials or the environment have adamaging effect on the treatment?

(8) After using the treatment is it possible to applyother coatings, e.g. paint, without serious difficulty?

(9) May or should the protective medium becoloured and if so will the colour be fast (notethat the colour may be useful as a means ofchecking that treatment has been carried outand its depth of penetration)?

Martin Weaver points out that practically everypesticide is either toxic to man or can cause harm-ful effects. Toxicity tests are carried out in laborato-ries on animals such as rats and the lethal dose isrecorded, when 50% of a group die, as LD50 andexpressed in milligrams of chemical per kilogram ofanimal bodyweight. LD50 less than 50 mg/kg is verytoxic, 50–500 moderately toxic and 500–5000slightly toxic. Normal aspirin has a LD50 of 1375.Toxic poison may also be released on evaporationof the vehicle in which the pesticide or preservativeis dissolved, such as methanol or methylhydrate.

Most chemicals that are effective against termitesmust only be applied by licensed specialists. Thelocal medical officer can advise on municipal orprovincial and state legislation regarding use of pes-ticides, as can the Forestry Department or Ministryof Agriculture.

Application of insecticides

In historic buildings it is generally impossible or verydifficult to apply insecticides using vacuum or pres-surized techniques. Oil-based preservatives andinsecticides mostly need drywood for their applica-tion to be effective, and it must be remembered thatthe solvents used give off fumes which are toxic andmay be dangerous in high concentrations. These factors limit the effective application of insecticidesand preservatives. Among the practicable tech-niques, brushing may be assumed to have 2–4 mm(0.08–0.16 in) penetration. Emulsions are less liableto produce toxic hazards and fire risks. Infiltration,by drilling staggered holes and filling them until saturation is achieved along the grain, is effective insoftwoods but tests should be made for hardwoods.Impregnation at high pressure by guns fitted on toplastic nozzles is a pressurized type of infiltration butneeds smaller holes and has advantages.

Liquid insecticides are mostly organic solvent-type preparations containing contact insecticidesand stomach poisons. In addition to eradicantaction, these preparations give some protectionagainst reinfection. Emulsion-type paste insecti-cides show promise for treating large-dimensionedtimbers by virtue of the amount that can be appliedand their good penetrating powers.

Thoroughness of application is most important.First, all disintegrated wood must be cut away andall dust and dirt should be cleaned up with anindustrial vacuum cleaner. Cracks, splits and holesfor plumbing and electrical wiring should receivespecial attention. Low-pressure spray application,working up and down the timber and flooding thesurface with about 1 l to each 3–4 m2 (1 gal to each

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150–200 ft2) of surface area, is the most convenientmethod of treatment and is necessary where accessto timber is difficult, such as undersides of floors,ends of rafters and wall plates. Flight holes in largetimbers may be injected, or specially drilled holesmay be repeatedly flooded with preservative.Application by brush is an alternative to sprayingfor small areas; the liquid should be flowed onfreely, not rubbed in.

Brush applications of wood preservatives are notfully effective unless repeated at frequent intervals, intropical conditions as often as 6–12 months. Vacuumimpregnation processes are in a different category;with adequate absorption of suitable preservatives,wood can even be made to outlast its mechanical life.Where new timber is being prepared for buildingpurposes it must be soaked in preservative or givenrepeated brush coatings, each coat being appliedbefore the previous one is dry. No cutting or boringshould take place after treatment unless the exposedsurface is re-treated. Structural timbers already builtinto the structure should receive two or more flowingbrush coats, care being taken to soak the preservativeinto the end grain of beams or posts, since it is herethat the attack generally begins.

For timber in contact with the ground in tropicalconditions, the following preservative treatmentsare recommended:

(1) Pressure creosoting in accordance with BS913:1972.

(2) Pressure impregnation with a water-borne cop-per–chrome–arsenic preservative in accordancewith BS 4072:1966.

(3) Hot and cold open-tank process using creosoteor preservative, as described in FPRL TechnicalNote No. 42.

For timber protected from the weather and not inground contact an additional treatment is recom-mended:

(4) Timberizing diffusion impregnation of greentimber with disodium octaborate tetrahydrate,as described in FPRL Technical Note No. 41(this treatment is not considered effectiveagainst termites).

It is important for both vacuum pressure and hotand cold tank processes of timber impregnationthat the wood be at a moisture content of less than25%. Brushing or dipping with preservative is ofdoubtful value in the tropics, any protectionafforded being literally only skin deep.

There are toxic hazards in the application ofpreservatives that are poisonous to human beings,

and protective clothing must be worn. Goggles orvisors and dust or fume face-masks should be used,and respirators will be necessary if work is in con-fined spaces which cannot be ventilated properly.Hands must be washed before eating or smoking.Great care must be taken not to contaminate watertanks, as anything greater than 1 �g (106 g) perlitre of water may require the whole water systemto be replaced due to contamination, some waterauthorities even insisting on more stringent stand-ards. Naked lights and unprotected bulbs must beprohibited; the fire and explosion risk is reduced ifan emulsion-type preservative is used. There is arisk of staining plaster, and bitumen bonding maybe dissolved by the organic solvents in the insecti-cides. Aqueous solutions of preservative, whichmay cause damage by making the timber swell, areless desirable. It is always wise to test samples ofnew preservative solutions for their staining effectbefore use. Some preservatives damage plasticsused in electrical insulation or elsewhere.

Damage by animals and birds

The danger of pest-borne infection inside an his-toric building depends on three factors: its location,its use and its construction. Risks are high in foodstores, food preparation areas and restaurants;medium in farm buildings and buildings with mul-tiple occupancy such as flats, terraces, schools andinstitutions; and generally low where one owner isresponsible and careful with regard to hygiene andcare is taken to dispose of waste regularly and notlet it accumulate. Location close to docks or someother use liable to encourage pests, including farmbuildings and high density building, increases therisk, as does demolition and redevelopment.Unfortunately, the construction of historic buildingsoften enables pests to establish themselves. Prevent-ive measures must rely on controlling the internalenvironment. Mice can squeeze through holesabout 6 mm (0.24 in) in diameter when young andyoung rats through a hole of 9 mm (0.35 in). Miceare excellent climbers and rats can burrow todepths of 750 mm (30 in) and will dig long dis-tances horizontally, especially if the soil is loose,along the course of buried pipes or cables. Ratshave even been known to dive through intercept-ing traps and the water-seal of a W.C. pan. Pigeonscan be kept out by reducing gaps to 40 mm (1.6 in)and for sparrows to 20 mm (0.8 in). Generally, allglazing must be kept in good order to preventingress and detailing construction of roofs, close fitting external windows and doors, sealing round pipes and ducts with compartmentation and

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trunking of services should be given priority. Self-closers for doors and metal sheathing at the base ofdoors may also be considered.

Animals, including man, can damage buildings byurinating and defecating. Dogs can cause the decayof brickwork at street level and cats are said to dam-age zinc roofing or galvanized surfaces. Rats causedamage by building nests, which provide a likelyspot for the start of a fire, and by gnawing at electricwires, for which they have a strange predilection.Old-fashioned ‘combined’ rainwater and soil systemsgive rats many opportunities for climbing upuntrapped rainwater pipes and entering a roof spacevia a gutter. Their entry is best prevented by trappedgullies, balloons over vent pipes and properly pro-tected air bricks. In Ghana, mice are serious agentsof destruction in houses built of unbaked earth.

Birds, in particular pigeons and to a lesser extentstarlings and jackdaws, can damage and disfigurebuildings. Their droppings can block roof rainwateroutlets and can cause grass and other vegetation togrow in gutters and in re-entrants on sloping roofs,and the bodies of dead pigeons frequently blockdrain outlets and downpipes. Jackdaws andpigeons like nesting in stairs and turrets of historicbuildings, and it is necessary to wage constant warfare to keep them out.

As the excrement of birds, bats and insects isboth alkaline and acid, it promotes decay of thesurface, particularly of stained glass and wall paint-ings from which the dark deposits are difficult toremove. If birds win entry they build up so muchmess and rubbish that it is a major task to get rid ofit—and so unpleasant that workmen have refusedto tackle the job owing to the lice and filth thathave to be faced. The dirt birds introduce leads toinfestation by beetles, particularly the longhornbeetle.

Roosting and nesting birds can be prevented bynetting or spikes; sticky bird repellents can beapplied to masonry, but there is a danger of stainingthe stone. High-voltage wires have been tried butthese are difficult to maintain in practice, for whena sitting bird receives a shock it rises and instinc-tively defecates, often on to the wires, thus tendingto create a short-circuit, so that the device itself isfound to need too much maintenance. A simplermethod which often works is the fixing of blacknylon thread about 25 mm (1 in) above sills andlanding edges. Glass sheets fixed above cornicesare also reported to be effective.

Prevention of damage by animals and birdsneeds vigilance and routines of regular inspection ifit is to be effective.

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Introduction

Man-made causes of decay are complicated andhave widespread implications in the conservation ofhistoric buildings. So little has been done to preventthis type of decay that the present chapter can pro-vide few answers to the questions it raises, becausethe problems are immense, involving economicsand industrialization. What can be said is that unlessthe causes of decay of cultural property are properlyanalysed and the effects of each harmful agent tosome extent quantified, there is a danger that thewrong priorities will be applied to protective meas-ures. Much more measurement and evaluation ofthe effect of man-made causes of decay is needed.To obtain an approximate measure, comparativestudies should be made of the rates of decay in dif-ferent environments. The American practice of hav-ing Environmental Impact Statements is a step in theright direction. If decay were measured on signifi-cant buildings internationally, we could use them aslaboratories of experience.

Industrial production, together with electricitygeneration, is the main cause of atmospheric pollu-tion as well as the heavy traffic that causes vibra-tion damage. However, several major industriesalready have conservation officers and are able toconsider the effects of their proposals at the planningstage instead of bearing the cost of correcting mis-takes at a later date. The American EnvironmentalProtection Agency has helped in the development ofthis responsible trend, and it is hoped that in futureevery industry will have conservation advice avail-able to top management.

Damage by vibration

In dealing with the effects of vibration on historicbuildings, it is apparent that little research has been

11

Man-made causes of decay

Figure 11.1 Bankside Power Station from St Paul’sCathedral, London, England(Courtesy: Feilden & Mawson)

Electricity generating stations produce about one-quarter of theatmospheric pollution in Britain. Bankside Power Station, builtshortly after World War II, has undoubtedly caused damage toSt Paul’s Cathedral and should never have been sited so close toa national monument. Expensive plant was installed to reducethe emissions of sulphur dioxide and it was claimed that 98%had been eliminated. The post-Wren statuary by Thomas Bird(fl. 1710) in the foreground has suffered severe damage andshould be moved inside before it becomes meaningless. Banksidehas now been converted into the Tate Modern Gallery – a goodexample of adaptive reuse

done and practically none of it has been financedby those interested in historic buildings. Noise andacoustic consultants are oriented towards the prob-lems of new buildings rather than to existing ones,to the prevention of damage by initial design, ratherthan the limitation of damage by restricting thecauses. Further, it is very difficult to measure vibra-tion, which, although small, may be sufficient tocause long-term damage in an historic building inpoor condition. Such a programme would requireintensive instrumentation to cover all the permuta-tions of a massive indeterminate structure, and nosuch programme has yet been financed or initiated.Positive proof of damage resulting from a given inci-dent is almost impossible to obtain, as it is very dif-ficult to distinguish between damage from vibrationand the inevitable aging of a building. In the event,vibration pollution probably accelerates the agingprocess in proportion to its intensity. It is wise toremember that damage caused by vibration is gen-erally irreversible and in practical terms irreparable.

It is extremely difficult to get any certain proof ofwhat damage may or may not have occurred due to

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vibration. Ground-transmitted traffic vibration, par-ticularly that from heavy diesel vehicles, is becom-ing more regarded as a serious problem, althoughboth the airborne and ground-transmitted energyinputs are small. Damage from pile-driving vibra-tion is certainly common.

The practical difficulties of measurement to therequired high degrees of accuracy over a suffi-ciently long period are very considerable, takinginto account variable weather and temperaturechanges due to the annual cycle of seasons.Standards of permissible vibration input have beenprepared which specify for well-built new buildingshow much input can be received without notice-able damage occurring. To allow for the conditionsof historic buildings, the German DIN standardshave reduced the permissible input to one-fifth ofthat allowed for modern buildings. These stand-ards, it should be remembered, are aimed only atshort-term identifiable damage, and ignore thelong-term cumulative effect of vibration; the authortherefore believes that the permissible input shouldbe reduced to one-hundredth for historic buildings.

Whereas the threat of vibration from supersoniccommercial aircraft may not materialize, vibrationcaused by heavy vehicles is very much a fact and amatter for immediate public concern. A vehicle trav-elling along a road generates vibrations in adjacentbuildings in two ways. First, the variations in thecontact forces between the wheels of the vehicle andthe road surface generate oscillatory stress waves inthe road structure which are transmitted through theground to adjacent buildings. These stresses increasein proportion to the cube of the axle weight of thevehicle, so a 10 t (9.8 ton) axle load is one thousandtimes more damaging than a 1 t (0.98 ton) axle load.Secondly, pressure waves arising from the size,shape and speed of the vehicle, much like a bowwave, are transmitted directly through the air,together with pressure fluctuations mainly due to theengine exhaust, and the other mechanical noisesproduced by the vehicle. A noise of 100 dB gives anequivalent pressure of 2 N/m2 (0.00029 lbf/in2). Thevehicle’s wheel-suspension system, the dynamic axleloads and the stiffness of the chassis are all import-ant factors in inducing vibrations. As axle loads areincreasing in magnitude and heavy vehicles are notusing greater numbers of axles, vibration problemsare now becoming more widespread. In time, thecumulative effect of the damage they are causingwill become more apparent.

In the short term, lath and plaster ceilings are par-ticularly vulnerable to vibration. The key to the plas-ter and the condition of the lath should be carefullyexamined before any exposure to exceptional vibra-tion such as piling. Wall panelling is also vulnerable as

Figure 11.2 St Paul’s Cathedral, London, England, southportico

Cracking and splitting of the masonry is caused by the compaction of the rubber core due to vibration throwinggreater loads on the outer casing of ashlar. A traffic countshowed sufficient vehicle units to halve the life of St Paul’sCathedral. The City of London co-operated by keeping the roadsurface smooth and now heavy vehicles have been banned, animportant factor in preventive conservation

loose material may wedge behind the panelling andforce it outwards. In Rome, valuable frescoes havebecome detached from walls due to traffic vibra-tion. Vibrations may well initiate cracks in materialsalready subjected to temperature and humiditychanges and settlements, and it is suspected theycontribute to the fatigue of building materials. Inextreme cases, instantaneous damage might beinflicted on fragile glass, loose plaster mosaics orpieces of stone, as well as insecurely attached fea-tures such as memorial plaques.

It is known that vibration can cause loss of foun-dation strength by affecting the subsoil. In somenoncohesive soils, such as sands, the long-termeffect of vibrations is to increase the soil density bycausing compaction. In some cohesive soils, suchas silts, the effect can be destructive in terms ofbearing capacity, and may even reduce load-bear-ing silt to a fluid. Therefore the problem is two-fold:first, possible loss of foundation strength; secondly,loss of structural strength in the superstructure. The architect must consult an expert if there is suf-ficient circumstantial evidence to make investiga-tion in depth worth while, but must warn theowner of the building that such investigation

involves sophisticated instrumentation and will prob-ably be a long and expensive operation.

Measuring vibrations

The academic scientific approach to the problem ofvibration pollution is that if you are going to bancauses of vibration that may damage historic build-ings, such as traffic, piling or the sonic boom, youmust state the level or amplitude of vibration thatshould not be exceeded. This might be done byextrapolating data from long-term fatigue tests, thefatigue concept being based upon possible reson-ances in the individual structural members of thebuilding when the waveform of the disturbingvibration contains these resonant frequencies. Thisapproach was adopted by the Royal AircraftEstablishment at Farnborough, England, in itsattempt to assess the damage that the supersonicaircraft Concorde might cause to historic buildings.The attempt was praiseworthy but did not take intoaccount sufficiently the nature of historic buildings,in that they are of such great variety of constructionand condition as to defy, for practical purposes,purely scientific analysis. If such an analysis werepossible, it would probably cost unreasonably largesums of money.

Vibration from road vehicles

Studies to date have been mainly concentrated onthe vibrations generated by vehicle wheels actingon the road surface. Irregularities in the road sur-face of about 20 mm (0.8 in) in amplitude can causepeak particle velocities in the ground of 5 mm/s(0.2 in/sec). At this level it is assessed that minor,so-called ‘architectural’, damage may occur inhouses of normal construction, but at half this level,i.e. 2.5 mm/s (0.1 in/sec), it is reported that vibra-tions become intrusive and annoying to the occu-pants. The frequencies of these annoying vibrationslie within the range 1–45 Hz, those above 15 Hzbeing audible but those below that figure alsobeing capable of inflicting damage.

An English expert has written that there is agree-ment between German researchers, upon whosework the British Research Establishment’s work isbased, and Hungarian researchers, that no damageof any kind should occur to structures in a reasonablygood state of repair at velocities below 2.5 mm/s(0.1 in/sec) applied to the foundations of the struc-ture. This level lies in the upper limit of the easilynoticeable classification in the Reiher Meister Scaleof Human Perception.

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Figure 11.3 St Paul’s Cathedral, London, England,column in south portico

The compaction and uneven settlement induced by heavy traffic caused this column shaft to split near the base

The Institute of Building Materials and Structurein Holland suggests a velocity limit of �2 mm/s(0.08 in/sec) for the onset of plaster cracking and �5 mm/s (0.2 in/sec) for structural damage, whilethe German DIN 4150 proposes a limit of 10 mm/s(0.4 in/sec) for residential buildings in good condi-tion and 2 mm/s (0.08 in/sec) for historic buildings—a factor of only 5 in favour of historic buildings.

It must be emphasized, however, that these fig-ures are for buildings of normal and sound con-struction and do not take into account long-termeffects of fatigue and accelerated aging. If a struc-ture is highly stressed for any reason, e.g. settle-ment, shrinkage, thermal stresses, these limitscannot be applied directly but may be used as theeventual reference point which is necessary for anyassessment of the problem to be made.

Studies of the effects of vibration on new build-ings were reported in 1971 by L. Kapsa of theResearch Institute for Building and Architecture ofCzechoslovakia. Extensive field tests were carriedout and tables were produced giving the reductionof expected life in well-constructed dwellings sub-jected to various traffic densities. Traffic densitieswere measured by the number of vehicles per hour,vehicles of over 5 t (4.9 ton) each counting as 1 unitand lighter goods vehicles as 0.4 unit. Trams ontracks with poor foundation (i.e. rails with sleepersonly) count as 1.5 unit. Table 11.1 is set out with a‘decrease-of-life’ factor which for certain favourablecriteria is reduced; for example, by one for a bitu-minous road surface, by two if the buildings are ofnew brick, by three for a concrete road surface andby four for a steel- or concrete-framed structure.

Certain layout criteria increase the decrease-of-life factor: if the buildings have a footpath less than1.5 m (5 ft) wide or if the frontage interval is greaterthan 8 m (26 ft), there is an increase of one; if thetraffic speed is more than 20 km/h (12.5 m.p.h.) andif there is no footpath, there is an increase of two. The

above criteria are added or subtracted from thedecrease-of-life factors given in Table 11.1 for traffic.

The above summary of the effects of vibration ishighly simplified but at least enough work has beendone to prove that traffic vibration reduces the lifeof well-built modern houses. Although the resultsgiven here are not directly applicable to historicbuildings, they clearly suggest that there is a seriousrisk of reducing the life of such buildings throughsubjecting them to severe traffic vibration. Whenapplied to St Paul’s Cathedral, these figures gave alife reduction of over 50% before the City ofLondon banned heavy traffic. In practice, the main-tenance of a smooth road surface, as well as areduction of axle loads, is of great importance inalleviating the effects of traffic vibration.

M.E. House of the Wolfson Unit for Noise andVibration Control, at the Institute of Sound andVibration Research, Southampton University,England, has listed several areas where further inves-tigation is required with regard to traffic vibration:

(1) A statistical survey of the road force inputs for avariety of locations, road construction and states of

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Figure 11.4 St Paul’sCathedral, London, England,base of south-west tower

The internal condition of themasonry can be judged fromthis core sample. The outer ashlar is backed by rubble setin lime mortar which has broken up and become severelyfissured. Traffic vibrationcauses and accelerates this typeof internal decay, which canonly be rectified by groutingwith epoxy resins

Table 11.1 Life Reduction of Houses due to Traffic

Vehicle flow units Decrease-of-life Life reduction (per 24 hours) factor (%)

up to 260 1 0260–600 2 4.0600–960 3 7.5960–1540 4 10.0

1540–2660 5 15.02660–3440 6 20.03440–4660 7 25.04660–7440 8 35.07440 and above 9 50.0

repair would enable better forecasts to be made of long-term exposure of buildings to vibration.

(2) The propagation of waves (in particularRayleigh waves) in a range of soils and sub-strata commonly encountered needs to be stud-ied, with particular reference to frequencydispersion and damping.

(3) Much more experimental work is needed todetermine the relationships between stresses inbuilding elements and controlled ground inputswith known frequency distribution.

(4) Studies of age susceptibility would be valuablein buildings of similar construction, some ofwhich have been subjected to higher than nor-mal vibration levels over a long period andwhose vibration history can be estimated withsome reliability (e.g. near railway lines).

(5) It would be helpful to have tests on typicalbuilding elements to relate ‘failure’ stresses inrelevant principal modes of vibration to com-monly measured vibration parameters.

Vibration from pile driving

Vibration damage from pile driving may be themost common cause and source of danger to anhistoric building, particularly if it has poor founda-tions, cracked walls and spreading roofs. Boredpiles generally give rise to very little trouble, drivenpiles may cause some damage, dependent on sub-soil conditions, whereas piles with expanded insitu bulb bases are particularly liable to cause dam-age. Ground shock waves from the latter are unpre-dictable in their action, but can be strong enoughto crack 300 mm (12 in) of reinforced concrete.

An example is the church of St John, at Ousegatein York, England, which was in poor condition andrested upon an almost fluid river silt. When conven-tional driven piling was used for a new building nextdoor, it was soon apparent that damage was beingcaused to the church. The floor heaved, cracks wereopened and closed, and plaster was loosened anddamaged by cracking. Complaints were made, andinjunctions were threatened but could not be pressedhome. A payment for the identifiable damage wasnegotiated, but concealed damage had undoubtedlyoccurred which might take years to be revealed in itsfull extent and could never be put right, nor couldthe real cost be quantified and claimed.

The argument might be advanced that rebuildingof city centre sites is a thing that must be anticipatedand an historic building must in the nature of thingsexpect this treatment. It was clear, however, that inthe case of St John’s, Ousegate, the wrong sort of pilehad been specified. Soon afterwards, a nearby site

was developed with another large building and thearchitect in charge of St John’s, being forewarned,immediately wrote warning the developer’s archi-tects of the dangers to the church fabric. A meetingwas arranged, rotary bored piles were agreed upon,and no difficulties or vibrations were experiencedunder exactly the same subsoil conditions. Thisexample shows that prior negotiation is desirable,and that reasonable requests for a choice of pilethat will not cause vibration should be met.

To protect historic buildings against damage frompiling, recognized good practice should be for a‘stop clause’ to be written into all piling subcon-tracts for all adjacent historic buildings. If this isdone, the piling may be stopped immediately with-out incurrence of extra costs due to disturbance ofthe building contract; so that when a genuine com-plaint is made by the owner of the historic build-ing, it can be met. As the cost of the delay will fallon the piling contractors the very existence of this‘stop clause’ will make him more careful whenadvising on the choice of a pile, which, taking sub-soil conditions into account, would not cause vibra-tion damage to adjacent buildings.

The emphasis should be on prevention ratherthan cure of damage, for the cure is costly, doubt-ful and frequently impossible. Local authorities withtheir role of protecting the public interest couldinsert an appropriate clause in any planningapproval to give nearby historic buildings adequateprotection. Precedents for this type of protectionexist in the St Paul’s Preservation Act drawn up inLondon in 1935. The criteria for the decision canonly be determined by qualified professional judge-ment, unhampered by commercial pressures.

Methods of protecting historic buildings from vibration

One method of protecting historic buildings fromground-borne vibrations has been suggested by theBuilding Research Establishment, England, in theirpublications; this is the insertion of vertical curtains ofthixotropic grout in trenches to insulate the founda-tions of the building from vibration. The trench, how-ever, would have to be at least equal in depth toone-third of the wavelength of the vibration con-cerned, and for low frequencies, dependent on thevelocity of the wave propagation in the soil, thisdepth could easily exceed 5 m (16 ft). Before pro-posing such methods of insulation it would, ofcourse, be necessary to carry out a thorough siteinvestigation using soil mechanics techniques. Such asolution might be applied to the Colosseum in Rome,which at the time of writing is the centre of a large

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traffic roundabout and has been partially closed tothe public on grounds of safety because pieces ofstone are reported to have fallen from it.

The frescoes in the Villa Farnesina in Rome havebeen successfully protected from vehicle vibrationdamage by mounting the heavily trafficked roadoutside upon absorbent rubber pads.

The removal of the source of vibration is ofcourse the best policy, as in industrial plants wherethe vibration is eliminated by proper mountingsand insulating pads. In the case of traffic, townplanning measures should be initiated to removetraffic from areas where there are important or largenumbers of historic buildings. At the very least,road surfaces near historic buildings should becarefully maintained, heavy vehicles banned andvehicle speeds restricted.

Because historic buildings were built long beforethe increase in the vibration environment, whetherairborne or earth-transmitted, the onus of proofshould be on the people whose project might causevibration damage to show that this is not the case,taking full account of the fact that an historic build-ing is old, probably decrepit and full of latentdefects. This is not just a debating point, as the factsare that vibration damage is irreversible and gener-ally incapable of repair, except by rebuilding. Inpractical terms or for insurance purposes it is virtu-ally impossible to assess the quantum of the dam-age resulting from a known incident, e.g. aseismographic survey for oil using explosivecharges, let alone an unknown or unidentifiableincident, such as a passing supersonic plane trailinga sonic bang in a path 80 km (50 mile) wide.

It is impossible for the owner of an historic build-ing to maintain a constant vibration watch and inspecthis charge each time a suspected incident occurs—thecost would be phenomenal, the results at most impos-sible to prove and the culprits unidentifiable. When a severe vibration incident damages an historic

building, it may be likened to someone scratchingthe surface of an ‘old master’. There is no realrepair—it will never be the same. Because positiveproof is unobtainable, it is therefore essential thatlocal and central government should be persuadedto act in a civilized way and take steps to protecthistoric buildings from traffic vibration.

Water abstraction

As with pollution and vibration, water abstractioncan have macro- as well as micro-effects. At themacro level, water abstraction for industrial purposeshas caused Venice to sink and thus become morevulnerable to damaging sea floods. London has alsosunk about 200 mm (8 in) because of underdrainage;the flood wall along the tidal Thames Embankmenthas had to be raised to meet the threat of floodingcaused by high tides and a barrage has been built.The long-term effects of water abstraction have notyet been fully studied, but it appears that large,heavy buildings may sink relatively more than lightstructures, and if such buildings have differentialloadings on their foundations, differential settle-ments may well be induced.

Both St Paul’s Cathedral and York Minster stand onperched water tables which are liable to have theirlevels changed unless carefully controlled. In bothcases, regular measurements are maintained. The St Paul’s Preservation Act gives authority to protectthe perched water level by control over the design ofunderground works within a rather small ‘prescribed’area. Studies show that the cathedral would be par-ticularly vulnerable to a rapid change in the watertable. In the case of York Minster, cracking and down-ward movement of the main piers coincided more orless with a lowering of the perched water table,which might also have upset the load-bearing capac-ity of overstressed clay soil. Milan Cathedral sufferedseverely from ground-water abstraction and has hadmajor repairs to cracked piers and superstructure dueto differential settlements of about 25 mm (1 in) in itslength and 9 mm (0.35 in) in its width.

The invention of the Newcomen pumping enginein 1746 enabled mining technology to be devel-oped, with consequential enlargement of its scopeand increase in underground water abstraction; atthe same time, the area of mining subsidence wasgreatly enlarged. Such subsidence is likely to affecthistoric buildings, particularly large long ones.

Alteration of the water table has several possibleeffects, depending upon the characteristics of theload-bearing soil and the building. First, as thewater table is lowered the surcharge on the subsoilis altered. Secondly, the load-bearing characteristics

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Figure 11.5 A thixotropic curtain

of the soil itself may change, and both will cause dif-ferential movements. In addition, if a building is setupon wooden piles the lowering of the water tablemay expose these and cause them to rot. Many build-ings constructed on piles in mining areas such as theRuhr have suffered in this way. In flat waterloggedareas, the changes in underdrainage due to miningare liable to be extremely difficult to deal with.

Soft-ground tunnelling, being liable to upset thewater table, may therefore be of vital interest to theowners of historic buildings with shallow foundations.Such tunnelling is likely to increase in towns and citiesin the future, particularly for large-diameter sewersand underground railways. Sewers, in particular, mayhave only a small surface cover and may have to bedriven between the piles supporting buildings above.

Some new building works may raise under-ground water table levels. For instance, if solidfoundation walls are constructed to such a depthand in such a position that they dam an under-ground water flow, this would cause lowering ofthe water table down-stream and raising of levelsupstream, with resulting difficulties in disposal ofwater to soakaways and increase of rising damp. Asthere is in general no legal protection of groundwater under a building, the matter should bewatched carefully if new buildings, sewerage orroadworks are proposed in the vicinity of an his-toric building. Underground water levels can alsobe affected locally by the bursting or leakage ofsewers and drains and defective rainwater pipes. Itis therefore of importance to record ground-waterlevels near historic buildings. The instrumentdesigned for this purpose is a piezometer.

The flooding of the Holy Shrines in Kerbala, Iraq,was caused by the raising of the water table throughthe modernization of the sanitation arrangements byan introduction of water-borne drainage to soak-aways. Unfortunately, the town lies in a depression,so the water table came up. In the case of the HolyShrine of Al Abbas, a ring main was installed roundthe shrine and pumping instituted, but this was toovigorous and abstracted silt from under the founda-tions causing the four corners of the building to sub-side and the brickwork to crack. There are twopossible cures: first, provision of a thixotropic curtain

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Figure 11.6 Mavis Bank,Midlothian, Scotland

Mining subsidence causedthese severe settlements whichled to the house being abandoned, so making it vulnerable to vandalism andfinally fire. Yet it is notbeyond redemption

Figure 11.7 Mavis Bank, Midlothian, Scotland

A detail of damage caused by mining subsidence, neglect and fire

to isolate the shrine, although this depends on findingan impervious layer of soil; secondly, installation ofsewers to drain and remove the cause of the watertable level being so uncomfortably high. Mohendjaro,in Pakistan, is also threatened by a major rise in thewater table caused by improved irrigation, and thismay be one of the causes of the recent increase in thelevel of the water table under the historic city of Cairo.

Atmospheric pollution

Atmospheric pollution is the by-product of indus-trial and commercial activities, heating and traffic.The effects of industrial pollution are international;it is believed, for instance, that British aerial efflu-ents affect the whole of Scandinavia.

The most meaningful statistic is the amount ofSO2 produced per person. East European countriesare the worst offenders as their controls are floutedby industry, however there is considerable room forimprovement in the UK. The Chernobyl disaster in1987 introduced a new dimension of pollution byatomic radiation which spread into Lapland andwestern areas of UK rendering meat from livestockgrazing on contaminated vegetation a severe healthhazard. Pollution control is an important factor inpreventing damage to our cultural heritage.

The reduction of such effluent is an expensivematter, and its control should be international sothat consistent standards are applied world wide.The greatest part of the pollution of the atmospherearises from the burning of fuel in boilers, furnaces,

domestic fires and in internal combustion engines.There are three normal categories of pollutant; first,particulates, grit and dust, emitted mostly from indus-trial chimneys; secondly, smoke or finely dividedsolids, which coagulate to form soot; thirdly, gases,the two most important of these being carbon dioxide(CO2) and sulphur dioxide (SO2).

In zones polluted by industry, which in effectinclude much of North America, Europe and Japan,rain is more strongly acid than natural rain which hasa pH value of 5.6 due to dissolved carbon dioxide.Town rain may be as acid as pH 4 and is often pH4.6. The acid strength of pH 4 is 25 times greaterthan pH 5.6, because sulphuric acid, although inmuch lower concentration, is very much more pow-erful than dissolved carbon dioxide.

Pollution is worse in anticyclonic weather whenthere are clear skies and low winds. A temperatureinversion can aggravate the situation seriously,when the usual condition of the air getting coolerwith height is upset by warm air acting as a lid andpreventing the pollutant gases from rising and dis-persing, so that their concentration rises.

Measuring pollution

Pollutants are measured in micrograms (millionths ofa gram) per cubic metre of air, which is abbreviatedas �g/m3. To convert �g/m3 to parts per million themolecular weight of the gas must be known.

It has been observed that the rain washed partsof alkaline stone, i.e. limestone and marbles and

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Figure 11.8 St Paul’sCathedral, London, England (Courtesy: Feilden &Mawson)

A good example of the build-up of soot that occurredon London’s architecturalheritage before the Clean AirAct. This type of pollution is apiece of social history relatingto the pea-soup fogs ofVictorian London, but itseffect was to damage the fabric and distort its architectural values

some sandstones, are the worst affected since thesulphate formed is continually washed away expos-ing a fresh surface to attack; and that sheltered partsare protected to a much greater extent, but black-ened with a coating of soot and sulphate. OnSt Paul’s, London, the whole surface is attacked bysulphates to a depth of about 3 mm (0.12 in). Afterrain, the gutters show how much decomposed stonehas been washed away. The extreme pollution hasincreased the corrosive attack on the embedded ironcramps, so causing further damage to the stone.

Portland stone is noted for its resistance to pollu-tion, yet at St Paul’s, erosion on exposed parapetsand copings was about 30 mm (1.2 in) in 250 years ascompared with 7–10 mm (0.3–0.4 in) of less resistantstone on provincial cathedrals. The maximum ero-sion noted was about 22 mm (0.9 in) in 45 years onthe sculptured vases of the south portico gates.Examination of decay shows that the greatest effectoccurs on cold, damp misty days when full officeheating supplements the normal industrial emissions.Levels of pollution occur well above average on suchdays, while in contrast, when there is a fresh windwith rain, the SO2 is either blown away or diluted.

In Britain smoke emission fell remarkablybetween 1951 and 1968, in spite of a 10% increasein population and 17% increase in annual grossenergy consumption, and a continuing downwardtrend is forecast. It is clear that smoke emission ishighest where domestic coal consumption is high-est, for at least 85% of smoke appears to arise fromdomestic open fires burning coal. It follows thatthe modernization of domestic heating should bepressed forward energetically, especially in thenorth of England, where smoke and sulphur dioxideare still at high levels.

The Clean Air Act 1956 was one of Britain’s firstmeasures against atmospheric pollution. It has hadbeneficial effects in reducing grit, soot and gaseouspollution at ground level by making the use ofsmokeless fuel obligatory in certain zones, by con-trolling the emission of black smoke and by insistingthat new chimneys be of greater height so as to dis-perse the products of combustion over a wider area.The Act does not have any jurisdiction over the emis-sion of sulphur dioxide. Prior to the Act, soot depositsbuilt up to a great thickness, indeed as much as 125 mm (5 in) was recorded on Saint Paul’s Cathedral.The success of the Act means that it is now worth-while to clean the exterior of buildings in urban cen-tres. It has been pointed out that when smoke hasbeen removed from the air more of the sun’s heatreaches the surface of the earth to warm it up withrespect to the air and so sets up turbulence, which bypreventing stagnation of the air, prevents the buildingup of high concentrations of pollutants.

Wet and dry deposition of pollutants in buildings

Clifford Price, formerly of English Heritage, inIndustrial Co-operation in the Study of PollutionEffects (1989), writes:

‘Gaseous pollutants can find their way on to asurface of a building by two main routes; by

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Figure 11.9 The acidity of rain falling in the USA in 1966

pH 7 is neutral, while below this figure rain is acid. One digitdown on this scale represents a ten-fold increase in acidity;thus pH 4 is 10 times as acid as pH 5 and 100 times more acidthan pH 6. Damage to limestone masonry also increases withascending intensity according to the amount of pollution

Figure 11.10 St Paul’s Cathedral, London, England,parapets(Courtesy: Feilden & Mawson)

Originally the joints were filled with lead but severe erosion hasworn the stone away leaving the joints standing proud about25–30 mm (1–1.2 in) after 250 years of severe exposure

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Figure 11.11 St Paul’s Cathedral, London, England,cornices(Courtesy: Feilden & Mawson)

The projecting cornices protect the ashlar walls, but acid-ladenrain finds out any weakness of detail, especially where conden-sation and rain water drips. The projecting cyma recta topmoulding and fascia is badly eroded and grooved by rain water

Figure 11.12 St Paul’s Cathedral, London, England, detailof middle cornice(Courtesy: Feilden & Mawson)

The top moulding shows how the rain water has collected andrun down the fascia forming deep grooves about 30 mm (1.2 in)deep. The surface of the stone has also been destroyed by sulphate attack to a depth of at least 5 mm (0.2 in). The totalerosion may be of the order of 50 mm (2 in)

dissolving in the rain that falls on to the building,or by reacting directly with the building itself.The first route is known as “wet deposition”,and the second as “dry deposition”. (The term“dry deposition” can be misleading, forpollutants will not react with a completely drysurface.) The distinction between wet and drydeposition is important. Wet deposition takesplace when it is raining or snowing, whereas drydeposition takes place almost continuously. Wetdeposition brings in pollutants from high up inthe atmosphere (and so from distant sources),whereas dry deposition brings in pollutants fromlocal sources as well. Theoretical calculationssuggest that dry deposition accounts for much ofthe calcium sulphate (see below) that is foundin sheltered limestone surfaces in polluted urbanenvironments, though this does not necessarilymean that dry deposition is the dominant meansof decay.‘Since calcium carbonate is soluble in acid, itfollows that the pollutants described above willinevitably attack limestone buildings andmonuments. Even unpolluted rain or air mayhave some effect, for the carbonic acid resultingfrom naturally occurring carbon dioxide iscapable of dissolving calcium carbonate.However, chemical attack may only be the firstand lesser form of attack, for the chemicalreaction between the calcium carbonate and thepollutant can produce salts that can continuethe decay indefinitely. Sulphur dioxide andsulphur trioxide, for example, lead to theformation of calcium sulphate. Calcium sulphateis not very soluble and is not readily washedout of the stone except in very exposedconditions. However, it is soluble enough that itcan partially dissolve and then recrystallize asthe stone wets and dries, and the pressuresgenerated by crystal growth are enough toweaken and break down stone and mortar.There is still the possibility that episodes of rainof exceptionally high acidity may contributedirectly to the dissolution of stonework, but wecan discount the notion of buildings fizzingaway gently every time it rains. Researchsupports the hypothesis that stone deteriorationis enhanced by the pick-up of sulphur dioxidebetween showers of rain, whilst not beingaffected by the acidity of the rain itself.’

Carbon dioxide

Carbon dioxide occurs naturally, being given off byall living organisms as a product of respiration, as

well as being a product of artificial combustion offuel; when combined with rain water it producescarbonic acid. It must be appreciated that there ismuch more carbon dioxide in the world’s atmos-phere than there is sulphur dioxide, even the worstsmog might have a concentration of 600 000 �g/m3

of carbon dioxide and 1000 �g/m3 of sulphur diox-ide. The amount of dissolved undissociated carbondioxide is fairly constant over the whole of Britainat about 0.7 mg/l, but the amount of dissociated car-bon dioxide may vary widely from place to place.

Carbon dioxide is capable of dissolving lime-stones made of calcium carbonate by converting intocalcium bicarbonate, Ca(HCO3), which is water sol-uble. Acid rain penetrating limestone buildings dueto poor pointing can dissolve the stone. Very little isknown about the actual mechanisms of stone decayand whether some pollutants act as catalysts to others. This is a field where research, based on stan-dard testing procedures, is much needed.

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Figure 11.13 St Paul’s Cathedral, London, England, south-west tower cornice(Courtesy: Feilden & Mawson)

The important function of the cornices in protecting the wallsbelow having been analysed during the inspection of the wholefabric, it was decided that these had to be restored to their original profiles, using the Wren drawings. The first priority wasthe western tower, where new stones were prepared and liftedinto position. Some weighed nearly a tonne. The photo showsan experienced fixer mason at work, pointing-up a joint aftergrouting a large curved stone into position. The lead will berefixed with a projecting drip, in order to throw rain waterclear of the stonework to prevent decay

Sulphur dioxide

Sulphur dioxide occurs as a man-made by-product,although quite significant amounts occur by naturalmeans. It is produced in proportion to the sulphurcontent of a fuel as it is burnt. The amount of sul-phur in oil varies typically from 0.75%*, for light oilto 3.5% for heavy oil, and in coal from 1.5% to2.3%, although the effective emission from coalburning is lower, as about half the sulphur isretained in the ash. The sulphur content of naturalgas is negligible. The density of emission of sulphurdioxide and of other major man-made air pollutantsvaries widely according to the locality, but it is gen-erally highest in the centres of large cities, withmaxima on cold misty days.

The concentration of sulphur dioxide in the airnow has no correlation with the domestic con-sumption of coal, as it is the product mainly of largescale users as well as diesel-engined vehicles. InBritain the emission of sulphur dioxide reached amaximum in 1963 and had declined slightly sincethen because of the increasing use of natural gasand nuclear energy and the reduction of sulphurcontent in oil fuels.

Ozone

Ozone is created in the upper atmosphere by theaction of ultraviolet radiation on oxygen and dif-fuses down to ground level, giving a natural back-ground of 40–80 �g/m3. The activities of man canconsiderably augment this background amount,which may itself be damaging, to around 500 �g/m3

in industrial zones. The series of chemical reactionswhich result in man-made ozone start with nitrogenoxides from automobile exhausts activated by sun-light breaking up nitrogen dioxide in a complicatedchain of reactions resulting in the formation ofozone and the notorious peroxy acyl nitrate (PAN).

Thomson points out that in an industrial cityobservation shows the following pattern:

‘1. Traffic increases in the morning before thesun is high, causing nitrous oxide (NO) andhydrocarbons to build up in the atmosphere.‘2. Sunlight as it gets stronger, sets the cyclegoing. Ozone remains low so long as it is beingused up in attack on NO and hydrocarbons.‘3. The final stage occurs after nitrogen dioxide(NO2) has taken over from NO as the predomi-nant nitrogen oxide. The NO supply is reducedas the gases diffuse over the city. Now theconcentration of NO2 in turn falls as it takes partin the formation of ozone and PAN. Since ozonehas less NO to attack its concentration rises.

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Table 11.2 National Ambient Air Quality Standards (From the Tenth Annual Report on Environmental Quality, bycourtesy of the US Environmental Protection Agency)

Pollutant Averaging time Primary standard Secondary standard levels levels

Particulate matter Annual (geometric mean) 75 �g/m3 60 �g/m3

24 hours 260 �g/m3 150 �g/m3

Sulphur oxides Annual (arithmetic mean) 80 �g/m3 —(0.03 p.p.m.)

24 hours† 365 �g/m3

(0.14 p.p.m.) —3 hours† — 1300 �g/m3

(0.5 p.p.m.)Carbon monoxide 8 hours† 10 mg/m3 10 mg/m3

(9 p.p.m.) (9 p.p.m.)1 hour† 40 mg/m3 40 mg/m3

(35 p.p.m.) (35 p.p.m.)Nitrogen dioxide Annual (arithmetic mean) 100 �g/m3 100 �g/m3

(0.05 p.p.m.) (0.05 p.p.m.)Ozone 1 hour† 235 �g/m3 235 �g/m3

(0.12 p.p.m.) (0.12 p.p.m.)Hydrocarbons 3 hours 160 �g/m3 160 �g/m3

(non-methane)* (6 to 9 a.m.) (0.24 p.p.m.) (0.24 p.p.m.)

*A non-health related standard used as a guide for ozone control.†Not to be exceeded more than once per year.

*This refers to oil from North African fields. Oil from other pro-ducing areas has a higher sulphur content. (Table 2, Shell andBP Industrial Fuels, 5th edition, Jan. 1970.)

‘Thus the chief final pollutants are ozone and PAN,which characteristically build up to a maximumshortly after midday. PAN is troublesome to allliving things, both animal and plant, but probablyof minor importance to antiquities. Ozone, as wehave seen, is a potent antiquities poison.’

Ozone, as an intensely active oxidizing agent,causes metals to corrode rapidly. This is the proba-ble cause of the rusting of embedded iron crampsin St Paul’s Cathedral, London, which in the pastyears have begun to corrode and, by the resultantexpansion, cracking and spalling the ashlarmasonry. Exposed iron ties on St Giles’s Cathedral,Edinburgh, have wasted to 40% of their sectionalarea in the past 50 years. The danger of ozoneattack on the metal cramps in the Taj Mahal, India,due to the increase in pollution, may be serious.

Carbon monoxide and nitrogen dioxide

Carbon monoxide from motor vehicles is also aserious pollutant. Southern California had the worstshort-term exposures to nitrogen dioxide at levelsabove 500 �g/m3, Los Angeles in particular being36 times worse than other parts of USA with 72 days above this level.

Chlorides

There have been no definitive calculations of chlo-ride emissions in the UK, but it is estimated thatby far the largest source is coal burning (240 ktin 1983), followed by manufacture of chlorine(15 kt) and refuse incinerators (over 5 kt). Chloridescan activate electrochemical actions between twodifferent metals. Chlorides can be extracted fromstone by using poultice techniques as they areeasily soluble.

Other pollutants

The following hazardous pollutants were listed in1971 in the USA: asbestos, beryllium, mercury.Since then vinylchloride and polyvinylchloride,benzene, arsenic and coke oven emissions havebeen added to the list.

Other aggressive acids are produced by industry;they are generally diluted rapidly. It is only in the immediate neighbourhood of their point ofpropagation that they call for special protective

measures, but they increase the erosive effect ofrainwater over a much larger area.

Bacterial decay

It has now been confirmed that bacteria producesulphur dioxide which augments that in the atmos-phere and so increases the overall decay of sensi-tive stones.

Effects of atmospheric pollutants onbuilding materials

Stone

Building stones have a wide range of durability aspollutants affect the calcium component of stones;limestones and calcareous sandstones suffer most.Natural weathering by rain, wind and frost is accel-erated by pollution, in addition the expansion ofsalts within the pore structure as they crystallizeand hydrate causes damage. The pore size distribu-tion, mechanical properties and chemical composi-tion of stones all influence their resistance.

The dissolution and recrystallization of calciumsulphate within the stone is termed ‘memory effect’because of the likelihood that some of the sulphatemight have been deposited in the past. Due to thiseffect, even if levels of pollution have dropped,stone decay may continue unabated.

The rate of decay may depend on catalysts.Particulates, i.e. smoke and soot, contain carbon,silicon, sulphur, aluminium, calcium and vanadiumfrom oil-fired plants, and car exhausts containmany trace elements. NO2 can enhance SO2 pickup without producing any nitrates which can bedetected.

There is really no satisfactory means of long-termprotection of stone on the scale of buildings, nor isthere any cheap method of preserving stone. Con-servators of sculpture and similar decorative fea-tures have the choice of techniques based on limefor limestones or impregnation of sandstones withsilane based preservatives, which need close con-trol in their application. Lime treatments rely on ashelter coat which will need renewal at regularintervals.

Wood

The problems caused by atmospheric pollution aresmall compared by those caused by water, humidityand sunlight. Wood is protected by paints, oils,

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waxes and resin impregnation none of which isgreatly affected by pollution.

Bricks, roofing tiles, terracotta

If bricks, roofing tiles and terracotta are resistant tofrost they are unlikely to be affected by pollution.

Burnt clay products such as bricks, tiles and wellmade terracotta are rarely affected by the crystal-lization of soluble salts, so are generally sulphateresistant; but common fletton bricks, which containconsiderable amounts of sulphates and have a badpore structure, are a notable exception and shouldnot be used on historic buildings. Good sand/limebricks are also rarely affected, although poor qual-ity ones suffer badly.

Mortars, renderings, cement, concrete

Lime mortars are affected by pollution as well asrain, wind and frost. The lime is gradually eatenaway, exposing the aggregate. Lime mortars infoundations may be damaged by polluted groundwater. Renderings tend to fail by cracks admittingrain which may cause sulphate attack in the sub-strate. Portland cement is attacked by pollutants,leading to an increase in volume and consequentdisruption of mortars and masonry. Concrete mayerode due to the action of weather and pollutants.The alkaline protective quality may deterioratecausing reinforcing steel to rust. Anticarbonationtreatments include limewash, two pack poly-urethene epoxy formulations, bitumen, acrylics andchlorinated rubbers.

Glass

Modern glass contains a high level of sodium andsilicon, while mediaeval glass has a high level ofpotassium with lower levels of sodium and siliconso is less durable in polluted atmospheres.

Modern glass is affected by surface leachingwhich increases its durability. Regular washing isnecessary to remove soiling.

It has been suggested that mediaeval glassshould be protected from both water and SO2 bycoating but there is concern that such coatingswould be penetrated by water vapour.

Externally mounted double glazing, with ventilationof the inner space, is considered the best way to pro-tect important window glass; alternatively the historicglass may be refixed behind new glazing sharing theinternal environment (isothermal glazing).

Ferrous metals

The resistance of plain carbon steel in open expo-sure to the atmosphere is poor. Corrosion is prim-arily due to oxygen and moisture but is acceleratedby SO2, particulates and chlorides. Additions ofcopper, nickel and chromium reduce the corrosionsusceptibility of steels.

Painting is the commonest form of protection.Painting may fail through several different mechan-isms and these may act in combination. The directeffect of pollution on the paint vehicle or pigmentscan lead to cracking, blistering or thinning of thepaint film. Degradation of the substrate can damageor detach the paint film.

Rusting of iron and steel in polluted atmospheresproduces corrosive salts. Corrosion products arerecycled causing further corrosion and they must beremoved from pits and crevices. Abrasive, grit blast-ing or acid pickling are possible treatments; if thecorrosion is serious wire brushing is inadequate, andthorough cleaning to remove the whole of the cor-rosive product before any restorative treatment isessential. Exposed metal should be given a protec-tive coat immediately after cleaning. Repainting com-ponents before they have become heavily corrodedis advisable. Zinc rich paints and patent productswhich combine with rust have their uses.

Non-ferrous metals

Layers of oxide produced on non-ferrous metals indry conditions usually have a considerable effect inprotecting the underlying metal. However, relativehumidity, condensation and rain water can producecorrosive conditions. Rates of corrosion depend onthe time the metal is wetted or during which thecritical relative humidity is exceeded. Particulatescan initiate localized corrosion and increase theagressiveness of SO2. Copper, lead, aluminium,nickel and tin and their alloys are all resistant tocorrosion in polluted atmospheres. Zinc and cad-mium corrode slowly.

Zinc

In rural areas zinc sheet or galvanized steel maygive satisfactory life, as is shown in Australia wheregalvanized steel tiles have lasted over a hundredyears. Zinc coatings form a useful protective coatfor steel due to the sacrificial action of zinc whichprotects small areas of exposed steel such as local damage or cut edges. Galvanizing must beallowed to weather before paint is applied. Zinc

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rich priming paints can provide a satisfactory tech-nique for restoration.

Copper

Protective treatments are not usually applied to copper or its alloys. If the green ‘patina’ resultingfrom weathering is not liked, as in the case of statu-ary, an acrylic lacquer containing benzotriazole canbe applied. ‘Bronze disease’ caused by organic acids,or other gross outbreaks of corrosion must be treated.Acids from moulds and lichens are destructive but thegrowth of these is inhibited by atmospheric pollution.

Lead

Lead is protected by a thin layer of lead sulphatewhich is insoluble. However, after 100 years, aboutone third of the thickness of a 3–4 mm (0.12–0.16 in)lead roof may have been dissolved (forming leadsulphate and lead carbonate). Lead carbonate isalso produced by the attack of acetic acid. This acid(found most commonly in vinegar) occurs in vari-ous kinds of timber, especially in oak, where togetherwith tannic acid it produces a vapour that canattack the underside of a lead roof.

Aluminium

Aluminium is highly resistant being protected by acoherent and unreactive oxide film, however, thiscan be broken down by chlorides or highly pollutedatmospheres in industrial areas where pitting is alsolikely to occur. Pigeon faeces are also destructive.

Anodizing is an electrochemical process bywhich the natural oxide is thickened and can bedyed and treated with corrosion inhibitors. Contactwith some timber preservatives can be damaging toaluminium.

Combating atmospheric pollution

It is hoped that new techniques of ‘dry scrubbing’for removal of SO2 will be developed using pulver-ized limestone. Wet scrubbing techniques can reach90% levels of reduction of monthly averages. Thereis probably an acceleration of the decay of stoneand metals, exacerbated by the catalytic action ofiron oxides, titanium and vanadium in dust particles.The effect of atmospheric pollution on buildings is cumulative, whereas human beings for whomhealth standards are established have a remarkable

recuperative ability. For cities with fine buildingsbuilt of marble, such as Agra, Athens, Rome andWashington D.C., G. Torraca (verbal communica-tion) considers the target annual average for sul-phur dioxide should be in the order of 20 �g/m3

with a maximum of 50 �g/m3. This would alsomake those cities more healthy.

Design precautions to counter air pollution

Chimneys and fuel

It may not be possible, because of aesthetic consid-erations, to build the chimney of the heating plantin a historic building high enough to disperse anydamaging products of combustion sufficiently toavoid affecting the building. For this reason, choiceof fuel to be used can have a direct effect on the lifeof the building, and natural gas is therefore recom-mended, with electric storage as second choice.

Choice of materials for repairs

Some building materials are more pollution resist-ant than others. From this point of view sulphateresistance is one of the properties distinguishing agood limestone from an indifferent one. In Britain,good examples of pollution-resisting limestones arequarried at Portland, Ancaster, Clipsham andWeldon, while the best magnesium limestone hasbeen found near Cadeby in Yorkshire. Although silica, the main constituent of sandstone, is notattacked by carbonic or sulphuric acid, calcareoussandstones, having calcium carbonate as a matrix,are subject to erosion in the same way as limestoneand lime mortar. Sandstones such as the excellentCraigleith are not attacked, but unfortunately theycollect soot in their pores, which is almost impossi-ble to wash out. Thus highly corrosive hydrofluoricacid, which will dissolve silica, or grit blasting insome form, has to be used if it is necessary to cleansuch sandstones.

Some preventive measures against air pollution

Atmospheric pollution is so universal that effectivepreventive measures are bound to be difficult toachieve for whole historic buildings. In principlethe polluter should pay and pollution is best treatedat its source. Obviously, the first step is to see to thereduction of local sources of sulphur dioxide. Newindustries should not be sited where their emissions

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threaten a historic building. The second precautionis to ensure that all weatherings, cornices and stringcourses shed acid-laden rain water clear of thebuilding and do not drip on to valuable features.Regular maintenance and washing of stone inappropriate cases is the third type of precaution. Insome cases the application of infrared heating maybe useful in preventing condensation in shelteredporches or recesses, for by this action the gases inthe air remain undissolved and much less aggres-sive. Indeed, in general terms the prevention ofingress of moisture through joints in masonry byrepointing also reduces the damage from pollution.

The internal environment

Gary Thompson (1994), in The MuseumEnvironment, deals with the removal of pollutantsby air conditioning plant in museums. Where abuilding does not have air conditioning it is possi-ble to use sorbents in display cases. James R.Druizik of the Getty Conservation Institute reported

(Getty Conservation Institute Newsletter, Vol. IV,No. 3, Fall 1989):

‘Tests in both an active mode, in which air waspumped through the sorbent, and in a passivemode, in which the pollutant simply diffused tothe reactive surface, were completed. The activemode showed that many sorbents meet the targetperformance—that is, removing 20 parts per billion of pollutant for one year of continuoususe by flowing air at 0.1 litres per minutethrough 200 grams of sorbent—but that activatedcarbon and potassium permanganate/alumina arethe two most effective, as they removed virtually100% of all nitrogen dioxide, sulphur dioxide,formaldehyde, and hydrogen sulphide. Activatedcarbon excelled in ozone removal. In the passivemode where flexibility of design is preferable toactive filtration, the efficiency of removal wasexplored by changing case construction design,varying the amount and surface area of the sorbent, and examining the interactive processesamong sorbent, art object, and plexiglas.’

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173

Introduction

The main function of architecture is to modifyexternal climatic conditions to suit the occupants ofbuildings, thus enabling them to better pursue theirdomestic, social, economic and cultural objectives.As scientific measurement of the external and inter-nal environments of buildings has scarcely begunand as there is also the basic difficulty of measur-ing the comfort of occupants, the reasons for arather simplified approach to the study of the inter-nal environment of buildings will be understood;and just as subjective assessments of comfort maybe adequate, so it is hoped that a brief discussionof the factors involved will be useful. It should beremembered that numerous microclimates existwithin the internal environment, for example dampbasements, unheated attics and exposed corners, aswell as behind panelling or sculpture.

The internal environment of a building is a com-plicated interacting system, comprising the move-ment of air and water vapour, and the transfer ofheat. Thus we have to deal with two main factors—relative humidity and temperature—and the waysin which a building modifies the external condi-tions to create an internal environment.

Moisture exists in the air and in most buildingmaterials except metals, glass, paint and plastics. It isadded to the environment by a building’s occupantsand their activities (each occupant can produce over100 W of heat and 40 ml of moisture per hour, andintroduces moisture by activities such as washing).Moisture can also be produced by evaporation fromindoor plants, by direct or indirect infiltration of rainwater, and by capillarity or rising damp. Moisture islost by molecular transfer through walls and roofs (ifthere is no efficient vapour barrier) and by the loss ofwarm humid air. Provided materials are not satur-ated, their moisture content tends to adjust whenthe relative humidity changes, thus providing what

12

Internal environment of historic buildings

is called ‘buffer’ material. Stone, brick, lightweightconcrete, wood (not painted or polished), plaster,cotton and other textiles are good buffer materialsand so reduce variations in relative humidity.

Low relative humidity may cause serious damageto the furnishings, fittings and other contents of abuilding, as well as minor discomfort to the occu-pants. Hygroscopic materials such as wood andivory will shrink, while textiles, leather and paperwill become brittle. Canvases will tighten and maysplit. High relative humidity results in expansion ofwood, corrosion of metals, growth of moulds andfungi, and prevalence of wood-boring insects. Lowrelative humidity damages the contents of a build-ing; high relative humidity is destructive alike of thecontents and the structure. It is therefore desirableto keep relative humidity within reasonable limits.

Heat in a building is gained from the occupants,from the winter heating and other plant such asrefrigerators, from electric lighting and from solarenergy. Too large windows are a liability, whilethermal mass is an advantage because it reduces thevariations of daily temperature change. The albedofactor (see Chapter 7) of external materials is alsoimportant. Clearly, the complicated functions of theexternal membrane of a building are highly import-ant—good insulation, thermal mass and permeabil-ity to moisture are beneficial.

The concept of a wall ‘breathing’ should be con-sidered as a condition that facilitates the transfer ofmoisture in liquid or gaseous phases more than thepassage of air. Tests have indicated that ordinarywalls of tufa, brick or sandstone of medium thick-ness, as used in domestic structures, allow the pas-sage of some 300 g/m2 (1 oz/ft2) of water daily,when not protected by a coating that renders themimpermeable.

Since the internal environment of a building is sucha delicate balance of influences, before undertakingan intervention involving any historic building it is

advisable to arrange for readings of internal andexternal temperatures and humidities throughoutan entire year, so as to study the climatic variationsand the building’s response and performance.Thermohygrographs make such readings onweekly charts, but they should be calibrated regu-larly against measurements taken with an accuratepsychrometer.

It is vital that all the effects of an interventionshould be beneficial to a building, its contents andits occupants. Some new requirements imposedupon a building (such as new forms of heating)may cause damage, and under the altered environ-mental balance, materials which had been effectivefor centuries may fail. The building, and the way ithas been and will be used or abused, must all beconsidered together.

In Figure 12.2 the complicated functions of theexternal membrane, including windows, of a build-ing are examined. From the environmental point ofview, it can be concluded that good insulation, highthermal mass and permeability to moisture are

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beneficial characteristics in the external membraneof a building, and that buffer material is helpful inequalizing changes in the internal environment.

Moisture content of air: relative humidity and vapour pressure

Differences of temperature between the inside andoutside of a building tend to be equalized by thetransfer of heat. Likewise, differences of water vapourpressure tend to be equalized by the transfer of watermolecules. Air containing a large amount of watervapour has a higher vapour pressure than drier air, somoisture from the wetter air readily disperses towardsdrier air. This is important for two reasons: first,because it means that a concentration of moist air,such as in a kitchen or bathroom, readily dispersesthroughout a dwelling, and secondly, because watervapour at higher pressures inside buildings tries toescape by all available routes to what are usually thelow vapour pressure conditions outside. Escape

Figure 12.1 Man and his environmental components(Courtesy: J. Marston Fitch and Aesthetic Education)

Human experience takes place across two distinct but complementary levels—metabolic andperceptual. The human body’s perception of its environment is accomplished by a complex interplay of discrete sensory systems, each responding to the stimuli of its ‘own’ sub-environment.But this, the highest level of human experience, is totally dependent upon a prior condition—that the perceived environment also provides the required support for the metabolic process

may be through ordinary ventilation routes, butvapour can also pass through many building materi-als. In winter, as warm internal air holds morewater vapour than cold external air, the vapourpressure being higher inside a building than out-side will cause water to move outwards throughpermeable walls in vapour form. In summer, theinternal and external environments are much morein equilibrium.

Water vapour moves by two methods: first, bybulk transfers of air containing vapour, that is bywinds, draughts and convection, and secondly, by the more subtle process wherein the differenceof vapour pressure is the driving force through thestructure itself. Many modern buildings are con-structed with vapour barriers that cause them to actin an entirely different way from a traditional build-ing. For a vapour barrier to be effective it must beimpervious to water in both its liquid and gaseousstate.

Insulation and condensation

When insulation is added it should ideally be onthe warm side. It is a major factor in saving energy.

Fortunately, with thick walls most historic buildingsare reasonably well insulated. However, roofs aregenerally areas of major heat loss, although theycan be insulated relatively easily. In a cold climatethe improved insulation often requires that there bean efficient vapour barrier, which should also be onthe warm side.

Warm air at 22�C (72�F) may contain 6–8 times asmuch moisture as the external air at 5�C (41�F). Thissurplus moisture is liable to condense if the aircools. Structural insulation can play a part, but onlya part, in reducing the likelihood of condensation.It will be appreciated that no amount of insulationmakes a cold room warm, but that a small amountof heat will raise the temperature of a well-insulated room in proportion to the insulation valueand thermal capacity of the structure. Placing theinsulating materials on the inner side of the struc-ture will allow the inner surfaces to respondquickly to heating—an obvious advantage inachieving comfort. The overall insulation valueaffects internal surface temperatures and thus theprobability of surface condensation, while thearrangement of the insulation determines the waytemperature varies through the structure and there-fore whether interstitial condensation is likely to

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Figure 12.2 Diagrammatic function of a wall(Courtesy: J. Marston Fitch, with comments by the author)

Lightweight construction

(1) Tendency to overheat andtrap infra-red rays

Poor insulation value, highheating costs, cold radiationdiscomfortCondensation of cold surfaces often in hiddenplacesSolar overheating compen-sated for by costly mechani-cal cooling plant.High overall running costs

(2) Resistant to atmospheric pollution

(3) Lack of privacyToo much daylightToo much snow glare

Glare from over-large win-dows without gradation of light

(4) Difficult to absorb soundsDifficult to keep out noises

(5) Easily vandalized or broken;difficult to repair, with long delay for deliveriesVermin, if established, diffi-cult to removeGenerally resistant to micro-organisms unless framed in timber, then very vulnerable

Heavy construction

(1) Absorbs heat by day; releasesby night—thermal flywheeleffectGood insulation, low heatingcosts, warm walls

Absorbs and transmitsmolecular moisture outwardsBalances day and nighttemperatures and gives pleasant dynamic changeThermal storage reduceswinter heating costs

(2) Some materials vulnerableto pollution

(3) Good privacyDaylight controlledSnow glare a pleasant variation of climateLight gently modulated,giving pleasant internalluminosity by reflection

(4) Easy to absorb soundsEasy to keep out noises

(5) Easily protected; relativelyrobust and easy to repair

Vermin easily dealt with

Vulnerable to some micro-organisms if badly maintained

take place within wall material permeable tovapour. As surface condensation depends uponsurface temperature, the total amount of insulationis important, unless the surface can be heated byradiant sources.

The occurrence of interstitial condensation withinthe thickness of the fabric depends upon how easilywater vapour can enter and whether it will reach aposition where the temperature drops to the dew-point. With an impermeable vapour barrier at theinside surface to prevent the passage of any vapour,interstitial condensation is prevented, but with animpermeable barrier at the cold exterior surfaceand the remainder of the construction permeable,condensation within the structure is almostinevitable. This is typical of some non-traditionalwalling systems, or when historic buildings arepainted with an impermeable plastic paint.

Prevention by an internal vapour barrier orarrangements to drain condensed water by a cavityare two methods that may be used. Although com-pletely impermeable vapour barriers at the insidesurface are difficult to achieve, a partial vapourcheck is still useful, if it can be installed easily.Traditionally, birch bark was used for this purposein Finland.

Condensation and ventilation

A sizable proportion of outbreaks of wet and dry rot are caused by condensation. If a building is leftunoccupied, particularly in winter, local condensationof stagnant air when the temperature drops can pro-duce suitable conditions for such fungal growth asmoulds on walls and ceilings and dry rot in the struc-tural timbers. Wallpaper often becomes detached dueto the dissolution of the glue. Occupants cause airmovements by opening doors and windows and,when walking about, by causing floors to deflect,thus moving air through the joints in the floorboards,reducing the danger of stagnant air. Imperviouscoverings, particularly on the ground floor if there is no damp-proof membrane, increase the risks of dry rot.

Ground floors should never be covered withlinoleum unless there is a damp-proof membranewhich is also vapour proof. If an old floor withouta damp-proof membrane underneath must be covered, a perimeter band of 200–250 mm (8–10 in)should be left to allow vapour to escape, so avoid-ing driving moisture into the wall. With suspendedwood ground floors it may even be necessary topromote circulation by drilling holes in cornerswhere air may become stagnant. Where a carpet

or other floor material needs hardboard underlay in order to provide a flat subfloor, it should be aperforated type if there is the slightest danger of dryrot to the timber subfloor. Air bricks which ventilatesuspended ground floors must always be keptopen—a point that should be specifically checkedon inspections. Air ducts with grills by a fireplacehelp extract air from the subfloor and also reduceroom draughts. Grills under radiators are also worth considering as they assist in subfloor air cir-culation by drawing air upwards and warming it. Ducting may have to be introduced into sub-floors to ensure air movement, assisted by windpressure differentials, from one side of the buildingto another.

Excessive internal moisture

Dampness is a common but vague word. It gener-ally means unwanted moisture either in materials orin air which has sufficient vapour content to causecondensation if the surface temperature falls lowenough.

Nearly all historic buildings suffer from dampnessin their basements because the introduction ofdamp-proof courses, tanking and vapour barriers isrelatively recent. This dampness may be an asset tothe contents, as it keeps the relative humidity high,but as it is uncontrollable it may also be a liability.It is always a liability to the fabric because itinduces condensation and high moisture contents.If the moisture content of wood is above 20% thereis a serious risk of attack by Merulius lacrimans,called ‘dry rot’ because it can carry its own mois-ture long distances from its source and attack drywood, or ‘champignons’ because it smells ratherlike mushrooms. There are many other forms ofdecay induced by excessive moisture content inorganic materials.

To cure dampness, the source must be found, butit is always wise first to eliminate the possibility ofcondensation by taking readings on a thermohygro-graph which should be properly calibrated and regu-larly checked. The source may be ground water orwet soil feeding capillarity and assisted by salts dis-solved in the ground. In this case, the cure is to cut ina horizontal damp-proof course if possible. Thesource may also be faulty rainwater disposal, leakinggutter and downpipes or broken drains. It is some-times caused by rain penetration through a wall.However, a wet wall if dried quickly by wind canbecome so cool that it causes condensation in theinterior.

The interior of each building has a varied micro-climate. If there is lack of ventilation, moisture

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vapour builds up in recesses and external cornerswhich are liable to be those most exposed to heatloss. Gentle air movement is one of the simplestways of avoiding condensation and ensuring safestorage for the contents of historic buildings. Excessmoisture can be removed from the air of basementsand storage areas by using local extractors basedon heat pump principles.

Occasionally, when after a long cold spell thereis an influx of warm humid air, usually in thespring, the moisture in this air will condense on the walls of an unheated building. Unless heat canbe applied, all one can do is close the windows andso reduce the amount of incoming air and cut offthe source of moisture.

Windows

Architects generally took great care in placing win-dows in historic buildings so as to provide naturalventilation in addition to light. An account of the1860s competition for design of the Law Courts inLondon shows how carefully ventilation require-ments were considered in planning, but windowsalso admit light with its dangerous ultraviolet com-ponents. Our grandmothers knew the danger andkept the blinds down or shutters closed until theroom was used and they also used to put dust-cov-ers over the best furniture. Nowadays, an historicbuilding gets more intense use, but we seem tohave forgotten the damage that light causes, espe-cially to sensitive water-colours and valuable tex-tiles. Blinds and ultraviolet filters can be fitted towindows to reduce this damage. However, muchpractical knowledge has now been lost, so a reca-pitulation of basic factors is desirable. Most historicbuildings will continue to rely upon natural ventila-tion because of the cost and difficulty in installingducts and plant for air conditioning.

Excessive ventilation, i.e. above 0.3 m/s (1 ft/sec)through windows and doors can be reduced bydraught stripping. Such weather stripping maycause an increase of internal moisture content inwinter and dehumidification in summer, and if wellfitted it is valuable. If not well fitted, it may actuallyincrease rates of ventilation.

Because today we have electrical and mechanicalmeans of solving these problems artificially, wetend to ignore the way a building can help by itsown design and construction. The acute condensa-tion problems that now affect contemporary build-ings were avoided in traditional architecture by theskill of their designers in using natural ventilationand permeable materials.

Ventilation

Stack effect

Air is moved by temperature as well as pressure dif-ferentials. Warm air will tend to rise and escapethrough high level outlets or vents, and it isreplaced by cooler air entering at low level. Thegreater the temperature difference the greater therate of the flow. This type of air movement, calledstack effect, is greater in winter than summer.Unfortunately, historic buildings used as museumsreceive far more visitors in summer than in winter,so there is a danger of insufficient ventilation, ashappens even in St Paul’s Cathedral andWestminster Abbey with over ten thousand visitorson some days. Natural ventilation in buildingsdepends both on wind pressure and stack effect,singly or in combination. In hot humid climates ver-nacular designs encouraged natural ventilation forits beneficial cooling effect, through promotingevaporation and thus absorbing heat carried off aslatent heat in water vapour. The amount of ventila-tion achieved in practice is measured by the num-ber of air changes in a given time, which dependson the exposure of the building and such factors asthe size of air inlets and outlets and general air-tightness of the building. The main disadvantage ofnatural ventilation is that it is too variable. In windyweather, undesirably large heat losses may occurdue to excessive ventilation.

For good ventilation from the stack effect, outletsshould be placed as high as possible on roofs andwalls, whereas inlets should be as low as possible.Cracks around doors and windows at low leveloften provide sufficient infiltration in winter, but itshould be remembered that persons near perimeterwindows may suffer from draughts while the rest ofthe room is not adequately ventilated. Outlets onthe roof have to be designed so as to draw air outeffectively and prevent rain being driven in, evenwhen the wind is blowing strongly. Vertical fluesmust be considered as outlets, even when no fire islighted, and they may induce excessive air changesin winter.

Effect of wind on natural ventilation

Air flow rates are normally greatest in rooms on thewindward side of a building, from which air willtend to move through the rest of the building. Forthis reason, when planning alterations, rooms pro-ducing odours or moisture should not be on theprevailing windward side—for example lavatoriesand kitchens.

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Control of draughts is partly a matter of detaileddesign and adequate weather stripping. Attentionmust be drawn to the danger of cold draughts caus-ing freezing of water in plumbing systems whichincidentally is more likely if there is little movementof the water inside the pipes. One of the most vul-nerable points is the rising main to the cold waterfeed tank if this main is run up an external wall andpasses close to draughty eaves.

In hot climates the sizing of openings to provideeffective air movement is crucial. In Europe it is lessimportant, but nevertheless worthy of design atten-tion, especially in buildings with heat gain from toomuch glass or ‘wild’ heat from electric lighting andplant such as refrigerators. Well-fitting vertical slidingsashes have practical advantages for natural ventila-tion because they have a wide range of control. Notonly can they provide appreciable opening areas atlow levels to take advantage of summer breezes, butthey can also be opened simultaneously at top andbottom to provide stack ventilation in still weather.In winter weather the top part only need be opened,thus avoiding the risk of draughts at low levels.Although they may rattle in high winds they cannotbe blown off their hinges like casements, and theydo not gather sound from the street below as is thecase with centre-hung pivot windows.

Published research on ventilation problems inhousing in hot climates is relevant to assessing ven-tilation performances of an historic building. Theobjective was to maintain cool interiors in rectan-gular buildings in a Mediterranean climate, and thefindings can be summarized as follows:

(1) With windows on one side only, typical averagerates of air movement are of the order of 15–20%of free wind speed, regardless of whether thewind is head on, diagonally on or sideways on.While the size of inlet affects internal velocity, itdoes so at a regressive rate. The recommendedminimum free opening area is one-tenth of thewall area. Above this amount an increase inopenable window area has a small, anddecreasing, effect on the internal velocities. Therate of heat gain during daytime is directlyrelated to window area, hence the desirabilityof reducing window area in hot dry climates.

(2) When the inlet and outlet are of different sizes,the internal velocities are governed mainly by the size of the smaller opening. The increasein the larger opening tends to increase the heatgain without producing very much increase inair movement, so it is best to keep inlets andoutlets of the same size.

(3) In long blocks with deep, narrow flats extend-ing across the building, with external exposure

on opposite sides, it is preferable to orientatethe building with its long elevation at anoblique angle to the prevailing wind instead ofperpendicular to it (this echoes a recommenda-tion by Vitruvius).

(4) Contrary to common belief, the greatest amountof general air movement is produced when theair flow has to change its direction within aroom. The change of direction produces moreturbulent mixing than when the flow pattern isstraight through, i.e. the whole room benefitsfrom increased air movement rather than only asmall part of it.

Effect of height and volume on natural ventilation

With taller buildings, special points will have to benoted, particularly due to the increased exposure atthe upper levels. Stack pressure differences can berelatively large because of the height of some inter-nal volumes. Air entering at low levels will move upany central volumes such as domes or stairwells.Vertical service ducts can tend to act as warm airchimneys, so that the sealing off of these at each floorlevel is desirable to prevent excessive vertical airmovement (this is also essential for fire-stopping).Stack effect in tall buildings can produce noticeablepressures on the openings of doors and cause largeheat losses when these doors are left open. Strongdoor-closers should be fitted. Again, in the upper partof tall buildings there is a danger of the wind catch-ing opening lights on windows and swinging themsharply outwards. For this reason conventional side-hung sashes are not to he recommended; slidingsashes or centre-hung sashes are more acceptable asthey provide ventilation without these risks.

In temperate climates, most small churches neverneed to open a window because sufficient airchanges percolate through the glazing, roofs anddoors to ventilate them adequately, and as they areonly occupied for short intervals there is sufficientfresh air in the volume of the fabric to meet all theventilation need of intermittent human usage. Oldbuildings are notorious for their lack of air tight-ness, and accordingly, exposure should be wellcompensated for in heating calculations. The prob-lem of increasing the number of air changes in his-toric buildings rarely arises, because of their largevolume and low usage, but if the usage increasesthe demand for fresh air might exceed the supply.

Summarizing, the natural forces inducing ventila-tion are much greater in tall buildings. Where a build-ing is not in constant use, satisfactory ventilation cangenerally be achieved by using stack pressure forces,but it should be remembered that these forces are

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less effective in summer. The location of the ter-minal outlets for stack systems should be checkedparticularly to avoid down-draughts due to adversewind pressure from adjoining parts of the buildingor adjacent trees or other obstructions to air flow. Ifthe building has an irregular roof silhouette, diffi-cult problems may arise from wind turbulence.

Artificial ventilation

Air conditioning uses mechanical plant to clean anddeliver air, as well as controlling the temperatureand the humidity. The Capitol, in the USA, was thefirst building in the world to rely completely on arti-ficial ventilation. Dependence on the process hasreached such a state that many modern designersrely upon it entirely and fail to use any of the natu-ral thermal characteristics of a building. This isextravagantly wasteful of energy.

Air conditioning can have side effects which maybe totally unexpected if the environmental behav-iour of the historic building is not fully understood.If a positive pressure is built up internally the haz-ards of pollution and dust ingress are reduced, butthe danger of interstitial condensation is increased.If a negative pressure is created by recirculation ofair or internal air intake, then in a humid climatecondensation will occur in parts of the buildingalready cooled below the dewpoint. As air condi-tioning of individual rooms, to preserve sensitivegroups of objects, is recommended on grounds ofeconomy, the side effects must also be assessed.

Air conditioning is useful in museums to controlthe environment within the precise limits requiredfor certain objects such as paintings on wood. It isalso beneficial for historic buildings situated in anunfavourable environment of dust, dirt and sulphurdioxide, as it reduces the damage caused by theseagents to furnishings and the contents. The controlof humidity prevents wall panelling from shrinkingand cracking if central heating is installed. It fur-thermore assists in dealing with the fluctuatingenvironment created by large numbers of tourists.

However, if the electricity supply is variable andthe air conditioning liable to be cut off, a conse-quent rapid change in the relative humidity of theinternal environment can cause severe damage tothe contents and wooden elements of the building.Power cuts due to energy crisis are particularlydamaging, because they tend to occur when theexternal temperatures are very low.

Fortunately most historic buildings contain a largeamount of buffer material in wood panelling, floorsand ceilings and to a lesser extent porous permeablemasonry, which give up moisture when relative

humidity is too low and absorbs it when too high.The mass of an historic building helps to protect itscontents against violent environmental changes by‘damping down’ the rate of change. Frequentchanges in internal environment are probably moredamaging than the wrong relative humidity, so airconditioning if installed must be run continuously.

Lighting

Natural sources

Natural lighting of historic buildings is a subject inits own right. The placing of windows in rooms,and reconciling their internal requirements with theneed for order in the external elevation, is part ofthe stuff of architecture, for the quality of an archi-tect’s work depends on how he solves such prob-lems. There are three important aspects of thenatural lighting of a building: first, the window/wallratio in relation to the thermal mass; secondly, thequestion of heat loss, down-draughts and air infil-tration caused by windows; thirdly, the danger ofunwanted thermal gain from sunlight.

Besides problems of solar gain in historic build-ings with valuable collections, there is generally toomuch light, as the UV component in particularfades textiles and paintings, embrittles leather andcauses textiles to decay. Good housekeeping in thepast consisted of drawing blinds and putting dust-covers on furniture and over carpets when the fam-ily was absent. Nowadays, historic buildings get farmore intensive use than in the past, so reduction ofincoming light is a part of the general environmen-tal strategy. Methods of achieving this range fromadding blinds or shutters, which should be keptclosed whenever possible (i.e. after visitors havedeparted), to application of UV-resistant varnishesor films to the inside of the existing glass.Experiments have been made with various types offilms by C.V. Horie, and he found that a bronze tintwas the most acceptable. When fixed to windowpanes there is generally a thin line of white glassleft round the perimeter, but this is not consideredobjectionable as it throws relatively more light onthe architectural mouldings of the window glazingbars and frame. Roof lights were traditionally covered with a layer of whitewash in the spring,which was gradually washed away before winter,providing a simple way of preventing the entry oflight and heat. Heat-resistant glass panels can befixed externally in certain cases; however, the silverreflecting surface or the dead bronze colour ofthese types of glass are generally unsympathetic tohistoric buildings.

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Artificial lighting

Historically, light levels were very low until incan-descent sources, either gas or electric, were devel-oped. Previous to this the candles and lamps thatwere available emitted a lot of soot. In the past cen-tury artificial lighting has developed dramatically andsome comments on its use are made in Chapter 20.

Artificial lighting of historic buildings introducesnew aesthetic and technical problems. Apart fromvisual effects, it affects the internal environment byradiation and heat input which, if high, can haveundesirable side effects such as timber shrinkageand may even in an extreme case be a cause of theoutbreak of fire. To maintain suitable low levels oflight and reduce the danger from UV rays, we arenowadays more and more reliant upon artificiallight. Research into the environment of theScrovegni Chapel, Padua, showed that two factorswere critical to the health of Giotto’s frescoes: thedraught entering under the door and the con-vection currents set up by the heat emitted by theelectric lighting. The effect of each could easily bereduced, in the case of the lighting by fitting up-to-date low heat output fluorescent tubes.

In lighting for television a new order of intensityof illumination has to be faced, with consequentialgain of heat (about 300 kW for black and white and800 kW for colour, in the case of St Paul’s, London).This tremendous heat input from lighting fittings isdangerous to the internal environment, but luckilyis usually only occasional. When the use of televi-sion is regular, the heat must be extracted bymechanical ventilation and this can cause the sud-den lowering of relative humidity. The heat fromelectric bulbs, however, must always be dissipated,as otherwise it can become a serious fire risk.Dimmers, which run bulbs at a lower output untiltheir full capacity is required, are useful both inprotecting the environment of the building and alsoin lengthening the life of the electric light source.

Precautions must he taken to control the lightfalling on most art objects, as damage caused bylight cannot be reversed. Paints, pigments andsome dyestuffs are the most seriously affected.Textile materials such as wool and silk aredegraded by light, becoming brittle and eventuallydisintegrating when the material is handled. Cottonand linen can deteriorate and discolour. Theamount of damage is proportional to the quantity ofUV light that the object has received. For equalquantities of light, the following are arranged inorder of increasing likelihood of causing damage:tungsten filament, warm fluorescent, daylight andnorth light, fluorescent, sunlight and blue sky. Forvaluable objects, the amount of illumination should

be measured with a lightmeter, and for objects sus-ceptible to damage, 50–150 lux is generallyaccepted for display purposes. Glass and plastic fil-ters for fluorescent lights should never be percepti-bly yellow. Chemical filters are also available inspecial fittings, all of which reduce the damagefrom the UV element in light. Similar filters shouldbe applied to glazing, particularly on north lightwindows.

Electronic flashes used in photography, beingalmost instantaneous and producing no heat, neednot cause concern, but the strong lights used in cinephotography and colour television of say 1000 luxare a more serious problem, together with theirassociated heat build up, for the radiant heat cancause sudden excessive dryness in wood, ivory,paper and parchment, thus causing cracking anddistortion. Rehearsing with dummies and usingheat-absorbing filters and air cooling can reducethe impact of the powerful lights required.

The amount of UV light that falls at any point in abuilding can be compared by using standard bluedyed fabrics as specified in BS 1006:1961. The fadingof the fabric is measured against standard shades ofgrey and thereby classified for comparative purposes.

Of special interest is fibre optic lighting, whicheliminates heat and ultra violet radiation. It is flexi-ble and adaptable to install, and most suitable forillumination of sensitive objects in museums andhistoric buildings.

Heating

Heating is the major environmental factor whichcan be adjusted or controlled by the occupants.Three states should be considered—no heating,intermittent heating and continuous heating.

M. Koller and W. Beck have reported on anextensive study of unheated church buildings inAustria (preprints of International Institute ofConservation (IIC) Vienna Conference, 1980) andthey sum up their study, which excludes veryexposed Alpine positions, as follows:

(1) Massively built rooms undergo no rapid alter-ations of (internal) climate.

(2) Internal temperatures of walls can be taken asbetween 2�C and 5�C (in winter); maximum insummer between 13�C and 15�C.

(3) Atmospheric room temperatures in winter havean average minimum of 0�C and in summer amaximum of around 20�C.

(4) Relative humidity of non-heated rooms liesabove 60–65%, except for a few extremely coldwinter days.

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A study of this type establishes the environ-mental baseline against which the value of interven-tions should be judged.

The choice of heating systems depends on manyfactors; for instance, if floors have to be renewedthen floor panel systems are possible, otherwise thecost may be excessive. On the other hand, an intri-cate inlay of marble floor of historic value wouldpreclude the possibility in any case. The choice ofheating systems must be a three-cornered compro-mise between the needs of the occupants andavoiding damaging conditions for both the contentsand the building itself. For example, in a cold cli-mate to insist on 55–60% RH throughout a longwinter may cause frost damage due to freezing ofthe moisture passing outwards through a wall withno vapour barrier. Convected intermittent heating isnot to be recommended, because it does not givereal comfort to occupants and induces greatstresses in materials due to sudden temperature andhumidity variations, and the theoretical savings incost are usually illusory. Ideally, low but continu-ous heating should be provided to protect the fab-ric against frost, but not so much as to lower the RHmuch below 50% as then wooden furniture may bedamaged, and to provide local radiant heating foroccupants’ comfort.

There is a need to establish ranges of heating thatwill not cause cycles of crystallization of ground-water salts. A flexible approach relating the insidetemperature to the average daily outside tempera-ture is recommended, as the differential can be setat a figure that is unlikely to cause damage to thefabric or contents.

In Austria, temperatures of 10�C (50�F) with amaximum of 12�C (54�F) are recommended so as to

keep RH above 50–60%. If RH drops below 50%some humidification may have to be considered(subject to no interstitial frost damage), or, alterna-tively, objects which are extremely sensitive to dryness (or moisture) can be put into closed show-cases with plentiful buffer material.

Regular maintenance and checks on the operat-ing controls of the heating system are essential. Thebest way of monitoring performance is to haverecording thermohygrographs, but these must becalibrated every month.

Various types of heating systems have been used:

(a) local radiant heating (open gas or electricheaters with directional effect);

(b) local heating elements (warm water or electricconvectors, storage heaters, heating panelsattached to walls or fixed seating);

(c) ducted hot air heating, either convected or radiantlow temperature floor panel heating.

Defects arising from heating

Defects observed as a result of improper heating of the interior of historic buildings vary accordingto the nature of the surface finishes. The main onesare listed as follows:

(1) Deposition of dust and dirt together with pat-tern stains on plaster areas of low insulationand greasy dirt on the inside of windows. Dirtis either brought in by the air or by detritusfrom the users (i.e. hair and fluff ) or by dirtbrought in by their feet.

(2) Condensation causing mould growth and decayof painted and stained glass.

Heating

181

Figure 12.3 Fireplace in house at Cathedral Close,Norwich, England

A contemporary fireplace with under-floor controlled draughtinserted in an early sixteenth century fireplace, which gave evidence of having a smoky chimney. The reduced amount ofair required by the new grate and a well-shaped flue cured thesmoky chimney

Figure 12.4 External environment, Ospizio di San Michele, Rome, Italy (Courtesy: ICCROM)

Outside temperatures in March vary over 16�C, from 1�C to 17�C, in one week with 14�C change on Friday. External relative humidity varies by 61�C with 50% change on Thursday and 25% change on Friday

Figure 12.5 Internal environment, Ospizio di San Michele, Rome Italy (Courtesy: ICCROM)

Inside temperatures vary by 8.5�C, about half the outside temperatures, even though there is no heating, as the heavy walls give upheat. The greatest change occurs on Friday. Relative humidity changes by a maximum of 12%, the maximum change being onThursday, about 7%, i.e. just over one-quarter of the external change

EXTERNAL AND INTERNAL TEMPERATURES AND RELATIVE HUMIDITIES COMPARED IN AN UNHEATED BUILDING IN ROME,SHOWING THE INFLUENCE OF A FAIRLY HEAVY STRUCTURE

Figure 12.6 Environment inside an unsealed showcase, Ospizio di San Michele, Rome, Italy (Courtesy: ICCROM)

The temperature changes a maximum of 5.5�C in the week, with 3�C on Friday, about one-fifth of the external change. Relativehumidity changes by 5% nearly all occurring on Thursday, about one-tenth of the external change

Figure 12.7 Environment in a sealed showcase with buffer material, Ospizio di San Michele, Rome, Italy (Courtesy: ICCROM)

Temperature changes a maximum of 4�C in the week, with gradual fluctuations of 2�C on Thursday and Friday. Relative humiditychanges by 2% on Thursday

TEMPERATURES AND RELATIVE HUMIDITIES COMPARED FOR UNSEALED AND SEALED SHOWCASES AT THE SAME TIME AS FIGURE 12.5

(3) Shrinking, warping and cracking of wood andother organic materials.

(4) Blistering, flaking and powdering of paint layers. Changes in chemical composition of somepaints and damage by crystallization of salts.

(5) Failure of animal and fish glues, lifting ofveneers, break-down of intarsia work andblooming of polished surfaces.

(6) Breakdown of church organs due to the abovereasons and condensation in metal pipes anddesiccation of leather valves and bellows.

It is generally the convection component in heattransfer that causes the above defects, althoughradiant heat from powerful electric light bulbs canalso be damaging.

The walls of most historic buildings built ofmasonry are thick but permeable and generally havegood total thermal resistance, although the materialsthemselves may be poor insulators. Their thermalmass is great, so therefore they do not respondquickly to intermittent heating, but are able to main-tain remarkably uniform internal temperatures whenheated continuously. In an unheated state there arebut few internal air currents; however, when heatingis introduced draughts inevitably appear, but thispractical problem can be mitigated by skilled design,after investigation using smoke to indicate the pathsof air movement.

The tendency to dispense with domestic openfires and the removal or sealing of old-fashioned airbricks has greatly reduced natural ventilation andcaused an increase in condensation. Ventilatorsshould be provided for old flues, not only to preventcondensation and hygroscopic salt deposit in theflue itself, which can penetrate through and damagedecoration, but also to maintain air changes in theroom. Gas heaters with inadequate flues, oil stovesand domestic appliances burning neat fuel producelarge amounts of water vapour which may inducecondensation. For instance, one litre of paraffinwhen burnt produces about one litre of water. Theexplanation is simple: a hydrocarbon, when burnt,forms water and carbon dioxide. Gas-fired boilersproduce great quantities of water as a product ofcombustion and require specially insulated flues toprevent condensation at the top where the gases willhave probably cooled below their dewpoint.

In an old damp building or even a recently con-structed one, rapid drying out by newly installedcentral heating can be dangerous to the fabric, espe-cially for the first few weeks. Also, if the building isnot kept well ventilated during this period, moistureextracted from the porous fabric will saturate the airwithin, and in the cool parts of the building, such asunheated roof spaces or attics, heavy condensation

may occur. Windows should be opened top and bot-tom so that the hot moist air may be expelled andtemperatures raised only gradually, thus allowingmoisture to dissipate slowly and reducing damageby shrinkage of materials and expansion of thestructure. Months, even years, may elapse beforeequilibrium is achieved in a heavy structure.

Temperature and relative humidity are interde-pendent in forming the internal climate of a build-ing. This climate affects both occupants andcontents; people are rather sensitive to tempera-ture, only achieving comfort when the effectivetemperature is between 18�C (64�F) and 25�C(77�F), whereas historical artefacts are moredemanding because many require strict humiditycontrol to reduce the rate of deterioration. Effectivetemperature as an index of comfort has four com-ponents: radiant temperature, ambient temperature,air movement and humidity. Air movement is desir-able for comfort but too much—a draught—cancause discomfort, and relative humidity if too lowcan cause discomfort to people and desiccation ofleather, wood and other sensitive organic materials.

Preservation of art objects and furnishings inhistoric buildings

The relative humidity inside a building is the mainproblem with regard to the preservation of objects.However, it is one of the most difficult to controlwithout mechanical plant. Wood, paintings onwood, horn, ivory, embroidery or weaving in woolor silk ideally require humidities of 55% with a �variation of 5%. For wood and paintings a constanthumidity is important and should not go below 50%or above 60% because of the danger of mouldgrowths at RH over 65–70%, especially if the air isstagnant. With precautions, short periods at ahigher RH would normally be safe, but prolongedperiods are too risky. There is some evidence thata high RH causes dyestuffs to fade more readily.

Stone is not affected materially, but with high RHthe effect of sulphur dioxide attack would be greater.Paint on stone would be more inclined to becomedetached or break up in high RH conditions. If painton stone has weakness then it should be treated asif on wood and kept between 50% and 60% RH.

At relative humidities below 40% organic sub-stances can receive permanent damage; marquetryand veneers are particularly susceptible to overdry-ing, and paper, parchment, leather and the adhesivesused in making furniture can all be affected. Churchorgans are sensitive to low humidities. At the otherextreme, an RH of above 70% will encouragemildew and mould and the formation of corrosion

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184

on metals. The absolute limits are therefore 45–65%,but for safety 50% should be aimed at, as measuringinstruments and controls are not too accurate.

It is rapid changes in humidity that are most dam-aging to organic materials, and valuable objectsshould be kept in a glass case to protect them fromtemporary changes and, incidentally, from atmos-pheric pollution. A simple way of reducing the RH isto insert an absorbent such as conditioned silica gel ora quantity of buffer material into the case. Conditionedsilica gel can also be used to increase the RH.

Acoustic environment

An historic building may nowadays find itself in an environment of intense noise and vibration forwhich it was not designed. On a hot day, it may benecessary to close all the windows and forgo natu-ral ventilation because of the external noise—themost common cause of environmental complaints.Intrusive noise and also high levels of backgroundnoise may have to be countered and minimized bydouble glazing, the sealing of all cracks and instal-lation of air conditioning.

The external acoustic environment is measured indecibels using a soundmeter. The internal acousticalcharacteristics are assessed by the reverberation timeof a building, which is a function of its soundabsorption and volume. Generally, the reverberationtime of large historic buildings is too long for mod-ern usage and there is not enough acoustic absorp-tion, particularly in the lower ranges.

In the acoustical field, problems arise in historicbuildings when they are required to perform in adifferent way from the one for which they weredesigned and built, a typical example being theGothic or Romanesque cathedral which wasdesigned for services to be chanted in a languagenot understood by the laity. So strong is the effectof acoustics on the architectural personality of abuilding that certain types of music may be said tohave been composed for buildings of certain types,e.g. chamber music for small salons and Gregorianchant or plain-song for cathedrals and abbeys.

Nowadays, every word of a sermon must beheard or there are complaints. These complaintscan be reduced by the introduction of sound rein-forcement. However, in any proposals to improveaudibility in an historic building, its acoustic per-sonality should be respected as much as its visualqualities. Illuminating the speaker helps audibilitygreatly and is a boon to deaf persons who maypractise lip reading. An additional aid is the loop

system, which links with a microphone in the deafperson’s ear. It should be installed in auditoria, butmay involve ducting.

The balance of the internal environment

An attempt has been made to outline factors whichaffect the internal environment of historic buildingsand to show that a delicate balance exists amongthem. It has been demonstrated that the internalenvironment is modified by atmospheric, thermaland aqueous influences. Wind causes air movementwith consequential pressures and suctions whichvary the rate of internal air change, so affecting heatlosses and the comfort of the occupants. If changesin methods of usage, heating and artificial lightingare proposed, their effects on the fabric and con-tents of the building must be carefully assessed. Animprudent alteration of the internal environmentmay upset a very delicate, long-established equilib-rium. It has been shown that this environment ispeculiar to each building, depending upon itsdesign, construction, materials, thermal mass buffereffect and insulation and upon its maintenance,condition and usage, as well as its acoustics, light-ing, heating and ventilation. In this context theatmospheric, thermal and aqueous components allinteract to produce a spatial environmental systemwhich if thrown out of balance may create a newdanger for the building and its contents.

Typical examples of interventions which mayhave an adverse effect are:

(a) Portland cement rendering, external or internal;(b) Portland cement pointing;(c) insertion of damp-proof membranes without

‘safety valves’;(d) introduction of heating at too high temperatures;(e) introduction of air conditioning;(f ) application of impermeable plastic paints;(g) sealing up natural ventilation systems, e.g. fire-

places;(h) preventing air movement by changing tiles or

slates to metal or plastic roofing.

Lastly, mention must be made of the effects ofbuilding operations which generally introduce largeamounts of water into the structure, and internalarchaeological excavations which encourage a con-siderable amount of evaporation of ground waterfrom exposed surfaces. These, however, are excep-tional and temporary changes of the internal environment.

The balance of the internal environment

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Part III

THE WORK OF THE CONSERVATION ARCHITECT

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We pay lip service to interdisciplinary collaboration,but do we know what each profession can andshould offer to a conservation project? Possiblythese profiles will help people starting to work inthe field of conservation. They cannot be completeor detailed enough, and some points emphasized inone profile may apply equally to another. Many inthis list of professionals may not have a formalqualification, but may well be highly specialized,having a thorough mastery of their own area ofknowledge and techniques, and an understandingof its context and the ability to work within a team.A ‘professional’ is defined as someone who con-tributes intellectually, artistically or practically to theprocess of conservation. The role of the profes-sional will change with age and experience.

The document, initiated by COTAC (Committeeon Training and Architecture) was discussed in aCOTAC meeting in England in 1994. The profilesfor Conservation Officer, Landscape Architect,Materials Scientist and Surveyors have been draftedby John Preston, Peter Goodchild, Nigel Seely andJohn Gleeson respectively, and helpful commentsand revisions have been made by Poul Beckmann,Deborah Carthy, Richard Davies, Gerald Dix,Francis Golding, Gersil Kay, David Lindford,Warwick Rodwell and TG Williams.

First (unless the discipline is fully dedicated toconservation), what might be described as thestandard role of the professional is outlined—then, the additional skills needed for conservation. Forexample, it is useful if architects combine generalpractice with conservation, as design is their coreskill. Practice gives a sense of proportion, whichmay be lacking in specialists dedicated to one single aspect of conservation. The tasks listed inpara. 5 of the ICOMOS Guidelines for Education

and Training for the Conservation of Monuments,Ensembles and Sites are repeated. From the chart,it will be seen that all professionals can contributeto at least half the tasks, and some to all. Each pro-fession will approach these tasks differently, butwhere appropriate, make its contribution:

01. Administrator or owner02. Archaeologist03. Architect04. Art/architectural historian05. Builder or contractor06. Conservation or historic buildings officer07. Conservator08. Engineer (civil or structural)09. Environmental engineer10. Landscape architect or historic gardens

conservator11. Master craft worker12. Materials scientist13. Buildings economist (quantity surveyor)14. Surveyor15. Town planner16. Curator

The ICOMOS (International Council onMonuments & Sites) Guidelines for Education andTraining for the Conservation of Monuments,Ensembles and Sites was prepared by theInternational Committee for Training and wasapproved by the Executive Committee for submis-sion to the Colombo General Assembly of ICOMOSin August 1993.

For ready reference, para. 5 is reproduced in full.This is followed by a chart, which shows the special relevance of particular sections to each professional.

13

Multi-disciplinary collaboration projects inthe UK based on the ICOMOS Guidelines forEducation and Training for the Conservationof Monuments, Ensembles and Sites

ICOMOS Guidelines, para. 5 (Colombo, 1993)

Conservation works should only be entrusted topersons competent in these specialist activities.Education and training for conservation should pro-duce from a range of professionals, conservationistswho are able to:

(a) read a monument, ensemble or site and identifyits emotional, cultural and use significance;

(b) understand the history and technology of mon-uments, ensembles or sites in order to definetheir identity, plan for their conservation, andinterpret the results of this research;

(c) understand the setting of a monument, ensembleor site, their contents and surroundings, in rela-tion to other buildings, gardens or landscapes;

(d) find and absorb all available sources of informa-tion relevant to the monument, ensemble orsite being studied;

(e) understand and analyse the behaviour of mon-uments, ensembles and sites as complex systems;

(f) diagnose intrinsic and extrinsic causes ofdecay as a basis for appropriate action;

(g) inspect and make reports intelligible to non-specialist readers of monuments, ensembles orsites, illustrated by graphic means such assketches and photographs;

(h) know, understand and apply UNESCO conven-tions and recommendations, and ICOMOSand other recognised Charters, regulationsand guidelines;

(i) make balanced judgements based on sharedethical principles, and accept responsibility forthe long-term welfare of cultural heritage;

(j) recognise when advice must be sought anddefine the areas of need of study by differentspecialists, e.g. wall paintings, sculpture andobjects of artistic and historical value, and orstudies of materials and systems;

(k) give expert advice on maintenance strategies,management policies and the policy frameworkfor environmental protection and preservationof monuments and their contents, and sites;

(l) document works executed and make themaccessible;

(m) work in multi-disciplinary groups using soundmethods;

(n) be able to work with inhabitants, administra-tors and planners to resolve conflicts, and todevelop conservation strategies appropriate tolocal needs, abilities and resources.

Chart showing the relevance of para. 5sections to each professional

In the UK, sixteen different types of professionalsnormally involved in Conservation can be identified.A professional is a person who can contribute artis-tically, intellectually or practically to the process ofconservation, and so includes craft workers, contrac-tors and builders. Of these professionals, six may be involved in all the fourteen tasks, but all areinvolved, to a greater or lesser degree in more thanhalf the tasks as the chart below shows:

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A B C D E F G H I J K L M N score

01 Administrator/owner x x x x x x x x 8

02 Archaeologist x x x x x x x x x x 10

03 Architect x x x x x x x x x x x x x x 14

04 Art/architectural historian x x x x x x x x x x x 11

05 Builder/contractor x x x x x x x x x 9

06 Conservation officer x x x x x x x x x x x x x x 14

07 Conservator x x x x x x x x x x x x x x 14

08 Engineer x x x x x x x x x 9

09 Environmental engineer x x x x x x x x x x 10

10 Landscape architect x x x x x x x x x x x x x x 14

11 Master craft worker x x x x x x 6

12 Materials scientist x x x x x x x x x x 10

13 Building economist x x x x x x x x x 9

14 Surveyor x x x x x x x x x x x x x x 14

15 Town planner x x x x x x x x x 9

16 Curator x x x x x x x x x x x x x x 14

7 12 11 14 11 12 14 16 16 9 13 15 15 10

ICOMOS Guidelines para. 5

Profession Tasks

It is important for all professionals to understandthe respective roles of conservators, consultants,owner, site manager, and maintenance staff, as wellas understand the part played by national govern-ment policies, local government, non-governmentalorganizations and international bodies in historicalconservation.

The chart can also be read vertically, as a checklist to indicate which professionals might be involvedin a particular operation, e.g. ‘diagnose intrinsic andextrinsic causes of decay as a basis for appropriateaction’, may involve some twelve disciplines.

Given below are draft outline profiles of the mainprofessions who may be asked to collaborate in aproject for conservation of a monument, ensembleor site in the UK.

The administrator or owner

The administrator or owner should be able to

1. Take part in policy formulation ensuring that allpotentially viable courses of action are consid-ered and costed and their merits and draw-backs assessed.

2. Implement agreed policies faithfully by approv-ing projects and controlling funding.

3. Monitor the effects of agreed policy and forecastadequately the long-term costs of a building inuse.

4. Make decisions early enough to enable the pro-ject team to do their work properly.

5. Ensure that agreed proposals are adhered to,monitor progress and handle publicity.

For conservation:

6. Accept responsibility as a trustee for future gen-erations for preserving and handing on a pieceof heritage.

7. Understand the unique qualities of a building andwork for their preservation and enhancement

8. Promote studies of the building to increaseknowledge for future generations.

9. Take advice to formulate policies after consid-ering all viable options.

10. Understand the ‘framework’ of conservationincluding its theory.

11. Make sure that the use to which the building isput, directly or through an agent, is compatiblewith its conservation, and make sufficient fundsavailable for continuing maintenance whichwill help its preservation.

12. Accept that there are risks inherent in a project.These should, if possible, be exposed by pre-liminary opening up.

13. Select professional advisers carefully throughthorough references and appreciate their differ-ent roles and the potential contributions of eachprofession.

14. Ensure that causes of delay are properly inves-tigated and diagnosed.

15. Define the objective of a conservation project.16. Approve the project and programme.17. Make available steady and sufficient funding.18. Allow a separate budget for research and doc-

umentation and ensure that the documentationneeded is complete.

ICOMOS guidelines para. 5 sections c, d, h, i, j, l,m and n are specially relevant.

Note: In a large institutional project, a project man-ager may undertake some of these responsibilities.

The archaeologist

The archaeologist should be able to

1. Understand all techniques for investigating andrecording sites, gardens and structures and beproficient in these techniques.

2. Make a detailed study of the building itself inthe context of documentary and other researchcorrelated with the physical evidence as to thenature and sequence of the changes it hasundergone in its history.

3. Understand all methods of dating artefacts andstructures and arrange for this work to be car-ried out where appropriate; advise on thearchaeological potential of sites and structuresbefore development begins and recommendany investigations that may be justified.

4. Supervise the detailed recording of structuresbefore and during works, by drawn, photo-graphic and written means.

5. Supervise archaeological excavations and theirproper recording. Excavations may be either ofa ‘rescue’ nature, to recover evidence that maybe lost during the course of development, or ofa ‘research’ nature, designed to reveal hiddenevidence and that which is required to informother specialists (eg architects, engineers) intheir work.

6. Record contractors’ excavations and chancediscoveries, and interpret their significance.

7. Carry out investigations into the fabric of build-ings, to elucidate historical sequences, revealhidden features, study mortars and plasters etc.

8. Estimate for and organise excavations andbuilding recording projects, and manage sitelabour, within agreed schedules and timetables.

9. Be familiar with the briefs and requirementsaffecting building sites generally, understand

Chart showing the relevance of para. 5 sections to each professional

191

the different pressures of costs and time underwhich contractors work; work alongside and inclose collaboration with contractors and otherspecialists; be prepared to modify tactics andprocedures if circumstances so dictate, provid-ing this can be done without serious detrimentto the quality of the archaeological work.

10. Understand the conservation and curation ofartefacts and records; coordinate conservationon site with competent conservators.

11. Write regular progress reports and supply information as required to other specialistsengaged on the project; write annual reports onextended projects and produce a final report on completion, suitable for deposition in anarchive, or publication if appropriate, within anagreed time scale and cost.

12. When conservation depends on reuse, acceptminor losses of archaeological material of sec-ondary importance to enable the overallscheme to go ahead.

ICOMOS guidelines para. 5 sections a, b, c, d, h,i, j, k, l and m are specially relevant.

(With acknowledgement to Dr W.J. Rodwell.)

The architect

The architect should be able to

1. Design significant spaces, forms and structuresin accordance with peoples’ needs, which havethe qualities of ‘firmness, commoditie anddelight’ with the desired environment, in cooper-ation with the building owner.

2. Understand the nature of materials and theirappropriate uses; write specifications in suffi-cient detail to allow the contractor to preparepriced schedules or for the quantity surveyor toprepare bills of quantities, and for the work to becarried out by the contractor.

3. Consider the climatic conditions and the causesof decay when designing.

4. Obtain the necessary statutory consents for thework proposed.

5. Co-ordinate the work of consultants and special-ists, select suitable contractors, obtain tenders,oversee and administer contracts and settle finalaccounts; act as an ‘enabler’.

6. Provide for proper maintenance through designand follow-up services.

For conservation work the architect should also beable to

7. Understand the social significance of historicbuildings, the evolution of their styles and thetechnology of building; appreciate architectureas a social art objectively, without preferencefor any style.

8. a. Visualise solutions to complex problems andadvocate new uses to which a building couldbe put with a minimum of adaptation if any;design any necessary adaptations so that theypreserve essential historic features; knowenough to be able to question engineeringproposals that run counter to conservationprinciples; co-operate with planners, surveyors,landscape architects and other specialists.

b. Appreciate the different approaches that areappropriate to ancient monuments (struc-tures and sites not in beneficial use) and historic buildings which should be kept inbeneficial use; investigate the effects of dif-ferent levels of intervention on the financialvalue of the building, usually with a view topersuading owners that less radical solu-tions make good financial sense.

c. Understand the scope and effect of limita-tions on the introduction of new services,and have a sound knowledge of effectiveand acceptable measures for fire protection,means of escape and security.

9. Commission and control the necessary surveywork including photogrammetry.

10. Write, as well as specifications, schedules ofwork, and ensure that the conditions of con-tract face up to the hazards inherent in workingon an archaeological site; decide on the extentof opening up or cutting back.

11. Understand grant possibilities and availablesources of financial assistance.

12. With reference to the ICOMOS guidelines, para 5,the architect should be able toa. Read a monument, ensemble or site and

identify its emotional, cultural and practicalsignificance.

b. Understand the history and technology ofmonuments, ensembles and sites in order todefine their identity, plan for their conserva-tion and interpret the results of this research.

c. Understand the setting of a monument,ensemble or site, their context and surround-ings in relation to other buildings, gardensor landscapes.

d. Find and absorb all available sources ofinformation relevant to the monument,ensemble or site being studied.

e. Understand and analyse the behaviour ofmonuments, ensembles and sites as complexsystems.

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f. Diagnose intrinsic and extrinsic causes ofdecay as a basis for remedial action.

g. Inspect and make reports intelligible to non-specialist readers of monuments, ensemblesand sites, illustrated by graphic means suchas sketches and photographs.

h. Know, understand and apply UNESCO conventions and recommendations andICOMOS and other recognised charters, reg-ulations and guidelines.

i. Make balanced judgements based onshared ethical principles, and acceptresponsibility for the long-term welfare ofcultural heritage.

j. Recognise when advice must be sought anddefine the areas of need for study by differ-ent specialists, e.g. wall paintings, sculptureand objects of artistic and historical valueand/or studies of materials and systems.

k. Give expert advice on maintenance strate-gies, management policies and the policyframework for environmental protectionand preservation of monuments and theircontents, and sites.

l. Document works executed and make docu-mentation accessible.

m. Work in multi-disciplinary groups usingsound methods, and being aware of andapplying where appropriate the contribu-tion of art-historians and archaeologists.

n. Work with occupiers, administrators andplanners to resolve conflicts and to developconservation strategies appropriate to localneeds, abilities and resources.

Note: the architect should also train as a projectmanager.

The art/architectural historian

The art/architectural historian should be able tostudy all aspects of works of visual arts, what theylook like, their style, what they depict, their icono-graphy and what techniques have been employed intheir production. They are also concerned aboutwhat part art plays in the society in which it is cre-ated, and what art can tell us about those societies.Being first and foremost historians, they study andresearch the documents as they relate to the livesand works of the artists, as well as the works of artthemselves. A high degree of general culture isabsolutely requisite for the full enjoyment of a workof art. Art history is built up by research and publica-tion, and creates a corpus of knowledge and inter-pretation, which is vital to conservators in their

work. It can help them to become fully aware of the significance of a building or an object, and itsmessage to the present day.

1. Investigate and report on the motivation and his-tory of the creation of a work of art or historicbuilding, ensemble or site in its cultural context,researching sources and influences.

2. Make a detailed study of the building itself in thelight of documentary and other research corre-lated with the physical evidence as to the natureand sequence of changes it has undergone during its history.

3. Analyse and advise on the authenticity and sig-nificance of the work of art, monument, ensem-ble or site; such advice should be objective,based on a sufficient level of understanding ofscientific conservation techniques to make collaboration meaningful.

4. Understand and accept the need for re-use, as a prerequisite for conservation in some cases,and the attendant minimum adaptations this mayrequire.

5. Distinguish between historically essential fea-tures that must be preserved, and those of secondary importance that may have to be sac-rificed to enable conservation of the essentials tobe realised.

6. Recognise, as part of the professional team, thecontractual rules and professional practices anddiscretion required between members of theteam and the client, be they an individual or apublic body; be aware that aesthetic and struc-tural considerations must be taken into accountfor the successful completion of the project.

7. Always remember the joy and wonder thatworks of art can communicate.

ICOMOS guidelines para. 5 sections b, c, d, e, f, g,h, i, l and m are specially relevant.

The builder or contractor

The builder or contractor should be a good employerof good labour and have a reputation for the qualityof work which is appropriate to the project. The suc-cess of any project is dependant on the knowledge,experience, competence, general attitude andapproach of the contractor who carries it out. Theskills of craftsmen and effective organisation of thework are essential—there is no substitute for them.

The builder or contractor should be able to

1. Obtain a contract for a project either in competi-tion (which may be open or closed), or by negotiation.

Chart showing the relevance of para. 5 sections to each professional

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2. Undertake to complete a contract within an agreed time for an agreed price, with thehelp of sub-contractors, specialists, artists andtradesman. The responsibility for vetting andselection of sub-contractors and others for skills,insurances, health and safety etc must bedefined.

3. Undertake to provide the skilled craft workersand labour required to execute the programme.

4. Make a programme which brings all activitiesinto harmony; this can be a computerised net-work programme.

5. Hand over the project complete, with all plant,mechanical and electrical installations testedand working properly.

The contractor is entitled to claim extras fordelays in providing information necessary forprogress from the design team, or for additionalwork required through no fault of the contractor egpreviously undiscovered defects.

For conservation

The contractor should become part of the team andshould be paid for his management skills. Heshould be able to

6. Integrate into the contract the contribution thatskilled craft workers and conservators whilstkeeping sub-contracting to a minimum; main-tain staff for all levels of general craftwork, sur-veying and management. Without such a policythe contractor cannot develop the workforce norprovide career development—the only methodby which quality and effective team workingcan be guaranteed.

7. Advise on and adopt the most efficient way ofworking in relation to the time and resourcesavailable, the correct size of labour force and asuitable contract duration allowing the timeneeded for skilled work.

8. Take responsibility for the protection of all theoriginal fabric and historic contents, againstpotential causes of damage including wind,rain, frost and mechanical damage during oper-ations; temporary works and fixing of scaffold-ing must not affect the fabric.

9. Cooperate in minimising non-productiveexpenditure and overheads, and anticipate haz-ards and reduce risks, taking all precautionsagainst the outbreak of fire.

10. Produce a programme sufficiently flexible togive time to resolve unexpected problems.

11. Accept that a complicated and hence expensiverepair can from the conservation point of viewbe preferable to replacement.

ICOMOS guidelines para. 5 sections b, e, f, g, h, i,k, l and n are specially relevant.

The conservation officer

The conservation officer or historic buildings officeroperates within the context of local or national gov-ernment and is concerned full time with all aspectsof architectural conservation.

The conservation officer’s job combines knowl-edge and skills which are applicable generally—thelaw, conservation, philosophy, general techniquesetc—with specific local knowledge—architecturaldesign, building traditions, local conservationissues, sources of expertise etc—which require longservice in one area to be most effective. Constructiveuse of the powers available comes only with experi-ence; the importance of experience and continuityis not yet sufficiently realised by employers.

Conservation officers and historic buildings offi-cers should be able to

1. Appreciate architecture both grand and vernac-ular sufficiently to be able to assess the specialcharacter of any individual building and theeffect of any proposed works on it.

2. Appreciate issues of design, and in particularthe challenges involved in providing for newneeds within a historic environment.

3. Understand thoroughly the planning and otherlegislation affecting historic buildings and con-servation areas and use this to achieve success-ful conservation; use the powers available forintervention and exercise the authority, knowl-edge and expertise to be a competent witnessin court and at public inquiry.

4. Understand thoroughly local building tradi-tions, and relevant sources of information,expertise, materials etc.

5. Communicate their knowledge to and encour-age awareness among both professionals andlay people, particularly building owners.

6. Have a working knowledge of other legislation,especially building regulations, fire regulations,environmental health, disabled access and high-ways works, and of statutory and non-statutoryagencies affecting historic buildings and areas,so as to be able to resolve conflicting require-ments to achieve successful solutions.

7. Understand the factors affecting the detaileddesign process, including the availability ofappropriate products, and be able to suggestsolutions to specific problems in broad terms orin detail as required.

8. Act as a negotiator, competent to take the initiativeand bring together disparate (and occasionally

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desperate) bodies and individuals to work con-structively and achieve successful solutions;sometimes in situations (eg in relation to unau-thorised works), which may require tact andsensitivity under extreme pressure.

9. Provide expert input to the planning process inthe form of contributions to the preparation ofpolicies, design and planning briefs, and act ascase officer or provide detailed advice to otherson all matters affecting historic buildings andconservation areas.

10. Diagnose decay and its causes, and adviseowners and others on the appropriate measuresto be taken for remedial work, including alter-native solutions where appropriate.

11. Develop good working relationships withsources of specialist advice with regard to tech-nical, historical and other matters.

12. Organise and manage photographic and otherrecord systems as both sources of informationabout specific buildings and the basis forunderstanding forces for change.

13. Have a thorough knowledge of statutory, non-statutory and voluntary organisations workingin the conservation field, and of their respectiveroles as consultees and sources of specialistinformation and advice.

ICOMOS guidelines para. 5, ALL sections are relevant.

The conservator

The conservator is wholly devoted to a career in con-servation. The profession is defined in the ICOMdocument.

The conservator should be able to

1. Appreciate the significance of an object or feature of a building with its contents, under-stand the building as a whole and the import-ance of the feature in its context, and have agood working relationship with the architect,curator, archaeologist and architectural historian,and other members of the conservation team.

2. Consider, when presenting a programme for theconservation of the object or building, the culturalsensitivities surrounding the subject whether reli-gious, historical or social, and present such pro-posals on sound ethical conservation principles.All these matters as well as aesthetic and struc-tural implications must be taken into considera-tion for the successful completion of the project.

3. Assess conservation priorities and maintain the quality of workmanship within budgetaryconstraints.

4. Undertake contract work on a sub-contract basis,working under conditions dictated by the maincontractor, accommodating other trades, andunder the main contractor’s programme and siteregulations.

5. Understand and practise with manual dexteritythe techniques that were used to create theobjects, often works of art, being conserved.

6. Diagnose the causes of decay, including envir-onmental causes related to climate and build-ings, with methods of monitoring these.

7. Offer a programme for preservation and restora-tion in such a way as to present the object to itsaudience.

8. Lead a team of craft workers productively whenappropriate.

9. Have sufficient theoretical knowledge of the rel-evant craft skills to supervise members of theteam in the execution of their work; recognisewhen less traditional processes should be used,and when modern chemicals, be they solvents,resins or consolidants, should be introduced ona purely scientific basis.

The selection of techniques will not only be gov-erned by the condition of the building or artefact butalso by whether it is practical to carry them out in theconditions dictated by the site, the degree of conser-vator and craft skills available and the suitability ofmaterials be they traditional, modern equivalents orchemicals. The team should consist of a correct bal-ance of craft workers, conservation technicians andconservators, which the conservator must determinewhen assembling the team for the project.

1. Understand the chemistry of treatments, materi-als and methods of investigation, research andanalysis.

2. Recognise when meaningful monitoring isbeyond their expertise, and identify the specialistcentres to which samples can be sent for analysis;and identify the relevant specialist or institution toturn to if specialist advice is required.

ICOMOS guidelines para. 5, ALL sections are relevant.

The civil or structural engineer

The civil or structural engineer should be able to

1. Analyse the stress, strain and torsion due to alldead and live loads that may be imposed on thebuilding as well as those arising from drying outand imposed deformations eg settlement.

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2. Understand the nature and behaviour of build-ing materials, especially traditional materialsand methods of their use, including theirbehaviour under stress and under changingenvironmental conditions.

3. Understand the nature and behaviour of soilsand geological strata.

4. Understand the causes of decay in buildings.5. Produce solutions to structural problems

including designing structures using first prin-ciples as well as Codes of Practice andStandards; consider alternative structural solu-tions and advise on structural economy andmaintenance as well as fire-protection.

6. Collaborate with architects and other consultants.

For conservation

7. Understand and practise the ethics of conserva-tion, on the basis of several years’ experiencein working on building structures before under-taking conservation projects.

8. Appraise an existing structure and report on itscapabilities, understanding the real three-dimensional behaviour of structures asopposed to the simplified assumptions onwhich most text books and design codes arebased; similarly the real behaviour of materials,particularly obsolete ones, within and beyondthe elastic range as well as their time-dependantbehaviour under load.

9. Be aware of the reasoning that determines con-ventional design of safety for new constructionand the difference from real factors of safety forexisting structures, and assess whether testing islikely to materially improve the appraisal ofstrength and serviceability and to specify, super-vise and interpret the results of tests. (Architectsshould also be aware of these matters.)

10. Organise meaningful tests and analysis of materials.

11. Advise on necessary studies and investigationof structures, including the use of physical andcomputer models.

12. Examine alternative schemes and proposeinterventions that are the minimum necessary,and monitor these on a regular basis after completion.

Civil and structural engineers should have severalyears’ experience working on buildings of tradi-tional construction and should preferably haveundertaken a post-graduate course in conserva-tion—at present there are few engineers who reallyunderstand historic buildings.

ICOMOS guidelines para. 5 sections b, d, e, f, g i,l and m are specially relevant.

The mechanical services engineer and power electrical engineer

Control of the environment was almost non-existentin historic buildings being attempted by open fireswith flues, although it is true that the Romans hadsophisticated hypocausts, and the Chinese similararrangements for heating their beds. Plenum andcentral heating was introduced in the 19th Centurywith beneficial results. It was not, however, untilair-conditioning was introduced in the early 20thcentury, that full environmental control was possible.This control is an essential element in modernarchitecture and receives a large portion of thebuilding budget.

For conservation, he should be able to

1. Understand older building technologies eg to findinterstitial space suitable for running services.

2. Understand the properties of old materials.3. Diagnose problems to find the right solution

in consultation with architects, surveyors andhistorians.

4. Deal with mechanical and electrical systemswithout irreversible damage to architecturalintegrity; provide adequate access to systems.

5. Design installations that are compatible with thespatial, thermal and physical characteristics of abuilding bearing in mind the need for mainten-ance and future renewal; including hot and coldwater services, piped heating systems, plenum airconditioning systems for heating, cooling and fil-tering, fire and intruder alarm detectors, sprink-lers and dry risers, electric lighting and powersupply, telephone and other wired installationsincluding audio loop and speech reinforcement.

6. Understand the effect of local climate on a build-ing, and its physical and thermal characteristicsas a spatial structural and environmental system.

7. Cooperate closely with adjacent trades and takeaccount of existing systems (eg routing electricalsupplies separately from water pipes); provideemergency auxiliary power for pressurisation andfire-fighting, and advise on the protection ofstructure and surroundings during construction.

8. Obtain and approve specifications and esti-mates; work with other consultants, supervisework in progress, set up and balance systems,and settle contractors’ accounts where necessaryin the context of a main contract.

9. Provide maintenance manuals and schedules forthe owners’ use.

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For conservation

10. Special design skills and judgement are neededto obtain the different needs of occupants, con-tents and building fabric. Particular expertise isrequired to harness the potential advantages oftraditional buildings to meet modern standards,for example the effects of thermal mass and theadvantages of natural ventilation combinedwith shutters and blinds.

11. Design systems which, in order to respect thecharacter of the building, utilise componentswhich would normally be considered inefficientor uneconomical eg air ducts of unconventionalcross-sectional dimensions.

12. Understand the history of electrical andmechanical installations.

13. Test and report on the condition of existing sys-tems and advise on refurbishment or renewal.

14. Skilfully conceal new installations to avoidinappropriate intrusions.

15. Understand air movement, deposition of pollutants and condensation in historic buildingvolumes.

16. Find and digest all available sources of infor-mation relevant to the monument, ensemble orsite being considered.

The power electrical engineer

The power electrical engineer should be able to(with acknowledgment to Gersil Kay)

17. Get electrical power from source to systemwithout disrupting the original design.

18. Be aware of other trades so that they commu-nicate and coordinate their work, to avoiddrawing one system in the space of another.

19. Design emergency power systems capable oflasting long enough in disaster situations toallow for evacuation of the occupants. (This mayrequire more than the cheapest installation.)

20. Anticipate the effects of natural and manmadedisasters, avoiding placing electrical installa-tions where they will be immediately vulnera-ble to water.

21. Adapt existing products to older buildings.22. Consult architects or historians on the selection

of appropriate equipment eg light fittings.23. Document as-built installations carefully for

future reference.24. Determine which methods and systems are

capable of being re-used and which are not.(Most wiring must be renewed after thirtyyears.)

25. Control the routing of electric power cables andtransformers in environmentally sensitive areas.

ICOMOS Guidelines para 5 sections c, d, e, f, g, h,i, k, l and m are specially relevant.

The landscape architect or historic gardens conservator

The professional expertise of landscape architects isconcerned with the planning, design and manage-ment of outdoor spaces. These may be large or small,urban or rural; commonly they are related to build-ings, and the landscape architect must consider theircharacter, appearance, layout and composition,working with landform and soil, plants and naturalvegetation, water, views, paving and structures suchas fences and walls. This holistic approach carrieswith it a responsibility to promote the coordination ofall elements of the outdoor environment such as theuses, processes, interests and values it encompassesand which affect its character. The landscape archi-tect must consider both ecological and culturalinterests, including historical, aesthetic, associativeand recreational values.

The landscape architect should be able to

1. Understand local climate, micro-climate and soilconditions, the cultivation of plants including thesafe use of fertilisers, herbicides, pesticides andother chemicals.

2. Contribute to the preparation of a brief, formu-late and present clearly proposals and advice inthe form of drawings, written text and the spoken word.

3. Supervise effectively the execution of proposals,often working as part of an interdisciplinaryteam.

For conservation

4. Be familiar with the history of gardening andlandscaping including planting design, both as anart and as a craft; and with the history of differenttypes of features including plants found in historicparks and gardens, and including the history oflandscape and conservation practice in othercountries; be aware of the sources of specialistinformation beyond their own expertise.

5. Understand the relationship of gardening andlandscaping with other art forms especiallyarchitecture, the graphic arts and literature, andthe social and historical context within which asite was created or developed.

6. Observe with an objective, critical and histori-cally informed eye all the elements of a site

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including land form, earthworks, rocks, waterfeatures, planting, structures etc and keeping inmind subterranean archaeological evidence andmaintaining an interest in natural flora and fauna.

7. Provide a critical assessment of the historicaland aesthetic character of a site in consultationwith architects and historians, remaining intel-lectually flexible and not prejudiced by per-sonal preferences.

8. Recognise the criteria of authenticity and theimportance of details to the character of a sitebut that because of their natural cycles ofgrowth and decay elements may have to bereplaced more frequently than the elements ofbuildings, particular attention being paid to thehistorical accuracy of replacements.

9. Understand the theory and practice of land-scape conservation, including the survey andrecording of sites, making assessments, formu-lating and executing policies and proposals andmonitoring existing programmes and takinginto consideration the timing of work.

10. Apply practical techniques for landscape con-servation.

11. Understand the relationship between conserva-tion and other aspects of management of thesite, including the raising of income, provisionof domestic facilities, private or public amenityand the conservation of the natural heritage, orother aspects of cultural heritage.

12. Appreciate the roles and relationship betweenconservator, curator, site manager and mainten-ance staff.

13. Understand the role of national government,local government, non-governmental organisa-tions and international conservation bodies.

14. Formulate proposals for landscape conservationwhich allow for the presentation of sites to vis-itors and for visitor facilities, having regard tothe particular vulnerability of landscape todamage for unsustainable tourism.

15. Ensure that adequate records are maintainedincluding documentation of condition beforework starts, the rationale of decisions and thedetails of work carried out.

ICOMOS guidelines para. 5 ALL sections are relevant.

The master craft worker

The master craft worker is a specialist who supple-ments the general skills available to the contractor.

The master craft worker should be able to

1. Supervise a group of related trades and producereplicas of high quality.

2. Guide and lead a small group of craft workers.3. Know the history of his trade and how it has

developed.4. Know the characteristics of the relevant materials

and how these affect workmanship and design.5. Sketch details and take all relevant dimensions

allowing for tolerances, shrinkage and movements.

For conservation

7. Understand that repair is always better thanrenewal although it may take more time and skill.

8. Advise other members of the conservation team atthe outset of the project and explain the scope ofcraftsmanship and efficient working methods.

Often in conservation normal building practicefails due to the complexity of the problems, and themaster craftsman should be asked to lead in reviv-ing historic practices.

9. Command a group of related historic trades andrepair, and contribute to the conservation of,objects and building elements as well as pro-duce original work and replicas of high quality.

ICOMOS guidelines para. 5 sections b, f, g, h, i, k,l and m are specially relevant.

The materials scientist (with acknowledgment to Dr Nigel Seeley)

There is a variety of circumstances in which a materials scientist can provide evidence which isvital to well-founded decision-making in architec-tural conservation projects.

The materials scientist should provide informa-tion on all aspects of the materials of historic build-ings, and on the materials, traditional or modern,used for their conservation and repair. To be effec-tive, this requires that the materials scientist shouldhave a sound knowledge of the history of buildingconstruction in all periods, and the technology ofthe materials concerned, both in order to ask theright questions and to interpret scientific data in auseful way. Knowledge of the scientific techniquesalone is not sufficient, as incorrect interpretationcan lead to the drawing of false conclusions.

The various ways in which the material scientist canprovide assistance in historic building conservationmay be summarised under the following headings:

1. Identification. The identification of the materialsused in historic buildings, including the provision

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of information on their source, date of intro-duction, history, mechanical properties and technology.

2. Deterioration. The recognition of evidence ofdeterioration, and explanation of the cause(s)and process(es) involved.

3. Preservation. The recognition of steps to betaken to assist in the preservation of historicmaterials.

4. Prediction. The prediction of behaviour withrespect to performance and compatibility, andlikely life, of both historic materials and modernmaterials used for conservation purposes, and oftheir interaction with each other under differentenvironmental conditions. The effect of paintson timber, rendering and other materials shouldbe carefully assessed.

5. Interpretation. The interpretation of analyses andother scientific data obtained, by material scien-tist or by others, during the examination oranalysis of historic or modern materials.

6. Specification. To contribute to the specificationof materials and methods to be used in the con-servation of historic buildings in so far as thisrelates to the properties and performance of thematerials forming a part of the structure. Also,the specification of analyses or other scientifictechniques to be employed in the examinationof historic or modern materials, in order toexplain their history or technology, or to deter-mine their suitability for use in the conservationof historic buildings.

7. (S)He should understand the effects of climate,microclimate and pollutants in the atmosphere.

8. (S)He should visit sites, ensembles and monu-ments with members of the conservation team toestablish causes of decay and advise on anyresearch necessary.

9. For modern buildings of reinforced concrete spe-cialists may be needed to diagnose the causes andextent of decay. The pathology of the new structural materials, such as glass, aluminium andplastics—will also have to be studied.

The building economist (quantity surveyor inthe UK)

It should be noted that in countries other than theUK the work of the building economist is integratedinto the architect’s or the contractor’s office.Normally the architect produces the drawings andspecification but too often the quantity surveyorincludes the specification in the Bills of Quantities,which incorporate the Conditions of Contract.

Specifications should always stand alongside bills ofquantities rather than be absorbed in them.

The building economist should be able to

1. Analyse what work needs to be done and con-verts this analysis into a budget.

2. Make approximate estimates of cost of the project,taking into account all relevant factors includingthe availability of labour, materials, subcontractors,access etc and the ‘tender climate’; take the spec-ifications by architect, surveyor and engineer andprepare bills of quantities which measure theamount of work to be done and specify its quality, often by reference to Standards and Codesof Practice prepared for new construction.

3. Advise on the economic aspects of a project.4. Advise on the most suitable form of contract.5. Provide tender documents based on design

drawings and specifications prepared by others.6. Check tenders received and advise on

acceptance.7. Prepare valuations for interim payments taking

any claims into account.8. Check and prepare the final account.

For conservation

9. Understand the possibilities of conservationand rehabilitation in a project; using imagina-tion and experience to assess what the timeand total scope of the works might be in orderto prepare an initial budget robust enough tocope with the full extent of the likely works.

10. Explain the build up of the estimate in simpleterms and provide an independent cash-flowprogramme for the building owner.

11. Advise on contract procedures which give flexi-bility in the event of unforeseeable difficultiesarising during the execution of the works andwhich serve the needs of the building, indicatingforeseeable risks so that the contractor can organ-ise his work properly and preventing increases incost and eliminating grounds for claims.

12. Avoid conflating incompatible sub-contracts.Encourage craftsmen to contribute skill and effi-ciency, and make provision for conservators.

13. Understand the uses of scaffolding and otherfixed plant such as temporary roofs and struc-tural supports and their effect on programmingand costs of the building operation.

14. Report at monthly or quarterly intervals to theclient on the cost of the project taking intoaccount all changes initiated by the client,architect or others, in order to ensure strict con-trol of costs against budget and to verify workbeing done against grants provided.

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15. Be solely responsible for control of costs, and act to avoid excessive and unproductiveoverheads.

ICOMOS guidelines para 5, sections d, g, h, i, k, l,m and n are specially relevant.

The surveyor

The profession of chartered surveyor is thought to beunique to the UK, but has parallels in many coun-tries. Within the UK the profession is split into anumber of specialisations, all of which may haveroles in the field of conservation. Whilst the buildingsurveyor is particularly active in the field, the quan-tity surveyor (q.v.), the general practice surveyorand the planning and development surveyor arealso involved, in their own specialisations.

The general practice surveyor specialises in valu-ation, land transactions and property management.

For conservation the general practice surveyorshould be able to

1. Develop management techniques for improvingthe condition of historic buildings and areas.

2. Organise planned and preventive maintenancestrategies.

3. Secure, in collaboration with other professionals,beneficial new uses for redundant historic build-ings and carry out rehabilitation or refurbish-ment projects, which respect architectural,archaeological and historic values.

The building surveyor specialises in a wide rangeof technical problems affecting buildings and con-struction projects. The core skill of the BuildingSurveyor is an in-depth knowledge of both modernand traditional building construction and materialscoupled with project control and property andbuilding law and an appreciation of architecturaldesign and style.

For conservation the building surveyor should beable to

1. Inspect buildings and carry out surveys to iden-tify defects and analyse their causes.

2. Draw up and supervise programmes for repair,refurbishment and adaptation for new beneficialuses.

3. Advise on the future repair and maintenance ofbuildings and prepare conservation plans.

4. Act as team leader or project coordinator forconservation projects.

The planning and development surveyor spe-cialises in all aspects of urban and rural planning,strategic planning and planning law and procedures.

For conservation the planning and developmentsurveyor should be able to

1. Advise on the planning and economic aspects ofconservation and urban renewal schemes

2. Advise on property values, finance and generalproperty law.

3. Exercise skill in finding new uses for redundanthistoric buildings.

The rural practice surveyor traditionally spe-cialises in the management of rural property includ-ing the sale of live and dead stock, and has recentlybecome increasingly involved in forestry and estatemanagement and rural planning with an emphasison the conservation of the countryside and the natural heritage.

The land and hydrographical surveyor specialisesin the measurement of natural and man-madefeatures. In conservation this involves the recordingof historic structures.

ICOMOS guidelines para. 5, ALL sections are relevant.

The town planner

The town planner is primarily trained in land use,development control and planning policies. In theUK the conservation officer or historic buildings offi-cer works within the context of town planning legis-lation. Their special role is to persuade owners ofbuildings to respect the historic and cultural valuesof their property, to give helpful technical advice onrepairs and preservation, and to advise on the suit-ability of projects which require formal ListedBuilding Consent. It should be noted that the scopeof these tasks varies widely from authority to author-ity, and may increase in the future.

There is a presumption in favour of the conserva-tion of monuments, ensembles and sites, but thisdoes not mean an unquestioning policy of preserva-tion at any price—there may be tired old buildingsthat want to lie down.

The town planner should be able to:

1. Be aware of design issues and appreciate urbanlandscape and spaces, and take a constructiverole in the preparation of proposals for the repair,maintenance and re-use of historic buildings,based on a clear understanding of their individualmerits and of what is significant and what is not.

2. Read a monument, ensemble or site and identifyits significance.

3. Understand the historical, morphological, socialand economic aspects of monuments, ensemblesand sites.

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4. Review past plans and projects and evaluatetheir successes and failures and appraise the rea-sons for these.

5. Collect and use national data on population, traf-fic and commerce as it relates to the area beingconsidered; identify the needs of the communityand guide the economic forces to support con-servation.

6. Offer options for future actions for public partic-ipation and political decision making, allowingfor continuing financial implications.

7. Manage change and ensure the best possible useof resources balancing the economics of reten-tion versus redevelopment.

8. Operate controls on the height, massing, silhou-ette, window–wall ratio and materials, includingtheir colour and texture, used in development;extend this control to encompass paving, street-furniture and planting.

ICOMOS guidelines para. 5 sections c, d, g, h, i, k,l, m and n are specially relevant.

The curator

The curator should be a scholar with wide terms ofcultural reference, trained in museology includingmanagement, documentation, preventive conserva-tion, security and administration. Continued self-education is essential.

The curator should be able to

1. Conform to the ICOM Code of ProfessionalEthics with special reference to personal respon-sibilities to the public and colleagues.

2. Inspect the collection with a conservator at reg-ular intervals and make formal reports on itscondition—conservation of objects should be acollaborative procedure with limitations on aes-thetic reintegration.

3. Arrange for a specialist architect to inspect themuseum buildings at five yearly intervals or lessto advise on environmental questions whichmight affect the collection; with the architectprepare a formal report.

4. After the architect’s inspection, carry out a ‘fireand security’ audit, and arrange for regular firedrill rehearsals at not more than six-monthlyintervals; initiate a salvage plan in conjunctionwith conservators and other professionals.

5. Monitor the internal environment if no specialistassistance is available.

6. Present the collection with sufficient informationin legible format; provide visitors with options fortours of different duration and content; prepare

literature for sale; arrange exhibitions providedthey do not prejudice more important activities.

7. Fulfil the obligation to educate the public and tosafeguard public interests.

As conservation is a single discipline, and encom-passes objects in historic buildings the guidelinesshould be extended to include all objects of culturalheritage.

ICOMOS guidelines para. 5, ALL sections are relevant.

Postscript

It must be recognized that the contractual situationin the building industry in the UK is changing rap-idly. The author’s experience, on which this book isbased, related to work done in the 1960s and 1970s,using the RIBA form of contract, which is nowobsolete. This contract gave the architect consider-able authority, which has been gradually eroded.

In the current situation, the project manager hastaken over the executive and co-ordinating role ofthe architect, who is important in conservationwork. Ideally, the conservation architect shouldtrain as a project manager, and then he can fulfil histrue role. Conservation practice has become morespecialist, and more bureaucratic, making it moredifficult for its artistic input to survive.

Alan Robson of Feilden & Mawson has kindlymade some relevant comments relating to the situ-ation in the UK in 2002, but this will continue toevolve. The broad sweep of this chapter, however,still stands up. He writes as follows:

‘All I would add is a few points that relate toconservation in practice in the UK now, andsome of the practical points that occur. Youmay think that these are not relevant to thegeneral principles that you express, but they doapply with some vigour in the UK and haveconsiderable bearing on typical projects beingcarried out now for government and its agen-cies, including English Heritage, Historic RoyalPalaces and others. They also have significantlyaltered the role of the conservation architect,who has had to learn the new language andvocabulary involved.

1. Project manager—a new key player inconservation is the project manager. Mostprojects now have an independent consultantappointed before all others in the designteam, who will advise and often assist in theprocurement of all the design professionals.

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This role is now enshrined in the governmentform of consultants’ appointment—GCWork/51999, which sets out the specific duties of eachteam member. This links to the governmentform of building contract, where the contractadministrator is now titled project manager,and is more often used now than the RIBAform. Often the project manager can be anarchitect, but usually she/he is not. There isalso the new role of lead consultant, separatefrom the role of architect, but usually carriedout by the architect. In its basic version, thiseffectively relegates the architect’s role to thatof any of the other designers with no overallco-ordinating responsibility. The worryingelement of this is that the project manager’sinterest and responsibilities relate solely toprogramme and budget, and very few of theICOMOS Guidelines (a) to (n) would usuallyapply to their role. They usually have nospecific training in conservation, and often nointerest or real understanding of the principalissues involved. I believe they should haveboth, and that there is a need for specifictraining for project managers in conservation.

2. CDM Regulations (properly theConstruction, Design and ManagementRegulations, introduced in 1994)—theseregulations impose a new health and safetyculture into the design perception, so suchfactors as safety of materials in the design,construction, use and eventual removal/alteration or demolition have to be taken intoaccount. This imposes an additional needupon the designer, in all areas, to beenvironmentally and life-cycle aware, as wellas introducing a new professional skill of theplanning supervisor.

3. New forms of Procurement—Constructionmanagement (CM), management contracting(MC) and design and build (D&B)—manylarge conservation projects or projects with asubstantial intrinsic conservation element, areprocured by one of these routes (usually CMor MC) rather than the conventional builderand specialist sub-contract trades. The twomajor projects at Somerset House for theGilbert Collection and the Courtyard projectwere CM and MC respectively. The Treasuryrefurbishment, working with Fosters is MC.Control has moved across towards themanagement contractor, and specialist workscontractors, and not the design team whoeffectively simply prepare schematic designs,and importantly deal with some of thequality issues. Design teams tend to prepare

documentation based on performancespecification, which puts high reliance uponthe specialist trades, and is attractive in manyways to clients, as it transfers the majority ofthe design and execution risk to the contractor.This is a large subject and is constantlyevolving. What is still true is that theconservation architect is still an enabler, butthat levels of responsibility and influence arestrictly limited to, an often ill-defined scopeof services/duties required.

4. PFI and PDS—this relates to the increase ofPrivate Finance Initiative (PFI) and PrivateDeveloper Scheme (PDS) routes for privatelyfinancing and procuring buildings in thepublic sector. This applies to schools, courtsand government offices, and importantlyintroduces the principle of designing withlifecycle costs in mind, which should increasethe likelihood of a conserved building beingmaintained correctly in accordance with aconservation-based maintenance specification,along with quadrennial and annual inspections,a conservation manual and in the light of aconservation plan. In our experience, this ispaying dividends.

5. Clients are changing—Governmentagencies and bodies take a very critical lookat their existing estate, and its suitability forcontinuing use. In many cases, like theNational Health Service and Ministry ofDefence, this can include disposal strategiesfor redundant or under-utilised existing(often listed) building stock. Advice we giveis often on town planning and listed buildingissues, and responsibilities presented by thiscircumstance. This requires understanding ofadditional areas such a development marketvalue and commercial feasibility.

‘As a practice, F&M have had to embrace all theabove, with certain members of staff and partnershaving received training in project managementand planning supervision. We have to beconversant with the current procurement vehiclesand the implications of each.‘I realise that this may have strayed off the pointa little, but these are all factors that come intoplay for any architect today, and becomeespecially important in relation to conservationarchitect projects.’

In many schemes, conservation is regarded as a‘risk to be managed’, and a consultant is appointedto fulfil this role. Conservation plans are helpfuland important, as they indicate why a building isimportant, and what its special values might be.

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The methodology of all conservation depends uponmaking an inspection and report at regular intervalson all items of cultural property, recording the vis-ible defects factually, in order to diagnose thecauses of decay and propose an effective cure thatinvolves only the minimum intervention. Thismeticulous examination requires the ability toappreciate the ‘messages’ in the cultural propertyand its values. The extent and nature of the historicbuilding must be defined and its relationship to itssetting must be included, as architecture cannot bedivorced from its site—it is immovable culturalproperty which must be seen as a whole. Thebuilding must be looked at with a seeing andunderstanding eye, and allowed to speak to you. Atthe start, your mind should be cleared of precon-ceptions, and know that you know nothing.

Legislation, listing and scheduling cultural prop-erty gives the framework and structure of conser-vation. Inspections and reports give the facts asthey relate to each individual building and, if pre-vious reports are available, they are invaluable evid-ence and helpful in assessing the rate of changeand in making decisions. Making an inspection isgenerally the first encounter the architect will havewith an historic building and is an excellent way ofgetting to know a building well. Inspections are thebasis of future action, so it is important that theyshould be thorough and accurate. The purpose ofthe initial report is to record and evaluate the sig-nificance and condition of the historic building.Most importantly, the report can be used as a basisof the maintenance plan, so it is an essential part ofthe strategy of preventive maintenance which is thehighest form of conservation.

It is important to remember that the report willbe read by laymen. Technical words and jargonshould be avoided as far as possible, but, if neces-sary, the words used should be explained in a glos-sary. Sentences should be short and informative, asprecision and clarity are the hallmark of a well-written and well-presented report.

14

Inspections and reports

Reports worked up by stages

A full report may be worked up by stages, as follows:

(1) Initial report based upon visual inspection, list-ing all defects and describing and studying thebuilding.

(2) A maintenance plan. Approximate itemized esti-mates for immediate, urgent, and necessaryrepairs and other desirable works.

(3) Historical research and analysis supported byphotographic records.

(4) Recording of the initial state of the building; soilmechanics, humidity studies and opening upsuspect parts.

(5) Further studies. Structural analysis.(6) Final estimates and proposals with specifica-

tions and full report for submission for govern-mental grant covering all the above factors, asthey modify each other.

Making initial reports

The conservation architect should have an openmind when making his initial inspection, and beprepared to receive all the evidence of his fivesenses. Preconceptions are dangerous, as they mayblind the inspector to vital evidence. By detailedinspection a trained architect can detect a syndromeof significant evidence before most measuring sys-tems. He must work in four dimensions: length,breadth, height and time, i.e. the history of the site,of any previous buildings and of how the presentbuilding came into being and has and will react tothe forces of decay.

The report, based upon an initial inspection, maybe used for many purposes. Besides being an essen-tial basis for a maintenance plan, a theme developedin Chapter 16 of this book, it is an essential prelim-inary before embarking upon historical research orany further study of the structure such as structuralanalysis, including soil mechanics, investigations into

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Figure 14.1 South choir aisle vault, west bay, YorkMinster, England(Courtesy: Feilden & Mawson)

Multiple diagonal cracks indicate settlements of the centraltower on the left-hand side. The cracks have been filled and re-pointed several times by masons. The distressed arches havebeen pushed sideways and strutted with heavy oak props, thenlater filled with brick. Cracks also show in the vault. The situa-tion is complicated by the eleventh century masonry of an oldstair and the 65-year pause between completion of the choirand the tower, which being relatively much heavier settled more

Figure 14.2 Gallery ofcentral tower, YorkMinster, England(Courtesy: Shepherd BuildingGroup Ltd)

Repeated filling of this crackdid nothing except conceal itsever increasing width. Thereal cause of the movementlay in the over-stressing of thesoil below the foundationssome 40 m (130 ft) down.Such a diagnosis can only hemade after inspection of abuilding as a whole

moisture, or opening up suspect parts in order toidentify all causes of decay. Such studies are onlyrequired if the initial inspection shows that they arenecessary and they must be kept in proportion to theimportance of the problem.

Full reports consolidate all the information col-lected with regard to the building and identify thecauses of decay and propose cures. They should beaccompanied by specifications and estimates ofcost in the form required for any governmentalgrants which may be sought. These estimatesshould include an allowance for recording the con-servation work and making a final report.

In making initial reports it is useful to give sketchoutline floor plans of the building and, if at all com-plicated, a roof plan as well. For a full report, meas-ured plans of site, boundaries, rainwater and soildrainage disposal, and mechanical and electricalservices, should always be included. The primaryaim of the initial report is to record in a factualmanner the condition of the historic building.Preliminary opinions, which may be varied later,should be given, but in setting out the report theyshould be shown explicitly as such, for facts andopinions must not be confused with each other.

Legal aspects

Remembering that further defects can materializequickly, it should be clearly slated that the defectsrecorded were those visible at the date of inspec-tion. The limitations of the survey should always begiven, i.e. certain roof spaces were inaccessible,floorboards could not be lifted and floor coveringsand furniture prevented a full inspection. If a woodground floor is covered with linoleum or otherimpervious material, it must be stated that no guar-antee can be given that it is not attacked by someform of rot and unless the floor is opened up andexamined by a specialist, no estimate can be pre-pared for repairs. Again, in the inspection, caremust be taken to note the location of all insectattacks and whether the flight holes are old or new.

Climate affects the types of insect attack and theincidence of plant growth and moulds. In giving opin-ions based on experience in one locality, one mustremember that in another locality the climate andmicroclimate of the building may differ and affectperformance materially; e.g. exposure can increasechemical actions and fungal attack and proximity tothe sea can increase danger from salt aerosols.

Writing the reports

All reports should start with a summary stating theobject of the report; final reports should include

considerations and alternative courses of actionbefore making a recommendation. The use ofupright A4 (normal photocopy size) paper, withdrawings folded in, generally makes filing andretrieval easier and should be standard practice.

Reports are working documents and should be asshort, concise and specific as possible. Using dictat-ing machines gives a tendency to verbosity, whereasreports written direct on the site in an extended noteform are briefer and more accurate. In this way,observation is made more acute, for the act of writ-ing makes one consider the possible complicationsof the defect that is being noted, and this again sug-gests further points which can be checked instantlyby a more detailed investigation. One can also back-track and easily make insertions in the correct placein a written draft document, whereas this is a verytedious matter with a tape recorder.

The initial report is not a specification and itshould be made clear to the client that it is danger-ous to attempt to use it as such. Indeed, it is usefulto insert the following paragraph in any report:

‘This document is a report, not a specification: itlists defects found but does not give detailedinstructions for remedying them. Buildersshould not be expected to quote for or carryout the specialized work required without further guidance; they should be provided witha proper specification, or, if the work is veryminor, should be asked to submit their detailedproposals for the architect to check. Even smallerrors in workmanship or materials can be functionally or aesthetically disastrous.’

Those small works which do not need profes-sional supervision can, in some cases, be indicatedin the summary of the report of the survey, and ifthe builder is available can be gone over while thearchitect is at the site.

It is undesirable to be too rigid about the form ofthe report, which must be related to the building andto the purposes for which the report is required. Ifthere is much repetitive detail in a building, a stand-ardized pro forma or schedule can be devised—buta word of warning: complicated pro formas oftenbecome an end in themselves, meaningful to the per-son who devised them, stultifying to those who fillthem in and later a curse to those who are trying todecode them. As each building is individual, it is betterto use specific words with which to describe it.

Making the initial inspection

Equipment for an initial inspection should includea writing-board and note pad, pen or pencil, goodelectric torch, penknife or awl, measuring tape,

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Figure 14.3 South transept, east arcade, and tower abutment, York Minster, England

Cracks and distortions are related to the settlement of the tower. The narrow arch was filled in theeighteenth century to improve its stability, but masonry and piers have cracked. When makingrepairs to the vertical crack (in the flat panel below the roundel), an eleventh century shaft wasdiscovered and left exposed

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Figure 14.4 Northtransept, west arcade, adja-cent to north-west pier ofcentral tower, York Minster,England(Courtesy: Shepherd BuildingGroup Ltd)

The north-west tower pier hadsettled about 345 mm (13.6in) and caused severe distor-tions in the masonry of thethree-storey arcading of thetransept. Some of the distor-tions were, however, due tothe collapse of the previoustower in A.D. 1407

Figure 14.5 Northtransept, west wall,York Minster, England(Courtesy: ShepherdBuilding Group Ltd)

The same cracks as inFigure 14.4, from theoutside. Their activemovement was moni-tored with a Demecstrain gauge. Noteattempts to point up withhard cement and a certain amount ofsuperficial straighteningup done by masons inprevious repairs whichconcentrated uponappearance rather thanstructure

plumb bob and bricklayer’s level, field glasses withseven times magnification and a large 50 mm (2 in)objective lens, camera with flash attachment(Polaroid if quick results are wanted), a screwdriverfor lifting access traps, a short hooked crowbar forlifting manhole covers, a 2 kg (4 lb) hammer fortesting masonry and timbers, a magnifying glass,containers for insect samples, a moisture meter, apocket mirror and overalls or protective clothing;gumboots or even waders are sometimes necessary.Nylon overalls that slip on and off easily are apleasant refinement; finally, towel and soap forcleaning oneself after a survey are required, as it isunavoidably dirty work.

For buildings with high ceilings or open roofsand for the inspection of roofs and gutters extern-ally, two extending ladders should be providedwith men to move them. These ladders are essen-tial to allow the fine adjustment necessary to getclose up to inspect and test roof timbers. A buildershould be asked to send men who can move oneladder while the architect is using the other. Themen should not be kept longer than necessary, butthey can be instructed to clean out gutters andblocked drains in their free intervals, so they shouldbe reminded to bring the necessary tools.

Searching for clues

To make an inspection one must be able to under-stand what one sees, interpreting the meaning ofwater stains, frass from insects, dust-like spores fromfungi, thread-like mycelia and damage to paint films,wallpaper and plaster; one must be able to smelldamp from wet earth, mustiness from moulds andfungi and the sour odour of defective drains; onemust listen to the note of wood, metal or stone whenit is tapped or struck; one must touch and probeand, with due respect for personal safety, jump onfloors. All the senses are used in searching for clues.

When inspecting wood members in the structure,one looks for shakes circumferential to the originaltree trunk and radial checks and twists and largeknots which may cause weaknesses. The opengrain at the end of timbers is a danger point,because it can absorb moisture readily and also dryout more rapidly, so detailing here must be studiedcarefully. Shrinkage of timber can cause defects,longitudinal shrinkage being least and circumferen-tial shrinkage being greater than radial, so causingboards to warp and often causing indirect damage.Rapid wet/dry sequences fatigue wood, even insmall members such as window glazing bars whichsuffer from daily condensation; abrasion and thewear and tear from heavy foot traffic must be noted;erosion from wind and dust occurs and ultraviolet

light causes the breakdown of the lignin making itsoluble in rain water. Clear varnishes give no pro-tection against ultraviolet light, however much plan-ing hardens wood surfaces. Wood is always a firerisk and can be set alight by faults in electric wiring,by hot light bulbs and, of course, by lightning.

Rust around nails indicates excessive moisture;nails standing proud may indicate alternateswelling and shrinking. Surface mould may be aprelude to fungal attack, while fruiting bodies offungus are evidence of advanced decay and realdanger to the fabric. Paint areas may fail, particu-larly if near the vulnerable end grain. Drawn orbroken joints must be searched for, as their failuremay cause a collapse. In appropriate places timbersmay be tested by prodding with a knife, screw-driver or awl. The condition of softwood structuraltimbers may be tested by lifting up a splinter, whichif sound will be a long sliver or if deteriorated ashort weak piece.

Procedure on a visual survey will vary according tothe problem, but in essence the building must bedivided into parts and dealt with methodically. Alwayswork to a standard routine, e.g. vertically, from top tobottom, horizontally clockwise, so that if there aregaps or obscurities of meaning when the report iswritten out, they can be disentangled. It is usual tostart the inspection of a building at the north-west cor-ner, because it is conventional for plans to have thenorth at the top and because it is customary to readfrom left to right. If true north is not at the top of theplan it is best to use a notional north so as to simplifydescriptions. Jambs (vertical sides) of all openingsshould be described as ‘east’ and ‘west’ or ‘north’ and‘south’, as this description is accurate wherever onestands, whereas left and right can be misleading. Theinterior of a multi-cell building should be inspectedroom by room in a similar sequence starting at theceiling and working clockwise and downwards,inspecting walls, floors and then doors, linings, skirt-ings and windows in each room.

Inspection of roofs

The inspection will report on the roof structure andhow the loads are collected and carried down tothe walls. Wind bracing is important to preventrafters from all tilting in one direction and pushinga gable wall outwards.

In roof timbers, the principal defects in the ori-ginal timber may be large dead knots leading topartial failure of the member, longitudinal fissuresdue to shrinkage and radial cracks, only visible atthe ends, which together with the fissures mayweaken a member and wane due to faulty conver-sion or decay of sapwood. Fungus and insect attack

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must be noted and their effect on structure judged.The joints must all be examined carefully as thiswill give the most helpful information in assessingthe roof structure’s condition. Tapping with the endof a penknife or hammer will give a great deal ofinformation about the interior condition of struc-tural members, the ends of which must always be carefully inspected for decay by prodding withthe penknife blade or drilling, in which case the

turnings should be put into an envelope, labelledand kept for future examination.

Eaves and gutters must be checked from ladders.Any deposits therein are evidence of inadequacy,either of design or maintenance. The strength andfrequency of fixing brackets should be noted.

The overhang of the eaves is important in shed-ding rain water clear of the walls, as also are size andslope of the gutters which, if faulty or inadequate, are

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Figure 14.6 Choir, north arcade, east end, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The foundations supporting the pier and shafts on the left-hand side (west) have settled considerablymore than the east wall, causing distortions and distress in the masonry. The east end has rotated outwards, causing the vertical elements to lean. The cracks had been mortared over but had reopened

a source of much trouble. Flashings to abutments andchimneys should be inspected carefully for cracks.Parapet gutters, valley gutters between roofs, are par-ticularly vulnerable, and if snow is common may bea special source of trouble. The slope of all guttersshould be checked (using a bricklayer’s level) as thisaffects their performance.

Roof surfaces and hips and ridges should be exam-ined overall to see if any plane is deflecting. Theroofing material should be examined for slipping orbroken tiles or slates and also previous repairs,which will give an indication of its overall condition.The slope of the roof should be measured to see if itis adequate for the covering. Metal roofs tend to suf-fer from creep due to fatigue and failure of the nail-ing at the head of the sheets. Flat roofs are generallyeasy to inspect, but if there are any faults these areexceptionally difficult to locate. For asphalts, the con-dition of the surface, if covered with cracks and craz-ing, indicates age and brittleness. Metal roofs havehigh thermal expansion which may lead to bulging,and there is also the danger of electrolytic actionwhere two metals join or where nails in the sub-roofhave not been punched home. Solder repairs gener-ally fail due to thermal stresses. With flat roofs thereis also danger of capillary attraction of water at abut-ments and joints, particularly in gutter steps. Bitumenfelt roofs and other substitutes for lead and copperhave such a short life that, in the writer’s opinion,they should not be used for historic buildings. If theyare found to be split, cracked, wrinkled, puffed up orblistered they must be replaced as soon as possible.

Inspection of chimneys

Chimneys that are cracked vertically have probablysuffered from flue fire damage, which would alsocause the internal parging to come down. The mor-tar at the top of chimneys tends to decompose dueto condensation from fumes, particularly from gasappliances and slow combustion stoves. Chimneysthat lean do so as a result of the decomposition andexpansion of mortar upon crystallization of sul-phates in the joints on the cold, wet side.Embedded iron cramps may even lift whole chim-ney stacks due to expansion of rust. Many oldstacks are tied back to the ridge with iron ties, butthese are useless if rusted through or slack.

Rain can penetrate down old flues, showing atthe bends in dark stains of deliquescent salts. Theparging of old flues is nearly always defective dueto condensation and the salts and tars produced bycombustion. Besides gutters, the most vulnerablepoints for rain penetration in most buildings are thechimneys, which until recently were not built with

damp-proof trays, thus allowing water to penetratedown the stack. The joints between roofing materialsshould always be carefully examined to see thatthere is sufficient lap or cover to resist climaticexposure and that details do not allow capillaryattraction or penetration through porous materials.Chimneys in historic buildings are nearly alwayssuspect, and if used, should be lined with flexiblestainless steel tubes, especially for central heatingor wood-burning stoves.

Rain penetration will cause rotting of roof tim-bers at abutments, as these are rarely properlyflashed and damp-proofed in historic buildings.

Clogged wall ties in cavity construction can causecondensation spots.

Inspection of rainwater disposal

Ideally, the rainwater disposal system should beinspected in heavy rain as then the defects are self-evident, e.g. gutters overflowing, downpipes blockedand so on. Otherwise, wall staining and rust marksand internal moist patches point to defects.

The fixing of rainwater downpipes should bechecked, and so should their condition at the back.Often they are so close to a wall that they cannotbe painted. They should be fixed with spacers tomake painting easy.

Rainwater drains should be inspected togetherwith the drainage system. Generally it is sufficient ifrain water is taken about 3–4 m (10–13 ft) from thefoundations. Broken rainwater drains are a threat tofoundations and can cause moisture penetration inbasements and crypts.

Driving rain will often penetrate doors and win-dows and cause rot to sills and the base of frames,especially if painting has been neglected.

Inspection for excess moisture

The initial inspection for excess moisture must notethe height and where this varies and, if possible, thelevel of summer and winter evaporation. Most his-toric buildings do not have horizontal damp-proofcourses or underfloor membranes. Any evidencehelping to establish the level of the water table andthe existence of salts in the soil should be recorded.The amount of rising moisture can be crudelyassessed by placing a sizeable glass sheet over a solidfloor for a day. Any precautions against rising mois-ture should be noted, together with the lack of them.

Good ventilation of wooden sub-floors, avoidingdead pockets of moisture-laden air, is essential.Underfloor ventilation should be at not less than 3.5 m (12 ft) centres and close to the corners of therooms. Previous repairs and insertions of various

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types of patent moisture extractors (generally use-less) are an indication of whether rising moisturepresents problems.

Inspection of windows and doors

Windows and doors are generally inspected at thesame time as walls. For windows, the condition ofthe joinery and ironmongery needs careful inspec-tion. Rot is often found at the bottom of frames andin wooden sills and then may spread into the walllining or frame. A sagging arch or lintel indicatestrouble—either structural settlement or a localdefect such as dry rot in concealed timbers.

Defective putties and paintwork are commonfaults which can lead to more serious trouble. Withlead glazing, the mastic may harden and drop outleaving the panes loose and subject to rain pen-etration. In time, lead windows bulge and creepdue to the fatigue of the leadwork which is

dependent upon metal tie bars which should be atabout 250 mm (10 in) centres. If made of iron, theembedded ends of these bars rust and break themasonry. Bronze bars are to be preferred.

Condensation from windows can also be a seriouscause of trouble. This may be the result of insufficientopening lights or the placement of such lights at lowlevel leaving a cushion of moist, warm air in the topof a room. Condensation trays, draining outwards,are desirable. Windows and doors should always beinspected for their fit and draughtproofness andresistance to the climatic conditions to which theyare exposed. Doors should also be examined fortheir fireproof qualities.

Inspection of masonry walls

The walls of an historic building need meticulousstudy on the first inspection. This should be fol-lowed by physical tapping, which can give valuableinformation, for if the note of the tap is dull and

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Figure 14.7 Gallery, eastwindow, York Minster,England(Courtesy: Shepherd BuildingGroup Ltd)

The gallery is bowing some150 mm (6 in) and the window above about 225 mm(9 in). With the very slenderstructure there was a dangerof over-stressing

there is no rebound in the hammer then themasonry is soft and in poor condition, but if thereis a bright ring and the hammer rebounds, themasonry is generally sound for some depth.Listening to hammer taps through the thickness ofthe wall is also useful. Further techniques are thetaking of cores to investigate the method of con-struction and the condition of the heart of the wall.Water can also be injected into walls in order to testpenetration and observe where it leaks out.

All cracks must be recorded and studied. Thetendency for movement should be deduced fromthe tapering and angle of any cracks; many signifynothing more than thermal movement and the slowwearing out of the structure, but a few may be verysignificant and indicate a likely failure.

In time, dust will tend to settle inside cracks thusindicating ‘old’ cracks, which will have dark interi-ors, whereas new ones can be identified by theirclean faces which possibly contain loose fragmentsof masonry. Other clues to the history of structuralactions, such as previous repairs to cracks, shouldbe taken into account. Light tapping with apenknife quickly reveals where plaster has comeaway from a wall.

The preliminary report should merely indicate thata crack exists. Later, suitable measured drawingsshould be prepared with all cracks marked up,showing their length and width. If the situation iscomplicated, a perspex model, showing the mainfeatures of the building together with crackingrecorded on both inside and outside of walls, piers or whatever, is of great help in analysis of the structural actions. Internal cracks can be markedin, say, red ink and external ones in black to showhow cracking patterns go through the structuralmasonry.

It is often convenient to mark the extent of a crackunobtrusively on the building itself with a pencil, giving the date (but this date may be covered up by redecoration). It is important also to recordwhether cracks are through the mortar joints onlyor go right through masonry of stone or bricks.

Photographs with a scale included can be madeand enlarged to full size in order to record cracksin detail. Photographs of structural elements areinvaluable for this record; they can be marked upin ink with all pertinent information and the defectsnumbered for reference. If any of the cracks areconsidered serious, arrangements should be made

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Figure 14.8 Choir triforium, York Minster,England(Courtesy: Shepherd BuildingGroup Ltd)

The creeping movement of the east end, which totalled610 mm (24 in) over six centuries, was compensatedfor by the opening of manycracks, of which this in thefifth bay is a large exampleuntouched by previous cosmetic repairs

for regular recording of their width by means of a‘Demec’ gauge or a micrometer reading acrossthree pins. Such measurements should be con-tinued for as long as possible and reviewed each year.

Any necessary structural analysis will follow later;at this stage it is necessary to record the facts. The plane of the wall surface can be tested with abricklayer’s level to see if there is lateral displace-ment across a crack and the level is also useful formeasuring out-of-plumbness. Bulges should benoted most carefully, as they are potentially dan-gerous.

Even though the condition of the wall can give agreat deal of information about the foundations, onan initial inspection it is often wise to have a trialhole dug in order to ascertain the depth of thefoundations and the nature of subsoil, and if pos-sible the level of the ground water. Digging such ahole may have implications for an archaeologist,who should be asked to attend and record archaeo-logical information.

If the foundations are on clay and less than 1 m(3.3 ft) deep, soil shrinkage cracks may damage thestructure, and adjacent trees and shrubs or wallcreeping plants may cause settlement by extractingwater from the clay in summer. In cold countries,frost heave is a serious consideration as the waterin the soil expands on freezing.

The movement of moisture through the wallsmust be studied and any impervious surfacesnoted. Walls may be composite with rendering, tileor slate hanging externally and linings of plaster onwooden or metal laths internally or even foamedpolystyrene, if recent repairs or improvements havebeen carried out. For an initial inspection, moisturemeters give a useful indication of the amount ofwater in the surface layer, but they are influencedby condensation and can be short-circuited if metalfoil has been used in the lining paper.

Penetration of rain water must be carefully noted.Projecting cornices and plinths in the outer face ofthe wall can cause rain penetration if not properlyweathered and flashed. Moisture often penetrateswindow sills without damp-proof courses; and con-densation frequently occurs around windowswhere the insulating effect of the wall is lower.Cold bridges can be formed by embedded metalcramps and even Portland cement grout.

Inspection of floors and staircases

Floors and staircases may be the elements most likelyto collapse and care should be taken if there is anydoubt. Scaffold boards can be used to spread the sur-veyor’s weight. Collapse or damage is generally dueto fungus and insect attack in the ends of the beams,but beams may have been weakened by walls mov-ing out, thus loosening their end bearing, or by thefloor’s strutting and wedging working loose.

Many floors in historic buildings deflect muchmore than in modern structures, due to the use ofsquare-section timbers, yet they are perfectly safe.Floor timbers can be tested in the same way as rooftimbers. Damage is often caused by single-mindedelectricians and plumbers cutting joists at theirweakest points to insert cable and pipes.

The floorboards should be carefully inspected.Electricians’ traps can be opened and if possibleboards alongside each wall lifted to enable the endsof beams to be viewed. A small mirror is useful tolook at the sides of beams and also the underside, ifthe floor is of double construction. The dimensions ofstructural members and thickness of the floorboardsshould be recorded. The joints of the floorboardsshould be noted. Square joints without tongues aredraughty and, if wide, allow dirt to accumulate. Ifthe floor has moved down from the skirting base-boards one’s suspicions should be aroused.

Staircases in historic buildings are either of wood orin masonry. Sometimes the design of stone staircasesfills one with wonder at the daring of the masonswhose skill in dispersing floor loadings relied uponanchorage in firm walls. In wooden stairs it is the

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Figure 14.9 Al Hadba Minaret, Mosul, Iraq

Like many chimneys this minaret leans, bending its back to theprevailing wind. Wind vibrations have caused loose mortar todrop and cause bulges in the decorative outer casing. There is ashear crack where the flexible tower joins a stiff base

thickness of treads and condition of the wedges andstrength of the undercarriage that counts. If the stair-case has an open soffit it is easy to inspect, otherwiseone must look carefully for any clues to decay. Thejoints at newel posts and the stiffness of these mem-bers are important as well as the strength and stabil-ity of balusters and firmness of handrails.

Tiles and plaster are often used as floor surfaces onsuspended floors in historic buildings. Stone/marbletiles and brick are used for solid ground floors where,as has been mentioned, rising moisture through cap-illary action is probable. The wearing of all floors isa problem in historic buildings, and where this isliable to cause difficulties to future users it should bespecifically noted in the report.

Inspection of internal finishes

Most of the defects likely to be found, unlessaccounted for by structural actions, are due to poorworkmanship; shrinkage cracks, plaster detachedfrom lath (quite dangerous in ceilings) and the sep-aration of plaster coats are examples. The cause ofall such defects should be analysed.

Mosaics and wall paintings of all types need special consideration, since they are vulnerable tocondensation and penetrating water and capillaryaction. Care must be taken to note canvas liningsand wallpapers which may have historic and artis-

tic value. Wallpaper may also have been applied toconceal cracks and other defects.

Ceilings should, if possible, be inspected fromabove to see if the plaster is still keying. Ornateplaster ceilings are very heavy, so special attentionmust be paid to the fixing of their armatures.Cornices also present similar problems, particularlyif their framing is of wood and liable to decay; cor-nices were often run in wood which can bededuced when one sees a scarfed joint or mitre.

Previous decoration if its date is known acts as abase line for the assessment of defects and their rateof action. Historic buildings often have many coats ofpaint and analysis of the colours and types is inter-esting from the archaeological point of view.Unfortunately, the thickness of the repeated layersmay clog decorative detail and spoil the crispness ofbeautiful plasterwork. Careful scraping will reveal thelayers of paint and suggest the colour scheme forrestoration. Old gloss paint on joinery becomes brit-tle and chips easily if knocked, so it is important torecommend in the inspection report whether theexisting paintwork must be burned and scrapeddown to the bare wood, as preparation for com-plete repainting.

The state of decay of paintwork must be noted withthe nature of paint finish. All too often wrong specifi-cations have been used in the past, such as paintsmade of bitumen or plastic-based paints or varnishesto refresh worn paint, mistakes which pose problems

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Figure 14.10 Mosaics atJerash, Jordan

Rain penetration causes watererosion which causes soil toleach away forming a depression that collects rain,so accelerating the process.Patching with Portlandcement mortar is no answer tothe complicated problem ofconservation and presentation

for redecoration. Because they can be renewed easily,only traditional paints should be used. In some cases,the original decoration may exist and its retention maybe recommended after special feasibility studies havebeen made for its conservation.

Traditional paints were based on lead pigments,which are poisonous, and ground in linseed oil.Without proper precautions, these were dangerousto use, especially when being rubbed down duringpreparation for redecoration. Unless rubbed wet, agreat deal of toxic dust was generated. Their advant-age is that they age gracefully and preparation forredecoration is far easier than with modern plastic-based paints. In England and Wales, the use of tra-ditional lead-based paints is restricted to Grade Ilisted buildings.

Inspection of fittings

Wooden fittings and fixtures must be carefullyexamined and scheduled. Evidence of insect attackmust be looked for, which is time consuming.Evidence of an unfavourable internal environmentcan be found in fittings—shrinkages and blisteringof veneers if the relative humidity is too low, andswellings and haze on paint and polish if it is toohigh, leading to fungal attack. Church organs areparticularly sensitive and unless they are of modernconstruction they are not compatible with relativehumidities much lower than 55%.

The fixings of war memorials and tablets shouldalways be checked, as these may be of metal andbadly corroded.

Inspection of mechanical and electrical services

Mechanical and electrical services need carefulinspection at two levels: first, to see that they do notpresent a hazard to the fabric of the historic build-ing; secondly, to see if they are functioning ade-quately. This should be done by a specialist.Remembering that such services generally have auseful life of 15–25 years, they may be obsolescentat the time of inspection; if they are much older thanthat, they may only have value in the context ofindustrial archaeology and the history of technology.

Rust spots and blisters inside a galvanized steelstorage tank indicate that it should be renewed. Leaksin pipework, faulty taps and valves, faulty connec-tions, particularly of toilet bowls, insufficient supportsfor pipework of different types and corrosion shouldall be noted. Dripping taps indicate defective wash-ers and are a hazard in frosty weather.

Protection of pipes and storage tanks against frostmust be checked and any lack of precautions against

condensation dripping from the cold-water tanknoted. The age of the pipework can be assessedfrom the type, the historic order being: lead (fromRoman times), wood (mediaeval), iron, galvanizedmild steel tube, copper, stainless steel and polythene.Insufficient supports or a faulty ball valve can causewater hammer. Corrosion and repairs indicate poorcondition. The hardness of the water supply maygive rise to furring of heating and hot-water pipes and two further special dangers must be mentioned—dezincification (as at Winchester), wherezinc leaches out of brass fittings, and impingementattack (as at Cambridge), where copper pipes fail ifthe bends are too sharp or water velocities too great.Tapping pipework will give some ‘hit and miss’ infor-mation, indicating furring possibly by a dull note.

Heating boilers may be weakened by corrosionand generally only have a life of 20 years. High per-formance oil fuel boilers need their water tubesrenewed even after five years.

The main water supply must be sufficiently deep toavoid frost and salting of roads and protected againsttraffic. The system must be capable of complete empty-ing, with isolating valves provided for repair. Thewater should always be turned off and the systemdrained down if an historic building is left unoccupied.

The sizing of pipes, condition and performance ofthe plumbing, hot water and heating systems shouldbe checked by a technical specialist if they are inuse. If it is proposed to adapt these installations,experience indicates that it is far better to renewthem in their entirety, but material can be salvaged.

Electrical installations are likewise subject torapid obsolescence, as the material of which theinsulation is made decays and becomes brittle.Historically, system followed system, as can be seenfrom the following:

1880 Cotton-insulated copper wire in woodbattens (a fire risk).

1900–1920 Vulcanized india-rubber with cotton braid.1910–1930 Lead-sheathed cable (vulnerable to rats).1925–1935 Tough rubber insulation.1928–1939 Vulcanized india-rubber in conduit

with pin grips for earthing (grounding)continuity.

1933–1960 Tough rubber sheathing with earth wire.1950 Polyvinylchloride compound insulation

with two or three wires in conjunctionwith ring mains wiring.

1950 Mineral-insulated cable.

Insulation to wiring will, if in good condition, bepliable, but even if in bad condition it may give asatisfactory resistance test, so that the architect mustwherever possible check the outer condition of the

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wiring. Workmanship standards can generally beassessed by the proper fixing of wires and the useof junction boxes.

Conduit may be rusty and the joints pulled,thereby breaking earth continuity. Drops shouldalways be in conduit embedded in plaster.

The size and position of the electrical intake, thedistribution boards, arrangement of circuits andwiring system should be given with readings fortheir insulation polarity and earthing resistance andcontinuity. Socket outlets and lights should bechecked for polarity. Light pendant cables are par-ticularly liable to decay and short-circuit. The spe-cialist should be asked to report on potentialhazards, as poor electrical installations are a majorcause of fire in historic buildings.

Inspection of drainage

It is often very difficult to trace drainage runs; elec-tromagnetic detectors may be found useful for thispurpose and also finding other buried services. It issometimes possible to send sound waves down apipeline by tapping, using a garden fork as a lis-tening device, and thus find a lost drain.

Almost all old drainage systems are defective andwould be damaged by water tests as applied to newwork. It is a matter of judgement whether the faultsreally matter to health or the structure of the historicbuilding. For example, broken drains may leach outsoil from under the foundations or cause moistureto penetrate basement walls. Using a smoke test, itmay be possible to detect a breakage by the greatervolume of smoke percolating through the soil.

Other defects will show by smoke emission at jointsand between drain and shaft and toilet bowl. Tomake the test, a smoke machine which pumpssmoke into the system is used after all unsealed out-lets have been stopped. Another method is thepneumatic test, which uses the same machine butwith a pressure gauge and has the advantage that bymoving a plug down the drain it can detect wherethe rate of air leakage is greatest, thus indicating abreakage. The danger points for broken drains areat the point of entry to a building, if settlement hasoccurred, and under a lightly constructed drive overwhich heavy loads may have passed.

Visual inspection will show the general conditionof drains which should be clean and allow a bucketof water to run freely from manhole to manhole. Ifthere is a delay or only percolation, there is a fault.The condition of manholes should be checked aswell as the fit of manhole covers, which may becracked and rusty and without lifting lugs. Theyshould be bedded in grease and made airtight.Ventilation of the top and bottom of the drainshould be checked, together with the condition ofthe septic tank and sewerage disposal.

Provided that an old drainage system is workingwithout offence, it should be left alone, as otherwisethe bacteriological system for disposal of effluent maybe upset.

Presenting the initial report

The initial report will have listed all the visibledefects such as cracks, poor masonry, rising damp

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Figure 14.11 Original rainwater disposal system,St Paul’s Cathedral, London,England(Courtesy: Feilden & Mawson)

A view along the north branchbefore cleaning out took place.The drain was found to beblocked, causing storm waterto flood over the sensitive foundations of the north-westtower. After cleaning out, themovements of the tower ceased,at least for the time being

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Figure 14.12 West porch, St Paul’s Cathedral, London, England(Courtesy: Feilden & Mawson)

A view inside the jack-arch on the middle cornice of the west front porch shows the Lewis boltwhich appears to be in good condition: it was not known that the lintel was held up by the Lewisbolt until it was opened up

Figure 14.13 South transept, west wall, St Paul’s Cathedral, London, England(Courtesy: Feilden & Mawson)

Differential settlement in the west wall of the south transept is due to the enormous weight of thedome on the right-hand side

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Figure 14.14 Simple diagnosis of cracks

The strength of materials, form of structure, relative stiffness of partsand standard of workmanship must be considered.

(a) More cracks at top of facade and at end of facade indicate thermal movements. Vertical cracks generally indicate poorlybonded material or material that has lost its cohesion and istherefore weak.

(b) Diagonal cracks indicate failure of shear, due to ground settlement or subsidence. Note, shear cracks may combine withthermal cracks. Crack wider at bottom—ground may be slidinghorizontally as well

(c) Fine cracks (left) due to wind and salt crystallization. Shearcracks (right) due to failure of masonry—serious

(d) Settlement increases as load gets more and more eccentric(e) Horizontal vibrations caused by earthquake. Cracks worse in

middle. Flexible buildings on hard soils and stiff buildings onsoft soils have comparatively more resistance than stiff buildingson hard soils and flexible ones on soft soils

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Figure 14.15 Failures of walls and piers

(a) Column on piers with vertical cracks due to over-stressingof poor masonry. Poor foundations spreading under loadof column

(b) Buckling failure of wall indicated by bulge and horizontal crack

(c) Thermal movements and wind vibration give dust thechance to drop

and defective roofs, and these will have been con-sidered and discussed. Then, if further investigationis necessary this will be specified and authorityrequested. Certain items may need immediateattention, and ideally the architect ought to beauthorized to give a builder on-the-spot instructionsfor such works up to a specified value. This proce-dure would save a lot of time and prevent damagefrom spreading; it need not conflict with adminis-trative ideas of accountability, as the architectshould be a trusted professional man.

Clear recommendations for action must followfrom an initial investigation. The architect must berealistic with regard to the appropriate standard ofmaintenance and remember that recommendingsomething obviously outside the financial capabil-ity of the client is not helpful except in cases ofstructural danger, when public safety must be thefirst consideration. Recommendations must bescaled to what is possible in the context of the sit-uation. They should be given in order of priority asfollows:

(1) Immediate work is what must be done straightaway to deal with work necessary for thesafety of the fabric or its users.

(2) Urgent work is that required to prevent activedeterioration, i.e. attack by insect or fungus orpenetration by rain water.

(3) Necessary work is that required to the ‘standard’appropriate for the building and its present orproposed use in the context of the client’sresources and includes items of preventivemaintenance. This category can be subdividedinto ‘good housekeeping’, ‘rolling programme’and ‘major works’.

(4) Desirable work is what is recommended toenhance the use or appearance of the buildingor what is necessary for re-evaluation or adap-tive use of the building.

(5) Items to be kept under observation are, forexample, active movements and roofs or instal-lations that are nearing the end of their life andmay need renewal within 10 or 15 years.

Considerable skill and knowledge goes into balancing the various factors that lead one to put anitem into a certain category. The major considera-tion is to evaluate the damage that could occur ifthe repair were not put in hand. Renewal of roofcoverings is one of the commonest items of work.

A further consideration is the grouping of the sug-gested works into logical building sequences; forexample, in order to avoid having to work over arecently repaired lead roof, any wall surface aboveshould be repaired first. Work should, if possible, be organized by trades so as to give contractors

worthwhile amounts of work that can be carriedout at economical prices.

Besides being used as a basis for preparation ofa maintenance plan, the initial report may revealserious defects which require further studies andmore detailed reports.

Preliminary estimates

To recapitulate, an initial report should give theclient (owner or trustees) a clear picture of the stateof the building, the steps necessary to get the build-ing into the condition that is appropriate to its use,and the order in which those steps must be taken.To be realistic, it should also give an approximateestimate of the cost of the proposed work. If estim-ates are prepared, labour and materials should becalculated separately, for then they are easier toupdate against inflation as the unit cost of each can be re-worked at current rates. In work of thissort, with so many unknown hazards, giving thepossible high and low range of costs providesvaluable information for the client. Professionalfees and expenses and any taxes (such as VAT inEU countries) should be included in estimates.Archaeological investigations, art historical studies,research, photography and documentation shouldall be estimated separately.

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Figure 14.16 Pantheon, Rome, Italy

A detail of a structural crack, probably due to thermal movement. One of only a few deformations visible in this well-maintained monument

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History of construction: documentation

The initial report, dealt with in Chapter 14, shouldhave stated what requires to be investigated ingreater depth. The history of the building will have tobe unravelled and research may have to be made intosite conditions and the building technology of theperiod or periods of construction. All other relevanthistoric and archival evidence should be found,digested and recorded, but there is a danger, espe-cially with inexperienced persons, of doing too muchresearch and analysis, treating it as an end in itselfand thereby delaying decisions and necessary action.

To understand a building, one must know thestory of its phased construction and the whole his-tory of the ground upon which it stands, and havea record of any external environmental changes.Obtaining this information is not always simple.Archaeologically, ground levels tend to rise steadilyas the dust and rubbish of generations build up. Forinstance, Roman historical site levels may average2–4 m (6–13 ft) in depth and sometimes reach evenmore than 7 m (23 ft) down. Some prehistoric levelsare 14 m (46 ft) or more below the present soillevel; in the town of Arbil in north Iraq, which issaid to have been inhabited since the time ofAbraham, the street level has risen some 16 m (52 ft)above the plain, the city always having beenrestricted within its walls, with each new building ris-ing upon the ruins of its predecessor. Troy tells a sim-ilar story, of seven cities built one above the other onthe same site before it was sacked in 1180 B.C. Oncomplex sites, the archaeological levels are oftenrelated to documented events such as the captureor burning of a city.

There may be a direct relationship between thehistoric development of the site and the engineeringproblems of reconstitution of the fabric; thus it willsometimes be necessary to undertake exploratoryarchaeological excavations, using properly qualifiedpersonnel, in order to get down to original ground

15

Research, analysis and recording

levels and uncover buried parts of the structure andpossible earlier versions. In this way the sequenceof building operations will be more surely estab-lished. Such excavation has sometimes revealedhitherto unknown stages in the development ofmajor churches. Examples are numerous, but perhapsCologne cathedral, the basilica of St Denis in Parisand York Mister, England are noteworthy.

Analytical studies are necessary to ascertain all thefeatures of the edifice, including those which werenot executed and those left unfinished. Geometricdiagrams indicating modules or proportional systemsand indications of design techniques are also of thegreatest interest. Old drawings, photographs, mod-els, plans and sketches and general views includingthose in which the historic building forms a back-ground, bas-reliefs, and illuminated manuscripts maygive information, even if only of a general nature.Ancient manuscripts relating to the establishment ofthe building, building accounts, descriptions of mod-ifications, enlargements or demolition should bestudied. Information may also be obtained fromadministrative documents, orders, contracts, sales,receipts, wills, donations and other deeds and grants,as well as censuses and, for churches, accounts ofpastoral visitations. Old newspapers and journals,both popular and technical, together with street ortrade directories, are excellent sources of informationon more recent construction. Records offices,archives and museums should all be enlisted to assistin the search for relevant information.

Information obtainable from the building

The building methods and materials and general styleand artistic composition, proportions and aestheticsprinciples give an approximate dating for many buildings. Stonemasons’ and carpenters’ marks canalso be of assistance, particularly in following theprogress of a building, but may be misleading, as it

is not certain that the same mason would be allot-ted the same mark on every building site. The tool-ing and cutting techniques are a rough indication ofthe date of masonry. Stamp marks may be found ontiles and bricks. Occasionally, documentation maybe concealed within the walls or foundations.

Other information obtainable from the buildingitself may consist of initials, monograms, signatures,epitaphs, marked dates (particularly in foundationstones), coats of arms, escutcheons, emblems andmural decorations; even casual graffiti accompan-ied by dates and signatures may give valuableclues. An expert in heraldry can often identify theindividual arms of a known armiger and thus providecircumstantial dating evidence.

Recording information

A combination of drawings, both freehand andmechanical, and photographs should provide a clearand exact picture of the building. Although drawingscannot always show ornamental details and may failto convey shapes, colours, general appearance andperspective, as well as the surroundings and thebeauty of the landscape, small sketches are invalu-able for attention to a special point. Irregularities ofshape and outline, and damaged parts, can be seenmore clearly on photographs than by any othermeans, hence their vital importance for this purpose.Photographs also have many uses for publicity pur-poses in raising funds for the preservation of culturalproperty.

Defects can be shown exactly and specifically onannotated photographs. Detailed photographs ofcracks, for instance, can provide valuable records if a scale or common coin is included. Anotherhelpful use of annotated photographs is for givinginstructions.

Because survey record photographs of elevationsrequire special techniques and lighting, a photogra-pher with experience of this type of work should beemployed, using special film which defines linearedges and avoids halation. A 2 or 3 m (6 or 10 ft) scaleshould be inserted in the plane of the photograph.Photographs are particularly helpful for recording flatsubjects. If the camera is set up truly normal to thesubject and dead vertical, with two full-sized scalesinserted, negatives can be enlarged to a known scaleand used as drawings. Such photographs show everystone or brick in the correct position and should beproduced when information of this sort is required, asit seems rather wasteful for highly trained personnelto spend time making large-scale drawings to a lesserdegree of accuracy. Photographs can be transferredinto dyeline negatives for cheap reproduction usingspecial kinds of film.

Survey drawings

It is highly desirable to have an accurate surveydrawing of a building before making a final report ofrecommendations for alterations. This not only assistsin identification of features, pricing of necessaryworks and easy interpretation of the report for some-one, possibly a layman, who does not know thebuilding, but can also be a useful working tool indiagnosis of structural defects. Nevertheless, an accur-ate measured survey of a complicated historic build-ing is usually a difficult and time-consuming job.Idealized drawings often exist together with typicaldetails and these may be sufficient for strategic plan-ning purposes, but to obtain accurate measurementsof deformations and to plot all irregularities is alengthy and costly process, probably involving a spe-cialist firm. However, to embark willingly on anyrepair or restoration work without accurate plans,sections and elevations is to deny the architect one ofhis fundamental skills of thinking three-dimensionallyand in effect ‘seeing through walls’. Without suchplans, historical analysis is difficult and co-ordinationof mechanical services and design of alterations arealmost impossible. Even a humble vernacular cottageshould be fully measured and recorded before it isaltered. If such plans were sent to a central agency asa matter of routine, they could be made available tothose studying aspects of the history of the building,and in time considerable benefit would accrue to thecity or nation concerned.

The historic building and its parts should bedrawn to scale, with conventional signs to indicatetheir type, composition and position. The most con-venient scales are 1:500 for site plans; 1:100 and 1:50for general plans, isometric drawings and isometricprojections; and l:10 and 1:5 for details. A 1:2 scaleshould not be used as it can be confused with 1:1rather too easily.

As a general rule, one plan should be drawn foreach horizontal section being taken 1 m (3.3 ft) abovefloor level. If inappropriate in relation to the config-uration of the historic building, the horizontal sectionmay be varied, but this should be shown with a dotted line on the elevations for the sake of clarity.

A broken line is used to mark any parts notincluded in the horizontal section that may facilitatean understanding of the building. The intersectionpoints of vaulted surfaces should likewise be markedon the floor plans by a chain dotted line. Higher features can be shown with a dash and two dots.The same method can be used to indicate the soffit profile of barrel or circular vaults.

All the facades should be drawn in orthogonalprojection, from a point in infinity in relation to theplan. If desired, faces that are not right-angles can

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be drawn in true elevation so as to be useful foraccurate measurement.

Sections should be taken through the most sig-nificant parts of the building so as to reveal the concealed architectural features and show the con-struction. All plans should, of course, indicate thetrace of the predetermined vertical planes throughwhich the ideal sections have been taken.Surveyors should accurately check the curve andthickness of the bearing walls, and all significantstructural and decorative details (the latter beingdrawn large scale or even full size).

Because of a building’s particular volumetriccharacteristics or its special architectural features,the height of the various floors must be given whena detailed graphic analysis is necessary. The surveymay be supplemented by key or location plansshowing its surroundings, explanatory diagrams orisometric projection drawings.

Field measurements should always be kept andpresented with other supporting documentation. Theaccuracy of a survey should always be proved bytaking diagonals or offsets or by using triangulation,both vertical and horizontal, with a theodolite.

Modern surveying equipment has opened uppossibilities previously undreamed of. With a laserbeam directed to specific spots aimed by a tele-scope on a theodolite, and a computer link, it ispossible to measure details accurately up to 100 m(325 ft.) distant. This is work for a specialist, who should be consulted before a major recordingprogramme is put in hand.

Photogrammetry

Photogrammetry offers another method of takingmeasurements and providing a full recording of theexterior of a building. Although simple in principle,it can be an exceedingly complicated subject inpractice. Pairs or series of stereoscopic photographsare used, as in air photography, and from these itis possible to delineate on a plotting machine aplan, section or elevation of the subject and socompute its volume. Photogrammetric techniquedepends on the accuracy that is desired—the lessaccuracy required, the simpler the equipment andthe quicker the results. Photogrammetry excels inplotting rounded and irregular objects and thosethat are impossible to measure because of difficultyof access. It has also immense potential for recordingand storing all the visual information relevant to abuilding in such a way that it can be retrieved andspecific measurements taken at a later date.

If an historic building has been destroyed, it can be reconstructed from information stored on

photograms. The first case of this being done inEngland was at Castle Howard, by use of two ordinaryphotographs of the dome before it was destroyed byfire, which were fortuitously available. Needless tosay, photographs especially taken for the purposewould have been even more informative.

The main advantages of photogrammetry are, inbrief:

(1) Speed in photographic recording (no scaffold-ing of buildings is needed).

(2) Precision and uniformity in measurements.Gives accuracy of high order.

(3) Can save time and money in survey, especiallyon curved or irregular objects.

(4) Possibility of measuring fragile or delicateobjects. In some cases, X-ray photogrammetrypermits measurement of invisible features.

(5) Can survey buildings impossible or dangerousto reach.

(6) Reveals distortions not appreciated by the eye.(7) Photographs need not be plotted immediately;

storage with pertinent data allows for later restitution, if need arises.

(8) Photographs taken at intervals of time (evenyears apart) can also be used to demonstrate orcheck the deterioration rate of an object.

Photogrammetric documentation is also veryvaluable in the case of damage to a building and inspecial cases can be used for interiors.

Considering the cost of the necessary precisioninstruments and the need for skilled operators,photogrammetry is most economical if it is usedcontinuously. Groups of users could combine formore cost-effective utilization.

In making any drawing, even in taking measure-ments, there is an element of interpretation. To besuccessful, architectural photogrammetric drawingshave to be made by people who know about his-toric buildings so that they interpret them correctly.Photogrammetry can be used to give the co-ordinatesof key points with great accuracy and these can beconnected together by drawing and filling in detailwith rectified photographs.

Photogrammetry reveals in a fascinating way thecorrections made by architects and sculptors foracute angles of vision, and even at a simpler levelthe difference between a roof drawn on elevationand a sloping roof as seen from the ground.

Models

Surveys and photographs give a two-dimensionalpicture; models and casts can be used to obtain a

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three-dimensional representation. Whereas it takesmuch experience to read drawings, particularly ele-vations, models can be understood by the layman,as the three-dimensional aspects are immediatelyapparent. An extension of this is the use of perspexmodels to show three-dimensional relationshipsand to analyse the effects of structural cracks andtheir causes. Internal and external cracks can beindicated by different colours and all cracks can beviewed simultaneously.

Models made of wood, wood derivatives, metal,plaster, cardboard or transparent or non-transparentplastic substances can be prepared to illustrate thevolumetric and spatial arrangement of urban unitsor a group of historic buildings, or a general viewof ruins and site topography in the case of archae-ological excavations. They are useful in visualizingmissing parts and even deciding how they mighthave been constructed, for skilfully illuminatedphotographs of models can be used to bring thepast to life with amazing vividness. Special modelscan be used for calculating and testing the resist-ance of existing or projected structures.

Models of historic centres to a 1:500 scale provideinvaluable assistance in considering town planningproblems and their implications. The ‘modelscope’,an instrument with a viewing lens at the bottom ofa tube and an eyepiece at the top, enables one tosee inside models and also take photographs. By itsuse, the effect of any proposed restoration or alter-ations for adaptive use may be assessed.

Casts and rubbings

A cast gives an exact reproduction. Into a matrixtaken from the original, a fluid substance (plaster,wax or a compound of plaster and synthetic rubber)is poured and removed after it has solidified. Thismethod, excellent as it is, may present serious dif-ficulties when it comes to complicated pieces ofsculpture, necessitating a number of carefully madematrices. Another drawback is that making thematrix involves coating the surface with varioussubstances which may harm the colour, the polish,or the surface itself. The surface can be protectedby covering it with a thin sheet of aluminium foil orsimilar material, taking care to avoid folds beforemaking the cast. The foil can easily be removedafterwards. Casts can also be taken to reproducethe shape, position and surface of mosaics, frescoesand epigraphs, or of any section whose surface andstructure is to be studied. Papier mâché gives goodresults; when dampened, it adheres to the surface andcarries the imprint when removed after drying.

In some cases, rubbing is convenient; blackwax (heel ball) or a small cotton bag containing

powdered graphite or a powdered dye is rubbedover thin paper lying on the surface of an area ofwhich a record is required. For small areas such asepigraphs it is often enough to rub a soft pencilgently over a sheet of paper laid on the engravedsurface. If a broken memorial slab or piece ofsculpture has to be taken down, a rubbing showingall the pieces is indispensable for putting it togetheragain. Stained glass windows are also recorded byrubbings before they are dismantled for conserva-tion and releading.

Recording

When a building has been examined initially ‘as awhole’ and a preliminary descriptive report prepared,the need for further specific structural and analyticalstudies may then have to be considered. The prelim-inary report is essential in order to ensure that allsuch further studies are properly conceived and willprovide highly significant information. It is essentialfor briefing specialists, especially engineers.

If active movements are suspected, measure-ments of vertical and horizontal deformations usinga theodolite and various types of plumb bobs, andrecording of movements in cracks, should be initi-ated at this stage. Such records should run for at least a year, in order for the effect of seasonalthermal expansion to be taken into account.

One of the benefits of accurate recording andanalysis of movements is that one may be able todecide to ‘wait and see’. For example, superblyaccurate measurements taken over a period of 40years at St Paul’s, London, enable one to predictwhen future action is likely to be necessary. Thissubject is dealt with in detail below.

Statical analysis of historic buildings is dealt withmore fully in Chapters 2–6. Other major subjectswhich may require further study are humidity ordampness, vibration and atmospheric pollution.The latter two are dealt with in Chapter 11.

After an initial inspection, the erection of scaf-folding for detailed inspection, the making ofrecord photographs and the opening up of suspectareas are some of the first of the additional studiesthat are recommended. Cleaning, dusting andwashing a building all enable an inspection to bemore accurate, especially as such work involvesonly light scaffolding which also gives access for aclose study of the fabric. Such a close study enablessamples of materials to be taken for laboratoryanalysis. Woods and metals can then be identifiedand the geological and palaeographic study ofstone made, together with dendrological and car-bon-14 studies of timber, if necessary.

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Structural analysis method—measurements ofcracks and deformations

Poul Beckmann (1972) of Ove Arup & Partnerswrites:

‘The two operations (of analysis and recording)must go hand in hand, as without records nomeaningful analysis can be made, and withoutanalysis, records have no meaning. For our purposes, structural records include any information describing the structure of thebuilding in the three dimensions of space andthe fourth of time. This therefore includes thestate of the structure as it exists. Structuralanalysis will include all methods by which theavailable data can be processed to produce an assessment of strength, stability and deformations, past, present or future.

‘If an ancient building appears in good repair and a visual inspection gives no cause for concern, one would only resort to structuralanalysis in order to assess the effects of a proposed change of its environment, such asmay be caused by major construction or demolition works in the vicinity.

‘When an ancient building appears to be in apoor state of preservation, structural analysiscan help to assess the following:

(a) the present structural safety;(b) the effects of any observed defects;

(c) the possible cause of the observed defects;(d) the remedial works necessary, if any.

‘For a structural analysis the first requirement isa complete description of the structure as itstands, warts and all. The most complete recordis, of course, the building itself, but in most casesthis is too big and too complicated to provide a picture which can be grasped as an entity.

‘What is needed before a safe diagnosis can bemade is a complete pattern of symptoms. Hencedrawings and models are essential. The drawingsshould be sections and elevations of smallenough scale for the whole of the building to beshown on one sheet. On these should be superimposed all significant defects. Whereas the geographical presentation of cracks is fairlystraightforward, deformations are more difficult todepict in a clearly comprehensible manner.Relative levels can be shown under an elevationas a line diagram with exaggerated vertical scale.Out-of-plumbness can be shown with arrowsindicating the direction with the magnitude at thelevel of the arrow superimposed in figures, andwhere the deformation of a particular line is ofspecial interest, this can be plotted to exaggeratedhorizontal scale away from the main elevation.

‘Cracks are, on the face of it, easily observed,but it is important to ascertain, as far as possible,what the structural gap is. This is often maskedby repairs done in the past so that what now

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Figure 15.1 York Minster, England, long section(Courtesy: Ove Arup & Partners)

A simplified drawing to 1/200 scale (now reduced) of a section through nave and choir showingsettlements, deformations and some cracks

appears as a 5 mm crack may in fact signify astructural gap of 25 mm concealed by re-pointingand/or stone replacement. As regards deforma-tions which have taken place between the original date of construction and now, one canobviously only achieve a fairly low degree ofprecision in the measurements due to theinevitable inaccuracies in the original construction. For this reason, fairly crude methods of measurement suffice; an ordinarylevelling instrument will do, but it should havethe best possible telescope to assist reading inpoor light. As one may have to take levels intriforium galleries and other hard-to-get-atplaces, the instrument should be as light andcompact as possible. When taking and recordinglevels it should be remembered that any onesection of the building which was built as anentity in one period would have been finishedas to within �10–15 mm on horizontal featuressuch as string courses, but anything built beforeor after may have been affected by interveningdifferential settlement.

‘For plumbing, simple plumb lines or theodolite-plumbing will be chosen on the basisof which is the easier to do; remembering thatplumb lines are not easily fixed to great heights,and they require a calm day to be of any useexternally. Where there is more than one storey,and particularly where the work above a flooris of a different vintage from that below, fairlyaccurate (�25 mm) correlations of pier shapesare necessary to ascertain possible eccentricities.Having thus obtained our description of thestructure in three dimensions at one particularpoint in time, one can perform structural analyses to various degrees of refinement.’

Study of cracks

The age of cracks can only be assessed approxi-mately. If very old, they may be covered by accu-mulated dust and dirt; if only relatively old, dust maybe seen in varying degrees in the length of the crack,and the edges will appear sharper, as they arenewer. New cracks have clean interiors and sharpedges. Other clues will be found in careful examina-tion of fixtures and plaster repairs and other inci-dental features, which, if datable, may indicatewhether a crack existed before they were fixed.

In considering cracks it is important to know thesequence of the construction of a building, since initial settlement cracks often remain but are probablyof no great significance because they have ceased to move. An example may be seen in St Paul’s

Cathedral, where quite a large crack exists in thesouth-west corner but stops below the tower whichwas built a few years later. Documentation of all pre-vious repairs is of great assistance in the study ofcracks.

The movement of cracks can be studied by fixingdabs of plaster to the basic masonry or fixing glasstelltales with epoxy resin, but such methods arerather rough and ready. Glass telltales should be only1–2 mm (0.04–0.08 in) thick, with ends notched toensure good mechanical bond to the resin, whichitself must grip the masonry: in one recent case asense of false security was given because the end ofthe glass telltale was not fixed properly and eventhough dangerous movements were active in thebuilding, the telltale did not break. Glass telltales arerather slow to react to movements, but can show out-ward movement as well as the opening of a crack.Pipeclay telltales fixed to knife-edge blocks of precastconcrete have been recommended, but the pipeclayis nowadays difficult to obtain, and fixing the knife-edge is difficult. The breaking of a telltale has obvi-ous and perhaps exaggerated significance to thelayman, whereas a movement of 0.01 mm may seemto have no such portent but may be of vastly greatersignificance if the syndrome of the building is fullyunderstood. Furthermore, once a glass telltale hasbroken, it cannot give much more information. Thus,for proper long-term study of movement in crackssuch simple devices cannot be recommended.

An elegant, accurate and not too expensive dialmicrometer called the Demec strain gauge is to be rec-ommended. It measures the distance between stainlesssteel measuring points fixed very easily to the wallmasonry with epoxy resin. The dots are set out in a tri-angle so as to give measurements in two dimensions,but only one plane. The points chosen must of coursebe firm. They are inconspicuous and, if decoratedover, can be cleaned. The gauge is so sensitive thatonly one man should use it in any scheme of meas-uring in order to eliminate the personal factor.Measurements are checked against an Invar bar, andafter averaging should be corrected for temperature.Micrometers can be used as well, in between plugs setin walls, in much the same way as Demec gauges. Theplugs should be protected against damage and corro-sion and, if they are substantial, they can measure outward movement in the third dimension. There isalso a rather complicated type of plug invented by J. Crockett that enables measurements to be taken inthree dimensions with one micrometer.

For most measurements there is an ‘envelope ofmovement’, the size of which can only be determinedby continued study. If no envelope can be estab-lished, the crack is moving actively, but most cracksor points in a building move in accordance with the

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seasonal expansion and contraction of the fabric.Initially measurements should be taken frequently at,say, monthly intervals; once the envelope is estab-lished it is sufficient to take them once or twice ayear, but always at the same time of year. In England,for example, spring and autumn are the best timesbecause average temperatures are less variable then.Cracking can be said to be significant if movement isfound to proceed beyond the established envelope.

Geodetic surveys

A geodetic survey using a theodolite from a fixedbase is part of the classic skill of the surveyor and

has reached a very high level of accuracy. It can beassisted by use of traditional plumb bobs with someform of damping or optical plummets. Sophisticatedequipment such as geodometers and tellurometers hasbeen developed. Such surveys need accurate datumpoints. Establishing a deep datum may be simple, as atYork Minster where rock was found at a depth of some25 m (82 ft), or extremely difficult as in London where,due to underdrainage of the clay strata, the whole cityis sinking at differing rates. A datum should be permanent and immovable and as close as possible tothe building; because it is the relative movements ofthe parts rather than absolute movements that lead to cracking and deformations, a datum may besimply a pile driven for that purpose or a non-rusting

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Figure 15.2 Perspex model of York Minster, England(Courtesy: Feilden & Mawson)

After a visual inspection with a written report, the information was consolidated intodrawings and finally a perspex model was made which enabled a three-dimensionalsimultaneous assessment of the complicated syndrome of cracking and deformation to becarried out, together with an analysis of the structural actions of the building as a whole

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Figure 15.3 Perspex model of York Minster, England(Courtesy: Feilden & Mawson)

Using this model enabled information on at least 16 drawings to be absorbed and co-ordinatedsimultaneously

Figure 15.4 Measuring cracks at York Minster, England(Courtesy: Shepherd Building Group Ltd)

Movement in cracks is measured with a dial micrometer ofaccuracy (�3 �m), enabling it to be used as a strain gauge.Because of its sensitivity only one man should be entrustedwith making a series of measurements. Five measurements ineach of the three directions were taken and then averagedand corrected for temperature

metal rod set inside a protective tube filled withdurable oil, sealed and capped with stainless steel.

The objectives of a geodetic survey must bedefined, and any assumptions must also be recordedfor posterity; provision must be made for continuityof the survey with regular review at suitable intervals.One psychological danger of a long-continued pre-cision survey is that conscientious measuring maybecome an end in itself and it might be no specificperson’s job to ask at intervals, ‘what does this sig-nify?’. Measurements help those responsible for thebuilding to assess its state of health, and also toavoid doing unnecessary repair work.

To assess these questions it is necessary to make afull study of the building structure and, from analysisof past movements, to formulate projections into thefuture, so that actual movements can be comparedwith forecasts. The forecasts enable one to specifythe degree of accuracy that is required from the geo-detic survey. In the case of St Paul’s Cathedral, dif-ferential settlements of up to 11 mm (0.4 in) occurredin the 40 years after the great restoration undertakenin 1925–31, while at York Minster, after the work of1967–72, although there has been an overall settle-ment of 1 mm (0.04 in) no differential settlement hasyet occurred, but 5–10 mm (0.2–0.4 in) is forecast asthe maximum that is acceptable. These examplessuggest that all measurements should be made to anaccuracy of �1 mm (0.04 in).

When the building has been fully recorded and measured and the structural action has beenunderstood, then the situation should be reviewed,as it may be possible to reduce the measuring programme to a quinquennial check of the mostsignificant points, provided that a full visual inspec-tion of the building is made at the same time. If anyfurther cracks are noted, the initial measurementscan be referred to and the change measured.

Soil mechanics

The linking of ground water to the study of founda-tions through the science of soil mechanics is fullydealt with by Professor E. Schultze in Techniques ofConservation and Restoration of Monuments. Certainpreliminary investigations should be made beforecommissioning a costly specialist report by a firm ofsoil mechanics engineers. It is often easy to have ahole dug down to the depth of the foundation andsuch an examination is always worth while. It is alsopossible to probe diagonally to discover the depth offoundation and, if water intervenes, this method maybe the only one possible without pumping.

Light hand-augers can probe the ground to adepth of 10 m (33 ft) or so and are useful for extract-ing samples; similar light equipment can be used tomake penetration tests, which give indications of the

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Figure 15.5 Demec mechanical strain gauge(Courtesy: Ove Arup & Partners)

The standard 200 mm (8 in) gauge is most useful for historic buildings because the stainless steel locatingcentres can be glued to the surface of the fabric using a locating jig. The extra width of the gauge allowsit to span multiple cracks. In practice, it is sometimes difficult to find a firm fixing. Movements in twodirections can be plotted

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Figure 15.6 Principle of the Demec mechanical strain gauge(Courtesy: Ove Arup & Partners)

The measuring points, a fixed and movable cone, are placedinto the locating centres which are glued either side of thecrack using a jig to place them sufficiently accurately. Patternsof measurement record that:(a) With accurate instruments there is always some

background ‘noise’ due to the person taking the measurement.

(b) Periodic oscillation is due to seasonal expansions andcontractions. If the fabric expands conversely, cracks willtend to close. Until the annual periodic oscillation hasbeen established (the envelope of movement) it is difficultto assess actual movements.

(c) Actual movements show clearly in the long run after thecrack has been measured for a year. Note, however, that ifjudgement were based on the first three months an exag-gerated picture would be obtained, and if based on thenext six months, a quiescent crack might be diagnosed,whereas the average movement would give a truer picture.

Figure 15.7 Measuring with alevel, York Minster, England(Courtesy: Shepherd BuildingGroup Ltd)

Light is necessary for accuratereading. For work on historicbuildings, levels should have alarge objective to gather as muchlight as possible under difficultconditions. Here, a check on thesettlement of the main piers,which moved downwards some30 mm (1.2 in) in five years, isbeing carried out

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Figure 15.8 Optical plumb bob, York Minster, England(Courtesy: Shepherd Building Group Ltd)

A plumb bob with illuminated cross-wires is set up in position over ameasuring point on the floor to monitor lateral movement in thegreat east window

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Figure 15.9 York Minster, England, central tower(Courtesy: Ove Arup & Partners)

A simplified drawing to show the differential levels of the fourcorners of the central tower measured at different heights. These measurements were used to test assumptions made in thecalculations

Figure 15.10 York Minster, England, central tower(Courtesy: Ove Arup & Partners)

An exploded diagram showing observed cracks and the horizontalforces calculated assuming the differential settlement shown above

bearing capacity and thickness of the respectivelayers of soil.

In commissioning a full-scale soil mechanics sur-vey, it is important to brief the engineers concernedon the problems you have in mind, so that the surveywill be as informative as possible. Such surveys areexpensive because heavy boring equipment and com-plicated laboratory tests are involved. Incidentally, theauthor has found that an archaeological excavation isone of the best ways of exploring a site.

Conclusion: making a final report

After the actions recommended in the initial report(Chapter 14) have been carried out and a routine of further inspection established and all historicaland environmental information has been absorbed,including measurements and recordings and suchfurther studies as were necessary, the time hasarrived for a full report which will cover all factorsof decay, and consider how they modify eachother.

From the final report a specification of works canbe prepared. Again, this is best written on the site inoperational form, dealing with the repairs, consoli-dation and restoration of distinct elements externally,and room by room internally. The writer has to visu-alize all the work to be carried out and describe it inthe order it is to be done. Plumbing and electricalwork can be dealt with separately as elements, butattendance must be fully described. Making goodand decoration can also be treated separately in atrade specification. The specification and drawingswill enable accurate costs to be obtained. Then it ispossible to submit the report and scheme for works

on the historic building for approval and allocationof such grants as are available.

Estimates of professional fees should show separ-ate figures for both the cost of recording the workas it proceeds and of a final report which, as wellas describing the initial condition, should record allwork done, with plans and photographs showingthe various operations and their results. This finalreport should also include plans of works, as exe-cuted, showing all hidden features. It is of particu-lar importance to give the chemical formulae of anysophisticated treatments used, as posterity will notnecessarily know the composition of trade namematerials. Ideally, samples of these products shouldbe stored in the archives.

After the report has been submitted to theauthority commissioning the work, two othercopies should be deposited in different places forfuture reference. The library or archives of thebuilding concerned should have one copy and theother should be placed in a national or localrecords office.

Non-destructive investigations

Non-destructive technology can be used for:

(a) Evaluation of the total structural performance.(b) Evaluation of the building envelope.(c) Analysis of the properties of individual building

materials, e.g. moisture content, porosity, per-meability, and strength in shear tension, torsionand bending.

(d) Detection of voids, cracks and discontinuities.(e) Detection of concealed details and elements.

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Figure 15.11 Settlements, York Minster, England

A hypothetical reconstruction of settlements since the building of the Norman cathedral in 1080.This diagram is most useful in visualization of the structural history of a building which had reached a crisis due to the foundation, long overloaded, having become sensitive to smallenvironmental changes such as lowering of the water table

(f ) Analysis of the chronology of the fabric forarchaeological and historical purposes.

(g) Site exploration, hidden services in the ground.

All techniques and testing procedures haveinherent limitations. Interpretation and evaluationsof the results needs experience. Field experience is essential in order to choose the most relevanttechnique.

Some of the more promising techniques arelisted below:*

Radiography using X-rays and gamma raysInfra-red detection, thermographyUltrasonics

Microwave analysisRadio detectionRadar detectionMetal detectorsMagnetometryFibre optic surveying, endoscope, borescope, flexi-ble fibrescopeMonitoring structural movement, tell tales, gaugesLinear Variable Differential Traducers (LVDT)Moisture metersRectified photographyPhotogrammetry

Non-destructive techniques are tools which shouldbe used to answer specific questions. (There aresome people who do tests for tests sake!) It shouldbe remembered however, that there is no substitutefor observation and the understanding which comesfrom inspecting many historic buildings.

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*See Fidler J. Non Destructive Surveying Techniques for the Analysisof Historic Buildings. Association for Studies in Conservation ofHistoric Building, Transactions Vol. 5 1980 pp. 3–11.

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The reasons for maintenance

Maintenance is the process by which a building iskept viable for the benefit of its users. With historicbuildings, properly executed maintenance is in thepublic interest. The desirable standard of main-tenance depends upon the intensity of the climaticand other causes of decay, as well as upon theneeds of the users. Maintenance of historic build-ings must have the support of owners and occu-pants. This is the simplest way of ensuring itsconservation, as under constant supervision defectsare more likely to be remedied as quickly as theyoccur.

One of the basic propositions of this book is thata policy of preventive maintenance and preserva-tion work is less expensive in every way than hope-ful neglect followed by extreme measures. Humannature being what it is, the latter procedure,although so wasteful, is all too common. It must beremembered that the more sophisticated the build-ing’s design, the more essential it is to organizemaintenance and the more difficult it is to carry outalterations without the danger of collapse.

A weakness of the architect’s professional prac-tice is that he has little experience of the after-careof the very building he conceives. This can bemade good by follow-up inspections about sevenyears after the building has been completed; butunless he has a lawsuit for negligence, usually thepressures of everyday affairs do not allow him tovisit and inspect his own creation. Because of this,there is little feedback to designers who, in theirignorance, often repeat the same mistakes.

We can learn so much from mistakes if they areanalysed and understood. The pity is that they tendto get covered up, for obvious reasons. In England, amaintenance appraisal should be included in theRoyal Institute of British Architects (RIBA) Plan ofWork. If this were done, and architects visited their

buildings after the glossy photographs had been pub-lished, we might get a better building technology.

Historic buildings are a laboratory experience.They can teach architects how buildings are usedand abused, how they react to their environmentand where design might have been improved, fortime is the shrewdest of fault-finders. This digres-sion is meant to emphasize the importance of learn-ing the lessons implicit in the after-care ormaintenance of buildings and its importance todesigners, especially those who think themselvesoriginal and avant-garde, but do not understandthe wisdom of the ancients.

Skills required for maintenance

Maintenance and preservation work is very skilledand needs responsible and competent craftsmen(who should be rated as technicians). These valu-able men are dying off and those that remain arediscouraged by the ‘stop–go’ policy from which thebuilding industry has suffered. Steady, planned,preventive maintenance would keep these special-ists continuously employed. Stop–go in the flow ofwork has seriously embarrassed small firms spe-cializing in high-class work on historic buildingsand has contributed greatly to their overheads. Thisunnecessary increase makes building ownersapprehensive about the cost of repairing an historicbuilding. A possible answer to this problem wouldappear to be in the establishment of building-crafttrusts by local authorities on a regional basis; thecraftsmen employed by these trusts would treat thematerials of historic buildings with a full under-standing of the conservation problems involvedand of the historic technology of each particularcraft. Of course, many interests would oppose sucha proposal, but we must put the interest of thebuilding first.

16

Preventive maintenance of historic buildings

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Building maintenance is a subject that tends to fallbetween several stools and thus to be neglected. Itis of importance, for in Britain it absorbs one-thirdof the building industry output, which fact isscarcely appreciated. Generally, the architect will beconcerned with major repairs and the aesthetics ofpreservation, whereas the maintenance staff comeinto action only when something breaks down.

The cleaners who look after a building and comeinto direct contact with every part of it do not knowhow to recognize symptoms of incipient problemsor to whom they should report. Indeed, large inter-mediate areas are neglected because no one has beenallocated specific responsibility for them. Most build-ing maintenance, as practised, is concerned with tac-tics, with solving a particular problem, often in vacuo,without considering its relationship to the building asa whole. What is required is a co-ordinated strategyinvolving the owner and users of the building, the

maintenance staff and the daily cleaners, all ofwhom can, by constant vigilance, provide an early-warning system.

A maintenance strategy

If maintenance were well carried out there wouldbe far less need for repairs or renewals. In WilliamMorris’s Manifesto of 1877, establishing the Societyfor the Protection of Ancient Buildings, he enjoined‘Stave off decay by daily care’. This policy can onlybe made to work on a basis of regular inspections.

Historic buildings differ from new ones in thatthey are expected to last for ever—a definition of‘for ever’ being ‘as long as it is wanted’. An historicbuilding is one that, for various reasons, society hasdecided shall be conserved for as long as possible.

Electrical and mechanical services, on the otherhand, generally have a safe life of about 20 years.

Figure 16.1 Ospizio di SanMichele, Rome, Italy

As a new use for this buildinghad not been decided, it wasneglected for a few years.Blocked rainwater gutters anddownpipes initiated decaywhich led to some parts of thebuilding collapsing

Thus the skilful installation of up-to-date services inhistoric buildings deserves careful study, as a usablestructure may be said to be only as up-to-date as itsservices. Ancient monuments such as ruined castlesand abbeys do not have such problems.

A second difference is that the whole building canbe considered as an ‘environmental spatial system’.We have the advantage that the internal environmentcan be measured, so any changes can be carefullyconsidered. Nevertheless, improvements which alterthe environmental balance may in themselves inducenew causes of decay; for instance, traditional build-ing construction ‘breathes’, i.e. allows the easy pas-sage of moisture vapour, and this should not beprevented by the use of new and impervious mat-erials such as Portland cement. At the same time, oldbuildings are much more vulnerable to damage frompenetrating rain and rising damp and must be pro-tected. The introduction of any vapour checks mustthus be considered very carefully in the full contextof the building’s environmental system. Continuousheating also alters the environmental balance sub-stantially and should be introduced only gradually.

Thirdly, old and decrepit buildings need constantsupervision and maintenance, applying the principlethat ‘a stitch in time saves nine’, i.e. preventive main-tenance should be part of the planned strategic pro-gramme. Preventive maintenance includes such actsas reducing traffic vibration and air pollution throughthe application of town planning controls. As it pro-tects the historic building without any intervention, itis the highest form of conservation activity.

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Figure 16.2 Pears Almshouses, Peterborough, England(Courtesy: Feilden & Mawson)

The slate roof has missing, broken and slipped slates and guttersblocked by debris and grasses, but the roof only needs smallrepairs, for it is basically sound if work is done in time

Figure 16.3 Pears Almshouses,Peterborough, England(Courtesy: Feilden & Mawson)

Rainwater penetration through the roof has caused the fall of plaster, and condensation hascaused the paint to peel off. Thedefects are mainly superficial but may lead officials to con-demn such buildings

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Responsibility for maintenance

The problems of organizing maintenance dependsupon an intimate knowledge of the building, its con-tents and its functions. For a ruin, the tasks are toprotect it against frost damage by weathering and re-pointing, to remove plants and control algae andmoss, to present it meaningfully to visitors, and toprevent vandalism by providing uniformed supervi-sion. For an abandoned church, the task is to keepit wind and watertight, to protect it against vandal-ism and to use it for special occasions. For a house,the task is to keep it wind and watertight, heated andrepainted every five years. The owner must see tothe repair of defects, and cleaning out of gutters andair vents twice a year, and keep a constant check onelectrical defects such as overheated socket outlets.

Although the cost of maintaining and conservingan historic building may seem a burden, it is theduty of owners and trustees to see that the buildingis handed on to the next generation in good condi-tion. In fact, when compared with the replacementcost of the building, the cost of maintenance willnot seem unreasonable, and of course the older an

Figure 16.4 Living room, Pears Almshouses, Peterborough,England(Courtesy: Feilden & Mawson)

Local water penetration from the faulty roof has caused reedlathing to rot and the plaster to fall, besides staining the walls.Reed lath was frequently used in East Anglian plasterwork untilthe end of the nineteenth century

Figure 16.5 Ground floor, Pears Almshouses,Peterborough, England(Courtesy: Feilden & Mawson)

Extensive water penetration from faulty gutters has ruined plasterand decoration and caused dry rot

Figure 16.6 Pears Almshouses, Peterborough, England(Courtesy: Feilden & Mawson)

Rainwater penetration has caused this dry rot in the skirting,which may spread rapidly in an unoccupied building and evenreach neighbouring buildings

historic building is, the more valuable it becomes asan artefact whose structural and aesthetic integritymust be preserved. In fact, the cost is low whencompared with the 2% of capital cost which mod-ern construction requires.

Maintenance policy

The objective of maintenance policy is to preservea building so as to secure its uninterrupted use atthe users’ desired level of activity. This level mustbe carefully considered, for to achieve it will neces-sitate a wide range of maintenance actions—fromsimply preventing damage by wind and weather toproviding for intense use with sophisticated levelsof comfort and decoration together with fire andsecurity precautions. The desired standard of main-tenance should be agreed upon with those respon-sible and laid down as a policy appropriate to thebuilding. It must also be economically viable. Theproblems of organizing maintenance are multifari-ous, but whether the structure is a museum or anhistoric house open to the public, a ruined castle, acountry parish church or a cathedral, the principlesare the same. Regular inspection by staff at specificlevels according to their competence should be laiddown, culminating in a fully professional inspectionat not less than five-year intervals.

The following points are made in a Departmentof the Environment bulletin on building mainten-ance which states that the main objective of build-ing maintenance is to keep, restore or improveevery facility in every part of a building, its servicesand surroundings, to an acceptable standard and tosustain the utility and value of the facility. The mainpoints are summarized as follows:

(1) The amount of available finance is a substantialinfluence in determining the acceptable standard.

(2) This standard should be explained to, andagreed with, the owner or trustees of the his-toric building, as it determines the amount ofwork necessary. Maintenance expenditure canoften too easily be postponed without immedi-ate loss or harm, but such a course will lead tounnecessary deterioration and depreciation.Expenditure on maintenance beyond thosethings dictated by relevant technical and eco-nomic considerations may be wasteful, althoughhigh standards can have a general beneficialinfluence on the attitudes of the users.

(3) Over its life and depending upon its use, theacceptable standard for a building can alter,and this will affect the amount of maintenancework that is required.

(4) Efficiency in the execution of maintenancework depends upon correct diagnosis, followedby effective remedies performed with goodworkmanship and, it must be added, controlledby good management.

(5) Maintenance is divided into planned andunpredictable work, the former being dividedinto preventive and corrective maintenance,while the latter has a sub-category of emer-gency maintenance. The less emergency main-tenance, the better the maintenance plan.

(6) It should be an important objective of propertyowners to develop an effective maintenancemanagement accounting system and acquireadequate records and data for forecasting pre-ventive maintenance tasks.

(7) The great majority of buildings provide shelterfor people whose wants and needs must beunderstood and taken into consideration. Infact, the maintenance of buildings involves asocial system in which maintenance manage-ment, supervisors and operatives, buildingowners and the occupants all play active parts.

(8) It must be accepted that more rather than lessmaintenance work is necessary if the value andamenity of cultural property is to be kept atpresent levels. The author has only seen onebuilding in his lifetime that had been over-maintained, and thousands which had inade-quate maintenance.

Each historic building, however small, needs alocal custodian who is charged to look around itinside and out, in all weathers, and to note anydefects. He must inspect after any severe wind orrain and record his observations in a log book.

If the custodian has the authority to instruct con-servation craftsmen to carry out immediate first-aidrepairs, needless delays can be eliminated and costsreduced. Problems can arise, however, because it isusually necessary nowadays for skilled guidance tobe given to workmen for even very simple repairs,and as the custodian would be unlikely to be tech-nically qualified he will often be unable to offersuch guidance. Frequent examples of misguidedunsupervised repairs include re-pointing of brick-work or stone with Portland cement mortar, the useof ‘patent’ gypsum plaster and common sulphate-bearing bricks in damp places. (For an historicbuilding, a good rule is to ban the use of Portlandcement and ‘fletton’ bricks unless specified by aknowledgeable professional.)

The custodian is backed up by the cleaning staff,who can be essential primary trouble-spotters of the internal maintenance operation, for, as partof their routine, they should see every single part of

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the building at regular intervals. Staff must be of asuitable grade for the building they care for, andthey should be given simple training in reportingdefects. Reliance upon cleaners for front-line intel-ligence is unrealistic if, as in so many buildings, theturnover of cleaners is frequent or they are simplynot interested. Contract cleaning presents otherproblems. The potential of, and the need for, good-grade permanent cleaners for valuable buildingscannot be over-emphasized.

It is most desirable to provide adequate access tothe internal structure of roofs by means of walk-ways, as well as good access externally over roofsand along gutters. Such provision is a good invest-ment because it makes routine checks easy andeffective. For the same reason, it is good policy toprovide electric lighting within roof spaces; socketoutlets for hand-lamps should be provided forviewing difficult places such as the underside ofparapet gutters. It is a wise policy to maintain allconcealed spaces clean and decorated and in goodorder, because this encourages a high standard ofpreventive maintenance.

Budgets

The budget should be divided into two parts: run-ning costs and maintenance costs. Running costsinclude day-to-day expenses of providing light,heat and water, cleaning the building, security andfire measures, etc., and providing staff for perform-ing these activities. Maintenance costs, on the otherhand, include payment for items needed to preventavoidable damage to, or decay of, buildings andtheir plant. Doors, windows and gutters and roofsare primarily vulnerable. Also included as mainten-ance is the cost of replacing any of these items.

Cyclical maintenance

While the simple categories outlined earlier inChapter 15 are a basis for scientific preventivemaintenance, J. Henry Chambers (1976) approachesthe problem differently, in his book CyclicalMaintenance for Historic Buildings, starting withdaily routines and working upwards. His book dealswith maintenance surveys, the role of conservationcraftsmen and conservators, supervision, workrecords, staffing, and all matters relating to organiz-ing a maintenance programme for buildings in areasonable state of repair. He makes suggestions asto what should be done by outside contract serviceand also touches on training, work space planningand maintenance tools, and covers cleaning. These

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Figure 16.7 St William’s College, York, England

The hard cement pointing stands proud, while the decay of thesofter permeable stone has been accelerated. An example ofwrong maintenance

Figure 16.8 Parish church, Bedfordshire, England

The poor pointing breaks up because it is too hard. The cementmortar has been spread widely across the joints but not inserteddeeply enough—it has accelerated the decay of the stone

maintenance techniques are based upon the prepa-ration of a maintenance manual which is a sophis-ticated document giving assessments of workfrequencies and calculation of work time units andmeasurement of areas. Ten different frequenciesthat are specified are given below:

‘A’ Policing as required: Policing is a high-frequency task which is performed during andimmediately after the use of the building by largenumbers of people, removing conspicuous soil andtrash so that it will not have a chance to becomepermanently embedded in the finish surfaces. Theamount of policing will depend upon weather con-ditions and the building use. Each historic propertywill have different priorities and different problems.

‘B’ Routine housekeeping and maintenance: Thisis a dry-type maintenance, covering all reachablesurfaces so that accumulations do not become per-manently embedded due to their oily content. Thefrequency could be daily, twice a week, or weekly.It may vary for different locations in the buildingand with the season because of peak visitor peri-ods, or it may vary because of seasonal weatherconditions or seasonal air quality.

‘C’ Periodic maintenance: This may be a dry,damp or in some instances a wet treatment whichcleanses surfaces, removing those accumulations notgenerally removed by the more frequent methods. Ifwet, it removes portions of the finish itself whichhave become chemically changed due to exposure,thereby renewing to a certain extent the surface. Thefrequency ranges from weekly to monthly.

‘D’ Periodic maintenance: The frequency ismonthly, bimonthly or quarterly.

‘E’ Periodic maintenance: The frequency is quar-terly or semi-annually.

‘F’ Periodic maintenance: The frequency is semi-annual or annual. Perhaps by a contractor.

‘G’ Periodic maintenance: The frequency isannual or biennial. Perhaps by a contractor.

‘H’ Maintenance: The treatment is prescribed bya conservator. It may be both routine and periodicat a frequency which would best protect the item.The conservator should suggest means of protec-tion as well as treatment.

‘I’ Maintenance: The treatment should be doneby a conservator or an outside specialist.

‘J’ Maintenance: Irregular frequency; use pastexperience as a guide; consider outside contractors.

A good deal of expertise and time is needed toprepare such a maintenance manual, but it isundoubtedly well worth while, as scientific preven-tive maintenance can save large sums of moneyand reduce the need for costly major works.

Maintenance programming

Having established the importance of maintenancein the care of historic buildings, the methods bywhich this can be implemented need consideration.In Denmark since 1883, and in the Church ofEngland, quinquennial inspections have long beenthe basis for maintenance of parsonage houses, andsince 1955 the same routine has been applied toparish churches. This is one of the most sophisti-cated and economical systems in the world, becauseit involves the users and voluntary cleaners in theoverall maintenance strategy as well as professionaladvisers. The extension of the system to include allimportant historic buildings is to be recommended.

Maintenance costs should be divided into the fol-lowing separate categories, which should berecorded in a log book:

(1) Small items (basically good housekeeping).(2) Repairs to services: (a) heating, (b) electrical,

(c) plumbing.(3) The rolling programme of long-term preventive

maintenance carried out year by year and usingscaffolding economically.

(4) Major items when in need of renewal, such as(a) roofs, (b) walls, (c) windows, doors andfloor coverings, (d) services.

(5) Emergencies. A reserve of about 10% should beallowed for contingencies.

Each of these categories should be budgeted sep-arately. If reductions have to be made, they shouldbe spread equally unless special reasons exist. Justas a doctor keeps a case history for each of hispatients, so the log book should be kept by aresponsible person.

A routine for the maintenance of an historic build-ing should be laid down, and a year-by-year log bookshould be instituted with records of costs allocated toheadings as given above. Such a procedure willenable rational policies to be established and shouldensure a constant feed of data from those with first-hand information. The records should pinpointweaknesses in design and construction and indicate‘cost-in-use’, thus providing the organization (and itsarchitects) with valuable feedback information.

The study of records can lead to an assessment ofthe frequencies of servicing and repair in the past,and with a detailed survey of the fabric it is possi-ble then to produce a detailed programme as thebasis of future preventive work. This may have tobe an elaborate document, and the clerical adminis-tration and documentation will be considerable.Indeed, in a large operation a computerized pro-gram is the most efficient way of looking after a

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group of historic buildings with complicated plantsuch as a college in an ancient university.

A technique of ‘resumption by computer’ hasbeen developed for St John’s College, Oxford. Thismeans that at, say, monthly intervals the computerproduces dockets listing that work should be donein each craft skill and, where applicable, how manyplaces need to be checked. (The computer throwsup a reminder if a previous docket has beenreturned uncompleted.) After he has done the job,the craftsman initials the docket and notes on it histime and materials. Most importantly, he also pointsout anything he is not happy about, and by thismeans a most valuable source of information is uti-lized and fed back to the clerk of works or equiva-lent supervisor, who then should investigate thecraftsman’s report. The analysis of cost of repairsmay indicate which items are deteriorating rapidly.The whole maintenance operation is thus based onsurvey assessment of frequencies of work loads andon responsible feedback by the staff. Systematicmaintenance also facilitates the initiation and pro-gramming of major items of repair, reconstructionand restoration, because there is a feedforward ofitems which may need attention.

For major national monuments, every 30 years(once every generation) it is desirable to clean andoverhaul the principal structural elements andmake any necessary repairs. This is called therolling programme and will necessitate the erectionof scaffolding, the cost of which dominates the eco-nomics of all structural maintenance work, espe-cially on large historic buildings. It enables a closeinspection to be made by the professional advisers.

Repair work of a quality to last for at least 30 yearsshould suffice for elements of the fabric of not verygreat height. On the other hand, towers, which needmuch more scaffolding, may be taken to justify repairwork of a 60-year standard and spires a 90-year stan-dard of durability. It must be remembered that theseparts are unlikely to receive routine minor repairs;furthermore, because the cost of reaching inaccessi-ble parts of a building is so great, a higher standardof repair is justified. These figures are fairly arbitrary,but are borne out by study of past records of repairsto historic buildings and are endorsed by the collec-tive wisdom of the 1976 Cathedral Architects’Conference, held at Westminster Cathedral, London.

Maintenance routines

Maintenance should ideally be tackled by routinesof daily, weekly, monthly, quarterly, semi-annual,annual and quinquennial inspections, followed byreports. Checklists have been prepared as an indi-

cation of what might have to be done for a cathe-dral. Other types of buildings might be simpler but,needless to say, each historic building is a specialcase and needs its own schedules based upon aknowledge of the individual building with its con-tent and of its specific environmental and structuralproblems. In working out a maintenance strategy, itis desirable to have categories of repair work asdefined for the log books, so that the performanceof buildings of similar types can be compared on astatistical basis. Such a study might throw up sig-nificant facts; for example, the cost of atmosphericpollution or damage from sonic bangs.

Daily routine

First ask cleaners to report any defects they note,i.e. broken windows or ironmongery, leaks in roof,falling pieces of masonry, telltale wood dust frombeetle infestation, lime dust from spalling plaster.

Check fire-detection systems to make sure theyare functioning properly. A good sense of smell isessential: someone on the staff should make a firecheck throughout the building in the morning andevening after work. False alarms are all too frequentin fire-detection and security installations, and it iscounter-productive if ‘wolf’ is cried too often.

Check heating plant, controls, temperature andhumidity recorders. A daily check on boilers is veryimportant—as well as a final look before leavingthe building at night. The sound of boilers andpumps working sweetly must be made familiar tothe ear, for when this sound changes it is a warn-ing that something is amiss. Always make a habit offeeling heating pipes and radiators on a tour of thebuilding; a cold pipe can warn of an airlock or aleak. Fuel oil in tanks should be checked daily.Time spent removing airlocks can be quite costly ifboilers are allowed to go out for lack of fuel. Theheating feed tank should also be checked, as run-ning water here may indicate a pipe leak.

Do a security check. Windows and doors shouldbe checked for security each evening; in a buildingused by large numbers of people during the day,one invariably finds doors and windows left openat night, with good intent, but with a real risk tosecurity. Keys borrowed by contractors and work-men must be returned each day. Security installa-tions should be inspected to see that they have notbeen tampered with.

Change defective light bulbs and fuses andattend to minor faults in the electrical system.Switch off the electricity supply at night (the care-taker or night watchman should have a special cir-cuit for his needs).

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Check lavatories and cloakrooms. Report drippingtaps (they may cause icing up or an outbreak of dryrot and waste a lot of valuable water).

Weekly routine

Change or clean air filters of the heating or air con-ditioning plant or organ with humidifier.

Check all thermographs, humidigraphs and otherrecording instruments, and change charts and studysame and report. Correct faults in these instruments’calibration.

Check loudspeaker and microphone units in PAequipment.

Check accuracy of all clocks, including electricand winding mechanisms.

Check all automatic fire-alarm and security devicesin addition to the daily check of control systems.

Monthly routine

Have rainwater disposal outlets, gulleys, etc.,cleaned out.

Lubricate and adjust all mechanical drives andbearings, e.g. pulley belts, flexible drives.

Check all log books. Report to Fabric Committeeor technical supervisor charged with the responsi-bility for maintenance and other matters in respectof running the building.

Quarterly routine

Inspect roofs (outside and inside), gutters, rain-water disposal outlets, gulleys.

Check glaring. Clean windows and painted sur-rounds.

Check doors for closing and locking and allmeans of escape.

Overhaul humidifiers.Service sound-reinforcement systems, tape

machines and turntables, replacing worn drivebelts, idlers, etc.

Clean light fittings.Oil clock bearings. Check ropes and weights.Oil ball bearings. Check frames and ropes of bells.Technical supervisor to conduct a maintenance

inspection of, say, one-third, one-quarter or one-fifth of the total fabric.

Semi-annual routine

Sound fire alarms and give staff fire-fighting practiceexercises.

Clean out all gutters, downpipes and rainwaterdrains in autumn to remove fallen leaves and inspring to remove winter debris, and leave every-thing clear to cope with the heavy storms of sum-mer. Grass growing out of gutters is a sign ofneglect—if not negligence.

Annual routine

Rod through all rainwater and soil drainage systems.Overhaul all electric plant. Change fuses, bulbs and

tubes, especially where these are not easily accessible.Inspect boilers and controls, overhaul boiler,

clean main stack, renew firebricks. Maintain feedtanks and ease ball valves.

Clean out ducts and fan-assisted heaters, etc.Oil locks, hinges and replace defective

ironmongery.Service lifts.Overhaul air conditioning plant.Fire brigade to test men and plant in mock

fire-fighting exercises.Check problems of fire-fighting access.Test all fire extinguishers and refill if necessary.Decorate and clean sections of the interior of the

building.Touch up poor spots on external decoration in

autumn.Test lightning conductors and earth resistance if

in an area prone to lightning.

Quinquennial routine

The architect or surveyor must make full reportsevery five years, especially noting structural defectsthat should be kept under observation. He shouldrevise and update the long-term maintenance planafter each such inspection, and he should drawattention to any problems that should be kept underobservation and studied for the next report. Heshould divide the proposed work into categories:Immediate, Urgent, Necessary and Desirable (seeChapter 14 for definitions of these terms). Typicalquinquennial housekeeping items would be:

Clean out all voids and spaces and report anydecay found.

Change tap washers, as a matter of preventivemaintenance.

Specialists to clean out sanitaryware to avoidinfections.

Check lightning conductors (note that on somebuildings with valuable contents annual inspectionsare desirable).

Inspect and test electric insulation and installation.Check on mechanical wear, wear of electrical

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contacts, corrosion and any signs of abnormal deterioration.

Inspect and test the heating installations.Redecorate externally to a good specification.

For large buildings or series of buildings thisquinquennial inspection becomes the basis of a 30-year rolling programme for preventive mainten-ance of the structure of the fabric.

Building maintenance has unfortunately not beengiven the status it deserves. It has not been consid-ered at a strategic level but only on an ad hoc basis.Skilful management of building maintenance whilerespecting the principles of conservation is a high-level occupation which deserves respect. Fewknow the names of the clerks of works and crafts-men who maintain our great monuments, althoughtheir job is to interpret great works of art in the faceof difficult environmental conditions. As in conser-vation of all cultural property, the key operation isthe expert’s inspection.

The hierarchy of skill and organization for efficientand effective maintenance should be examined.

Handymen who can carry out two or three tradescompetently are invaluable for the maintenance of thenumerous buildings that make up an historic districtor centre whose values are visual townscape. It isinefficient to wait for one trade to follow another in

this work, so multi-trade teams of three of fourhandymen should work together. They should under-stand that it is most important for them to use the correct materials and follow traditional workmanship.They should work under instructions of a builder specializing in this field. For important historic build-ings, where high-class work has to be maintained andrepaired, conservation craftsmen specializing in repairand reproduction work will be required. They mustknow the history of their craft, understand its tech-nology and the principles of conservation given in theIntroduction to this book (Chapter 1). They shouldwork under the supervision of a clerk of works andguidance of an historical architect and should be prepared to advise upon specialist problems.

The productivity of the conservator will be lessthan that of a conservation craftsman, but he willhave greater skills in diagnosis of faults and theapplication of scientific methods to conservation ofhistoric buildings. He will be asked to advise onmaintenance, repair and consolidation of works ofart such as sculpture and metalwork, stained glassor wall paintings. To increase productivity, heshould work with three or four craftsmen. Part ofthe skill needed in work organization is to get theright balance of skills for the particular problem.Clerks of works who look after historic buildingsshould have the skills of a conservator.

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Figure 16.9 Kedelston Hall, Derbyshire, England(Courtesy: D.W. Insall)

A plumber is repairing lead gutters at Kedelston Hall. One trustsmen such as this to give good conscientious craftsmanship. Ifthis trust is misplaced it will surely show in the future

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Figure 16.10 Kedelston Hall, Derbyshire, England(Courtesy: D.W. Insall)

Fundamentally, mortar joints in stone should be close in colour to the stone, but should not bemade black to match the soot. After re-pointing sandstone the mortar shows up lightly for a fewyears, but will then darken and harmonize naturally. The colour, thickness and surface textureof pointing are vital to the appearance of a building

Figure 16.11 Bridge, Isphahan, Iran

Maintenance of the bridge includes renewal of brickwork andpointing. A skilled eye can detect a slight colour and texturechange in the brick and a slight change in the mortar

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Figure 16.12 The RoyalPalace, Bangkok, Thailand

Maintenance of such superbroofs presents some problemswhich are shown in Figure 16.13

Figure 16.13 The RoyalPalace, Bangkok, Thailand

Even the ridge pieces of the roofcan be attacked by termites.Externally they are protected bythick black natural resin lacquerwork and by pieces ofembedded coloured glass whichare difficult to reproduce

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Figure 16.14 National Museum, Bangkok, Thailand

This eighteenth century structure showed cracks in the plaster,which when stripped off revealed distress in the brick masonry

Figure 16.15 National Museum, Bangkok, Thailand

The cause of distress was found to be that termites had completelyeaten away the timber post supportingthe roof which was encased by thenon-structural brickwork

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Figure 16.16 Roof spaces, north aisle, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Before application of preservatives, all accumulations of the rubbish of ages was removed and the roofareas were vacuum cleaned as part of a programme of good housekeeping

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Figure 16.17 The rolling programme of preventive maintenancefor York Minster, England

This programme was based on two quinquennial inspections; it should berevised and updated after each regular inspection

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Fire is no respecter of historic buildings, nor do regulations and codes for fire protection respect thecultural and artistic values in a historic building.Their aim is to protect life. The conservationist’saim is to prevent fire and minimize damage causedby disasters and this in effect also protects life.

Morally and psychologically the destruction of anyhistoric building by fire is worse than total loss, forthe loss could have been prevented in most cases. It is therefore desirable to examine first the cause offire and then the means of lessening its extent andeffect. It will be found that fire and security precau-tions must be taken together in order to resolve possible contradictions in their requirements.

The main problems in historic buildings can besummarized as follows:

(1) Failure to consult fire brigade officers and failure to appoint local fire prevention officersand to organize regular fire drills.

(2) Poor standards of management, housekeepingand supervision, e.g. accumulation of dust,dirt and rubbish in roof and storage spaces.

(3) The danger from smoking (11% overall).(4) The danger from cooking operations (mostly

due to frying and fat congealed in ducts 21%).(5) Faulty electrical installations (21% including

faults in wiring).(6) Flammable decorative materials and furnishings.(7) Lack of compartmentation, no internal sub-

divisions, stairways not enclosed, wall liningsnot fire-stopped.

(8) Deficient fire resistance; walls and floors inad-equate, doors not fire resisting.

(9) Inadequate means of escape; doors, passages,staircases have excessive travel distances; noalternative escape routes.

(10) The danger of arson (10% largely in historicbuildings, children with fire 9%).

(11) Lack of master keys and mastered locks.

17

Fire

Figure 17.1 Bedford School, Bedford, England(Courtesy: Bedfordshire Times Press)

Fire breaks out at night; it is too intense to be subdued by firemenwith hoses

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(12) The danger from workmen especially whenusing ‘flame’ for repairs.

(13) Possible danger from lightning.

Prevention of fire

One of the most important lessons of major fires,such as York Minster, Hampton Court, Uppark andWindsor Castle, is that every building should have afire audit at regular intervals. This might well be partof the architect’s quinquennial report. Certainly sucha review should take place every five years. Theparticipants in this review should cover every aspectof management and maintenance of the historicbuilding and should include:

The building owner or administratorFire prevention officerArchitect

Service engineerSecurity officer (this may be the police)Fire fighting organizationSafety officer (this may be a department of firefighting)Insurance companyFire engineering consultant.

The whole building should be viewed jointly;water supply and storage capacity, all weatherapproaches for fire fighting, the manning of the firebrigade and its response time. The condition of thestructure, flammability and disposition of furnishingsand condition of electric wiring should all be con-sidered. The audit should cover fire precautions, fireprotection measures, rescue, training, salvage anddisaster control planning. In conclusion: fire pre-vention depends on creating awareness in owners,professionals, the public and workmen.

Actions should include:

(1) Appoint a fire prevention officer. Organize firedrills and rescue practice.

(2) Ensure adequate water for fire fighting andgood access for fire engines. Alternative routesshould be planned in case one is blocked.

(3) Identify important risks and danger of firespread, and eliminate unnecessary hazards—here the fire brigade can help.

(4) Consult a competent fire engineer (the firebrigade can indicate some of the questions heshould study).

(5) See what can be achieved by compartmentation.(6) Consider what early detection systems can offer.(7) Consider the merits of sprinkler systems.(8) Make check lists for monthly, weekly and daily

routine inspections.

Fire prevention officer

The most important step in the prevention of fire isto appoint a suitable person as fire prevention manager. He should lay down safety proceduresand suitable staff should be appointed to carrythem out. Staff may be allocated duties such as firefighting, rescue work, supervising the evacuation ofvisitors, assisting the fire brigade, security patrolsand monitoring of automatic detection and security systems.

The fire prevention manager should ensure thatthe arrangements he has made comply with thelegal requirements for the uses to which the buildingis put and the recommendations of the insurers. Heshould be aware of the various sources of adviceavailable to him, i.e. the local fire authority, the

Figure 17.2 Bedford School, Bedford, England(Courtesy: Bedfordshire Times Press)

The burnt-out remains, with stone dressings spalled by the heatand all combustible material consumed except for a fewcharred beams. The cause of the fire was arson

insurance company surveyor, the building controlofficer, the Fire Protection Association, or LossPrevention Council (UK), and should work with hisarchitect or surveyor.

The fire prevention manager should:

(1) Establish a system of frequent inspections, usingcheck lists, in order to reduce the likelihood offire occurring.

(2) Determine the routes of services and identifythe positions of isolating switches and valves.

(3) Carry out regular demonstrations and train staffin the effective use of portable fire-extinguishingequipment.

It is the responsibility of the senior management to confirm regularly that these matters are being

properly attended to in order to avoid complacencyand to motivate all concerned to maintain a highstandard of effectiveness.

Management precautions—fire drills

Instruction of the permanent staff in fire drill isessential, so that they should know what to do incase they should discover a fire. When the firebrigade comes out on a practice scheme, the per-manent staff of the building should be involved;regular practices at, say, six-monthly intervals aredesirable as it should not be forgotten that personnelchange. Staff should practise the use of equipmentsuch as hand extinguishers, hose reels, sand and

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Figure 17.3 St Paul’s Cathedral, London, England(Courtesy: Feilden & Mawson)

The dome, one of the most perfect, is a major fire hazard due to the amount of timber used ( fire load)and its inaccessibility to normal fire-fighting equipment. A lift was installed against the south-west corner to enable four firemen, in full equipment, to be taken up the first 30 m (100 ft). A second lift tothe base of the dome has been planned. Repairs to the south-west tower are in progress

asbestos blankets. The alarm systems should alsobe tested.

Alarms range from handbells and triangles tohand sirens. Although manual alarms need littlemaintenance, they have two disadvantages: theoperator may have to retreat from the fire beforeeveryone is warned, and in a large building severalalarms will be needed (two being the minimum)and this depends upon a human chain reaction tohearing the first alarm. Electric alarms overcomethese disadvantages as they can be linked togetherand ring continuously. A large number of smallbells is more effective than a few large bells. Firedetectors and manual electric systems can be linkedtogether to provide an early warning.

Fire fighting equipment, which should be installedin consultation with the fire brigade, is primarily forimmediate action. Areas of special risk should befully covered. A small fire can reach unmanageableproportions in less than five minutes, so the firebrigade should always be called. The non-publicareas of the building should be clearly marked forthe benefit of the brigade and plans of all levelsfixed on the building and lodged with the brigade.

Common causes of fire and some precautions

The ordinary domestic fire or stove is a commoncause of fire, with heat and flame causing the ignitionof adjacent wooden members of the structure.Conversion to oil heating reveals latent weaknessesin old construction which might not have matteredwith a coal fire. Boiler blowback can cause fire ifcombustible material is stored in the boiler house.Boiler blowback can also occur in high winds,which then fan the flames of the fire. Sparks from aboiler flue may start a fire either by falling on a com-bustible roof material or by penetrating cracks in adefective flue. Flues should be swept at least once a year and should be surrounded by 170 mm (7 in)of incombustible material, with any structural timbers kept at least 50 mm (2 in) away from theflue. Wood burning increases the risk of a chimneyfire and is banned in the houses owned by theNational Trust.

Another common cause of fire is a hot spark, per-haps from defective electric wiring or from weldingoperations, landing on to a flammable material.Portable electric fires (providing radiant heat) canignite clothes, curtains or furnishings; likewise pow-erful modern light fittings can have the same effect.

Lighted candles, if left unattended, should besecurely fixed in holders that cannot be blown overor fall. Unattended candles should always stand on

a metal tray large enough to contain any candlesthat may fall over. No candle or naked light shouldbe placed near combustible material.

An accumulation of rubbish or loose combustiblematerial often causes fires or hastens their spread,so tidiness is an essential part of any fire preventionscheme. Rubbish deposited by draughts, or col-lected by insects or birds or by vermin to formnests, may be a fire risk, as heat can cause this tosmoulder or a spark can cause flame. A responsibleperson should make monthly inspections with thisin mind and ensure that any such hazards areremoved.

Used polishing rags and mops are liable to heatup and then ignite spontaneously, depending on thetype of polish. They are best kept in an outhouse ifrequired for further use. Cleaning materials, oilyrags, broken chairs, candle ends, clinker and ashfrom the boiler house should be disposed of safely.The burning of rubbish should be carefully con-trolled. No combustible material should be storedin the main volume of the building or areas linkedthereto unless proper fire doors or shutters are fitted.

Electricity is a big fire risk; faulty wiring, over-loaded circuits and badly maintained or carelesslyused equipment have all been known to start fires.Short-circuits in old wiring and defective insulationare a severe hazard. Nothing should be placedclose to a convector or tubular heaters so as torestrict air circulation around them and any non-luminous electric heater should have a pilot lightindicator by its switch. Storage heaters and the likeshould have fixed wire guards for safety. Becauseof these risks, all electricity should be switched offwhen not in use, particularly at night, and if thereis a nightwatchman’s room or special plant such as refrigerators which must be continuously connected to the main supply, this should have aspecial circuit arranged as a safety precaution.

All electrical work should be carried out by com-petent electricians in accordance with official stan-dards and regulations. In the UK these are given inthe current edition of the Regulations of the Instituteof Electrical Engineers. The whole of the electricinstallation should be thoroughly examined everyfive years and no unauthorized alterations permitted.It is found that 50-cycle frequency vibrations canloosen connections so causing heating and sparks.

The choice of wiring system is most important.Mineral-insulated, copper-sheathed, plastic-coatedwiring is undoubtedly the best. Wherever possible allcables should run clear of combustible material suchas wood and should not be fixed in inaccessiblevoids where they cannot be inspected. Electricalplant should be connected by armoured cables and

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have isolating switches with indicator lights.Temporary electric lighting and equipment isalways a fire risk, particularly as workmen are likelyto improvise. Such installations must be of the samestandard as permanent work. No loose cablesshould be permitted at any time.

Before Benjamin Franklin invented lightning con-ductors, lightning was a major cause of fires in his-toric buildings. All metal elements and electricwiring in a building should be bonded to the con-ductor system. The specialist firm responsible formaintenance of the lightning conductor installationshould inspect annually and report on any upgrad-ing needed to bond new electrical or structuralitems into the system and specially considering haz-ards from side flash. If codes have been revised themaintenance contractor should advise the owner ofany additional requirements.

The fire-proofing of fabrics, wood, plastics andpaints extends the time to ignition or retards the ini-tial rate of burning. Chlorine, bromide, fluorine,phosphorus and antimony are used to form industrialfireproofing compounds, chlorine being the mostimportant. For wood, ammonium hydroxide, ammo-nium phosphate pyro-antimonate are used most fre-quently, and are usually applied by the vacuumimpregnation process, but dipping or brushing maybe used if the former facilities do not exist.

Fire-retarding paints, varnishes and polishesshould be able to fulfil two conditions:

(1) To provide a layer of coating which is neitherflammable in itself nor likely to propagate fire,irrespective of the nature of the substrate.

(2) To protect combustible base materials such aswood against the effects of fire by thermal

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Figure 17.4 St Paul’sCathedral, London, England(Courtesy: Feilden & Mawson)

Fire protection was given toppriority. The timber constructionbetween outer roof and theinner brick cone can be clearlyseen in this photograph: thisrepresents a major hazard,which was reduced by dividingthe dome into eight compartments

insulation in the first stage of a fire and then bysmothering flames produced by the gases.Intumescent treatments can be effective.

Although no surface treatment can make a sub-strate absolutely incombustible, it can make a usefulcontribution by delaying the spread of fire, forwhen fire breaks out in a building the nature of theinterior surfaces may determine the time availablefor the occupants to escape. Finishes like wax pol-ishes on floors can melt and produce running fire,which can be especially dangerous in a publicbuilding. Escape routes should have incombustiblefinishes. A fire-retardant surface treatment givesfire-fighting personnel more time to save culturalproperty. The protection of steel in multi-storiedbuildings is a vital precaution, generally effected bygiving a minimum of 13 mm (0.5 in) cover of concrete and up to 50 mm (2 in) to give four hoursprotection. Plaster and preformed units also givegood protection.

Regulations relating to fire and historicbuildings

Fire regulations are framed chiefly with the designof new buildings in mind, rather than the improve-ment of existing buildings, and their primary con-cern is, quite rightly, the safeguarding of life ratherthan the safeguarding of the contents of the building.Historic buildings require wider priorities; it is sug-gested the objective should be broken down intothree parts:

(a) To prevent the outbreak of fire.(b) To minimize the effects of fire by preventing it

spreading (passive fire protection).(c) To enable the fire to be fought efficiently with

minimum damage to its contents (active fireprotection).

To meet the regulations in the UK the most typicalactions are:

(1) Planning alternative protected escape routes.Applications of intumescent paint or fire retard-ant to combustible materials such as wood panelling. Provision of hatches, crawl-ways andinternal ladders.

(2) Forming enclosed staircases, glazed screensand fire doors on magnetic latches. Hardwoodtreads on stairs.

(3) Upgrading of fire resistance of doors and rebates.(4) Provision of alarms, detectors, emergency

lighting and fire-fighting equipment such asextinguishers, hose reels and hydrants.

(5) Compartmentation with thickening of floorboards or other treatment above the floor joists,fire stopping of cavities and ceiling voids andincreasing the fire resistance of ceilings. Sealingof ventilation grilles.

(6) Provision of sprinklers and reserve water storage for fire fighting.

Structural elements must be protected againstfire. The amount of protection is specified innotional hours of resistance to a standard fire, butin fact the time the protection will be effective maybe less in a fierce fire and longer in a small fire.Load bearing walls must have sufficient fire resist-ance. The standard required depends on the use ofthe building, the number of storeys, height, floorarea and volume. Compartmentation can reducethe fire protection requirements as well as reducingloss by the spread of fire.

When use of a building is changed from domesticto public often the resistance of specific elementshas to be upgraded.

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17.5 Norwich Cathedral, Norwich, England

At Norwich Cathedral, fire-fighting drill is practised regularly. A hard standing has been formed so that the heavy fire tendercan put its 30 m (100 ft) ladder into position. Rehearsals takeplace every six months, so that every fireman knows his way inan emergency

The required fire resistance for walls, floors andceilings and doors depends on the height of thebuilding and its area. The UK legislation demandsthe following resistances:

Height Area ResistanceSingle storey Less than 3000 m2 Half an hour7.5 m Less than 500 m2 Half an hour15 m Less than 3000 m2 One hour28 m 1000–7000 m2 One hour28 m Over 7000 m2 One and a half

hours

Distance to the nearest protected route should notexceed 20 m.

Vertical compartmentation will involve the intro-duction of fire doors and screens, and horizontalcompartmentation the improvement of the resist-ance of floors and ceilings. Voids in the floor orceiling space can present serious problems in fire-stopping, especially when decorative ceilings andvaluable floor finishes are involved.

Metal structures in historic buildings are usuallyof cast iron for columns or wrought iron for beamsand trusses. These are generally exposed and willrequire enhanced protection which can be pro-vided by encasement or application of at least6 mm of intumescent paint, which unfortunatelytends to obscure detail and requires protectionagainst abrasion.

Timber structures can be assessed for fire resist-ance on the basis of sacrificial charring. As timberbeams in historic buildings are often oversized theamount of timber remaining after the requiredperiod may be sufficient for strength; however, ifregulations demand a non-combustible floor, seri-ous problems may have to be faced unless a relax-ation can be negotiated. Buildings clad with wattleand daub or faced with weatherboarding presentspecial problems in obtaining sufficient fire resist-ance, the required standard depending on:

the distance between walls and site boundary;the internal subdivision of the building into

compartments;the occupancy of the building.

Thatch and wood shingle roof coverings are vul-nerable to radiation and flying embers, and are onlypermitted in the UK when the building is 12 maway from its boundary. Timber partitions, espe-cially when panelled on both sides, are liable tohave insufficient fire resistance and may have to bereconstructed in order to give sufficient protection,but a half hour standard can often be obtained withintumescent paint. A clear matt fire retardant can beapplied to reduce flame spread.

Staircases have to be enclosed by fire-resistingdoorways. Sometimes regulations require higherhandrails and closer spaced banisters than thoseexisting in a historic building, so it will be necessary

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Table 17.1 Fire-fighting Agents

Agent Effective against fires of class: Principle of extinctionA B C D E Cooling Depletion Catalytic

of oxygen

Water (solid stream) �� ��Water spray �� ��Foam � � � ��Dry chemical, regular �� �� �� ��Dry chemical, multi-purpose � � � � � ��Carbon dioxide (CO2) � � �� ��Halons* � � � � ��Metal extinguishing agent � � �

*Only halon 1211 or 1301 is recommended for toxicity reasons. Note instructions of manufacturer.

Classification by material:Class A Solid combustible materials—wood, pasteboard, cloth, coal, etc. Soaking the material with water avoids the return of flames.

Spray is good because it avoids using too much water.Class B Liquid and flammable substances—fuel, lubricants, grease, paint, oil, alcohol, etc. Water must not be used as the burning

liquid floats on it and spreads. CO2 is useful in enclosed spaces only.Class C Flammable gaseous material—methane, butane, hydrogen, acetylene, city gas, etc. Water is not suitableClass D Light metals—magnesium and derivatives, aluminium, potassium, calcium, barium. Water is not suitableClass E Electrical appliances and conductors, telephone systems, electric motors. Water and foam must not be used as they are

conductors.

to obtain a relaxation in order to preserve its char-acter. The fire resistance of treads may have to beimproved by changing softwood to hardwood.

Internal doors are the element most likely to beaffected by fire protection regulations, as they arevital to protect escape routes for the safe exit ofoccupants. Upgrading is then necessary but thework to achieve this has unfortunate side effects.Sheeting over panelled doors radically changes thecharacter of a historic building, so it is not accept-able. Attention must be given to the thinnest por-tions and to the rebates around the door whichoften have to be changed to hardwood 25 mmthick. High quality doors have even been sliced inhalf in their thickness and refixed to a central fire-resisting sheet, so preserving their original appear-ance yet increasing their fire resistance.

Passive fire protection

Once a flame has started it will spread to anynearby combustible material and so build up untilit is checked in one of three ways; by being delib-erately extinguished, by running out of combustiblematerial, or by being confined in a particular com-partment with fireproof boundaries.

Compartmentation, to be effective, must have acomplete seal. It is preferable for each compart-ment to have at least two external doors to giveaccess for fire fighting. Roof compartments can bedevised with smoke vents operating by fusiblelinks. Passive measures of fire protection, which donot rely on mechanical devices or human interven-tion, should be given a high priority in historicbuildings as they are always on duty.

Automatic devices such as sprinklers can be useful, but it is wise to remember that sprinklersmay cause damage to the contents, so their usemay be ruled out if the contents are historicallyvaluable. In some cases after a fire, it has beenremarked that the fireman’s hose caused more damage than the fire itself.

Active fire protection

The strategy for protection of a historic building andits contents depends on preventing the outbreaks offire, particularly fire caused by human carelessness.A full system of fire warning alarms should beinstalled, and, if necessary, special detectors canreinforce human vigilance and can be wired bydirect line to the fire brigade at the cost of anannual rental. Arrangements should be made for aresponsible official to be available by day and night

in case of fire; an internal telephone or radio tele-phone system is invaluable for this. Closed circuitinfra-red television systems which can ‘see’ in thedark may become more common and be linkedwith special security systems by direct line to thepolice station. Locks should be standardized so thatthe fire brigade can open all relevant doors withone master key. At night all internal doors shouldbe left closed but unlocked, if security permits.

Fire detectors are designed for the following special circumstances:

(1) For hazardous situations such as(a) petrol and flammable vapour detectors;(b) butane and propane leakage detectors;(c) over-heat detection;(d) explosion and suppression.

(2) Ionization detectors—to detect combustion.

(3) Visible smoke detectors(a) using light scattering techniques;(b) using light obscuring techniques;(c) using sampling systems.

(4) Flame detectors (either ultraviolet or infra-red).

(5) Ultrasonic and laser detectors.

(6) Combustion gas detectors.

(7) Heat detectors of various types such as(a) spot or point detectors;(b) solid state detectors;(c) thermocouples;(d) fusible links (solder or quartzoid bulb);(e) line detectors using capillary tube;(f ) line detectors using cables with flexible

joints.

Line detectors are a small but interesting group,useful in rooms with moulded or ornamented sur-faces as the capillary tube can be concealed withinthe architectural decoration. The tube contains aliquid or gas which will expand under heating, thusdisplacing a diaphragm and activating a fire alarm.

The siting of detectors in historic buildingsdemands great care especially in large volumeswhere height reduces the sensitivity of the detec-tors. Internal air currents can behave differently byday and night when a stratification layer betweencool and warm air can form at different levels, soupsetting the functioning of smoke detectors.

Unfortunately the number of false alarms withmost detector systems is large—over ten to one—and this is like crying ‘wolf’ too often. The suppliers

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of detector systems will advise upon installationsand should also put forward proposals for regularmaintenance. Additionally they must be asked tostate (in writing) the limitations of their equipment,for in historic buildings special problems are frequently met which limit the performance of detec-tors designed for typical modern buildings havingsmall rooms and low ceilings.

The number of false alarms can be reduced byhaving detectors close spaced arranged in an ‘intel-ligent self-monitoring system’ linked to a micro-processor with a watchdog check and reset systemable to identify cable damage or the failure of adetector. Such systems are self-testing and will givemaintenance advice. In choosing a system one mustconsider capital costs, maintenance and running costsin comparison with the cost of equivalent protectionfrom manpower. Generally detection systems aremuch cheaper and constantly alert.

Escape routes should be protected by lobbiesand free of obstructions and combustible material.Glazing in doors and screens must be fire resistant,but even so they present a hazard from radiationtransmitting intolerable heat, so preventing escapeon the other side of the fire barrier. Additionalmeans of escape, such as external stairs, can disfig-ure a historic building and so may prevent its ben-eficial use. Means of escape cannot be dealt with bya series of hard-and-fast rules, but guidance can beobtained from regulations relating to the number,position and width of exits according to the max-imum number of people likely to be in the buildingat any one time. Sometimes the number of personswho may be present in a historic building will belimited by the available means of escape. Signsindicating escape routes can also erode the archi-tectural character of a historic building, as suchdirection signs must be plainly visible.

The construction of walls, floors and ceilings ofescape routes must be ‘incombustible’. To preventthe spread of smoke and fire into corridors andstairwells self-closing fire-stop doors must be pro-vided. In historic buildings, fire-stopping of inter-communicating voids must be meticulous. Anyreport on the fabric should recommend consider-able improvements such as fire-stopping at floorlevels or behind wall panelling. Roof insulation ofglass fibre or rock-wool also gives fire protection,provided that it is not bonded with bitumen.

Precautions during building operations

Repair, consolidation and reconstruction operationspresent an additional and severe set of hazards in ahistoric building. In the UK, the Joint Contracts

Tribunal form of contract places the onus of inform-ing the fire insurers about proposed works on thebuilding owner, who should be reminded of this bythe architect. A special premium may be payable.Workmen busy on repairs generally increase therisk of fire through carelessness or unfamiliaritywith the local fire precautions.

Some of the operations carried out by buildersand plant engineers involve the use of blowlampsand other equipment that produces flames and heatin areas of appreciable fire risk, for instance onroofs where heat may penetrate to concealedwoodwork. This equipment should only be used ifno alternative is available, and then the workshould be carried out in a safe area if possible. Ifthe work must be done in situ the operator shouldhave at hand an assistant with a portable fire extin-guisher to watch sparks as and where they fall.Flame should never be used if there is a noticeablewind, and tea or meal breaks must be staggered soas to keep the work under constant supervision.

Combustible materials should be protected by aheat shield. At least two portable water/gas extin-guishers should be provided in each area wheremen are at work, and there should be clauses in thespecification of work stipulating these precautions.Neglect of these in one case led to the completedestruction of a thatched house with valuable con-tents in less than thirty minutes after a painterstarted stripping external paint on a window with ablowlamp. No operation involving the use of flameshould be carried out within one hour of the end ofthe day, at the close of which the work must beinspected by a responsible person so that anysmouldering may be seen before the men leave.

The Fire Protection Association, together with theSociety for Protection of Ancient Buildings, havedesigned a Hot Work Permit, use of which wouldensure that workmen carrying out maintenance orrehabilitation of a historic building are subject toproper supervision.

Bitumen and asphalt boiler plants are a hazard,and should be set up well away from the historicbuilding. Tarpaulins used for temporary water-proofing are another fire risk, particularly if a ciga-rette is dropped carelessly into a fold. When not inuse, tarpaulins should be folded neatly. Smokingshould be permitted only in the men’s mess roomand site office; a workman found smoking elsewhereshould be subject to immediate dismissal from thesite as a term of the building contract.

The Fire Protection Association makes the following comments about insecticides:

‘Many insecticides are flammable. They shouldonly be applied by specialists who should be

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asked to take the following precautions beforestarting—remove all sources of ignition such aselectric fires and naked flames, clear the area ofdust, lumber, etc., and take up any fibrous insulating material such as glass fibre. While thetreatment is being applied and drying, particularcare should be taken to see that there is no smok-ing in the area. The space should be thoroughly

ventilated during the operation and afterwards forat least a week. The glass fibre or other thermalinsulating material should not be put back until thistime has elapsed. The treated area should not becovered with plastic sheeting. The use of temporaryfittings should be avoided and the men should bewarned not to spray electric fittings, junction boxesand hot surfaces such as light bulbs.’

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Before a conservation project is started, its object-ives should be defined, then the appropriate pres-entation policy can be proposed. The objectivesmay be simply to keep a building ‘wind and watertight’ to preserve it on the one hand, or on theother hand to present it in its full documentary andhistorical context to be studied for educational andartistic purposes within the context of culturaltourism. This will mean analysing the values inher-ent in the building. First, as mentioned in theIntroduction (Chapter 1), there are the emotionalvalues—wonder, a sense of continuity and identity;then the symbolic and cultural values of art, hist-ory, aesthetics, architecture, archaeology and thesite landscape and townscape; and lastly there arethe use values—functional, social, economic, edu-cational and even political.

In the forming of presentation policy these val-ues must be respected, but it may be found thatthere are conflicts between the claims of some ofthem which can only be resolved by mature judge-ment and cultural preparation. Such decisions aretoo important to be made by one man alone, butonce the individual guidelines of policy for presenta-tion have been made, they should be rigorouslyadhered to in order to avoid aesthetic confusion.This is where the advice of art historians andarchaeologists and the wide cultural preparation ofthe conservation architect are so important. Hemust see, understand and interpret. The presenta-tion should not destroy historical or archaeologicalevidence.

It is essential that consideration of the values incultural property should be assessed objectivelyand fairly. There is always a danger that the con-servation programme will only reflect the bureau-cratic objectives of the government department thatis responsible.

Therefore, it is wise to insist that the goals andpriorities of the presentation programme are estab-lished by an interdisciplinary, interdepartmentalworking group that includes people genuinelyinterested in all values in cultural property. Theirtask is to reconcile their purposes as well as thedirection of their movement.

W. Brown Morton III, who has had much experi-ence of work within government departments,writes in a personal communication to the author:

18

Presentation of historic buildings

Figure 18.1 The Holy Shrine of Al Hussein, Kerbala, Iraq

A building and its setting are inseparable, that is until townplanners advise on cutting wide avenues through a dense streetpattern applying western ideas of vista and axial approaches toimportant monuments

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‘The success of this interdisciplinary process to establish a successful … conservation …programme depends on each member of theteam having unquestioned authority to speakfor their department or professional disciplineand having the unswerving support of theirdepartment head. All too often an importantvalue is ranked too low in the order of prioritiesor ignored altogether, because the personresponsible for defending that value in theworking group did not have sufficient authorityor sufficient confidence in his own department’ssupport of his position to carry the day.

‘As you can appreciate, the order in whichwe rank the Values will dictate the goals andobjectives of the environmental design program. If you place the highest priority onarchaeological value your program will call forvery little new construction or landscapechanges. If you place the highest priority onspiritual value your program may severely limitvisitor access at certain times and impose verystrict controls on the type and frequency ofappropriate activities. If you place the highestpriority on the economic value, your programmay very well exploit the monument at theexpense of other values.

‘Therefore, it is essential that each of theValues for a given ancient monument and its sitebe thoroughly researched and evaluated inde-pendently before any priority ranking is done.’

When the relative importance of all the values incultural property has been established then, havingexamined all the practical alternatives, the ‘leastbad’ solution can be found. If the conservationprogramme goes forward before all the conflicts ofcompeting values have been thoroughly andthoughtfully resolved, there is the risk of destroyingfor ever the full integrity of the historic building andits site. Also, if the conservation programme goesforward prematurely, one will face the probabilityof time-consuming, expensive and professionallyembarrassing changes having to be made later. Weare indeed only trustees for historic buildings.

Presentation of the message

A piecemeal approach to presentation is disastrous.The conservation architect must guard the ‘whole-ness’ of the historic building in his care, so that it canbe presented in an intelligible way to the public.

Presentation must also take into account crowdcontrol, together with security, prevention of crimeand vandalism. Museums can show many examplesof good presentation.

When proposing the presentation of an historicbuilding or site, it is desirable to consider all the valuesthat have been listed earlier and define the ‘message’of the building under each of these headings.

One example is Baguley Hall, an early thirteenthcentury timber-framed hall, near Manchester,England, which needed structural strengthening toprevent collapse. It proved impossible to strengthenit in situ except by consolidation, inserting glassfibre rods and epoxy resin glues, which would havebeen irreversible, thus preventing any future repairsthat might become necessary and contradicting thetechnological message of the early timber frame.This would make it function in a way for which itwas not designed and in a way which might causeeven worse defects later on. This scheme wasrejected in favour of taking the framed structuredown and reforming all the broken joints withsmall inserts of new material, but this decisioninvolved removing and refixing wattle and daubpanels between the timbers with some consequen-tial archaeological loss.

Presenting wholeness by treatment

The treatment of lacunae or gaps in the design andsurfaces of historic buildings, which may be causedby the need to renew stone or brickwork, shouldbe given special consideration. Two examples maybe considered—the Arch of Titus and the Arch ofConstantine. The Arch of Titus was reconstructed c.1800–1830 on a core of brickwork in which quiteconsiderable areas of stone were renewed follow-ing the original detail in a slightly simplified, lesstextured manner and using a marble of slightly dif-ferent colour. The result is that the original workdominates, and only when one looks carefully canthe reproduction work be identified. Thus the general effect is of artistic unity.

The reverse is true of the Arch of Constantine,which gives the impression of a lot of holes beingfilled in, and unnecessary attention being drawn tothe lacunae because they are lighter in tone andharder in outline than the original material. Theresult is an impression of over-restoration and lackof artistic harmony and unity.

At the end of the nineteenth century it became adogma in Britain that lacunae should be filled in orrepairs executed in a different material, so one oftenfound brick patching in stone buildings. This givessome restored buildings a ridiculous patched appear-ance, which destroys their unity and character.

The treatment of lacunae should reduce neitherthe artistic wholeness nor the message of the historicsite or building or any element therein, and must not

aim at deception of trained observers. The generalprinciple is that lacunae should seem to recede visu-ally behind the original material, yet be so harmo-nious as not to detract but rather add to the whole.At Herculaneum this is done by drawing in the over-all lines of the fresco painting on the dull toned andslightly textured plaster that is used to fill in the gaps,thus carrying the eye over and across the lacunae. At some sites in Rome, the filling of lacunae withbrickwork has become rather a mechanical formulaof using rather dark bricks with broken faces, whichin fact become more noticeable than the originalmaterial and therefore break the principle of reces-sion. With brickwork, even a slight change of colourto indicate repairs and filling in of lacunae seems

preferable to a violent change of texture. The archi-tect will have to decide each case for himself, butshould carefully consider colour, texture and the rel-ative recession of surfaces in order to fill in lacunae.Lacunae should be identifiable on close inspection,new stonework being given a slightly different tool-ing to differentiate it, while new pieces of stainedglass and wood can have the date marked thereon.

Preservation of patina

Patina is acquired by the materials of an historicbuilding through age, by weathering or oxidizationand by use. It is something which cannot be pro-duced artificially, for the artificial aging which forgers

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Figure 18.2 Old Tarnova, Bulgaria

This dramatic site comprises the ruins ofthe last mediaeval capital of Bulgariaand so is of great historic, educational,touristic and political value.

The whole site is subject to carefularchaeological excavation and record-ing, but this raises problems in presen-tation and preservation of the ruins.Purely archaeological values have beenoverridden by the desire to make themonument intelligible to the Communistworkers.

The cathedral is a reconstruction onoriginal foundations but otherwisebased on conjectural analogy; theperimeter walls have been raised usingdifferent types of pointing so as to avoiddeception.

A coherent theory of conservation isessential in order to reconcile suchdebatable issues

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Figure 18.3 Arch of Titus,Rome, Italy

This is considered a good reconstruction by Italian expertsbecause it makes the message clearand the missing pieces (lacunae)are restored using a slightly different stone and having lessdetailed carving so that the intelligent observer can distinguishbetween original work and thatwhich has been added, but at adistance the unity of the wholemonument is not disrupted

Figure 18.4 Arch of Titus, Rome, Italy (detail)

By standing close to the arch, as in this detail, it is quite easy todistinguish the added material which because of its form completes the architectural design, but having less ornament itdoes not intrude and can be said to recede visually

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Figure 18.5 Arch ofConstantine, Rome, Italy

This monument was made upof pieces from several sources soperhaps it never had great artis-tic unity: however, the treatmentof lacunae has not improved itspresentation

Figure 18.6 Arch ofConstantine, Rome, Italy

The harsh texture and hardoutline of the lacunaeaccentuate their appear-ance undesirably, in thatthey protrude rather thanrecede

and commercial restorers apply will always lookfalse after a short time. For metals, patina is definedas a film or incrustation produced by oxidization,which protects the metal surface and which doesnot make the message in the design more difficultto read. Corrosion is different from patina in that itdoes not protect the object. The Pentellic marble ofwhich the Parthenon is built has acquired a marvel-lous patina through time, which makes new marblefrom the same quarry look quite out of place. Patinais precious because it can only be acquired by time.

Patina does not include accumulated dirt. Whenbuildings and objects have to be cleaned, it is essen-tial that the processes used should not destroy theirpatina. Time and circumstance can give an historicbuilding many irregularities: stones may becracked, edges worn or chipped and spalled anderoded; brickwork may have its arrises softened;wood may be textured by exposure and light; plaster, mosaics and floors may have uneven sur-faces. All these irregularities should be conservedas part of the patina of an historic building. Thispoint must be impressed upon craftsmen, for theirnatural impulse is to make something as good asnew, i.e. to destroy patina, because, unless they canbe given a sense of history, they will feel it is theirduty to eliminate these irregularities. For the truepresentation of historic buildings it is essential thatpatina, in all its forms, is respected.

Presentation and consolidation of ruins

Just as a skeleton is a more acceptable presentationthan a decaying corpse, a ruin is a more sanitarystate for a building when it is pronounced dead. Ifthe building has incontrovertibly come to the endof its useful life and its cultural values do not justifythe cost of re-evaluation and adaptive use, then aruin should be created. This is particularly neces-sary in order to discourage vandalism and to avoidthe shame of wanton decay.

A complete record drawing of the building shouldbe made and all features and details recorded. Photo-grammetry or simple elevational photos to scale canbe invaluable. In the case of legal demolition by adeveloper for profit, logically the cost of recordingshould be borne by the person making the profit.

Next, all that is valuable should be removed:doors, windows and joinery such as stairs and pan-elling, then roof covering and timbers, and timberfloors (but not vaults). The object is to remove allmaterial that may decay but to leave walls of stone orbrick with their openings standing. Some of the typ-ical details should be stored in a library of buildingelements, as these are invaluable for study purposes.

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Figure 18.7 The Pantheon, Rome, Italy (detail of brick-work on the drum)

The lacunae are too dark and textured so come forward visuallyand thus are unsatisfactory. Note the marvellous durability andtexture of the second century brickwork with wide joints madeof slaked lime and pozzuolana. Age gives material a patinathat cannot be reproduced

Figure 18.8 The Pantheon, Rome, Italy

Original work can he recognized with difficulty amid muchpatching and repairs done in different ways at different times.To devise a presentation policy for such a building is difficultand to explain it to maintenance craftsmen even more difficult,but to ensure continuity of presentation policy over generationsmay even be impossible

The walling must be cleaned of all humus, as thiswould encourage unwanted plant growth; the newlyexposed tops should be sloped so as to shed all rainwater and the walls themselves should be repairedand re-pointed if necessary. Usually, loose coats ofplaster should be removed. The weathering of thetops of ruined walls needs careful attention, and asthis area will be exposed to severe frost attack,asphalt or epoxy resin coatings will have to beapplied if the material of the wall is not frost resist-ant. Holes left by the ends of beams should be filledto within one or two centimetres (less than 1 in) ofthe surface and then textured. In Britain, timber lin-tels, which would rot, should be replaced with rein-forced concrete, but in some climates such timbersare durable. Vaulting should be retained with theupper surface waterproofed and weathered, pro-vided there is no doubt as to its stability. All exposedsurfaces must have good weathering to guide rainwater away, and if large flats occur, they should bewaterproofed and given rain-water spouts or drains.

The repair of a masonry wall that has lost its fac-ing requires special attention. Often the face is liableto separate from the core, so replacement of some ofthe ashlar by through-binders may be necessary, butinserting reinforced concrete needles using a dia-mond-toothed coring drill is probably the cheaperand better method of providing bonding reinforce-ment. In certain cases it may be possible to insert cor-rosion-resistant bronze or stainless steel dowels,anchored in epoxy resin grout, if it is possible to con-ceal the small holes made by the drill. A broken wallshould be racked back for stability while protectingthe horizontal surfaces against the entry of rain waterand frost attack. Stone dressings to copings, sills andcornices all require careful attention, just as in a livingbuilding. All ironwork must be removed to avoid ruststains and damage from expansion, and the scarspointed up. The ruin will have to be fully scaffoldedin order to get it into good order; however, to avoidrepetition of this expense, provision should be madefor firm anchorages for cradles or working platformsof an appropriate type to facilitate future inspections,maintenance and repairs.

The layout of the ruin should be made clear to thevisitor and this means marking out the alignment ofvanished walls. This can be done by inserting lines ofchipping between bricks or creosoted board kerbs inmown lawns. Building low upstanding walls whichare much more difficult to mow around create a falseimpression, but box or beech hedges or even flowerbeds can be used to indicate old alignments.

Lettering and information notices are a matter forthe expert and an appropriate type-face should besought; inspiration may be obtained by looking atthe local church monuments or tombstones of the

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Figure 18.9 The Curia, Rome, Italy

The Curia was reconstructed under Mussolini, and it is difficultto determine what was original. Its scale and bulk are much toodomineering with regard to excavations in the Forum and thehard outlines make it difficult to think that this building wascontemporaneous with the ruins

Figure 18.10 Witely Court, Worcestershire, England

An opulent Edwardian mansion in its heyday, then neglectedand finally destroyed by fire. Was it worth conserving as a ruin?The parkland was an attractive asset for public use. Whatshould the objective of the presentation policy be and howshould the ruin be presented?

period of the building’s greatness, thus enhancingthe genius loci, retention of which is one of theobjectives in creating a ruin. Ruins are romantic, sothe growing of creepers and plants need not beentirely discouraged. Ivy, however, should not bepermitted, and it should be remembered thatVirginia creeper makes the inspecting architect’s taskmore difficult. Limited amounts of moss and lichenare permissible and small plastic-lined cups of soilmay be introduced out of view on top of walls orledges in order to grow wallflowers and stonecrop.

Anastylosis as a method of presenting ruins

The word ‘anastylosis’ is probably scarcely knownto more than a few Anglo-Saxon practitioners ofconservation, while on the other hand it is almostequivalent to conservation in the minds of someLatin experts. It is defined as the re-erection of fallenfragments of ruins in their original position. In coun-tries where buildings are suddenly destroyed andtowns abandoned by reason of disastrous earth-quakes, the practice of anastylosis is general.

It is often difficult to decide whether anastylosisis justified. Meaningless heaps of stones do not givean instructive message to the beholder, but theymight do so easily if the stones were re-erected cor-rectly. The anastylosis of a few columns can givethe viewer an indication of the spatial qualities of acollapsed building, but on the other hand may pre-vent an instructed visitor from understanding thehistoric phases of development of the building. Themore interpretation is given before a visitor visits asite, the less anastylosis is necessary. The danger ofanastylosis is that it may obliterate one phase of thedevelopment of a building at the expense ofanother: re-creation of a church may obliterate theearlier synagogue or vice versa.

Where a ruin is of one period only, then anasty-losis is simpler, but it is never very simple; often,with the given evidence it is possible to proffer twoor three probable solutions. Indeed, anastylosis isfull of pitfalls, as the re-erection of fallen stones isnever certain to be correct. Many examples can bequoted, but one of the earliest is Sir Arthur Evans’sattempt to make Knossos more intelligible by re-erecting parts of the palace. Archaeologists nowsay he was wrong, but boatloads of cultural touriststo Crete have been grateful to him for the attempt,which helps them interpret and understand the site.

Perhaps the most noteworthy example of anastylosis is the re-erection of large parts of thecolonnades of the Parthenon, the Propylaea and theTemple of Nike Apteros in Athens. The durability of

the Pentellic marble was the saving factor, as mostof the materials had been left in a heap after anexplosion due to a bombardment. The problemnow facing the Greek authorities is how to rectifythe mistakes of the previous restorer, who usedtechniques and materials that are irreversible andwhich prevent effective action now that industrialpollution is seeking out all the weaknesses.

It must be accepted that every attempt at anasty-losis is potentially wrong; therefore the work mustbe made reversible, so that later, if more and betterevidence comes to light, the former anastylosis canbe changed.

Reconstruction as a form of presentation

Many historic monuments have been destroyed inwarfare or by earthquake or other disasters. As aninsurance against such events, full photogrammetric

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Figure 18.11 Witely Court, Worcestershire, England

The Ancient Monuments Board considered that the historic andarchaeological values were sufficient to justify the expense ofmaking a ruin and so recommended this course of action to theMinister. Monuments in the church suggested an appropriatelettering style for the notices

records are advisable; however, if a disaster occursit is necessary that immediate action should betaken by first making a full archaeological record,and collecting all the materials including stones,bricks and broken glass that might be redeployed.These should be recorded as to exact location on agrid-lined map and methodically stored and pro-tected against fire, theft, vandalism and neglect, anymaterial needing conservation being given first-aidtreatment. Such precautions immediately after a dis-aster can save great trouble and expense later.

The temples and monuments at Abu Simbel area special case of reconstruction, as these had to be moved because of the inundation following the building of the High Dam at Aswan. They were dismantled and re-erected on another islandsite modelled on the original. Although some oftheir significance has been lost as they are nowdivorced from their original site, it was the onlyway in which they could be preserved. It is theo-retically wrong to remove entire architectural unitsto museums, for they lose their poetry and artisticvalue when taken away from their natural setting. Itis always preferable to reconstruct them on thespot, giving adequate protection, as has been doneat Leptis Magna in Libya and Baalbeck in Syria andwith the Arch of Titus in the Roman Forum.

Anastylosis and reconstruction, if over-done or car-ried out without adequate study and documentation,

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Figure 18.12 South Triumphal Arch, Jerash, Jordan

The South Triumphal Arch was reconstructed leaving a ratherhard outline on the right-hand side. The distant skyline must he considered as part of the monument as new buildings out ofscale could destroy the message of a walled city, which shouldnot have buildings outside its perimeter

Figure 18.13 The Festival Area, Jerash, Jordan

The colonnade is nearly all the result of anastylosis which helpsthe visitor visualize the space, but this policy should not be carried to extremes as it can give the impression of being a filmset where everything is false. A spare concrete lintel still lies onthe right-hand side

Figure 18.14 Doorway to Byzantine Cathedral, Jerash,Jordan

This doorway and several columns were re-erected thereby giving the visitor a better chance to visualize the volume andarchitectural character of the building. Unfortunately, Portlandcement was used for the work, giving the joints an unpleasanttexture

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Figure 18.15 Undercroft,York Minster, England(Courtesy: Shepherd BuildingGroup Ltd)

To help interpret the messages ofthe site of York Minster a secondcentury Roman wall which wasfound during the excavations fornew foundations was left in position. It was waterproofed byinjection. Fragments of plasterfound in the mud were puttogether in three years of patientwork and then displayed, asshown on the right, together witha drawing showing the probablescheme of decoration

Figure 18.16 South transept, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The important discovery of the remains of the second centuryRoman legionary headquarters basilica under York Minsterposed problems of presentation. Where and how should this column drum be displayed and what was the objective of theirpresentation? An attempt was made to educate visitors and convey the history of the site

can turn an historic site into a film set. They are justified if they enhance the message in the monu-ment and make its spatial qualities more easilyunderstood.

Interpretation of the messages

There are many messages to be found in historicbuildings and sites, so interpretation may run the riskof manipulation. A good guide will always tell onesomething worth while, but well-trained guides withthe command of many languages are all too rare:generally one has to fight off importunate would-bepurveyors of misinformation and mispronunciation,who are more of a liability than an asset. The culturaltourist who has come a long way to visit, see andunderstand, is entitled to serious consideration andshould be willing to pay for interpretation of the site

or building. Interpretation can take many forms—simple printed leaflets, plans, illustrated guides andhistories, models showing phases of developmentand museums showing artefacts related to the site.Son et Lumière is yet another form of interpretation,using history in dramatic spoken form with dynamiclighting effects of great variety. All interpretationmust be based upon scholarly and accurate informa-tion derived from all of the conservation team.

Colonial Williamsburg is a good example of inter-pretation and the US National Park Service has ledthe way in showing how much interpretation canadd to one’s enjoyment in visiting a site. Interpre-tation facilities, together with restaurants, hotels, carparks and lavatories, need careful consideration inrelation to an historic site. The architects whodesign these facilities must be extremely sensitiveto the genius loci of the monument, as well as thesurrounding landscape.

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Figure 18.17 Undercroft, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The interpretation was arranged in historical sequence ending up with an exhibition of the work involved in consolidating the fabricbetween 1967 and 1972. Although the Roman column in the foreground did not conform to the historic sequence of the display, itwas re-erected in its original position to show the Roman phase of use of the Minster site

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Causes of increased costs

Efficient cost control systems that favour the con-servation of historic buildings are desirable in thatthey make scarce resources go further. Flexibility,however, is essential, as each historic building isindividual and in a sense is the real client orpatient—its demands must be taken as paramountif the situation requires it, as in the case of theLeaning Tower of Pisa or York Minster.

Inefficient systems increase the cost by as muchas 300%, thus working against conservation in gen-eral. In architectural conservation, expensive mis-takes can be made due to the lack of an initialinspection which considers the building in its set-ting as a whole, to wrong diagnosis, to restrictivecodes of practice, to clumsy administrative and con-tractual procedures, to lack of flexibility and poorsupervision, and above all to bureaucratic delays,due to lack of specific responsibility.

The effect of faulty contractual procedures maybe judged from the following authentic, but neces-sarily anonymous examples:

(1) A roof was damaged when glazing wasrepaired, because no protection was specified.

(2) Confusion results because of an unresolvedpolicy of presentation. There are frequentchanges of plan as art historical and archaeo-logical ideas alternately prevail when thereshould have been an architectural synthesis.Changes in plan disorganize labour, reduceproductivity and enthusiasm, and cost money.

(3) A building was virtually rebuilt by a contractor,because he was paid for the amount of newstone he incorporated. Supervision was poor.

(4) A contractor strengthening a building insertsconcrete beams cutting away wall paintings ofgreat historic value which were concealed bywhitewash.

(5) A beautiful dome has to be renewed, because acontractor, who had no knowledge of conserva-tion and no respect for a ninth century master-piece, was given a ‘design and build’ contract.

(6) Part of a building fell down after a contractor hadbeen at work several years, because nobody hadinspected the building as a whole and warnedhim that this part was the most vulnerable.

There are many examples of wrong technology,for example the use of cement mortars, wrong clean-ing techniques, chemical toxic hazards to occupantsby use of dieldrin and chemicals containing dioxin.

Numerous other cases could be quoted, but theultimate cause lies in faulty contractual proceduresand the fact that nobody was responsible. Personalresponsibility is the only guarantee that conserva-tion will be efficiently carried out. In bureaucracies,responsibility has the unfortunate propensity ofevaporating within a short time.

Preliminary estimates

After the initial inspection has been made, theproblems of the building as whole can be pre-sented with preliminary estimates by the profes-sional adviser for the information of the fundingauthority. Such estimates should express reasonabledoubt and be given in two inseparable figures, (a)and (b): (a) the realistic cost of the works, and (b)the worst possible cost of the works.

Inflation, which is a politico-economic problem,makes estimating very difficult as it introduces thetime element which is very much in doubt at thisstage. Estimates can only be given at current prices(i.e. allowing for inflation in the next six months);therefore, if the funding organization has a systemof indexing costs, so much the better. Estimatesshould ideally be built up with costs of labour,

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materials, plant and overheads. If any one of theseitems fluctuates then it is easy to revise. The unit ratemethod for defined quantities of work is extremelydifficult to apply to conservation projects, particularlyas rates may not exist for many of the items of work.

Operational specifications necessary

To assist pricing, an operational specification shouldbe prepared, which gives the general order of workon a room-by-room basis for the interior or for eachfeature externally, under five headings—removals,repairs, alterations, services and decoration or fin-ishing—and describes each operation in detail.From this, the labour can be extracted by trades anda list made of the materials needed. Heating, venti-lating, hot and cold water systems, electric installa-tions and plant generally are renewed, and must bedesigned as a whole so these can be costed separ-ately by specialists, but it is important to specify allthe attendance necessary on a room-by-room basis.

Pricing contracts

In normal contracts, building contractors add a sub-stantial element to their price for the risk and arequite legitimately paid for protecting the fundingbody. In conservation work, the risks are high andoften cannot be resolved until the work is wellunder way. It is considered that the funding bodyshould accept these risks and that is why estimatesare given in the (a) and (b) form mentioned earlier.The risk is reduced if full studies of all alternativemethods of conservation are made after the initialinspection. They are further reduced if it is possibleto open up and explore hidden parts of the build-ing, much as surgeons make exploratory operations.But it may be more expedient to consult a special-ist on non-destructive investigation techniques.

Scarce materials and skills are another problemthat may have to be faced. Shortages of bricks or tilesof the right type, lack of good hydraulic limes and theimpossibility of getting wrought iron or matchingglass are typical problems that have to be solved. Todo so properly assumes professional time and costsmoney, yet if they are not solved in advance thesmooth running of a complicated building contractmay be jeopardized and even greater costs incurred.

Programme of works—scaffolding and plant

The programme of works should now be consid-ered. There is a right size of team and right balance

of skills for each conservation operation.Archaeological projects, art historical investigationsand conservation of works of art have to be giventheir proper place in the programme. Generally it isbetter to have fewer highly skilled men workingrather longer than too many, for too many mencrowd a job and give less flexibility, although toofew get lost and overawed by a large building.

Closely linked to programming is the question ofsupply of scaffolding. Complicated conservationwork often needs special scaffolding for a longtime, or in a large project scaffolding may have tobe moved frequently. Scaffolding should thereforebe entirely under the control of the contractor,moved and adjusted by him, as and when required.The contractor must be responsible for and zealouswith regard to all safety precautions.

The use of construction plant is another aspect ofprogramming. It is expensive to have hired plantstanding by doing nothing. Nowadays, there is sucha diversity of plant that a skilled contractor can, byapplying it correctly, save considerable costs. Theprogramme and the scale of the work dictate thesematters.

On conservation works, because of the numberof unforeseeable hazards, flexible programming isessential. The principle is: continuous work for theright sized team. Stopping and starting work causesreal costs to escalate and leaves expensive plantidle. Programming building work is a specialist skill,but all operations follow the classic time/cost curve,being slow to start, rapid and productive in the mid-dle and slow to finish. In conservation work, evenmore time should be allowed for finishing, for thisis where artists and craftsmen need time to do goodquality work. Completion dates, however important,should always be arranged with a good contingencyfactor so as not to spoil the work.

It is nowadays possible to program a computerwith labour and materials, to which can be addedcosts per hour, plant and overheads, so giving anaccurate estimate of the anticipated cost of theoperation in print-outs at regular intervals. It shouldbe mentioned that this sophistication is only possi-ble for major operations. Otherwise, simple graphsof cost plotted against time are the most valuableand deception-proof techniques.

Control systems based on regular inspections

Control systems should now be examined. Theusual method of governments is to vote so muchmoney for conservation of historic buildings andthis is subdivided in various ways, often without

any relationship to the actual need of the buildingor availability of professional staff, so that unco-ordinated projects, carried out in a spasmodic andpiecemeal way, result.

Assuming that all documentation has been carriedout at a national level, ideally government shouldhave all its classified historic buildings inspected reg-ularly on at least a five-year basis for the purpose offormally estimating their requirements under theheadings described earlier, i.e. immediate and urgentrepairs and minor works, necessary works (majorworks or a rolling programme if suitable), and desir-able works (whose need is foreseen in 10–15years)—noting items to be kept under observation.

Such regular formal inspections and reports willbe supplemented by frequent supervision and informal visits by professional staff. After 10–15years, the real cost of the conservation of the his-toric buildings will be seen to drop, because theprinciples of strategic preventive maintenance havebeen applied. Professional staff will get more andmore expert in this matter as time goes on. It isimportant, however, to delegate appropriate respon-sibility for authorizing immediate and urgent repairsto qualified professionals, as this will save time andadministrative costs and above all prevent furtherdamage. For example, 1000 US dollars spent oneradicating an attack of Merulius lacrimans (dry rot)in good time, can save 40000 dollars one year later.Grant procedures and attendant bureaucracy can betoo slow for the reality of historic buildings.

Long-term planning

‘Necessary’ and ‘desirable’ schemes can be handleddifferently and brought forward by stages frompreparation to estimating and approval. Onceapproved, however, there must be sufficient fundsto complete the schemes according to programme.This will mean budgeting a contingency fund. Thisfund will be necessary, because however well theconservation of historic buildings is planned therewill be occasional unforeseeable surprises—forinstance, an unexpectedly severe winter may accel-erate the decay of stone which it was planned torestore in two or three years’ time, or there may bean exceptional gale, a flood or even an earthquakein some countries.

Approval and execution of a project

The funding body will consider the total cost of theconservation project. This should be comparedwith the cost of building anew on a unit cost

per square metre. If the cost is two-thirds or less, itcan be claimed that conservation is saving buildingcosts. If more, the cost of a new infrastructure ofroads and services, of demolition and delay willhave to be considered in economic terms. One mustnot forget, however, the cultural social and politicalvalues of conservation when making a final assess-ment of the cost and benefits of the scheme.

Also, before a conservation project is approved by the competent authority, the work should beevaluated according to the principles of conserva-tion: (1) is it the minimum necessary—not more; (2)is it reversible (this may not be possible but it shouldnot prejudice future interventions); (3) does it adhereto the Venice Charter (or its equivalent) and theethics outlined in the Introduction to this book?

The specific objective of the particular conserva-tion scheme should be confirmed and the presen-tation policy agreed by the competent authoritywith the responsible professional—the person towhom complete authority, within the budget, willbe delegated. Having had his scheme approved hewill supervise and co-ordinate the execution of theproject. Thereafter, the building becomes his client.These provisions are necessary to ensure: (a) rapidand correct decision-making, which saves money,and (b) coherent artistic treatment, or avoidance ofconfusion, which also saves money.

The expert in charge can always ask for advice,but his alone must be the responsibility for savingcultural property. He will lead a multidisciplinaryteam and ensure good communication by regularon-site meetings. He will confirm his instructionsclearly in writing. He should report the budgetarysituation once quarterly. In his control of his overallbudget he should break this down into target costsfor recognizable items of work, and so prevent oneitem from ‘robbing’ another.

Forms of contract

There are many hazards in a contract for conserva-tion work. One of the techniques should be toreduce the unknown dimension by preliminaryopening up and detailed exploration. All archaeolog-ical work should be done in advance of a buildingcontract, if this is possible.

Flexibility is therefore necessary in arranging suit-able forms of contract. If it is a simple item of fairlycommon work, not requiring skills that are difficultto obtain, an adjustable ‘lump sum’ contract with10% included for contingencies is reasonable. If alarge amount of carpentry repair is involved, provi-sional figures for labour and material can be pricedcompetitively within such a ‘lump sum’. ‘Design

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and build’ types of contract are totally inappropri-ate for historic buildings, for with these the archi-tectural conservator abdicates his responsibilitiesand, in effect, hands them over to a contractor nottrained in building conservation. ‘Design and build’proposals may lead to the cheapest solution, so areliked by administrators, but cost is not the only factorto consider in a contract for conservation work.

On anything complicated, it has been found thatpayment for the actual labour, materials and plantused is the best basis, provided one selects an effi-cient contractor, whose administration is sound andwhose standards of work are known to be good.Such a firm can save 15% or 20% of the costs ofconservation work by good organization, so it isnot worth quarrelling about 5% in his ‘on costs’.The system recommended is that competing con-tractors of equal quality should give target figuresfor the cost of the work, based on their assessmentof labour, materials and plant, and then should adda percentage for their managerial services. This per-centage is the competitive element. There are somesubtle and some too-subtle variations of this type ofcontract. All contracts depend on good and efficientco-operation, but if the builder is treated andtrusted as a professional, he will also make his con-tribution to reducing the cost of conservation.

Conclusion

A good professional will lead and educate hisbuilding team. The work may appear to be slow to

start with, but once the work-force understand,they will take great pride in the honour of givinggood work to historic buildings, which they knowalso belong to them.

One of the pleasures an architect has in this workis direct contact with skilled craftsmen—together adifficult problem is faced which neither architectnor craftsman can solve independently, so thearchitect says: ‘I do not know how to solve thisproblem, what are your ideas Mr Craftsman.’ A proposal will be put, and discussed and modifiedby the concepts of conservation which the architectmust apply within his vision of the building as awhole. Then, after perhaps an hour, the insolubleproblem is solved to each party’s satisfaction; thecraftsman knows what to do—and he executes thework with real satisfaction because he has beenconsulted as an equal. As bad workmanship andmistakes cannot be afforded in conservation work,the supervising architect must give his time to thisform of consultation, from which he will learn a lot.

Conservation of historic buildings is, as stressedearlier, multidisciplinary teamwork, in which wemust respect each genuine contribution and towhich we must all give of our best.

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Method A: a, slow start; a–b, major tasks and steady progress;b–c, slower progress due to detailed finishes andskilled work, d, furnishing and balancing ofmechanical services

Method B: a, slow start but stop: e, start again but stop: f, startagain but stop; g, start again but stop: h, start againbut stop; i start and j stop; k, somebody says job mustbe finished that year so it re-starts and is pushedahead regardless of cost and workmanship, but itcannot be completed by l; m, it is now late, and nfurnishing also needs doing

A cost/time graph is a simple way of monitoring a complicatedjob; every contract should use one, even if more sophisticatedmethods of programming are also applied. Of the two methodsshown, method B takes longer, costs much more, gives less jobsatisfaction to everyone and the workmanship is less good thanit should be. Method B is typical of administrations with‘lapsible’ funding

Figure 19.1 Two methods of financing a conservationcontract: method A (top curve), budget for whole cost;method B (bottom curve), annual budget increments

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Introduction

In this chapter we will mainly consider the vastnumber of buildings that are 100 years old or moreand which make up the bulk of our urban envir-onment. Historic buildings differ from most othercultural property in that they generally have to beused and also withstand dead and live loadings andresist all the causes of decay.

Often it is necessary to find an appropriate use inorder to prevent a building’s decay or destruction,this being one of the hardest problems to solve in the practice of architectural conservation. Thepractice of adapting buildings for new uses is as oldas time. A classic example is the Castel St Angelo,which began as Hadrian’s Mausoleum, was turnedinto a fortress, a papal residence, a prison and nowis a museum and tourist attraction. Another Romanexample are the Baths of Diocletian—Michelangelomade a church out of the main hall and the otherparts are now a museum, cinema and planetarium.In England, the King’s Manor at York was built inthe thirteenth century as the lodgings of an abbot,then used as a king’s palace in the sixteenth cen-tury, an administrative centre in the seventeenthcentury, fell on bad times in the eighteenth centuryas tenements, was used as a workshop for blindpersons in the nineteenth century and then as auniversity building in the twentieth century. In eachcase, the building was re-evaluated and found use-ful, so it survived, but with some rehabilitation.

As has been shown historically, rehabilitation wasa natural process in the fabric of a living town or inthe life of a well-built construction. Nowadays, dueto the rapidly changing patterns of life and scale ofactivities, a more conscious approach must beadopted, especially if all the values in historic build-ings and towns are to be recognized, preserved andused.

Rehabilitation has social, cultural and economicadvantages. Social, in that people and towns keeptheir identity; cultural, in that artistic, architectural,archaeological and documentary values can be pre-served both for their intrinsic value and their con-tribution to the identity of the town; economic, inthat (a) existing capital is used, (b) energy is saved,(c) demolition costs are avoided, and (d) the exist-ing infrastructure of roads and services is utilized.

In addition, rehabilitation causes far less humanupheaval, political friction and physical delay, so itis not surprising that when the total budget is con-sidered, rehabilitation in most cases saves money.

Setting up rehabilitation schemes

How does one start a rehabilitation scheme? Amulti-disciplinary team is necessary. In the schemeprepared for Chesterfield, England, in which theauthor participated, the town provided administra-tors, town planners, engineers, quantity surveyors,a traffic manager and a health officer, to whichwere added two historic architects expert in con-servation, a development architect, a landscapearchitect and an urban planner, and last but notleast a development economist. The team met reg-ularly to discuss their work and to establish priori-ties (which had to respect all the values in thehistoric town centre). Two aspects of this teamworkshould be emphasized: first, consultations withowners and residents, and representatives of com-munity organizations such as the Chamber ofCommerce and Civic Society in the case ofChesterfield; secondly, detailed surveys.

The study of the values in the buildings and spacesthat make up an historic district is based on severaldifferent surveys, which analyse the historic develop-ment, growth, functions, services and amenities of an

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area and the condition of each building under con-sideration. In one word the ‘typology’ of the actionarea or of an individual building is studied.Inspections and surveys of each building involve themaking of measured drawings, preferably to 1/50scale and a detailed schedule of all defects that canbe noted. This study is crucial and the work neces-sary to each building can then be assessed under themain headings: immediate, urgent, necessary anddesirable (which are defined in Chapter 14), andcosted to see that the proposals can be justified.

In the survey of the building any shortfall inpotential users’ requirements should be noted, butin considering the neighbourhood as a whole it maybe found that these requirements are met in anotherway. The rehabilitation team will recommend themost suitable use for each building after makingtheir studies. Ideally the new use should involve theminimum change, as this will preserve the values inthe building and tend to reduce costs, so the closerthe new use is to the original the better, generally.

Rehabilitation policy

When they understand the benefits of rehabilitation,town planners, building economists and architectscan co-operate to re-use our existing stock of build-ings either by reviving their original use or findingsome suitable use in the context of the needs of thecommunity. Historic buildings with a wide range ofdifferently sized rooms have survived successfullybecause of their adaptability to many different typesof use. It may be found that building regulations fora proposed new use require floors to be strength-ened and calculations may show that foundationsbecome overloaded and that costly strengtheningbecomes necessary. If this is the case, one shouldfirst reconsider the use and see if a more suitablealternative is possible. It is only by considering allthe relevant factors that the multidisciplinary teamwill find the ‘least bad’ solution.

Often the superficial appearance of buildingsleads people to pessimistic opinions, because theyonly judge by appearances and cannot imagine theresults of a rehabilitation scheme. The cost of reha-bilitation is something that seems to frighten peoplebefore a proper examination is made (and this isnot helped by the addition of VAT). It is true thatlack of traditional skills and bad site managementby builders without the flexible organization that isnecessary can inflate the cost. The real costdepends on the structural condition of the building,the proposed use, the skill of the architects indevising plans and the most suitable contract pro-cedures, and the skill and organization of the

builders. Contract procedures and cost control needthe special techniques dealt with in Chapter 19.

The ownership pattern will affect the possibilitiesand also the design solutions available. Protractedprocedures should be avoided, as these can lead toplanning blight and financial hardship, coupled withpolitical discontent. Two half-schemes are betterthan one long delayed whole. Another danger indelay is in lack of maintenance of the properties,and a lesson that can be passed on is that someoneshould be made responsible for the care of vacantproperties and see that roofs are repaired after galesand that gutters are not allowed to get blocked or,in case of frost, that the water system is drained.

No historic building should be pulled down untilevery effort has been made to find a beneficial useby rehabilitation. As cities are living things, theoccasional need for renewal is accepted, but this iswork for architects with special sensitivity and abil-ity to analyse the problem and design in the idiomof today, yet respecting the identity and characterof the historic town.

To sum up, to approach this complicated problemthe typology of an historic zone or building must bestudied fully before any proposals are formed, theprinciple of minimum intervention must be appliedand authorities must have a presumption in favourof conservation—then our cities will keep theiridentity, character and atmosphere and the commu-nities will benefit culturally and economically.

Studies and guidelines

To avoid unnecessary and damaging alterations, thenew use should be as close to the original as pos-sible. The history and archaeology of the buildingmust be carefully studied, so that the architect isaware of the sequence in which the fabric was puttogether. Art historians and archaeologists shouldstudy the fabric with the architect and advise himon what material is of special value. The architectmust work with history—not against it.

The US Secretary of the Interior has laid downStandards for Rehabilitation for certification in orderto obtain tax relief, which incorporate the aboveprinciples. The standards, together with guidelinesamplifying recommended procedures, have beenimmensely successful.

Rehabilitation is generally considered a soundeconomic proposition if the cost of such work doesnot exceed two-thirds of the cost of building anewthe same area. This figure includes an allowance fora less efficient (but often much more interesting)use of floor space in the historic building. To meetthis requirement the building should at least have

sound walls and floors. The roof may be defectiveand need re-covering, rainwater disposal may needredesign and renewal, windows and doors may befaulty and decoration in need of total redoing. It isalso to be assumed that all services are defectiveand obsolete, for it is generally the case that theywill need total renewal. It needs understanding ofthe building as a ‘spatial environmental system’ andgreat skill to modernize the mechanical and electri-cal services of an historic building. Of course, theuse of the existing urban infrastructure and avoid-ing costs of demolition is a bonus for rehabilitation.

Applications of building regulations

New regulations are always more strict and com-prehensive than the ones they replace, and thisprogress represents a danger to historic buildings,as often officials responsible for their applicationdo not consider the fundamental purposes of suchregulations, but seek to apply them mechanically ina detailed way, so as to avoid the necessity of mak-ing a possibly troublesome decision.

It is often difficult to comply with the details ofbuilding regulations, which fall into three groups:structural, fire and security and hygiene. The reha-bilitation appraisal should consider each group separately. Structural regulations and codes havebeen made to help designers of new buildings, soif the building has survived 100 years satisfactorily,it can be deemed to have met the purpose of theregulations.

Building regulations give the superimposed load-ings that have to be carried by floors for varioustypes of use. If there is a change of use, strengthen-ing floors to meet increased loadings in offices oftenpresents difficult problems and if storage of paperor books, as in a library, is proposed the greatlyincreased loads present serious problems first in thefloor structure, then possibly in the walls and foun-dations, in which case the proposal may not bepractical for economic reasons. Fortunately, wallsand foundations of historic buildings generally havea considerable reserve of load-carrying capacity.

In an earthquake zone, an historic building mayneed strengthening, which can be put in handwhen a suitable opportunity given by rehabilitationoccurs, but it should never be condemned todestruction because of failure to comply with regu-lations. The record of earthquakes in Skopje andMontenegro shows that well-maintained historicbuildings are surprisingly earthquake resistant,because of the high quality of their workmanship.

Fire regulations covering fire resistance andmeans of escape must be complied with fully, but

with intelligence, for fire is a deadly serious matter.The risk can be reduced by restricting the uses towhich the building is put, and to a limited extentassets such as thick walls and well-constructeddoors can be traded off against nominal deficien-cies. For safety, much can depend upon the instal-lation of automatic warning devices and sprinklers,as well as the efficiency of the local fire-fightingservice, including access for fire fighting, a matter towhich town planners responsible for historic quar-ters in cities should give consideration. Often, addi-tional doors required as smoke checks have to beinserted in such a way as not to spoil the aestheticsof the historic building. The fire resistance of doorsmay be improved by adding fire-resistant sheets toone side and by making rebates in the frame deeperand of hardwood. Ceilings and floors may beimproved by putting fire-resistant sheets under aplaster finish or by thickening the floor coveringwith plywood and treating timbers with a fire retar-dant. Joinery and external woodwork should bepainted with fire-retardant paints. In such detailedways the fire resistance and safety of an historicbuilding can be raised to meet modern standards.

Improved hygiene is one of the basic require-ments of rehabilitation, yet standards relating tospace about buildings, light and air are often notpossible to meet and should be waived if forcedventilation and adequate artificial light can be pro-vided. Such standards are not absolute, and experi-ence of historic quarters has proved that excellentliving conditions can be had without them, espe-cially if children do not have to be considered.Provision of clean water, good sewerage, gas, elec-tricity, heating, ventilation and efficient rainwaterdisposal are all necessary. Access must be given forrefuse collection, fire fighting and fuel deliveries.

An understanding of the purpose of the buildingcodes and regulations is necessary to deal withthem in a flexible way. Limitation of the possibleuses and type of tenant may help. If a building hasgood points in one direction, it may be possible totrade some of its assets for deficiencies in another.

Surviving historic buildings have ipso facto ‘longlife’, are ‘flexible’ and require ‘low energy’ input intheir construction. Insulation values in roofs, walllinings and between floors are generally easy toimprove during rehabilitation, so energy require-ments in use can be effectively reduced, by insert-ing glass wool in roofs and floors and liningsbacked with aluminium foil to walls.

Flexible planning

The suitability of historic buildings for a large num-ber of possible uses, i.e. flexibility in planning,

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depends to a large extent on the mix of room sizes.Small rooms of 2–3 m2 (20–35 ft2) are suitable aslavatories, bathrooms, larders and stores; rooms of8–12 m2 (85–130 ft2) as single bedrooms, kitchens,dining spaces, clerks’ offices, etc. Rooms of12–16 m2 (130–180 ft2) can be used as living rooms,dining rooms, double bedrooms, managers’ offices,workshops and garages. Above 16 m2 (180 ft2) thereis a wide range of possible uses, including subdivi-sion. The above figures are entirely subjective, as noproper study is known to have been done.

Measured drawings and full investigation of thebuilding are necessary before starting a rehabilita-tion project. Ideally, the internal environmentshould be measured and recorded over a year inorder to provide design data. Structural analysis andstudies of the moisture content of walls and relativehumidity will possibly be necessary. Using draw-ings to 1/50 scale, in order to show all the existingdetail, alternative schemes can be prepared andcosted. Drawings show possibilities that could notbe visualized in the first instance. Often architects,faced with the difficulties of rehabilitation, find sur-prising and exciting possibilities which could notbe produced when designing new buildings.

Introduction of modern building services

Modern services present a great challenge, so willbe dealt with in some detail, for often it is difficultto reconcile their technical requirements with theprinciples of conservation.

All mechanical, electrical and also acousticalservices must be considered together in the reha-bilitation of an historic building. In one sense it canbe said that nowadays a building is as old as itsservices; certainly, new life can be given to an oldbuilding by renewing the services. However, thefabric of the historic building was not designed totake modern plant, so the installation of new serv-ices raises acute technical and artistic problems andwill certainly alter the balance of the spatial envi-ronmental system.

In designing the services, their eventual renewaland replacement must be considered, as well asaccessibility for maintenance. Ducts should alwaysbe sized generously in case larger dimensions arerequired at a later date. It is always wise to insertone extra conduit for ‘X’, the service that has notyet been invented, or for which a need was notforeseen.

The heating system

Improved space heating is one of the most difficultaspects of rehabilitation, for the effect of this will beto lower the relative humidity and also cause con-densation in unheated spaces. There is also dangerin the use of old flues which are not capable ofwithstanding the temperatures produced by mod-ern boilers; ceramic or insulated stainless steel flueliners are probably necessary precautions againstthe risk of fire.

Continuous background heating at a low temper-ature is generally best for fuel economy and for thefabric itself. Local heating can then be used to boostthe background heat when required. With buildingsof large thermal mass, intermittent heating does notproduce real comfort, because the walls do nothave time to warm up and it has a damaging effecton the contents of the building, particularly if theyare art treasures made of wood.

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Figure 20.1 St Angelo in Pescheria, Rome, Italy

This building is almost completely made of recycled material

The following checklist gives the points that mustbe considered relating to the user, the building andplant requirements:

User factors(1) (a) Background, (b) full or (c) intermittent

heating.(2) (a) Temperatures required, (b) air changes,

(c) relative humidity.(3) (a) Cost of heating plant, (b) can running costs

be afforded?(4) (a) Type of control system suitable.

Building factors(1) Exposure, wind tightness.(2) Heat loss—can insulation reduce this effectively?(3) Dampness, humidity, danger to structure and

contents.(4) Thermal mass, internal volumes, window/wall

ratio.(5) Space available for plant and fittings.

Heating plant factors(1) Cost of fuel and labour.(2) Size of boiler and expected life of plant and dis-

tribution system.(3) Type of fuel and economic amount to be stored.(4) Possible methods of production, delivery, dis-

persal and control of heat output.

Fuel costs depend much on governmental policyand foreign affairs. The era of cheap energy is at anend and since the future is unpredictable, it isadvisable to plan for alternative fuels. In Britain,stoker singles have consistently been the leastexpensive fuel, provided the building owner hassufficient bulk storage and efficient handlingarrangements. Anthracite has become expensive,coke difficult to obtain, oil after being very cheap isnow becoming costly, and town gas was costly butnatural gas was cheap before government policyraised the cost. Electricity has always been costlyand is vulnerable to power cuts. In rural areas theamount of power available is often insufficient and,being a high-grade form of energy, electricityshould not be wasted on heating unless used topower a heat pump. One of the lessons of the pastis that heating plant should be convertible. Light oilis easily converted to gas. Sectional boilers willburn almost anything, but with varying output andefficiency. Labour costs are often critical in formu-lating a choice for the preferred fuel. Commercialefforts were made by adjusting tariffs favourable tomake electric heating popular through storageheaters and underfloor heating, but the latterproved dangerous to the fabric on clay soils as itdried out the ground and caused shrinkage of the

soil under shallow foundations. Solar energy is nowbeing exploited in countries with suitable climate, butwith the British climate it is unreliable for heating.

In an historic building, sufficient space may not beavailable for the heating plant of desired capacity, sochoice may be dictated by this factor. Water tubeboilers fired by high-efficiency gas or high-grade oilmay be found to be the most compact units, takingless space than a sectional boiler with underfeedstoker or conventional oil burner. The space neededto store fuel is another material consideration, itbeing normal to keep three weeks’ supply, but theeconomics of delivery transport may mean increas-ing the storage space. Coals tend to deteriorate whenstored, while oil does not, although it may precipi-tate some sludge. Gas and electricity, of course, poseno storage problems, but for this reason the buildingowner is vulnerable to breakdowns and strikes.

Besides the space needed for fuel storage, spaceand disposal arrangements must be made for ashesand clinkers. Storage of the products of combustionmust allow for the fact that they probably contain agood deal of sulphur which may cause corrosionand decay.

Soot deposit is a sign of poor combustion, whichshould be checked by flue gas analysis. Goodarrangements should be made for cleaning fluesand renewing fire bricks in boilers and flues. Thesize and height of the flue are usually recom-mended by the services consultant, recognizing thefact that under-sizing will reduce the life of theboiler. The air intake for combustion must be atleast three times the flue area. The flue should beproperly designed to meet the requirements of thefuel and to avoid condensation at the top, which isparticularly likely with gas heating.

It should be remembered that flueless gas and oilheaters produce water vapour, which increases therelative humidity inside a building, together withthe danger of condensation.

An obtrusive new chimney may be consideredobjectionable. One way of lowering its height is todivide the flue into several sections, another is to fitan extractor fan. The height in relation to the restof the building must be considered, as flue gasescontaining sulphur dioxide can be reduced by care-ful choice of fuel; some heavy oils having a veryhigh sulphur content of up to 6%, whereas light oilshave 1–111

2% and natural gas none. The sulphur con-tent of coals varies considerably, but about half isretained in the ash, so the emission of sulphur diox-ide is reduced.

Distribution systems for heat consist of pipe runsor ducts for hot air. Hot air heating has the advan-tage of being capable of upgrading to includehumidification and air conditioning, if there is

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Figure 20.2 Theatre ofMarcellus (23–13 B.C.), Rome,Italy

The ruins of the theatre wereturned into the Orsini strong-holdand later adapted as residentialaccommodation. All periods ofbuilding should be respected

Figure 20.3 Castel St Angelo(A.D. 135), Rome, Italy

Built first as the magnificenttomb to the great EmperorHadrian, later converted into apapal fortress and prison, nowa museum

sufficient space for the additional plant. It creates apositive air pressure which reduces the ingress ofdraughts and dust. However, long duct runs areawkward and expensive and difficult to install. Thearchitect must work out all pipe runs in detail, tosee that they rise in concealed places such asbehind shutters and curtains and generally followthe principles of camouflage. Encasing of pipes isnot always to be recommended, as their heat out-put is valuable and the casing may look clumsierthan the pipe itself. The placement of furnituremust be planned before radiator and thermostatpositions can be settled, after which pipe runs canbe confirmed. The cost of the builder’s work inconnection with heating, normally 10–15%, mayrise considerably if special holes have to be drilledin order to pass pipes through thick masonry.

In designing delivery and dispersal systems, theposition of doors and windows, which createdraughts, is an important factor. In high buildingsthe introduction of heating by convection will cre-ate air movement, resulting in down-draughts fromhigh windows. The path of draughts can be tracedby use of smoke. High buildings can have a steeptemperature gradient, which is not conducive tofuel economy, so a dispersal system such as radiantheating by overhead panels or floor panels is moreefficient. Forced warm air from local heater unitscan also overcome the problems of down-draughtand temperature gradient, otherwise a heating coilor tube must be placed under each high window,which is unsightly.

Heat is mainly dispersed in a building by radia-tion and convection, conduction playing only a

small part in the process. Floor panels and ceilingpanels are the usual method of providing radiantheat. Floor panels put the heat where it is wantedand do not induce draughts to such an extent asother methods, but are sluggish in their response tocontrols and suitable only for continuous heating.Edge and ground insulation is necessary. With nopipes and radiators showing, floor heating is theideal proposition for an historic building, especiallyif the floor needs relaying, but it is expensive.

Radiators, which are really convectors, are thecommon method of heat dispersal. Cast iron ismuch more durable than pressed steel, but valvesand fittings eventually corrode. Sizing and siting ofradiators requires the detailed attention of the archi-tect, as spaces can be ruined by badly proportionedradiators and clumsy pipe runs. Convector radiatorsare not efficient in high spaces, as they build up asteep temperature gradient. However, fan-assistedconvectors are better in this respect and are morepowerful in relation to their size, so are more eco-nomical in regard to pipework. The fan enables theradiator to cover a larger area horizontally and hotand cold air is mixed, reducing draughts. An exten-sion of this, using piped cold water in summer,gives a simple type of local air conditioning at theexpense of an extra pair of pipes, as was done inthe Jefferson Library in New York City. Fan-assistedconvectors are flexible in design and can be inte-grated with the fitting of an historic building in anunobtrusive way. However, they are noisy whenthe fans are running at high speed and have to becleaned out at least once a year to remove dust andfluff from the gilled convector tubes.

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Figure 20.4 Baths ofDiocletian (A.D. 302), Rome,Italy

The frigidarium was convertedby Michelangelo into a church,St Maria degli Angeli, in thesixteenth century, so retainingthe spatial qualities of the original structure. Other partsof the baths house the NationalMuseum (c. nineteenth century), a cinema (c. twentieth century), a planetarium and residences

Figure 20.5 Diocletian Palace (A.D. 300), Split, Yugoslavia

Much of the fabric of the palace remains, but it all has been re-used inmany ways; the mausoleum became a cathedral, while shops, officesand residences comprise the remainder

Figure 20.6 King’s Manor(13th and 17th cent.), York,England

This was originally the residenceof the mitred abbot of St. Mary’sMonastery and rebuilt as such,then taken as a palace by HenryVIII and used as administrativeheadquarters of the Council ofthe North; after that it becametenements, followed by a schoolfor the blind and now, after rehabilitation which cost 60% ofthe cost of the same area in newconstruction, is used by theUniversity of York

Figure 20.7 Gargonza (nearSansovino), Italy

A fortified mediaeval village wasno longer inhabited. Being inbeautiful countryside, the ownerhas made a success of turning itinto a self-service hotel withhouses of a wide variety of sizesand a restaurant which shows inthe foreground

Heated carpets, electrical tubular heaters andhigh temperature electric radiant panels, portableoil or gas heaters can all be used for intermittentheating with partial degrees of success where thecost of proper solutions cannot be met.

Electrical services

An historic building generally has a primitive elec-tric installation, which may have been altered andextended by either professionals or amateurs. Earlyelectrical installations with wooden covers or, later,conduit with vulcanized insulating rubber cables, orlead and rubber sheathed wiring, if more than 20years old, are likely to be defective and impossibleto alter safely. Obsolete wiring, bad earthing, over-loaded cables, defective insulation, contact withcombustible material giving rise to serious risk offire, are all to be expected. The first stage is a sur-vey and test by an electrician, who should providea wiring plan. The standard tests for insulation andearthing often give an optimistic picture, especiallyas they are made before any rehabilitation work,which could cause a breakdown in brittle insulation.

With rehabilitation, a greater use of electricity islikely. Certain uses of electricity, such as cooking orheating, may well have to be excluded if there isinadequate power supply. The regularity of thepower supply should also be ascertained and, withspecial uses, duplicate supplies may be essential oralternatively a standby generator provided, withautomatic changeover gear. If fire fighting dependsupon the electric supply, standby plant may beessential, and certainly all fire-detection plantshould have a secure supply such as storage bat-teries with a.c./d.c. conversion charging gear.

New wiring systems may be of polyvinylchloridesheathed cable, or mineral insulated copper cablecovered with plastic. The former is cheap, but the lat-ter, costing about 30% more, is much the bestbecause of its long life and remarkable fire resistance.It is neat to use and the reduced cost of the builder’swork offsets in part its greater cost. It can be run inold conduit, if this exists. All wiring should be hiddenby running it in conduit or, if on the surface, camou-flaged by following the mouldings and ornament inthe building. The path of all wiring must be approvedby the architect and, if possible, none should beallowed to run over wood or other combustiblematerial; in certain places, holes must be drilled toavoid unsightly wiring running across mouldings.

Installation of new lighting in historic buildings isone of the many areas where the architect’s artisticskill must be used, for the atmosphere, messagesand character of the building can be enhanced by

skill or destroyed by clumsy lighting. If lighting hasto be used in day time, it may be designed with anemphasis to support the sun and natural daylight. Itis a taxing problem to find fittings that are suitablefor historic buildings, for often far greater output isrequired than is usual for domestic products. Theauthor has found that simple and efficient fittingsare to be preferred, even in cathedrals, as they donot date or look false. Fitting should always betested in situ. Pseudo-historic fittings, such as chan-deliers originally designed for candlesticks, areunsatisfactory if equipped with too bright electricbulbs, whose heat output may amount to severalkilowatts and whose replacement can be costly andtiresome. The heat output of lights may be a firerisk if the fitment is not well ventilated, and willcertainly cause dirt streaking above the fitment dueto the convection currents induced. Also, the heatoutput of permanent light installations should betaken into account when designing the heatingplant. Dimmers are a highly desirable adjunct to thelighting of the building, which should have bothspot and general diffused lighting, usable in a vari-able way to express the atmosphere and reflect thechanges in use of the building. Modern dimmersand switches can be controlled by low-poweredrelays, so greatly reducing the cost of long cableruns needed previously. The extreme cases of inter-pretation of an historic building are when flood-lighting or Son et Lumière are installed.

When designing the layout of electric installations,the route of the main intake, siting of the distributionroom, and of controls for various groups of electricalequipment, such as sound reinforcement and heat-ing plant and ducting for wiring, must all be consid-ered. If provision is to be made for broadcasting andtelevision, it is best to treat this separately, as thesemay be provided by other authorities who willrequire their own control rooms. Provision for main-tenance and testing is necessary, and bulb changingmust not be made difficult or expensive by lack ofthought at the design stage. Damage by maintenancemen moving ladders is a common occurrence.

Air conditioning

The problem of large ducts and remote plant roomsrequired for air conditioning is difficult enough indesigning new buildings, but in existing historicbuildings it is acute unless the ducts can be treatedas sculptural forms themselves. In order to avoidthe expense of long duct runs, local plant roomscan be planned and they may have an advantage.As, in museums, different groups of objects mayrequire different relative humidities, so the architect

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Figure 20.8 The Patterson House, Leesburg, Virginia,USA, built c. 1762(Courtesy: Photoworks, USA)

Courtyard elevation in January 1979 before restoration by W. Brown Morton III

Figure 20.9 The Patterson House, Leesburg, Virginia, USA, built c. 1762(Courtesy: Photoworks, USA)

Courtyard elevation in September 1979 after restoration by W. Brown Morton III, including (a) restoration of original exterior paint colours; (b) re-installation of original eighteenth century window sash in second floor left windows; and (c) construction of new entrance porch.The former house is now used as offices

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Figure 20.10 The Maltings, Beccles, Suffolk, England(Courtesy: Feilden & Mawson)

These derelict agricultural/industrial buildings provided the shell for a scheme of rehabilitation

Figure 20.11 The Maltings, Beccles, Suffolk, England(Courtesy: Feilden & Mawson)

After rehabilitation into a holiday house complex with restaurantand moorings for boats. Note the sensitive treatment of pavings

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Figure 20.12 Houses atWoodbridge, Suffolk, England(Courtesy: Feilden & Mawson)

Badly maintained and derelicthousing in the centre of acharming coastal town

Figure 20.13 Houses atWoodbridge, Suffolk,England(Courtesy: Feilden & Mawson)

Rehabilitation of houses withreinstatement of missing windows and doors and general overhaul. The defectivechimney belongs to a house notin the scheme

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Figure 20.14 The Granary,Blakeney, Norfolk, England(Courtesy: Feilden & Mawson)

These barns had fine oak roofsbut were no longer required aswarehouses for export of wheat

Figure 20.15 The Granary, Blakeney, Norfolk, England(Courtesy: Feilden & Mawson)

The rehabilitation used the fabric of the granary to provide holiday houses and a shop. The bench,beloved by old people, was retained

should seek out suitable servant spaces adjoininggalleries when adapting an historic building as amuseum or for other public purposes.

There are many ways of manipulating heating byspraying and cooling and recirculating air in what iscalled air conditioning. This means that air condi-tioning design should be flexible, but its designdepends a great deal on experience and judgementand correct briefing of the specialist engineer by thearchitect and a client who knows what is needed.

Air conditioning is an important part of museumdesign; nevertheless, the need for it should be putinto perspective, for one should recognize thatmany countries can use the capital and runningcosts of air conditioning better elsewhere. Indeed,if the electric supply is spasmodic, an air-conditioning plant could do damage to culturalproperty. Air conditioning is efficient in reducingsulphur dioxide in museum galleries, but the dan-ger of ozone, particularly in hot urban climates,cannot be ignored. Plenum air heating is often nomore expensive than pipes and radiators. It has theadvantages of good air distribution and movementand the capability of filter installations, as well asconversion to air conditioning at a future date.

Acoustics

Rehabilitation of historic buildings often involvesacoustical problems, for example when a malting orcorn exchange is turned into a concert hall. Theacoustic characteristics of the building should bemeasured and compared with the desired require-ments. Often the building is required for both musicand speech, which have different requirements withregard to reverberation time. Long narrow historicbuildings with linked volumes either side give dis-continuities in reverberation, while cube and dou-ble-cube rooms, domes and barrel vaults haveproblems with regard to reflections. The materials ofwhich most historic buildings are made have insuffi-cient absorption in relation to their volume, makinga long reverberation time unavoidable. For instance,the reverberation time of St Paul’s Cathedral,London, is 12 seconds and the Albert Hall requiredacoustical corrections to reduce its reverberationtime. Faults should be identified and correctedwhere possible by optimum disposition of the soundsource and audience and the use of reflectors.

The acoustic specialist should attend typical performances in order to measure the reverberation

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Figure 20.16 The historic centre of Warsaw, which was destroyed in World War II

It has been reconstructed and rehabilitated as a popular tourist attraction with restaurantsand museums and other public buildings. There are some residences

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Figure 20.17 DarleyAbbey, Derby, Derbyshire(Architects: Wood NewtonPartnership, Ripley)(Courtesy: Civic Trust,London)

Before restoration—This is thelast remaining structure fromthe Augustinian Abbey of St Mary of Darley, outsideDerby. It may have been theGuest House of the Abbey, butfor almost 50 years since the1930s its future was in doubtand, in consequence, its condition worsened. Its frontwall, which had to be shoredup, was as much as 500 mm(20 in) out of true and thebuilding was given up by mostas being beyond economicrepair.

After restoration—The buildingwas saved through the imagination and courage ofnew owners who have given ita new lease of life by restoringit and converting it into a public house, not so farremoved from its original use.Secondhand materials havebeen used wherever possible;where new were necessary theyhave been selected to match orbe in character with the mediaeval structure

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Figure 20.18 Simpson’sTavern, Cornhill, London(Architects: Michell andPartners)(Courtesy: Greater LondonCouncil)

Before restoration—The upperfloor of a long-established Citylunch house, for years leftunused. It was ‘Listed’ nevertheless as being of architectural and historicinterest and had an interiorwhich retained many of theoriginal fixtures, notably fireplaces, mirrors and eatingstalls.

(Courtesy: Michell and Partners)

After restoration—As many of theoriginal fixtures as was possiblewere retained and refurbishedfor re-use in such a way as toretain also the character of a Citylunch house

time, decay patterns, frequency responses, echoes,flutters, resonances and eigentones. By walkinground he will find out many of the peculiarities ofthe historic building. Then he should be able toadvise on correction of faults, in the first place byadding reflectors and increasing absorption wher-ever the design and finishes of the historic buildingwill permit. Failing this corrective treatment, elec-tronic reinforcement will have to be used.

There is much intuitive and some unpublishedinformation on the role of public address engineers,who tend to be linked to firms with predeterminedsystems which may not suit the special problems ofan historic building. For good results, independentacoustic consultants with a wide knowledge ofelectronic equipment are indispensable, as also arestaff specially trained to operate the equipment andhaving a knowledge of the acoustic characteristicsof the building. Siting of microphones, switchingarrangements, placing of speakers and location ofthe central controls can only be decided in consul-tation between architect, equipment specialist,acoustic expert and the users of the building. Withlong buildings, time delay systems and multiplespeakers will assist in making speech intelligible in

spite of long reverberation (Haas effect). If thespeaker is illuminated well and clearly seen, he isalso more audible. Special short-wave radio circuitsand earphones may be considered as an aid to thehard of hearing.

Intrusive noise, both airborne and structureborne, can reduce audibility. With low ambientnoise, because of its siting, a Greek theatre hadmarvellous audibility given by the steep seating andlow grazing losses in sound transmission, helpedby a polished floor reflector and reflecting surfacesbehind the speaker. Most historic buildings, beingheavy, can resist intrusive noise, but there are weakpoints which may need attention. Doors may fitbadly, windows perhaps have thin glass and aloose fit, ceilings may be vulnerable to aircraftnoise and need extra insulation. Increasing theweight of doors, edge sealing and use of air lockswill help reduce intrusive sound penetration, whilefor windows, double glazing, heavy glass and sealing of edges will also help. The hum from heat-ing plant fans or even electric lights can be intru-sive, but one of the major causes of intrusive noiseis motor traffic which should, if possible, bediverted.

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Introduction

In addition to the traditional techniques alreadydescribed, the repair, consolidation and restorationof historic buildings requires a number of specialtechniques and some unusual skills such as drillingand grouting. Architects are not generally con-cerned with scaffolding, shoring and such mattersas planking and strutting, yet unless these tech-niques are skilfully carried out, the conservation ofan historic building may not be possible, or at leastmay be made much more expensive. This topictherefore deserves their attention—just as the build-ing must be seen as an individual ‘whole’, so thework of conservation must be planned as a totalityif it is to be efficient. The source and flow offinance is a major factor in work planning and hasbeen dealt with in Chapter 19.

Grouting, by means of a liquid cementacious mixinserted under pressure after drilling into a build-ing, is a means of consolidating its structure. Thespecial techniques of prestressing with jacks incompression and for post-tensioning reinforcement,subsequently grouted, depend also upon drilling.These are the universal methods of putting strengthback into historic buildings in such a way as tomaintain their structural integrity and conserve theoriginal materials. Doubtless there will be improve-ments in these techniques, but subject to whateveradaptations are necessary in an individual project,for a man who understands the principles of con-servation, can use a theodolite, aim a drill andinstruct labour in the art of grouting and reinforce-ment and can order materials, keep site records andpay labour, there is a great demand, in order tohelp save the historic monuments of countries inthe developing world.

Planking and strutting

Temporary works to prevent the collapse of exca-vations or building elements are called plankingand strutting. Although they are generally left to thecontractor to arrange, the architect should be satis-fied that the precautions are adequate—for if theyare not, fatal accidents can be the result. Woodenplanking should be treated against rot before beinginserted.

Scaffolding

Scaffolding is the temporary framework which pro-vides a working platform for the building of newwork or which gives access for repair to old. Theancient practice was to lay poles or stout timbersabout 150 mm � 150 mm (6 in � 6 in), called put-locks or putlogs, across the wall cantilevered out-wards to support the platforms which apparentlywere made of woven wood hurdles. Similar rampsare still used in the Middle East and are very con-venient for carrying loads up. On completion of theworks, the horizontal supporting timbers weresawn off and left inside the wall, or they may havebeen withdrawn, for the holes show clearly inmany buildings, e.g. the nave of Fountains Abbey,England, and the Palazzo Sforza in Milan. Old put-log holes now provide a useful fixing for new scaf-folding or an easy way of inserting needles forshoring or reinforcements.

Later, scaffolding consisted of independentframes or wooden poles lashed together with wireor rope which in hot weather tended to stretch andslip; refinements were developed using wroughttimber and prefabricated frames. Nowadays, metal

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tubular scaffolding is almost universal. One of itsadvantages is that it does not need putlogs, so thereis no need to cut into ancient masonry; still, it isnecessary to ensure that scaffolding is securelyfixed to the face of a building by passing tiesthrough windows and other openings or by form-ing permanent screwed anchorages drilled incon-spicuously into the face of a wall.

Accidents due to collapse of scaffolding are notuncommon, so care in following all safety regula-tions must be insisted upon. The limitations of thepermissible loads on the scaffolding should beclearly understood and a notice posted thereon;these limitations consist of maximum point loadsper bay and maximum total distributed loads. Steelscaffolding has the advantage that it can be easilystrengthened and adjusted for levels as necessary.

For major restoration works, taking years ratherthan months, there is no doubt that it is better forthe building owner to buy scaffolding rather than

pay cumulative hire charges. This may involve thearchitect in checking the design of the scaffolding,although being temporary work it is the contractor’sresponsibility. Aluminium scaffolding, althoughuseful for decoration and cleaning contracts, is notstrong enough if masons’ repairs have to be carriedout. Plain steel scaffolding is objectionable becauseafter long use it rusts and stains masonry, but thisdoes not occur if galvanized steel is used. Greatcare must be taken with the choice of suitable con-nectors that will not deteriorate. For anastylosis,when weights of several tonnes may have to belifted, a heavy scaffold made of three rough225 mm � 75 mm (9 in � 3 in) timbers clampedtogether and held by friction is sometimes used.

For heavy loads on a steel scaffold, it is not somuch the strength of the verticals that limits thedesign as the weakness of the horizontal members.The thickness of the scaffold boards should beadjusted to the class of work: normal 32 mm

Figure 21.1 Excavations,York Minster, England(Courtesy: Shepherd BuildingGroup Ltd)

Planking and strutting shouldfollow excavation immediately.This was of heavy steel designedto resist outward thrusts from theheavily loaded masonry and support a temporary floor above.The detail shows the special hightensile steel bolts used to tightenup the strutting. The planking is50 mm (2 in) thick and with thebenefit of experience should havebeen treated with a timber preservative, as some of it had toremain in position over threeyears in damp and poorly ventilated positions, and laterbecame affected by dry rot andhad to be renewed

(1.25 in), medium 38 mm (1.5 in), heavy 50 mm(2 in). Extra strengthening can be obtained by lay-ing 9 mm (0.4 in) Douglas fir plywood overall. Theledgers supporting the scaffold boards should bearranged to slope slightly outwards, say 25 mm in1.5 m (1 inch in 5 ft), in order that rain will runaway from the building and drip clear of its face, soavoiding rust stains.

For work at a height in an exposed position,wind is a major nuisance and so slatted windscreens should be provided for the operatives.Because scaffolding is subject to considerable windpressures, all boards must be tied or clipped downat both ends. There is also a danger of objectsbeing dropped or blown off the scaffold, so fan-boards must be provided to protect anyone below.Scaffolding must be well braced diagonally andsecured positively to the fabric of the building, orform a stable structure in its own right. Fixing bypressure on to wooden blocks set against masonryis objectionable on two counts: first, it might

damage the masonry, secondly, the wood mightshrink and the fixing become unsafe. Handrails andtoeboards are essential for personal safety. Laddersshould be fixed top and bottom and have easyaccess without the need for gymnastic exercises(which get more difficult with the increasing age ofthe architect as the work drags on!).

It is the contractor’s responsibility to obtain alllicences for scaffolding, to arrange for watching andlighting and to prevent unauthorized persons gain-ing access to the building. This last may mean theuse of barbed wire and sticky paint. After work,ladders should either be made unclimbable orremoved entirely and locked up by night and atweekends.

Tables 21.1 and 21.2 give ASTM recommendedscaffold dimensions for heavy, medium and lightduties. Heavy loads are those not in excess of75 lb/ft2; medium loads are those not in excess of 50 lb/ft2; and light loads are those not in excessof 25 lb/ft2.

Scaffolding

297

Figure 21.2 Strutting, choir,south aisle, York Minster,England(Courtesy: Shepherd BuildingGroup Ltd)

Strutting was erected in orderto repair an arch. Screw-typestruts and wedges hold masonryin position while it is repaired.Such work needs final groutingto consolidate any voids

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Table 21.1 ASTM Minimum Nominal Size and Maximum Spacing of Members of Independent Pole Scaffolds (From OSHA Safety and Health Standards 1978, §1910:28, Tables D7, 8 and 9, by permission)

LIGHT DUTY

Member* Maximum height of scaffold20 ft 60 ft

Pole spacing (transverse) 6 ft 10 ftLedgers 1

14

in � 4 in 1 14

in � 9 inBearers to 3 ft span 2 in � 4 in 2 in � 4 inBearers to 10 ft span 2 in � 6 in 2 in � 9 in (rough)

or or3 in � 4 in 3 in � 8 in

Planking 1 14

in � 9 in 2 in � 9 inVertical spacing of horizontal members 7 ft 7 ftBracing (horizontal and diagonal) 1 in � 4 in 1 in � 4 inTie-ins 1 in � 4 in 1 in � 4 inToeboards 4 in high 4 in high (min.)Guardrail 2 in � 4 in 2 in � 4 in

MEDIUM DUTY

Uniformly distributed load Not to exceed 50 lb/ft2

Maximum height of scaffold 60 ftPoles or uprights 4 in � 4 inPole spacing (longitudinal) 8 ftPole spacing (transverse) 8 ftLedgers 2 in � 9 inVertical spacing of horizontal members 6 ftSpacing of bearers 8 ftBearers 2 in � 9 in (rough) or 2 in � 10 inBracing (horizontal) 1 in � 6 in or 1

14

in � 4 inBracing (diagonal) 1 in � 4 inTie-ins 1 in � 4 inPlanking 2 in � 9 inToeboards 4 in high (min.)Guardrail 2 in � 4 in

HEAVY DUTY

Uniformly distributed load Not to exceed 75 lb/ft2

Maximum height of scaffold 60 ftPoles or uprights 4 in � 4 inPole spacing (longitudinal) 6 ftPole spacing (transverse) 8 ftLedgers 2 in � 9 inVertical spacing of horizontal members 4 ft 6 inBearers 2 in � 9 in (rough)Bracing (horizontal and diagonal) 2 in � 4 inTie-ins 1 in � 4 inPlanking 2 in � 9 inToeboards 4 in high (min.)Guardrail 2 in � 4 in

*All members except planking are used on edge.

Planned use of scaffolding in restoration work

During work on an historic building, many peoplewill want to use scaffolding. The restoration pro-gramme should be considered, so that time isallowed for all probable operations from the samescaffolding. Even if nothing more demanding than acleaning operation is envisaged, the possibility mustbe borne in mind that more substantial work mayturn out to be necessary when superficial dirt hasbeen removed and ceases to hide defects. The scaf-folding must therefore be strong enough for theheaviest routine work likely to be encountered andit may have to be strengthened to handle excep-tional loads, if for instance a decorator’s scaffold hasto be used for some heavy masonry work. The pos-sible operations that may have to be carried out fromone scaffold are given in the following checklist:

(1) Architect’s detailed inspection with consultants.(2) Preliminary repairs and pointing, protection of

windows, etc.(3) Cleaning and removal of lichen and algae.(4) Masonry or roof repair; repair of rainwater dis-

posal systems.(5) Re-pointing; renewal of defective plaster.(6) Electric work, fire alarms, lightning conductors.(7) Decoration: gilding, mosaic work, restoration

of heraldry.(8) Photography of detail in stone, glass and carving.(9) Photogrammetry and recording of mouldings,

statuary, etc.(10) Research by art historians, archaeologists and

other specialists.(11) Visits by those interested.(12) Final inspection by architect.

Scaffolding

299

Figure 21.3 Shoring, choir, north arcade, York Minster,England(Courtesy: Shepherd Building Group Ltd)

Timber shoring was erected in order to repair a defective archin the York Minster choir. See also on left side, triple 25 mm(1 in) dia. high tensile steel ties inserted as a safety measure tostrengthen the main piers during consolidation of foundations

Table 21.2 Tube and Coupler Scaffolds (From OSHASafety and Health Standards 1978, §1910:28, Tables D13,14 and 15, by permission)

LIGHT DUTY

Uniformly distributed load Not to exceed 25 lb/ft2

Post spacing (longitudinal) 10 ftPost spacing (transverse) 6 ft

Working levels Additional Maximum heightplanked levels (ft)

1 8 1252 4 1253 0 91

MEDIUM DUTY

Uniformly distributed load Not to exceed 50 lb/ft2

Post spacing (longitudinal) 8 ftPost spacing (transverse) 6 ft

Working levels* Additional Maximum heightplanked levels (ft)

1 6 1252 0 78

HEAVY DUTY

Uniformly distributed load Not to exceed 75 lb/ft2

Post spacing (longitudinal) 6 ft 8 inPost spacing (transverse) 6 ft

*Working levels carry full loads, while planked levels are foraccess only.

In major works of restoration the whole pro-gramme may depend upon the intelligent planningof the use of scaffolding. It should be rememberedthat there is a great deal of costly nonproductivework in erecting scaffolding, and a programmedesigned to move the scaffolding sideways—ratherthan up and down—is more economical. The samescaffolding at York Minster was moved and usedeight times over five years.

Shoring

Shoring is a temporary work designed to resiststresses arising from subsidence, overtoppling orbursting and landslip. Although it is a temporary workand therefore the contractor’s primary responsibility,

the architect and engineer should check the designand be prepared to comment upon it. In competi-tive tenders, a contractor may be tempted to skimpthe amount of temporary work, while on cost pluscontracts he may even over-provide. The correctprovision requires judgement and experience and itis better to over-provide than have an accidentwhich may involve loss of life and damage to thevery building one is seeking to preserve.

Shoring is of three types: dead shoring, which isdesigned to take vertical loads and enables walls,piers and columns to be rebuilt, or propping, whichis a simple version of dead shoring where only partof the thickness of a wall needs renewal; horizon-tal shoring or strutting, which prevents bursting andlandslip; and diagonal or raking shoring, which canprevent bursting and landslip and overtoppling as

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300

Figure 21.4 Cradling, northtransept, York Minster,England(Courtesy: Shepherd BuildingGroup Ltd)

A timber and steel cradling wasput up in order to hold a thirteenth century archbishop’stable tomb and canopy in position while the space belowwas excavated for foundationworks

Shoring

301

Figure 21.5 Scaffolding, west front, St Paul’s Cathedral,London, England(Courtesy: Feilden & Mawson)

This external scaffolding was put up to effect heavy masonryrepairs, so the verticals are just over 1 m (3.3 ft) apart. Thediagonal bracing gives stiffness and wherever work is inprogress there are scaffold boards and toe-boards. The doorways used by the public are well protected. As such workis likely to take several years it is generally most economical tobuy the scaffolding outright, together with an electric hoist inview of the bulk of the work being at heights greater than 25 m (80 ft)

well. When shoring is erected, it is not stressed andconsequently some movement must occur before itcan carry its load. Because this movement willinduce cracks or may cause other damage and inextreme cases may even be quite dangerous, it is

highly desirable to tighten up or prestress shoring toits calculated loading. This can be done by jacks ofsuitable type, either screw or hydraulic. Care mustbe taken to avoid damaging a tender old buildingby over-tightening the wedging or over-prestressing.

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302

Figure 21.6 Scaffolding, nave, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The scaffold itself is designed for economy, using a central and two side towers linked andbraced together. The scaffolding is being moved horizontally from east to west two bays at atime, since a ‘rolling programme’ is far more efficient than an ‘up-and-down programme’. Theamount of work in erecting and dismantling scaffolding should not be under-estimated, as infact one is building a temporary building within a building to gain access to all surfaces. Notethe system of bracing which is essential for stability and the toe-boards for safety. Verticals arenearly 2 m (7 ft) apart because this is a light-duty scaffold. The cleaning has exposed localfaults which have to be corrected by the masons, while quite serious defects, which had beenkept under observation during the consolidation of the foundations, were rectified in the baysimmediately adjacent to the central tower

Jacking shoring: an example

A refinement of jacking was devised at York Minsterwhere flat-jacks were placed under the bases of26 m (85 ft) long steel raking shores. These jackswere linked to a constant pressure mechanismwhich applied a horizontal force of 20.3 t (20 tonf).The shores were able to accommodate movementin the building and the jacks also absorbed the ther-mal movements in the shores themselves with atotal expansion and contraction of about 30 mm(1.2 in). When inserting shores, needles are neces-sary to transfer the stresses to the masonry, and ashas been said it is often useful to find the original

putlog holes, if they exist. Shores should always beremoved carefully; if they have prestressing jacks,the procedure is greatly simplified as the pressurein the jacks can be lowered in stages.

Hydraulic jacks

A building contractor with wide experience cangreatly assist the architect by suggesting the most up-to-date equipment and plant for any particular pro-ject; for example, many uses for hydraulic jacks arebeing found in restoration works. Post-tensioning ofreinforcement and extraction of lining tubes to holes

Hydraulic jacks

303

Figure 21.7 Shoring, east end, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Raking shores support the wall which is leaning outwards and near collapse. Flying shores act as horizontal struts between the raking shores. The whole wall had to be kept intact in order to avoiddamage to the famous early fifteenth century Alpha and Omega window which is as large as a tenniscourt

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304

Figure 21.8 Shoring, east end, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The raking shoring required massive foundations and the base-plate rested on four Freyssinet flat hydraulic jacks whichwere attached to a constant pressure system. The jacks compensated for settlement of the foundation and thermalmovements in the long steel shores, and resisted the thrust of thecathedral while allowing it to settle

Figure 21.9 Shoring, west end, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The heavy-duty scaffolding devised for the east end was alsofound necessary to stabilize the west end during the excavationwork preparatory to consolidating the foundations. The temporary covers over the excavations prevent rain affecting the foundations; the stoppage of work is also avoided by this precaution

drilled for reinforcement can also be mentioned; forYork Minster, Lee-McCall jacks were used with theequipment mounted on a convenient trolley.

This section, however, deals more fully with flat-jacks of the Freyssinet type, which are made of twoparallel circular plates of up to 450 mm (18 in) diam-eter, joined together at the perimeter by a flexiblering. Hydraulic fluid is pumped into the volumebetween the plates, which are forced apart accord-ing to the load and pressure. The pressure can bemeasured, so the load can then be calculated bymultiplying the pressure by the area of the plate.The pressure can be varied at will or, if desired, keptconstant by an automatic hydraulic mechanism.

The use of flat-jacks in a system of needles anddead shoring has great advantages as the jacks canbe inflated and the calculated load taken on theshoring before the wall is removed, thus avoidingsettlements and consequential cracking when theloads are transferred. It is a safer method of work-ing, too. Dead shores should always be pressurizedto take the full weight of a wall before the openingis formed; if flat hydraulic jacks are not available,then a simple screw-jack or even hardwoodwedges can be used. However, no automatic com-pensation is possible with such methods.

Another use of flat-jacks was in the foundationsto the central piers of York Minster. These weredesigned in two horizontal layers with flat-jacksbetween them (about 400 in all), each connected to

an individual inlet with associated pressure gauge.It was planned that when the jacks were inflatedthe lower layer of the foundations would bepressed into the clay and take up half the overallload, leaving the original foundations with the bal-ance of the load. By measuring the pressure oneach plate individually, the loads could be calcu-lated, and if settlements were unequal the neces-sary adjustments could be made, for the pressurescan be adjusted separately by individual pipingwhich is also a precaution against a failure of thejack. In the case above, about 7 out of the 400 jacksfailed but there were sufficient reserves. Schemessimilar in principle but on a smaller scale havebeen carried out at St John’s, Ousebridge, York, andin the cloisters of Norwich Cathedral. In both thesecases, flat-jacks were used on extensions to the but-tress foundations in order to ensure proper loadingof the additional new supporting areas.

Where rubble fill, in walls, has compressed and theouter skin takes a large share of the load, post-stressing by flat-jacks can be used in maintainingstructural equilibrium to new areas of masonry whereold defective work has been cut out and replaced.

Drilling techniques

Drilling through masonry and brickwork permitsthe insertion of both liquid grout and reinforcing

Drilling techniques

305

Figure 21.10 Enlarged foundations, central tower,York Minster, England(Courtesy: Shepherd BuildingGroup Ltd)

Hydraulic cells or flat-jacks werelaid on a large independent pressure pad of concrete and covered with precast slabs. A separate foundation is to be laidabove and linked to the existingmasonry with post-tensionedstainless steel ties

Special techniques of repair and structural consolidation

306

Figure 21.11 Enlarged foundations, central tower, York Minster, England(Courtesy: Shepherd Building Group Ltd)

The foundations proper have been cast, leaving ducts for the steel reinforcement onone side and the pipes to the hydraulic cells which will he inflated in due course

Figure 21.12 Enlarged foundations, central tower, York Minster, England(Courtesy: Shepherd Building Group Ltd)

After drilling through 15 m (50 ft) of concrete, stone, mortar and wood the hole is lined temporarily with a pipe to prevent local collapse and the tensile stainless steel bars inserted.These were then stretched and given a final tensioning after two months and then grouted. Theprobes are all ready to receive the liquid grout injection

steel in a way that is not readily visible afterwards.Such techniques have opened up new possibilities inthe field of building conservation, as they enable oldstructures to be reinforced in an invisible manner. Thetechnique of drilling and grouting was first developedin the 1920s by Harvey, in his work on Tintern Abbey.It enables the worker in the preservation and repair ofhistoric buildings to comply with some of the essen-tial principles of structural conservation work:

(1) Make maximum use of the existing structure.(2) Repair the structure in a virtually invisible way.(3) Adjust the strength of the repairs to the appro-

priate degree.

Drilling equipment

Drilling equipment is of two main types, poweredeither by electricity or by compressed air. Portableelectric hand drills up to

12

h.p. can drill up to1–1.3 m (3–4 ft) of hard limestone or brick. For workon remote country sites, a portable 5 kW generator,which will power a high-speed rotary percussive110 V drill with air-blast waste removal, is very use-ful. Holes of up to 5.5 m (18 ft) length have beendrilled in difficult flintwork with this equipment.

Electric power can be used for rotary cutters,discs, fretsaws and hammers which can save muchhard work and, if skilfully used, cause less damage

Drilling techniques

307

Figure 21.13 Enlarged foundations, central tower, York Minster, England(Courtesy: Shepherd Building Group Ltd)

View showing the enlarged foundations and one of the massive piers of the central tower, each of whichtakes 4064 t (4000 ton) or more, now linked to the adjacent nave pier. As the temporary planking andstrutting and floor supports are stripped away the enlarged 16 m (52 ft) square foundations show. Theyhave been designed to eliminate eccentric loadings which gave ground pressures of 8 t/ft2 (7.9 ton/ft2)which was equal to the ultimate stress of the soil. New loadings were all brought up to 3 t/ft2 (2.95 ton/ft2)under the direction of Ove Arup & Partners, the consulting engineers and authors of this elegant design

Figure 21.14 Enlarged foundations, central tower, York Minster, England(Courtesy: Shepherd Building Group Ltd)

A general view showing the enlarged independent foundations of the central piers which are linked toadjacent nave, choir and transept aisle piers. The concrete rings to prevent bursting are above the newfoundations proper. Measuring points are fixed on to each foundation, movements being checked eachweek. Prestressed stainless steel reinforcing rods were inserted diagonally under the main piers, 100 toeach pier, in holes drilled through the original masonry

Figure 21.15 Investigation,St Paul’s Cathedral, London,England(Courtesy: Feilden & Mawson)

A core was cut with a diamond-toothed bit in orderto investigate the condition ofthe wall. The sample obtainedwas much fragmented, indicating weakness of thestructure. The core hole wasused together with anadjustable sparge pipe to testwater penetration in themasonry

Figure 21.16 Coring, YorkMinster, England(Courtesy: Shepherd BuildingGroup Ltd)

A diamond drill coring machineused to insert needles for temporary work or localstrengthening. It cuts as a neathole with negligible vibration

Figure 21.17 Coring, York Minster, England(Courtesy: Shepherd Building Group Ltd)

This foundation was cored with a 230 mm (9 in) diamondauger to form a hole about 4 m (13 ft) long in order to insert a200 mm � 100 mm (8 in � 4 in) galvanized steel grillage orneedles to consolidate poor masonry

Figure 21.18 Coring, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Diamond coring was used to cut stone in order to form concealed anchorages for reinforcement. The piece of stonecould be re-set, thus respecting archaeological values andpatina. Compressed air motors were preferred for all operationsas they are lighter than equivalent electric power units andsafer on a wet building site

310

Figure 21.19 Drilling, York Minster, England(Courtesy: Shepherd Building Group Ltd)

A compressed air drill being set up on a cradle prior to drilling probe holes for insertion of grout on the north-west tower north face. Note the firm rear anchorage to resist the thrust from theautomatic screw feed of the drill and the adjustments to scaffold that are required. An electric hoistcage can be seen in the background. Such equipment is essential on large-scale operations withclimbs of more than 15 m (50 ft) or for smaller jobs some 30 m (100 ft) height or more simply tosave time and energy. Power supply for twin 10 h.p. electric motors is necessary

Figure 21.20 Drilling, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Accurate drilling horizontally through 15 m (49 ft) of concrete, mortar and stones of various sizeand condition, with timber baulks set in grout, was difficult. In any horizontal drilling operationit is difficult to keep direction, but much more so if the material is inconsistent. Note the wet conditions and the ear-muffs to protect against the intense and continuous noise

to the fabric of an old building than cutting withchisel and mallet.

For major works, compressed air supplied by adiesel- or electric-powered compressor is safer, asthe great amount of water used in removing thewaste in drilling operations tends to be a hazardwhen using live electric wires, even if only of110 V. The siting of compressors should be care-fully considered, as the large versions are noisypieces of equipment. Hydraulic-powered equip-ment is still in the development stage but isreported to be quiet.

For large buildings which have a continuousmaintenance programme, a permanent air mainsfrom a compressor is an installation worth consid-ering, especially as it might be possible to arrangefor the plant to be used in reverse to act as a cen-tral vacuum-cleaning system. Such a plant has been

installed and used in Lincoln Cathedral for manyyears. A permanent air main should cover theground plan and enable air to be delivered to anypoint using about 30 m (100 ft) of flexible hose.

Drilling equipment must be matched to the sizeand difficulty of the task. The power of the drillaffects the accuracy of the work, and in general, thefaster the rate of penetration, the more accurate theshot is likely to be. Stiffness of the drilling stem isanother factor assisting accuracy. High-speedrotary-percussive drills are fast, and in hard lime-stone, rates up to 135 mm (5 in) per minute can beobtained. Accuracy is improved if a mandrel isinserted behind the head; this mandrel must beable to pass the water-borne waste from the cuttinghead. Various types of cutting head, based on steelor tungsten carbide, can be obtained. The othertype of bit that can be used is a pure rotary drill

311

Figure 21.21 Drilling, York Minster, England(Courtesy: Shepherd Building Group Ltd)

A more powerful drill set on a movable cradle which can be adjusted for height was obtained. Itwas found that a stiff rod helped preserve direction and for most purposes the ‘down-the-hole’ volehammer was quickest and most accurate. Auger bits had to be used when embedded wood wasmet, and occasionally diamond studded bits were used. The operatives acquired a special expertiseby continuous work in shifts over nearly three years. Often the holes would collapse, so these had tobe lined with a 50 mm (2 in) diameter tube immediately after drilling. Later the steel could beinserted as shown and then the tube was extracted using hydraulic jacks. The drill inevitablybreaks out through the concrete, so finished work was planned to cover this

Special techniques of repair and structural consolidation

312

Figure 21.22 Drilling bits, York Minster, England(Courtesy: Shepherd Building Group Ltd)

All the drill-head components and assemblies described are powered pneumatically for both rotary and rotary percussive drillingunits. Advantages and disadvantages—high-speed rotary percussive is the most economical means of drilling; tungsten carbide tippedbits are much cheaper than diamond crowns. This type of drilling is fast, but demands a homogeneous mass, preferably of like material, to provide for accuracy in operations where long holes are required horizontally in masonry. Diamond core drilling israther slower and thus more costly, but under adverse conditions in bad materials is more accurate in maintaining alignment

1 Retro-bit, 3 in diameter, incorporating 1 58

in pilot bit. Theassembly as illustrated was used for the purpose of makingaccurate entry in protecting against drift in the initial stages ofrotary percussive long hole drilling.

2 Standard 3 in diameter cross-type tungsten carbide tippedbit used for drilling in homogeneous material by rotary percussive means.

3 Purpose-made 3 in diameter button bit with protrudingtungsten carbide inserts, ideal for drilling in limestone, doesnot require sharpening. Used for rotary percussive drilling, theinserts contain two main components, tungsten carbide, thehard component, and cobalt, the tough component.

4 Standard button bit, 3 in diameter, for drilling in brokenground by rotary percussive means.

5 Standard holbit 1 14

in diameter tungsten carbide tipped, usedfor short hole rotary percussive drilling.

6 Standard retro-bit 1 34

in diameter tungsten carbide tipped,used for normal drilling operations by rotary percussive action.

7 As above, but 2 in diameter and ditto.

8 Ditto, but 2 12

in diameter.

9 Standard holbit, 1 12

in diameter.

10 Standard retro-bit, 3 in diameter, used for normal drillingby rotary percussive action.

11 Purpose-made retro-bit incorporating blind pilot, used for reaming 1

58

in diameter hole up to 2 in diameter by rotarypercussive action.

12 Standard drill steel coupler type 408 rope thread for coupling 1 in hex steels for rotary percussive drilling.

13 Standard coupling showing a rope thread coupler used forrotary percussive action.

14 Purpose-made coupler for use with 1 in hex hollow drillsteels, designed to provide accuracy when drilling through broken ground, using 3 in diameter retro cross-bits. This typeof coupling assembly allows the drill cuttings to pass through internally in suspension and centralizes the drill steels at coupling points, ideal for drilling operations 50–70 ft horizontally.

15 Standard 4 14

in � 1 in hex shank and (water swivel) 408thread for rotary percussive action.

16 Standard 508 rope thread coupling used for coupling 14

1 in diameter drill steels for rotary percussive action.

17 Standard 1 12

in diameter lugged shank and 512 rope thread assembly for 1

12

in diameter round drill steels for rotarypercussive action.

18 Purpose-made reamer coupling, 3 in diameter, for use with1

14

in diameter drill steels, ideal for drilling operations incementatious material.

19/20 Standard walran-type rotary tungsten carbide tippedwinged bit used for rotary drilling in timber and decomposedmasonry.

21 Standard Trycon roller bit used for rotary drilling inbroken ground of material that yields. This type of bit isemployed with diamond tubes.

22 Standard Diamond Crown NX with bevelled wall, grade 10diamonds used for rotary diamond coring and employed withdiamond tubes. This bit cuts through masonry, concrete orsteel and recovers its core.

All drill head components, drill string assemblies, couplers anddrill string centralizers were driven by heavy-duty Drifter chainor screw-fed drilling machines, mounted on portable or purpose-made drilling rigs powered by rotary screw type aircompressors.

with diamond or tungsten carbide cutters. This givesabout 20 mm (0.8 in) per minute or less, and is rela-tively slow and therefore more expensive, but the stiffstem of the rotary shaft assists in accuracy. A ratherspecial type of cutter is a ‘down-the-hole’ vole, high-speed rotary-percussive hammer with a stiff rotatingshaft. Some standard percussive equipment causes fartoo much vibration to be used satisfactorily on oldbuilding structures, so preliminary tests are advisable.

Drilling works

Drilling vertically to great depths through homogen-eous materials, however hard, is a comparativelysimple and well-established practice, but accuratedrilling horizontally through masonry is much moredifficult. The tip of the drill has a natural tendencyto drop and may be diverted by each fissure, crack,void and joint in the masonry, not to mentionembedded timbers and metal. Drilling at an obliqueangle to the masonry is even more difficult becausethe angled joints are more likely to deflect the drillthan joints normal to the hole. To assist accuracy,as much grout as possible should be injected priorto the main drilling operation to fill the larger voidsand make the masonry more homogeneous. Thereis a possibility that adjacent drill holes may be filledby this grout and have to be re-drilled. The risk ofthis happening can be reduced by inserting sleevesin the holes, although the sleeves themselves pres-ent a problem, for, if left in position at the time ofgrouting, they will reduce the bond between thereinforcement and masonry and so must beremoved. Ideally the sleeve should be of thin-gauge polished stainless steel pipe. It should berotated just after the initial set of each grout injec-tion, and then withdrawn when all grouting that isnecessary has been done. In practice, galvanizedsteel is more likely to be available and hydraulicjacks may be necessary to extract the sleeves. Ifordinary mild steel sleeves are left in position, thereis a great risk that they will rust and cause damageby consequent expansion.

Horizontal shots of up to 20 m (66 ft) length havebeen carried out effectively on the central tower ofYork Minster through large blocks of hard lime-stone, after preliminary grouting. If a shot went offalignment, the drill was withdrawn and the holewas grouted with rapid-hardening cement. The drillused a crown-shaped drilling head with a specialguiding mandrel. Horizontal shots of 15 m (49 ft)length in fissured and disintegrated masonry in theNorman foundations had to be re-drilled more thanonce with a wide range of drill heads. The residentengineer, Norman Ross of Ove Arup & Partners,

described the work as follows, and his experienceis worth recording for future practitioners:

‘The 16 000 ton central tower is carried by fourmain columns. Each column has, as its effectivefoundation, a cruciform of Norman strip footings. Taking into account eccentricity, thebearing stresses on the ground are much heavier than desirable. The effective area ofeach column foundation is increased and theeccentricity reduced by adding slabs of concrete2.1 m (6 ft 11 in) thick in each re-entrant corner.The whole composite foundation is reinforcedby post-tensioned 32 mm (1.3 in) diameter stainless steel rods which form two layers ineach elevation. This involves drilling holes upto 15 m (49 ft) horizontally through the Normanfoundations with a high standard of accuracy.

‘The centres of the rods are 380 mm (1 ft 3 in)apart horizontally and 450 mm (1 ft 6 in) apart vertically in each direction. However, since onelayer in each direction bisects the two layers inthe orthogonal direction, the actual vertical distance between the layers is only 225 mm (9 in).From these figures it can be seen that the targetafter 12 to 15 m (40 to 50 ft) of drilling, allowingworkable tolerances, is a rectangle only300 � 225 mm (12 � 9 in). Such accuracy hasproved very difficult to achieve—perhaps not surprisingly.

‘For several months, before any drilling wasattempted on the foundations, similar requirements had been carried out at high levelsin the Central and Western towers. The walls ofthese towers have been protected from furthercracking by reinforcing them horizontally in certain areas with stainless steel rods. Thisinvolved drilling holes 20 m (66 ft) in length butmore tolerance was allowed than was laterrequired for the foundations. The work on thetowers, by comparison, went very well and success gave confidence for the drilling below—aconfidence which nearly turned to despair whenseveral months after starting on the foundationsdrilling, only 8 holes had been successful out of atotal of 38 attempts (with 400 to do).

‘The reason why drilling in the walls of thefabric was easier than in the foundations is nothard to find. Accurate drilling depends basicallyon two things:

1. The nature of the material being drilled.2. The use of the correct equipment to suit the

material.

The ideal material is a sound, homogeneousrock containing no fissures or voids. Mass concrete, of course, is equally acceptable. The

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degree by which a material departs from thisstandard is a measure of the difficulty one canexpect in drilling through it. The Minster fabric,in the main, is well-bonded magnesian limestone masonry and where rubble coresoccur, they are well compacted and reasonablywell mortared. On the other hand, the Normanmortar raft is far from ideal, for several reasons:

(a) It is non-homogeneous. The core has produced various limestones, red sandstone, millstone grits, a few igneousrocks, and even Roman tiles and bricks.

(b) This miscellaneous rubble is held togetherby a matrix of lime/sand mortar, generallyof a very low lime content. In parts themortar is hard where presumably the proportions were better but usually it canbe powdered between finger and thumb,presumably having undergone severedecomposition since it was first mixed inthe eleventh century. The soft mortar offersno resistance to the passage of the drillwhich can thus deflect easily when harderrocks are encountered. Also, since water isused to flush back the drilled material,small voids are often created when the softmortar is also washed back. Prior to drilling,attempts were made at consolidating the“mortar raft” by drilling holes for grout andpumping in a wet mix under pressure, but,with a few exceptions, only small “takes”have been recorded. To improve the groutpenetration Pozament is used at awater/cement ratio of about 0.6.Pozament is a proprietary cement consistingof roughly equal portions of pulverized fuelash and ordinary Portland cement. The oldmortar absorbs the water but not the solids.Experiments have also been made withepoxy resins as grout and excellent resultshave been achieved. There was excellentpenetration of the mortar by the resin, producing a solid mass. Unfortunately thecost of using resins is prohibitive—blanketgrouting of the existing foundations wouldcost approximately £500,000 (in 1969).

(c) In the vicinity of each tower column thefoundations have undergone differentialsettlements of up to 300 mm (1 ft 0 in). Asa result, they have fissured and deformed,producing shear planes which can deflectthe drill from its correct alignment.

(d) It was the practice of the Normans to rein-force their strip foundations with a continu-ous grillage of oak or elm baulks placed

centrally. In the Minster the longitudinalmembers were 450 � 300 mm (1 ft6 in � 1 ft 0 in) and the lateral distributionmembers 300 � 300 mm (1 ft 0 in � 1 ft0 in). Much of the timber has rotted, leaving voids which have since been filled with sand/cement grout, but somehas remained to provide yet another hindrance to easy drilling.

‘Compressed air was used for working mostof the tools used on York Minster. Two HolmanSilver III percussive drills between them completed the work at high level on the towers.The bits used were 63 mm (2.5 in) diameter,with star or cross tungsten carbide cuttingheads. The drilling rods were hexagonal andhollow so that the flushing water could pass upthrough them to the cutting heads. The 32 mm(1.3 in) rods were standard and came in lengthsof about 5 m (16 ft). At regular intervals specially designed 63 mm (2.5 in) diameter couplers were used which fitted tightly to the holeyet allowed water and debris to pass through.

‘The same rigs were employed initially whenthe foundation drilling commenced. After a number of “shots” most of which were badly offline, the situation was reviewed. The bits anddrilling rods tended to feather which indicatedthat the rods were curving in profile. More powerful machines of the same type appeared tobe the answer. The slightly larger Silver 83 modeland the SL 16A drifter were tested in turn. Thedrifter is a brute of a machine, very popular in mining engineering. At this stage also, experiments were carried out using other typesof cutting heads, namely “button” bits and tri-cone or roller bits. In addition all the conventional types and sizes of drilling rods andcouplers were tested but without the success wewere looking for. Even tube drilling wasattempted on the percussive rig, using tubes forgreater rigidity. The tubes we produced on thesite failed miserably and even specially designedfactory-made tubes could not withstand thestresses, especially fatigue, which this type ofdrilling sets up.

‘We now turned to diamond-core drillingwhich is both slow and expensive. The bits arehollow cylinders whose crowns consist of clusters of industrial diamonds set in a cobaltbed. Each bit cost about £70 and, on average, isgood for only 61 m (200 ft) of drilling. Theaction is purely rotary as a percussive elementwould obviously smash the diamond crown.However it has proved to be at least one

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answer to the problem. It is accurate over longlengths through poor material because drillingtubes of 75 mm (3 in) diameter may be used.These are much less flexible than the 32 mm(1.3 in) diameter hexagonal rods used by theSilver III. Even diamonds though, cannot drillthrough half-rotted timbers (the Norman reinforcement) and, when these are encountered, fly-cutter bits or rag-bits have tobe substituted for the diamond crown until thetimber has been bored. (Fly-cutters operate onthe same principle as a carpenter’s auger.) Onoccasions, a series of as many as five timbershas to be negotiated in this way in drilling justone hole.

‘The latest episode of the saga has been thesuccessful introduction of the “down-the-hole”vole hammer. This is a rotary-percussive toolwhich can be used on the same rig and withthe same equipment as for the diamond coring.The percussive element is a hammer bit whichhas tungsten-carbide cutting edges. The volehammer drills dry with compressed air passingup through the centre of drilling tubes and forcing back the loosened material. The sameair activates the percussive hammer.

‘This type of drilling has been accurate, quickand relatively inexpensive. Its secret lies in thestiffness of the drilling tubes and in the fact thatthe tubes are only required to transmit torque, allthe percussion taking place at the cutting face.’

Grouting

The object of grouting is to strengthen and consol-idate decayed masonry which is weakened by largefractures and voids. Although grouting is a usefulpreliminary treatment it cannot usually be regardedas a complete structural repair in itself, nor can it betrusted to fill fine cracks. It does, however, consol-idate and increase the stiffness of an old structure.

Searching out voids for grouting presents diffi-culties; often a hit or miss method has to beadopted, with holes drilled in a predetermined gridand water testing used to give advance warning ofthe existence of and probable size of the void.Other methods involve simple tapping with a ham-mer and listening to the note, which varies with thesolidity of the masonry, or the more complicateduse of gamma or X-rays, which can only penetrateabout 1 m (3.3 ft) overall, or ultrasonic testing. Eachmethod should be tried, as particular circumstanceslike multiple fissures or even fine cracks may ren-der the searching out of voids impracticable.

Grouting is the insertion of a fluid cementaciousmix, called grout, with good flow characteristics

into the cracks and fissures of masonry or concrete.Before inserting the grout it is first necessary toclean out the voids and wet all the surfaces. Thegrout is inserted under pressure of gravity or by ahand- or air-operated pump. Vacuum grouting isalso a hopeful development, but relies on suitableresins for its effectiveness.

Grouting mixes are formulated for each specificproject, in order to obtain the desired strength andpenetration characteristics. Sand and pulverized flyash may be added to the cementing material whichmay be lime, hydraulic lime, Portland cement or var-ious epoxy resins or silane formulations. Proprietaryadditives are used to promote flow and penetration.

The addition of pozzuolanic material to lime ingrouts and mortars is important. Lime itself sets bycarbonization—the action of carbon dioxide—andthe setting consists of hardening from the surfaceinwards, so that in thick walls the process maynever occur, leaving powdered calcium hydroxideinstead of hard mortar. However, carbon dioxide isnot needed if pozzuolanic material such as volcanicearth, including alumina and silica or crushed brickand tiles, is added in equal proportions to the lime.

Pulverized fly ash, which is extracted from powerstations, is a pozzuolanic material and can be usedwith lime to form a hydraulic mortar of attractivecolour; but the use of some types of fly ash with ahigh soluble salt content should be avoided. Twoparts pulverized fly ash with two parts lime and, inorder to keep the binding material in suspension, oneof bentonite clay additive, to promote flow charac-teristics, is a useful grouting mixture which avoids theexcessive hardness and strength of Portland cementgrouts. If Portland cement is used, there is a dangerthat the grout will be too hard and impervious andnot marry well with masonry. If hard and imperviousmaterial comes too close to the surface of masonry itmay promote frost attack and should therefore be cutback at least 50 mm (2 in) before it hardens, and inany case it does not have the necessary resilience tobe structurally sympathetic to old masonry.

The simplest form of grouting is practised whenlarge stones that have been set on lead wedges orbits of oyster shell of the correct joint width aregrouted with a mixture of sand and lime by pouringthis into the open joints; the water percolates awayand leaves the solids in position, the stone thenbeing completely surrounded by mortar. A form ofgravity grouting can be carried out by forming claycups against open joints in masonry and filling theserepeatedly with grout which flows through the openspaces and consolidates the masonry. The mixturemay need some help in its flow, by working a hack-saw blade or similar probe through the joint. Finesand and the addition of pulverized fly ash assist the

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Figure 21.23 Drilling marbleshafts, York Minster, England(Courtesy: Shepherd BuildingGroup Ltd)

The shafts were badly cracked, sothey were put into splints andencased in plaster of Paris beforebeing dismantled. Then a 40 mm(1.60 in) hole was drilled downthe length of the shaft and capital.The shafts were re-erected, havingbeen strengthened with 30 mm(1.25 in) stainless steel rods, andthe cracks were repaired withepoxy resin

Figure 21.24 Drilling, YorkMinster, England(Courtesy: Shepherd BuildingGroup Ltd)

Drilling through decayed eleventhcentury masonry was difficult asthe holes tended to fall in, so tubeswere inserted immediately. Thenthe stainless steel reinforcementwas threaded through and thetubes withdrawn using theimmense power of hydraulic jacksto overcome friction, and finallyeach rod was anchored, pre-tensioned twice and grouted intoposition. Work is shown on one ofthe piers of the western towers

Figure 21.25 Grouting, westfront, St Paul’s Cathedral,London, England(Courtesy: Feilden & Mawson)

A grout mixture is injected by airpressure into the open joints inthe stonework. Large areas ofwalling now need this treatment

Figure 21.26 Grouting,central tower, NorwichCathedral, England(Courtesy: Feilden & Mawson)

Holes for the probes weredrilled into the wide joints sothat their position would notshow after making good.During the work at 30 lbf/in2,it was found that grout mightspurt a considerable distanceand so the protective drapes ofpolythene were necessary. Allthe piers of the tower with thearcades and walls above wereconsolidated by grout

Figure 21.27 Grouting, central tower, NorwichCathedral, England(Courtesy: Feilden & Mawson)

The holes drilled ready for insertion of probes show clearly. Limeand fly-ash with a small amount of Portland cement was usedas a mix and the amount injected into each hole was recorded.The cracked capitals in the arcade were grouted with epoxyresin which only had a short pot life of 30 minutes

Figure 21.28 Grouting, central tower, NorwichCathedral, England

Probes are arranged at approximately 500–600 mm (20–24 in)centres with rapid hose connections and valves. The grout isinjected and runs both sideways and upwards: when it reachesa probe and runs out the valve is closed and the grout movesfurther. One hole ran 6 m (20 ft) sideways and received 250 l(50 gal) of grout. Leaks are plugged with tow and masonrywashed clean

Figure 21.29 Grouting,south-west tower, YorkMinster, England(Courtesy: Shepherd BuildingGroup Ltd)

Consolidating masonry on YorkMinster’s south-west tower bygrouting with a weak mixtureof cement and fly-ash. Notequick coupling to hose andhand on tap. Grout was hand-pumped at 20 lbf/in2

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Figure 21.30 Grouting, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Large quantities of pulverized fly-ash and sulphate-resistingPortland cement were used to consolidate the foundations ofYork Minster. Originally there was an oak grillage, but when thewater table was lowered these timbers rotted almost completelyand left voids which were filled with grout. Note the dark-coloured timber and the stratification in the grout

Figure 21.31 Grouting, foundations, York Minster,England(Courtesy: Shepherd Building Group Ltd)

After consolidation it is possible to open up masonry. This showsthe horizontal strata of grout in the foundations of eleventhcentury random masonry and also the ancient embedded oaksthat had not rotted too much here, being kept wet for centuriesuntil the water table had fallen in recent years

Figure 21.32 Grouting,Ospizio di San Michele, Rome,Italy

The walls, built of random rubbleand pozzuolanic lime mortar,were weakened by age and theoriginal workmanship was suspect. Load tests showed themto be very weak. Grouting withepoxy resin, although expensive,greatly increased the strength ofthe wall. It is, however, a rathermessy process

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Figure 21.33 Reinforcement, central tower,Norwich Cathedral, England

Steel reinforcement for the tensioned ring beams galvanizedafter bending and cutting. This has to be inserted in shortlengths; each piece of steel was hooked on to the next to providea continuous chain of four 20 mm (0.75 in) bars. The differentlengths enabled variations to be dealt with

Figure 21.34 Reinforcement, north-west tower, York Minster,England(Courtesy: Shepherd Building Group Ltd)

End anchorages of 150 mm (6 in) diameterstainless steel was used. Then the steel waspre-stressed using a hydraulic jack, allowedto stretch for two months and then givenfinal tension. Grout was inserted throughprepared probes

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Figure 21.35Reinforcement, north-westtower, York Minster,England(Courtesy: Shepherd BuildingGroup Ltd)

The mason prepares to makegood by cutting out a rectangular shape for the newstone. He should have beenconsulted about re-setting the piece cored out

Figure 21.36 Makinggood, north-west tower,York Minster, England(Courtesy: ShepherdBuilding Group Ltd)

Finally, the mason makesgood by inserting new stoneand grouting it into position

flow and, together with lime as the cementatiousagent, they make a good grout mix in the propor-tions 2:1:2; more fly ash can be added along with alittle Portland cement if quicker setting is desired.

For more sophisticated forms of grouting, probeholes are drilled into the masonry at appropriatecentres, the spacing of which depends upon thecondition of the masonry and the incidence ofcracks. For example, on Norwich Cathedral spire,where it was not possible to strut the external sur-face, holes were drilled at only 300 mm (12 in) cen-tres to reduce the outward pressure loading. In veryfissured masonry, probes at close centres are desir-able, whereas where large lumps of stone or flintconcrete have cracked, it is only necessary to havegrout probe holes at 1 m (3.3 ft) centres, followingthe line of the crack upwards.

The holes having been drilled, water is inserted towash out the loose materials and wet the masonry sothat the grout will adhere. For this, one works down-

wards, whereas for insertion of grout one must workupwards in order to avoid trapping air in pockets.The probe itself fits into the hole and may be caulkedthere, or merely held in position with a foamed rub-ber washer around it to stop undue leakage.

As all grouting work is liable to be messy, protec-tion of furniture and fitments is essential; if they can-not be removed they should be covered withpolythene sheets. The masonry walls themselvesmust also be protected or at least cleaned down withhoses immediately after a spillage of grout. It is alsobest to put a protective coating of potter’s clay toavoid staining or otherwise damaging precious his-toric masonry which may be difficult to clean thor-oughly. Recent developments of plastics also suggestapplication of a thin coat that can be peeled off later.

The grout is inserted working first sideways thenupwards. When the grout flows out of an adjacenthole sideways, this hole is stopped and the groutallowed to move as far as it can—even up to some

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Figure 21.37 Safety precautions for the Alpha and Omega window, East End, York Minster, England(Courtesy: Shepherd Building Group Ltd)

This repair consists of restraining the leaning and bowing east window of York Minster by tensioned cables withsuspension rods attached at each strong node point. No other simple way of solving this problem could be found.From ground level the wires are practically invisible, so this can be classed as a permanent repair

6–7 m (20–23 ft). Then one proceeds to the nexthole, and in this manner completes a horizontalrow, recording the amount of grout inserted intoeach hole and the distance of flow. After the hori-zontal row is complete one moves upwards to thenext row and repeats the process.

Gravity grouting with a head of about 5 m (16 ft) isnormal practice when consolidating ancient masonry.The advantage over mechanical pumping is thatpressures cannot build up if there is a stoppage. The

grout is mixed in a raised reservoir, from which it isfed by flexible pipe of about 25–30 mm (1–1.2 in)diameter and controlled by a plunger stopper.

A slightly more complicated method is to use ahand pump with 50 litre (10 gal) reservoir with themix continuously agitated by an electric or com-pressed air motor. A hand pump can be used toproduce pressures of two or even reaching six orseven atmospheres to achieve a deeper penetrationof grout. Pressures must be controlled carefully, as

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Figure 21.38 Pumping concrete, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Ready-mixed concrete deliveries can lessen labour costs and save space on a confined site, leaving it cleaner and reducingthe noise nuisance from concrete mixers. In combination with a pump unit, concrete can be delivered wherever required by

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Figure 21.39 Pumping concrete, York Minster, England(Courtesy: Shepherd Building Group Ltd)

Shepherd’s Contracts Manager organized the pumping of some 80 m3 (105 yd 3) of concrete to the top of thecentral tower, 63 m (207 ft) high. The work of laying this concrete took about five hours. Shepherd’s wereawarded a special Cembureau prize for this feat. In the conservation team the contribution of the contractorin using plant and equipment efficiently is vital to overall efficiency and economy of the project

there is a danger of blowing stones out of the faceof a wall and other damage. The pump operator issupported by at least one man on each side of thewall who stop up leaks as and when they show,and if this is not possible stop the pumping.Sometimes this has to be done very quickly, and ifcommunication by word of mouth is difficult thenthe use of throat microphones and radiotelephoneis the best substitute—telephones are too slow.With hand pumping it is possible to feel the rate offlow and judge the situation and react quickly. Thisis not possible with mechanically operated pumps,which should not be used on historic buildinggrouting work. However, reservoirs which injectusing compressed air, at a predetermined pressurethat cannot be exceeded, are probably the mostefficient, especially in large operations.

Epoxy resin formulations have been used in muchthe same way as cementacious mixes to consolidatefissured masonry or cracked stones. The dangersfrom staining and surface damage are greater, soprotective measures have to be more stringent. Thepot life of some formulations is short and may causedifficulties in practice. The plant may have to bestripped down and cleaned completely after eachinjection. As the epoxy resin material is expensive itis not practicable or desirable to use it on largevoids, so in some cases it may be desirable to fill thelarge voids with ordinary grout and then re-groutwith a weak penetrating mix of epoxy resin so as toconsolidate friable and broken-up areas. In suitablecircumstances, vacuum impregnation may be used inorder to obtain maximum penetration.

Vacuum impregnation should be carried out byspecialist firms with experienced operatives. It isessential to ensure that sufficient vacuum can beobtained on the section to be dealt with, for, unlessthe object is completely isolated like a statue or pin-nacle, there is a danger of air leaks around theperimeter and through the thickness of the chosensection. The object is enclosed in a sheet of imper-vious polythene. To allow the impregnating mixtureto flow and find the crevices, fissures and pores ofthe masonry, a layer of netting is placed under thesheet which allows visual inspection to make surethat the surface is flooded. When the vacuum isreleased, the grout is sucked inwards. Various groutsare possible; for the preservation of stone, silanegrouts have been used successfully and remarkablepenetration has been claimed. As these aremonomer resins, they require some six weeks or soto polymerize, before which time the outer sheetcannot be removed. By using vacuum methods it istheoretically possible to obtain deep penetration intothe pores of stone as well as fill the cracks and fis-sures, but there are many problems in practice.

Full records of all grouting operations should bekept and deposited with the archives of a building.The amounts injected are a rough guide to thestructural condition of the fabric: up to 2

12

% of thetotal volume is by no means uncommon, but farlarger amounts have often been injected into areaswhich have suffered high stresses over a longperiod of time, which is not surprising as onewould expect these parts to wear out more quickly.

After repair of an historic building involvinggrouting, particularly with Portland cement, seriouscondensation problems can arise—first, becausethe water used in the injections may cause damageas it dries out; secondly, because the grout, if dif-ferent from the wall mortar, may form zones ofunequal density and promote cold bridges causingcondensation which could result in disintegrationof the wall plaster or staining of wall paintings; andlastly, there is always the danger of soluble salts inthe cement causing damage by crystallization.

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Figure 21.40 Pumping concrete, York Minster, England(Courtesy: Shepherd Building Group Ltd)

After the enlargement of the foundations had been completedand the active settlement of the central tower stopped, it waspossible to reinstate the floor which was of reinforced concretelaid over plastic coffer moulds. The concrete was pumped intoposition, vibrated and tamped to form a level and smooth finish

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Modern buildings present new problems for thearchitectural conservationist. Conservation is abranch of architecture, and accordingly, no lessthan any other sort of design, requires judgementand a sense of proportion. In addition to an archi-tect, conservation of buildings constructed of iron,steel and concrete should involve a structural engi-neer and possibly a valuation surveyor.

The conservation, adaptation, re-use and subse-quent maintenance of modern buildings involve thesame principles that apply to traditional buildingsin aesthetics and philosophy and historicalresearch, but introduce the important aspects ofcommercial judgement and estate management.Experts in rehabilitation of traditional buildings arechallenged to expand their competence and knowl-edge base, to deal with the special problems andresponsibilities of working on modern buildings.

Traditional buildings of earth, brick, stone and timber could become historic, if they survived a hun-dred years—through being useful to as least threegenerations, and gradually acquiring ‘age value’, andeven ‘scarcity value’. They acquire these values moreby survival than by style, because they were designedto last. On the other hand, modern buildings acquiretheir interest through their style and innovation.Some were not even designed to last.

Some Avant Garde buildings were produced in the1920s and 1930s in a style devoid of ornament, muchinfluenced by Cubist painters and sculptors.Developments ceased in the decade of World War II,but the Modern Movement had caught hold of theschools of architecture, and new methods of con-struction were developed to express its aesthetic.Craftwork was no longer its basis, and the art ofbuilding became a matter of assembling components.

As John Allan points out:

‘After the Second World War, the changed socialand economic priorities of national reconstruction,

effectively converted the experimental architectural precepts of the 1930s into theorthodoxy of the Welfare State, and between1945 and approximately the mid-1970s, modernist architecture—albeit in many interpretations—was the prevailing tradition ofbuilding design used in Britain to meet the baserequirements of new national infrastructure inhousing, education and leisure, health and welfare, transport, industry and commerce.

The well-deserved criticism of much of thisoutput for its social and technical failures hasled—at least in some quarters—to indiscriminateand unjust condemnation of modern architecturein its entirety, regardless of the great benefits ithas also brought to post-war society in themany fields indicated above.

Meanwhile, from the conservationist perspective, the sheer volume of productionand the fact that much of this work was

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Conservation of modern buildings

Figure 22.1 Villa Savoie, Poissy, Paris, 1930(Photograph: John Allan, Avanti Architects, London)

This private house by Le Corbusier has become the definitiveexample of European ‘white modernism’, and is now a historicmonument conserved and protected by the French Government

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undertaken at great speed, often with untriedmaterials and techniques, and less than generousbudgets (to say nothing of the uneven standardsof after-care and maintenance), has now madefor commensurate problems of evaluation andclassification’ (from Conservation of ModernBuildings’ Ch. 11—Building Maintenance andPreservation—Edward Mills, 1980, SecondEdition 1994, para. 3.4–6).

Building technology had been developing slowlyin the late eighteenth century, starting with thefamous Iron Bridge of 1778, and fire resistant millsand industrial buildings, using cast iron for columnsand beams. Windows, railings and other fittingswere also mass-produced, with prefabrication ofcomponents, of which the Crystal Palace (for the1851 Great Exhibition) was the prime example.Defects in cast iron beams led to the use ofwrought iron, which was eventually superseded bysteel, whose production was greatly increased bythe demand for railway tracks. Buildings in the USAled in these developments, with whole buildingsbeing created in cast iron. Riveted and bolted steelframes opened the possibility of skyscrapers, butthese buildings were still clad in ceramics.

The first steel framed building in London was theRitz Hotel (c. 1901), followed quickly by theInstitute of Civil Engineers. Corrugated iron sheet-ing and asbestos sheeting were used on temporaryand agricultural buildings with no architectural pretensions.

In spite of these developments, a Roman con-struction manager could have taken charge of atypical building project in 1950 without difficulty,except that electricity would have puzzled him.Buildings before the mid-twentieth century weremassive and heavy, acting as heat reservoirs with

walls that could breathe, so one had a crude tech-nology that was a structural environmental system.

From the 1950s, reinforced concrete became thedominant architectural material, fascinating design-ers with its capacity to be moulded, and combiningthe functions of walls and frames with a wide rangeof finishes. Columns, beams, floor slabs and wallscould be poured in concrete. The defects of con-crete were not appreciated; its failure to weathergracefully, its dull grey colour, its tendency to crackor craze, and worst of all, the rusting of reinforce-ments after a time. It was not realized that concretewould slowly be subject to carbonization, so rob-bing it of its alkaline protection of steel reinforce-ment from rust. Also, concrete was vulnerable tochloridization. It was not the durable materialdesigners believed it to be.

New materials posed new problems. Besidesreinforced concrete, the behaviour and durability ofglass, aluminium, resins and plastics have to bestudied in order to provide effective conservation.In addition, modern buildings are dependant ontheir electrical and mechanical installations to pro-vide an internal environment, suitable to the occu-pants’ needs. These installations have a limited life,often about 20–25 years, so upgrading and renewalpresent problems. The conservation architect has tounderstand how a building works as a spatial struc-tural and environmental system.

Construction became more sophisticated, withlayers to first resist the weather, then to preventmoisture movement, then to give the wall enoughinsulation, and lastly a decorative finish. With eachlayer, faults in workmanship could materialize. (Thelate Bill Allen describes these problems in his bookThe Building Envelope.) In addition, the lightweightmodern buildings often could not deliver the en-vironmental conditions that the users needed.

Figure 22.2 The Penguin Pool, London Zoo, England, 1934(Photograph: John Allan, Avanti Architects, London)

Lubetkin & Tecton’s celebrated Grade I listed icon has beenrestored by Avanti Architects, using modern concrete repairtechniques

Figure 22.3 The Penguin Pool, London Zoo, England, 1934(Photograph: John Allan, Avanti Architects, London)

The original blue colour of the ramp undersides wasrediscovered and reinstated during the restoration project

Traditional buildings were generally over-designed, and indeterminate in their structuralactions, so if one system failed, another could takeits place, until the last option failed, and it col-lapsed. Modern buildings are scientificallydesigned, and often are structurally determinate,which means that if one member fails, the wholebuilding will collapse. This means that hiddenmembers have to be evaluated to ensure durability.The investigator has to be able to recognize all the various methods of construction used in thenineteenth and twentieth centuries, some of whichwere very ingenious.

Structural appraisal is a process which encom-passes the following: document research, inspec-tion, measurements, recording and structuralanalysis; sometimes it includes testing of materialsand occasionally load testing of entire structures isinvolved. Structural appraisal is a vital step in the

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Figure 22.4 Highpoint, Highgate, London, England, 1935(Photograph: John Allan, Avanti Architects, London)

The sustainability of this Grade I masterwork by Lubetkin &Tecton relies on conscientious maintenance and informedrepair. The integrity of its facade is dependent upon theuniformity of fenestration, making care in any windowreplacement of crucial importance

Figure 22.5 Highpoint, Highgate, London, England(Photograph: John Allan, Avanti Architects, London)

The intended aesthetic impact of the early modern style with itsgeometric purity, flat roofs, sheer planes and minimal trim wasespecially dependent on conscientious upkeep and perfectweather—both rare in Britain

Figure 22.6 The White House, Haslemere, Surrey,England, 1932(Photograph: John Allan, Avanti Architects, London)

This Grade II* listed house by Amyas Connell, architect,undergoing facade and window restoration by AvantiArchitects in the early 1990s

conservation of the building in question. PoulBeckmann’s book, The Structural Aspects ofBuilding Conservation (McGraw-Hill, 1995), dealswith every aspect. In addition, the Studies in theHistory of Civil Engineering (Ashgate Variorium,Vol. 8, ed. David Yeomans, The Development ofTimber as a Structural Material; Vol. 9, StructuralIron 1750–1850, ed. M Sutherland; Vol. 10, ed.Robert Thorne, Structural Iron and Steel 1850–1900)are authoritative sources.

The Institution of Structural Engineers has pro-duced an excellent report, the ‘Appraisal of ExistingStructures’, with a second edition in 1996. Thisdeals with procedure and components, and theprocess of appraisal, followed by testing and theuse and properties of the several materials likely tobe found in a modern building. The appendicesinclude ‘Sources of information on design, construc-tion and history’; ‘Health and safety considerations’;‘Test Techniques’; ‘Methods of monitoring struc-tures’. Types of defect in concrete and steel arelisted comprehensively in tabular form.

Carbon dioxide also affects concrete gradually, asit removes the alkali. In reinforced concrete, carbon-isation removes the alkali protection of the steelagainst corrosion. The action of carbonisation is slowand cumulative, but where carbon dioxides in theatmosphere are higher than normal, as in the PersianGulf, reinforcement with a minimum of 1–2 inch/13 mmcover will corrode in as little as 25 years.

Chlorides

Chlorides from sea spray, and the application of saltto roads in winter, cause corrosion in concrete.Reinforcement in concrete is vulnerable, but

corrosion can be prevented by cathodic protection,which depends on a continuous supply of low volt-age direct current electricity.

John Allan writes as follows:

‘Repairs to reinforced concrete depend onspecialist techniques, and it is advisable toconsult an experienced contractor.

The thorough removal of the products ofcorrosion from steel reinforcement is mostimportant in achieving a sound result. Damagedbars should be exposed beyond their corrodedlength, and at the rear, with portions beingreplaced where weakened beyond repair.Structural advice should be sought in cases of

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Figure 22.7 The White House, Haslemere, Surrey, England(Photograph: John Allan, Avanti Architects, London)

View of the completed concrete restoration, which involvedremoval of previous deleterious overpainting, replacement ofdamaged fabric, and application of anti-carbonation vapourpermeable fairing-coats

Figure 22.8 Concrete damage(Photograph: John Allan, Avanti Architects, London)

Typical instance of an incipient spall, where corrodedreinforcement in a slim section element has fractured theconcrete casing. Displaced and damaged fragments of concreteand rebar must now be removed back to sound material inorder to begin forming the repair

Figure 22.9 Concrete damage(Photograph: John Allan, Avanti Architects, London)

A damaged coping section showing break-out of defectivematerial prior to commencement of repair. This will requirereinstatement of lost reinforcement and local recasting inmatching formwork

replacement. Rusted reinforcement is bestcleaned by grit blasting. As soon as possibleafter cleaning, the prepared steel is primed intwo coats, using an epoxy coating or polymer-modified cementitious slurry—the second coatbeing applied while the first is still tacky—andincluding a quartz sand blinding, to optimisekeying of the ensuing repair.

The whole repair area should be dampenedto prevent premature setting, and a bondingbridge of slurry applied to enhance adhesion ofthe repair mortar, which should be placed inposition while the bonding is still wet. Thoroughcompaction is essential, and to achieve this, therepair mortar is best ‘punched’ home by hand,rather than being rendered over the area with aplasterer’s float. Further bonding bridges shouldbe applied between layers, if a number ofapplications is needed to complete the repair.

Having obtained an appropriate substrate, thefinal stage of the concrete repair process is toapply suitable anti-carbonation coatings (normallyin not less than three coats, but in any case, to aproscribed thickness in micrometers … if the areato be covered is likely to be subject to cracking, acoating with elastometric properties should beused. It is important to use coatings with resist-ance to freeze-thaw cycles and vapour-permeableproperties that allow any moisture within thefabric to migrate to the outside.

The unscientific use of non-permeablecoatings in the past has frequently led tomoisture becoming trapped behind the surface,and continuing to cause damage.

Cathodic protection

Cathodic protection is a well establishedtechnique, and could perhaps be regarded asthe traditional response to the problem ofchloride attack, and makes use of the

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Figure 22.10 Concrete damage(Photograph: John Allan, Avanti Architects, London)

Part of a damaged thin section canopy fascia, where spalledconcrete has been removed to expose rebars and establish therepair site. The bars must be brought back to bright metal andprimed for a bonding coat prior to packing replacement mortarand applying protective coatings

Figure 22.11 The Concrete House, The Ridgeway,Westbury-on-Trym, Bristol, England

Designed in the 1930s by Amyas Connell of Connell Ward andLucas. This is one of the least altered examples of thevanguard of modern design in Britain. The construction is areinforced concrete frame, infilled with concrete walls, finishedinternally with insulating board used as permanent shuttering

Figure 22.12 Vipuri Library(Architect: Alvar Aalto; Photo: Welin 1935 – Courtesy AlvarAalto Archives, Helsinki and Maija Kairamo)

The restoration strategy is to stabilize the building and preventfurther deterioration, to renew basic technical facilities, and torestore the original architecture. During this process, the buildingwill continue to be in active use. Theoretically, the restoration ofa modern building does not differ from the restoration of oldarchitectural monuments, but in practice, there are notable differences. The original building fabric plays a significant role,and in the case of the Vipuri Library, the extensive resources ofthe Alvar Aalto Foundation are consulted. These include theoriginal drawings, working descriptions and photographs fromthe 1930s

conductivity of reinforcement, to continuouslytransmit a small d.c. current through thestructure to prevent the steel reaching theelectric potential at which corrosion occurs.

Re-alkalisation

Re-alkalisation proceeds to the same endobjective as traditional repair – the restorationof an alkaline fabric – but employs a non-destructive method of achieving this for theareas of latent damage. Re-alkalisation cannotbe used for areas of latent damage, wherereinforcement corrosion and spalling damagehave already taken place. These must beidentified and repaired in the traditional way.For re-alkalisation, a series of battens is fixedtemporarily to the concrete, and a 50 mm steelmesh is attached over the surface, to provide amatrix for an alkaline poultice, which is createdby spraying a mixture of fibrous material,[usually shredded newsprint], and sodiumcarbonate, through twin hoses. Connections aremade at suitable points on the reinforcement,and to the external loom, and a low voltage d.c.current applied. With the reinforcement actingas a cathode, and the external net as an anode,the sodium carbonate solution is drawn into thepore structure of the concrete, by the process ofelectro-osmosis. The re-alkalisation technique isconcluded by removal of the poultice, cleaningdown and applying fairing and finishingcoatings.’

Alan Baxter writes:

‘After 1950, the nature of buildings and theirprocurement changed dramatically. Materialsoften have short lives and need replacement.Structural materials are highly stressed, anddecay becomes serious, unlike traditional mate-rials with much greater generosity and redun-dancy. Over optimistic innovation in design,and the use of (new) materials, led to somebuildings structures having even shorter lifespans than intended. The visible architecture isnot often accepting the patinaof age: glass, concrete, steel and plastic lookunhappy when decayed and some materialscannot be repaired. Age does not confer abeauty of its own—in fact, the reverse.’( Journal of Architectural Conservation, No. 2,July 2001, p. 28).

Baxter goes on to suggest that we should celebratethe ‘abstract intellectual achievement of modernbuildings, and not focus on the tangible steel andglass, concrete or plastic’, adding: ‘when materialsare in difficulty, if it is economic—replace them withbetter detailed materials, without any philosophicalqualms, but with good design and skill.’ This is anapproach that deserves serious consideration, but isstrictly refurbishment, dictated by economic values.

In the last quarter of the twentieth century, tensilestructures were developed with steel cables andplastic roofing. Their durability and longevity are notknown. Also structures clad with glass, having special qualities, have been developed. Replacementof broken elements may, in due course, present dif-ficulties, and destroy the aesthetic of the design.

From a purely economic point of view, a tradi-tional building may be worth conserving for its ‘usevalue’, if the cost is two thirds of building the samearea with modern technology. This two thirds is ade-quate if the walls and foundations are sound, andallows for renewal of roof coverings and services,and repairs to joinery and redecoration. This eco-nomic yardstick may not apply to modern buildingsif the attempt is made to replicate factory-produceditems that are obsolete, but a comparison with thecost of equal area of new building is useful.

So far, ICOMOS has produced no Charter specif-ically for modern buildings. It can, however, besaid that the principles in its Doctrine apply. Thesubject is, however, beyond the remit of the Societyfor the Preservation of Ancient Buildings, but is ofinterest to DOCOMOMO, whose EindhovenStatement reads as follows:

‘The architecture of the Modern Movement is asmuch at risk today as at any time since its

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Figure 22.13 De la Warr Pavilion, Bexhillon Sea, UK(Architect: Erich Mendelsohn; restoration by TroughtonMcAslan). © Peter Cook/VIEW(Photograph: John Allan, Avanti Architects, London)

creation, due to the innovative but often flawedconstruction technologies of the buildings, andchanges in the function for which they weredesigned. Preservation thus presents demandingphysical and economic problems.’

DOCOMOMO (documentation and conservation ofbuildings, sites and neighbourhoods of the ModernMovement), was founded to promote a greaterunderstanding of our cultural inheritance, and todocument and conserve the best examples of thisperiod. DOCOMOMO was launched in Eindhovenin 1989, and is now an international organization,with working parties in 40 countries, of which thatin the UK was among the first and most active. TheCharter of DOCOMOMO, which is based on theEindhoven Statement, which resolved to:

● Bring the significance of the Modern Movementto the attention of the public, local and nationalauthorities, the professions and educationalorganisations

● Identify and promote the recording of the build-ings of the Modern Movement, through drawings,photographs, archives and other documents

● Foster the development of appropriate techniquesand methods of conservation, and to disseminatethese throughout the professions

● Oppose the destruction and disfigurement of sig-nificant buildings

● Identify and attract funding for documentationand conservation

● Explore and develop knowledge of the ModernMovement

For a really great 20th century iconic building thathas a limited life because of poor materials, wemight consider rebuilding it in facsimile, but withbetter technology. This has difficulties, as exempli-fied by Mies van der Rohe’s Barcelona Pavilion, aspointed out by Maija Kairamo. Mies himselfaccepted the idea of reconstruction. The originalbuilding was planned as a transportable, loosething, a piece of art. The reconstruction was madeto last and many compromises were needed tomake it durable. The roof needed rain water drain-ing; heating, lighting, ventilation, security and alarm

systems, office space, storage etc. were needed.Although the new building is beautiful it is a trivialversion about what the bright, almost abstractexhibition object rather than a building once was.The brave effort and careful work was done by deSola-Morales, Cirici and Ramos and the result isbeautiful. But it is not authentic Mies’, it could becalled authentic nostalgia.

The Penguin Pool in London Zoo, designed byLubetkin in 1936(?) is slightly different. It was pro-foundly rebuilt and technical improvements weremade but the building has its original function andthe work was based on careful documentation ofthe original building. But still Allen himself hasdoubts about the matter.

John Allen writes:

Despite a certain intellectual appeal, this argument to exclude modern architecture fromthe tradition of conservation is not without itsown difficulties. For one thing, it does not reallyaddress the most common predicament confronting those actually involved with ailingmodern buildings, which is more often not asimple question of demolition and redevelopment, but how best to modify,improve and repair. Moreover, most of theadvocates of modern conservation can agreethat it should only be applied selectively, andthat even among those buildings for whichthere is a consensus for retention, there arelikely to be few so special, so valued for theirown sake, that they are able to ‘pay their ownway’, simply by being monuments—open to anadmiring public for admission charges.

Some iconic modern buildings have been restoredat considerable cost: Corbusier’s 1930 famous VillaSavoie at Poissy, and Goldfinger’s Willow Road,London home, have survived by changing their useto that of a museum.

As Baxter points out, it is the abstract intellectualachievement of outstanding modern buildings, whichshould be recognised, and this is best done by fullrecording and documentation with the immenselysophisticated recording systems now available.

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APPENDICES

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Introduction

Buildings, like people, are individuals—not in thesame way, of course, because the differencesbetween buildings are purely physical whateverwider meanings they may have for us. The dif-ferences are no less real for that, and they areparticularly important for historic buildings.Generalizations about particular ‘families’ can nevertake us very far, so I can only hint at a few possibi-lities in this review.

Like people also, buildings change and age withthe passage of time, and eventually die in the senseof ceasing to have any value to us. Structurally theaging process is a progressive narrowing of the rangeof resistances that can be mobilized to counter thedisruptive actions of gravity and the loads imposedby use and by wind, earthquake, etc. ‘Death’ may bedeemed to have occurred when the resistances areovercome in a complete or partial collapse or whenthe risk of this happening appears to be too great for further use of, or access to, the building.Interventions of various kinds can slow down theaging process and give new leases of life either to thestructure as built or by transforming it into somethingdifferent. But they can also accelerate the process;and this has, too frequently, been the result of pastinterventions made with insufficient understanding orwith too little regard for their possible effects.

In the broadest terms the resistances that can bemobilized depend primarily on two things—on thegeometry of the structure and on the characteristicstrengths and stiffnesses of the materials used. Themain loads to be resisted by most historic buildingsare their own dead weights and those imposed bywind and earthquake. These also depend on thegeometry and materials, although not in quite thesame ways, so that scale is important in the match-ing of load and resistance.

This dual dependence suggests that we mightattempt a first review in terms of either forms

(in the geometric sense) or materials. Forms are sovaried—even if we consider only those builtbefore, say, 1850—that the latter seems at first sightthe obvious choice, particularly since a material liketimber has such very different characteristics fromthose of brick, stone and concrete. In practice,however, there is an important secondary depend-ence of the resistances that we cannot ignore. Theydepend also on the manner, and even on thesequence, in which individual lengths of timber orblocks of stone are joined together. Since joints thatcould efficiently transmit tension were very rare, atimber structure differs much less from its stonecounterpart, for instance, than might otherwise be expected, and the difference tends to diminishwith age as joints become progressively looser.Superficially very similar masonry structures may,on the other hand, have markedly different capac-ities if one—say the triple arcade of the Pont duGard—is built throughout of closely fitted largeblocks of stone while the other—say the triplearcade of a Romanesque church—consists largelyof a poor rubble fill behind a thin ashlar skin.

In this review I shall therefore look at severallarge ‘families’ of historic buildings, characterizedprimarily by their uses of particular structural forms.In choosing these families I have concentrated onthe forms used to span between vertical supportsand enclosing walls, since it is these spanning elements of the total form that differ most and that,through determining what is required of the wallsand other supports, have the greatest influence onthe overall structural behaviour.

Beams and trusses

Until the introduction of the reinforced concretebeam (or, more questionably, that of the reinforcedplate-bande about a century earlier), beams werealways cut from single lengths of timber or blocks of

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Historic buildings as structuresRowland J. Mainstone D Eng, C Eng, MICE,FIStruct E, FSA, FRSA, Hon FRIBA

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stone with little or no understanding of the internalcomplexities of the bending and shearing actions towhich they would be subjected. What was import-ant, from the point of view of overall structuralbehaviour, was that they were considered as simplyweighing down vertically on their supports. Thiscould not be said of the simplest alternative adoptedwhere the span was a little too great for the avail-able timber or stone—that of a pair of rafters orblocks of stone inclined towards one another, whichconstituted a rudimentary arch. But it could be justas true of a similar pair of rafters whose feet wereadequately tied together, and of more complexforms of truss developed from this prototype.

In practice, there are requirements to be satisfiedat the supports to achieve this ideally simple trans-fer of load, and it probably never was achieveduntil these requirements were better understood.There is a need, in particular, for freedom of hori-zontal movement at one support. In the absence ofthis freedom some horizontal loading of the sup-ports is inevitable as a result of expansions andcontractions of the beam or truss and of its deflec-tions, even under purely vertical self-weight andimposed load. Especially in trusses, the deflectionswill often be found to have been considerable,even with ties of adequate strength in themselves,on account of stretching of the ties and movementsat their joints. In many more cases the whole designof timber ‘trusses’ was so poorly conceived andtheir joints were so inefficient for the transmissionof shear and the development of tensile strengths,that it would be much more correct to regard themas framed arches. The English hammerbeam ‘truss’should, for instance, always be regarded as a stiff-ened arch in its original form. Instances are alsofairly frequently found of stone beams or lintels thathave cracked vertically near mid-span and that aretherefore acting simply as three-pinned arches.

Restraint of horizontal movement at the endbearings of an unbroken beam or properly tiedtruss does, however, allow the beam or truss to actas a bracing element between its supports, and thisis a factor that should be taken into account on thecredit side in an overall structural assessment.

In any such assessment it is also necessary to con-sider the effects of non-vertical imposed loads. Windloads are the commonest example—both wind pres-sures and wind suctions, which are sometimes moreimportant. These are likely to act directly only onroof trusses but may be transmitted through beamsfrom wall to wall or from column to column. Inertialoads resulting from enforced displacements byearthquakes are fortunately a less common risk; butthey can, in some parts of the world, be a more seri-ous threat where roof construction is fairly massive.

The column-and-beam temple and related earlyforms

In the primitive hut, as envisaged by architecturaltheorists from Filarete to Laugier, lateral stability wasensured by driving the posts that carried the roofbeams into the ground or using as posts the trunksof trees already rooted in the ground. They couldthus act as vertical cantilevers fixed at ground level.

In monuments like Stonehenge, a somewhat simi-lar procedure was adopted. The great uprightstones were all sunk in pits dug in the ground. Butthey have depended for their continued stability(where they have not fallen) as much on their largebase dimensions, their weight, the good bearingcharacteristics of the chalk, and the absence ofmajor earth shocks, as on this partial burial. Theywould probably have stood just as well if they hadbeen set directly on a continuous horizontal base.Some of those that did fall may well have beenpushed over by a slowly developed thrusting actionof some of the lintels set in a continuous circle. AtLuxor there are two considerably taller colonnadescarrying massive stone lintels that have stood forthe same length of time without relying on anyrooting in the ground, and the unfinished Dorictemple at Segesta furnishes another example thathas stood for well over two millennia.

These structures were not, however, typical ofEgyptian and Greek temples and other buildings of these periods. Although all we now have of someof them are lengths of similarly free-standing colon-nade, these are only partial survivals or partialreconstructions of structures in which their lateralstability was originally ensured partly by continuouswalls to which they were braced by lintels and tim-ber roof beams. In the Egyptian temple and in mostother buildings, the principal walls were externaland columns were used internally to reduce thespans for the roof and any other beams. In theGreek temple, the walls of the cella were usuallycompletely surrounded by an outer colonnade, withfurther columns inside in the larger temples.Because of the usual massiveness of construction,additional lateral stability would have been calledfor chiefly in the event of earthquake, but wouldalso have been valuable if individual columnstended to tip over as a result of a poor foundation.The continuous wall is an excellent means of pro-viding this additional resistance to lateral loadbecause of its ability to carry directly a resultantinclined load in its own plane. Where collapseshave occurred and the fallen masonry has been leftas it fell, it is notable that it has usually fallen trans-versely to the line of the colonnade and a parallelwall. Adequate returns were not always provided

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and spaced sufficiently closely to prevent this trans-verse collapse, and it was made all the more likelyby a common practice of constructing the thickerwalls of two ashlar skins with a loose rubble core.

Later buildings with beam floors and beam or truss roofs

Beams or trusses, or both, are probably the majorspanning elements of most surviving historic build-ings of post-Roman date that are not merely rooflessshells. In addition, trussed roofs cover many masonryvaults. I shall leave for later consideration buildingsin which this is so and concentrate here on the sta-bility of multi-storey buildings and wide-span single-storey ones in which vaults, if adopted at all, areused in only minor roles. Typically walls, continuousexcept for window and door openings, provide themain vertical supports with columns, of much moreslender proportions than those considered hitherto,used chiefly to reduce internal spans. Such columnsare usually capable only of carrying vertical load, sothat lateral stability is wholly dependent on the walls.The rigid column-and-beam frame (with moment-resisting connections) was only developed slowlyfrom the 1840s onwards in cast and wrought iron.

The structural action is most clearly defined in thewide-span single-storey buildings, whether single- ormulti-bay. If the trusses are adequately tied and havenot spread, if they are adequately braced togethertransversely to their spans, and if they are carried(except where two trusses meet at the same level) bywalls capable of resisting any imposed side loads,stability should be ensured. The chief risk is of out-ward bowing and overturning of the walls if the tyingof the trusses is inadequate and the walls do nothave sufficient transverse strength to restrain themfrom spreading. Even with adequately tied trusses,there is a further risk in one particular type of build-ing—the aisled basilica in which the central row oftrusses is carried on clerestory walls which stand onopen colonnades below the aisle roofs. Such wallsare particularly prone to lateral bowing and eventualbuckling even under predominantly vertical load.This bowing can be seen in many places today andseems to have been particularly pronounced in theConstantinian Church of St Peter’s, Rome, before itsdemolition in the sixteenth century.

With one exception the action is much less clearlydefined in the multi-storey form. This usually hasnumerous walls running in at least two directionsand providing multiple possible paths for the down-ward transmission of all loads. Inherently it is a verystrong form, as is shown by our ability today to buildconsiderably taller buildings using brick bearing

walls of a thickness much less than was consideredsafe in the past. Older buildings may be just asstrong, or even stronger, if they are only subject tovertical and wind loads. Their strength may, however,be reduced (usually with a corresponding reductionin the number of paths available for transmitting theloads to the ground) and their stability made moremarginal in a number of ways. Inadequate founda-tions may lead to uneven bearing, differential settle-ments and other distortions. Poorly constructed wallsmay crack or bow under these circumstances or as aresult of repeated thermal movements, thrusting ofroofs, rotting of timber, or weakening by ill-consid-ered alterations. And there may be complete separa-tions between poorly bonded wall facings andeverything behind. Generalization is impossible here.Every building must be looked at individually. Wherethere is a risk of earthquakes, it is also likely that thewalls on which survival will principally depend areinadequately tied together. In addition, the massesand stiffnesses of the building may be distributedunevenly and unsymmetrically, so that it will tend,when shaken, to split into sections that will thenknock against one another.

The one exception referred to above is the build-ing with completely open or lightly partitionedfloors carried entirely by columns except along theexterior, where there is a continuous wall that isusually rectangular in plan. This was a commoneighteenth and nineteenth century form for ware-houses, mills and, later, for commercial buildings.Initially both columns and floor beams were all oftimber, with timber roofs also. From the end of theeighteenth century, cast-iron columns and then cast-iron and wrought-iron beams were progressivelysubstituted. Here again the structural action is clear.Vertical loads are transmitted fairly directly downboth the columns and the outer wall; all horizontalload is resisted by the walls on which lateral stabil-ity is wholly dependent. This high degree ofdependence on the outer walls, coupled often witha considerable interdependence of the lines of inter-nal framing between one wall and the opposite one,is the chief hazard to their stability. Where there isthis interdependence (meaning that each line offraming is only connected to, and thereby bracedby, the parallel outer walls through its connectionsto the other lines of framing) there is clearly a riskof a catastrophic internal collapse as a result of alocal failure. Such collapses are, indeed, on record.

Arches and barrel vaults

The most important characteristic of the arch is thatit does always thrust outwards on its supports as

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well as weighing down vertically on them. At leastit always does so in itself as part of its primaryaction, although the thrust can be contained by aneffective tie between its feet. In the absence of sucha tie, it is almost certain to spread to some extentunless its supports are being forced inwards bystronger opposing thrusts. In either case it will bedeformed and, since the deformation will affectboth its internal action and its action on its sup-ports, we must briefly consider the possibilities. Itis convenient for this purpose to consider a stonevoussoir arch with well-fitting voussoirs assembleddry, as was the usual Roman practice. With minordifferences other arches, even Roman concreteones, behave similarly—the general mass in theconcrete arch being divided into voussoir-shapedblocks by full bricks that penetrate, at intervals,right through its thickness.

All loads acting on the arch are carried sideways,as well as downwards, by means of inclined thrustspassing through the voussoirs and from voussoir tovoussoir. If the voussoirs fitted perfectly, were infin-itely hard and were unable to slip on one another,it would be possible for the line of the resultantthrusts to pass anywhere within the depth of thearch at any point. Even the smallest inward or out-ward movement of the supports would then beaccommodated by small hinging rotations at threejoints or groups of joints, and the resultant thrustline would have to pass through the three ‘hinges’.For a small inward movement the hinges would bealternately on the extrados, intrados and extrados.For a small outward movement they would be al-ternately on the intrados, extrados and intrados.The thrust lines would be, respectively, as flat andas steep as the depth of the arch allowed. It followsthat, for a given vertical load, the horizontal thrustat the supports would be a maximum in the firstcase and a minimum in the second case. This isexactly as it should be to minimize the risk of col-lapse: from this point of view the arch is an idealstructural form which deforms in such a way as toimprove its stability. The extent of the improvementdepends on its depth in relation to its rise, beinggreater the deeper and flatter in profile the arch is.Here, however, all is not for the best because a flatarch will thrust outwards most, other things beingequal, and will therefore be more likely to push itssupport aside.

In practice such ideal voussoirs do not exist.Where the ideal is almost achieved, as again insome Roman arches, a close approach of the thrustline to extrados or intrados of a large arch results insuch high local stresses that local crushing or split-ting of the stone occurs. This tends to precipitate alocal slip, which reduces the effective depth of the

arch. In practice also, an arch nearly always hasspandrel masonry above it, and it is usually part of alarger structure. Loads from above have to be trans-mitted through the spandrels. Because these havesome stiffness of their own they will press downmore heavily anywhere the arch tends to rise andless heavily anywhere it tends to fall. They willthereby stiffen it, or add to its effective depth. Wherethe arch is also part of a larger structure—spanningan opening in a continuous wall for instance—it mayhave to accommodate itself to movements of its sup-ports induced from outside as well as to the loadsacting directly on it. This it will usually do by a com-bination of hinging rotations and slips.

The fact that slips as well as hinging rotations do,in fact, occur is both an analytical embarrassmentand a factor of some importance in long-termbehaviour. Analytically it means that no simplethrust-line analysis can give a clear indication of themargin of safety against collapse. In the long term itis important because slips, unlike hinging rotations,are irreversible (although even hinging rotationsmay be partly irreversible as a result of the partialjamming of open joints by debris). Spreading ofarches as a result, for instance, of seasonal tempera-ture changes tends, therefore, to be cumulative.

Barrel vaults, being merely arches extended lat-erally, behave in much the same way as arches ofthe same depth and profile. They have, however,the further capacity to distribute loads laterally. Thismeans that they are likely to deform less and to besomewhat stronger when subjected to very localloads, because these will be distributed sideways tosome extent instead of passing, in their entirety,directly to the supports. It also means that they canact in much the same way as walls in resisting sideloads that act along their lengths.

Cast-iron arches almost constitute a separate familyof forms. They often seem to have been designedwith no clear understanding of their mode ofaction, with the result that they range all the wayfrom close counterparts of the masonry voussoirarch to three-pinned arches and beams or pairedcantilevers with arched soffits. Even when they doact as arches, they will usually thrust sideways lessthan masonry arches of similar spans on account oftheir reduced weights.

Timber arches usually have some bending stiffness, obtained by lapping the joints betweenindividual lengths of timber. They can thus deformfurther without collapse in accommodating them-selves to imposed loads and support movements.To prevent excessive deformation they were usually braced in some manner, and this bracingstiffens them in much the same way as the span-drels stiffen a masonry arch ring.

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Buildings with arcaded walls, vaulted floors, and arch-supported or barrel-vaulted roofs

Arches have been used in place of beams or trussesin most of the types of building referred to above,except the last. Requirements for lateral stability aregenerally similar with this substitution, apart from anincreased requirement for bracing or buttressingwhere the feet of the arches are not adequately tiedor their outward thrusts are not mutually opposed, asin continuous straight arcades. The requirementshave also been met in broadly similar ways,although, in compensation for its thrusting, an archspanning transversely to a wall to carry a roof canassist in bracing the wall if its spandrels are filled.Beams and trusses normally provide no such bracing.

Where barrel vaults have been used in place ofbeams to carry floors, the extra weight calls for moresubstantial walls, and these are usually well able toresist any unbalanced thrusts developed by thevaults. It is, in any case, unusual to find heavy bar-rel vaults so used in the upper storeys of buildingsof post-Roman date. Light tile vaults were used herein the eighteenth and nineteenth centuries, withsome care taken over their alignments to minimizethe unbalanced thrusts at the ends of the building.

Roman arched and vaulted buildings and theirderivatives (setting aside for the moment those withdomes or large groin-vaulted roofs) are a furthertype. They are characterized by the use of botharches and barrel vaults on a large scale as the prin-cipal elements of construction, including the use ofthe latter for roofing wide spaces. So used, theyinevitably developed large outward thrusts. To alarge extent these thrusts seem to have been delib-erately countered in the finished buildings byopposing arch to arch or vault to vault including, inthe case of principal longitudinal vaults, the use ofquadrant vaults alongside at a lower level or theuse, again at a lower level, of ranges of barrel vaultsaligned at right angles. The need to ensure stabilityof the incomplete building during construction usu-ally called, nevertheless, for supporting piers andwalls substantial enough to resist many of thethrusts at nearer their full magnitude. To this, andto the excellent quality of most Roman masonryand concrete, we owe the ability of many Romanruins to remain standing in a mutilated state.Examples of impending further collapse may alsobe observed—for instance at the north-east end ofthe break in the upper tiers of the outer arcade ofthe Flavian Amphitheatre (the Colosseum) in Rome,where major voussoir slips and arch distortionshave occurred.

Much post-Roman masonry is less sound, including particularly much of that found in

West-European Romanesque and Gothic churches.In addition, the testing of the structure in its inher-ently weaker incomplete state during constructiondid not extend to its ability—and certainly not to itslong-term ability—to contain safely the outwardthrusts of the high central vault or vaults. Masonrythicknesses were usually so generous that largevault distortions and associated tilts of their supportscould have been accommodated with the resultantthrusts still well within the thickness, if the masonryhad been of uniform strength and stiffness. But withwalls in which the core is a largely useless rubblefill, the resultant thrusts move much more rapidly topositions dangerously close to the outer faces. It isessential therefore to take into account the natureand present condition of the masonry in appraisingthe stability of such buildings.

The dome and associated transition elements

Potentially the doubly curved domical form is, from the point of view of strength and stability,ideal. The outward thrusts developed in its upperpart can be wholly contained by circumferentialtensions lower down, so that it exerts a purely vertical load on its supports. Its double curvaturealso fits it well to resist side loads from wind orearthquake.

What was achieved, again fell short of the ideal.A few small concrete or flattish monolithic stonedomes may have had sufficient tensile strength tohave contained the thrusts, if they had been free ofhorizontal restraints at their supports. But even thesingle domical slab that roofs the Mausoleum ofTheodoric at Ravenna is cracked in two, probablyby restraints to its thermal expansion and contrac-tion. The masonry or concrete dome in general cer-tainly lacks both the necessary tensile strength andthe necessary freedom of movement at its base.

The typical dome therefore acts, in its lower part,as a ring of incomplete arches. These incompletearches meet in a crown of continuous masonryunder both circumferential and radial compression,this crown often being open in the centre where itmay be covered by a lantern. Such arches need tobe considerably thicker than an ideal dome of thesame diameter if their stability is to be assured, butmore than ample thickness was always provided.Like any other arches they thrust outwards at theirfeet and this thrust must be similarly resisted by thesupports or contained by separate ties. Many brickdomes have been provided with circumferential tiesof timber or iron, but it is unlikely that any of themresist more than a part of the total thrust.

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From the present point of view the octagonalpavilion vault is no different from a circular dome.The most notable—that over the crossing of theCathedral of S. Maria del Fiore in Florence—wasdeliberately given a thickness sufficient to contain acircular form within and was constructed as if it wasa circular dome.

Where the circular form was adopted and thesupports were square or polygonal in plan, transi-tion elements had to be used. These have beengiven many forms, at least on the surface. All can beanalysed into either pendentives or squinches, butmost of the multiple-squinch forms are closer topendentives in their overall surface geometry andalmost certainly act as pendentives since they con-tain the pendentive form within their thicknesses.All forms (except for the uncommon merging pendentive) involve some change in direction of the resultant downward and outward thrusts fromthe dome at the level of its base. The pendentiveinvolves the least change, since the resultant thrustsremain radial or nearly so. But, taking into accountagain the thickness of the masonry, the differencesare unlikely to be of much importance in terms ofthe overall structural behaviour. All forms will addsomething to the total outward thrusts to be resisted.

A related form that calls for at least brief mentionis the semi-dome. In the complete dome, there is alarge resultant horizontal thrust acting in eachdirection across any notional vertical plane throughthe centre. If therefore the dome is actually cut onsuch a plane, it is potentially an excellent buttress.If there is nothing for it to buttress, as when it wasused in the apse of a timber-roofed basilicanchurch, its crown moves forward until an internalbalance of thrusts is achieved with its forward edgeacting as an arch spanning across the diameter inthe horizontal sense.

Domed buildings

The complete family of domed buildings includes aprimitive form of even remoter ancestry (in allprobability) than the column-and-beam temple.This is the widespread beehive hut which some-times achieved monumental proportions, as in several Mycenean tombs. The fact that the morepermanent stone huts and tomb chambers wereconstructed by laying each ring of stone on a flatbed projecting slightly forward from the previousring, did not eliminate the radial thrusts. These areresisted in the smaller huts by the ground fromwhich they directly rise or by a very thick wall atthe base, and additionally in the large tomb cham-bers by the earth piled against them on the outside.

In most later domed buildings, where the dome israised high above the ground, the thrusts are resistedprimarily or wholly by the buttressing action of thesupports. In the simplest form, typified by the RomanPantheon, the dome rises directly from a circular orpolygonal base, with or without transition elementsin the latter case. Usually this base is opened out intoa number of arched recesses around the circumfer-ence and, since the arches are not in line, their out-ward thrusts add something to the total that has to beresisted. But the overall thickness of the base, plusthat of any projections of the arched recesses beyondit, has clearly been sufficient in surviving structuresof this type to provide the necessary buttressing.

In the more complex forms the dome is still car-ried by arches spanning between four or more piers.But these are now much more deeply opened out,either into a single wider space as in the Church ofSt Sophia in Istanbul and the Ottoman Imperialmosques, or into the nave, transepts and choir ofmany domed western churches. In the former exam-ples, the semi-dome is used on the same scale as thecentral dome itself as a major buttressing element. Inthe Church of St Sophia, where it was first so used,it clearly demonstrated its superiority in this role overthe more conventional arched buttresses used on thenorth and south sides of the church. In the latterexamples, buttressing is provided by arcades extend-ing in two directions from each pier and usually ofsubstantial Roman proportions, although frequentlyof less than Roman solidity and strength. There is lit-tle reason to doubt the adequacy of this buttressing.Where the central dome has shown serious sign ofdistress, as at St Peter’s in the mid-eighteenth cen-tury, this has been primarily the result of interposinga tall drum between it and its more substantial base.

Only in the late-eighteenth century ParisPantheon was the final step taken of supporting alarge tall dome on slender piers sufficient only tocarry its vertical load, and relying on a combinationof circumferential iron ties and masonry struts arch-ing over to outer piers and walls to resist the out-ward thrusts. This gave again a structure with afairly simple and determinate overall pattern ofaction but one which, for this very reason, calledfor sound construction throughout. The fact that themasonry of the central piers was so constructed thatit had an effective strength far below that of thestone from which it was built, necessitated almostimmediate strengthening of these piers.

Groined and ribbed vaults

The chief structural difference between groined andribbed vaults and either barrel vaults or domes is

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that they bring all loads to a few widely separatedpoints rather than to continuous boundaries. Thelarger vaults were usually built over rectangularbays and bring all their loads down to the cornersof the bays, where they thrust diagonally outwards.They were also usually built in series. This meansthat in the finished structure (but probably not dur-ing construction) the components of the thrustsresolved along two sides of the rectangle are can-celled out by equal thrusts in adjacent bays exceptat the two ends of the series. The remaining out-ward components for the whole series of vaults willonly be roughly half the total outward thrusts of acontinuous barrel vault of the same span and riseand weight. Since ribbed vaults could be madesomewhat lighter in relation to their span and rise, there is usually also a further reduction in out-ward thrust plus a reduction in vertical load on the supports thanks to the exploitation of this possibility.

Much has been written about the extent to whichthe ribs in a ribbed vault do, or do not, carry thewebs. All that can be said with confidence is thatthe geometric configuration would always allowthe webs to stand on their own as groined vaults,but that the ribs will certainly stiffen them and willprobably, to a large extent, carry them where theribs were built first, where the webs are markedlyarched up between them, where the masonry of thewebs is more compressible and, of course, wherethere is no continuity of the webs above the ribs.The more complex surface form, as compared withother kinds of vault, means that spreading of thevault is accompanied by more complex patterns ofdeformation. But, from the point of view of overallstructural behaviour, it is sufficient to concentrateon the ribs. These deform by a combination ofhinging rotations and slips in much the same wayas freestanding arches with heavy spandrel fillsonly towards their feet (where the space betweenthe converging ribs was usually filled solid).

Gothic churches

Groined and ribbed vaults have been used in manyways in historic buildings, but there have been onlytwo applications of major structural interest. TheRomans used large and very heavy concretegroined vaults, sometimes with integrally embed-ded ‘ribs’ of brick, to roof a variety of large hallsfrom the early second century onwards. Even in thegreat halls of the Imperial baths and in the BasilicaNova the resulting structures did not, however, differ sufficiently from those discussed already tojustify further discussion in this brief review. I shall

concentrate here on the second application—that inGothic churches and cathedrals.

Gothic builders exploited fully the concentrationof all load from the vaults at a few points. Exceptin some southern churches, the vaults were onlyfireproof ceilings beneath trussed timber roofs. Butthe principal roof trusses were placed so that theirloads were brought down to the same points, andisolated piers were built up to them to carry thevertical components of the combined loads. Sideloads, both vault thrusts and wind loads, were thencarried over to outer piers by inclined masonrystruts—the flying buttresses that served as a modelfor similar struts in the Paris Pantheon.

The result was a highly lineal structural form withan unusually clear balance of thrust and counter-thrust throughout. At least this balance is qualita-tively clear. Quantitatively it is less clear, becausethere are numerous points at which the loads canbifurcate and because the forms are not truly linear.The principal piers, in particular, were given suffi-cient breadth to accommodate resultant thrustsalong many different paths. Herein lay the principalmargin of safety against collapse, and herein it stilllies unless deformations of the structure and differ-ential consolidations of cores and facings of thepiers have narrowed the possibilities too far. Wherecollapses have occurred they have probably beendue to excessive eccentricities of resultant thrustsleading to buckling with or without local splittingor spalling of the stone, or to local slips.

Margins of safety

There have been enough recorded collapses ofstructures that have previously stood for a long timeto show that margins of safety can diminish withtime, and not only as a result of ill-considered addi-tions or alterations to the structure. Weathering ofmasonry, rotting of timber, and other similar sortsof deterioration, are one reason, especially todaywith high atmospheric pollution. Another reason isthe progressive increase of deformations to a pointwhere equilibrium is no longer possible or localstresses are too high at critical points and lead tolocal splitting and bursting or spalling of masonryor other failures. Deterioration of materials and/ordeliberate cutting can contribute to this increase byreducing stiffnesses, and it can lower the safe lev-els of stress. Much of the increase occurs throughthe accumulation of small irreversible slips andopenings of cracks, and through differential foun-dation movements. The former accumulation islikely to take place at an increasing rate as morecracks form. Differential foundation settlements due

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to consolidation of the ground should, on the otherhand, diminish with time unless the settlements sig-nificantly change the distribution of pressures (as inthe case of a leaning tower) or the ground condi-tions change (perhaps as a result of adjacent worksor a fall in the water table). Normally they shouldhave reached their final values well within the first100 years of the life of a building. Further differen-tial settlements may, however, occur at any time asa result of such things as the rotting of piles or bod-ily ground movements.

It follows that the fact that an historic building isstanding today, although irrefutable evidence of itspresent stability, is no guarantee that it will still bestanding tomorrow, and that no analysis thatmerely assures us of its present stability is of anypractical value. The most difficult task for the struc-tural conservationist is to look into the future. Hecan safely assert that, if it is left alone, the buildingwill one day collapse. But when? The structuraldesigner is accustomed to considering time explic-itly only in certain special circumstances, notablywhen there is a possibility of fatigue failure undercyclic loading. Here we are faced with a situationthat has something in common with low-cyclefatigue, but with many complications.

Possibly the best that can be done is to start byascertaining as fully as possible how the building isat present carrying its loads, how it has beendeformed by them, and how the deformations arechanging. The present deformations are doubly rel-evant to the manner in which the loads are beingcarried; first because it is the deformed structurethat is doing the carrying, and secondly becausethey are often clues to the sequence of constructionwhich is itself very relevant. Also relevant are thedetails of construction, particularly the nature andcondition of masonry or brickwork throughout itsthickness and the nature and condition of joints intimber trusses and frames. Only when all of thesehave been taken into account can useful quantita-tive analyses be made. To ignore them is to tieone’s hands needlessly behind one’s back and riskproducing impeccable but useless analyses of struc-tures that might have been, rather than the one thatis. Realistic analyses should help to identify anypotentially dangerous deformations (includingcracks and slips). Observations of changes in thesedeformations should continue over a sufficientperiod to allow cyclic changes to be differentiatedfrom long-term ones.

Having made his observations and analyses, theengineer should be as well informed as he canhope to be about the structural health of the build-ing. But, except in cases of serious distress and nearcollapse, he will still usually be forced to make his

own judgement about its likely future safety andthe need, if any, for his intervention with remedialworks.

Possible structural interventions

The correct decision (from the point of view ofmaking the best use of available resources) maywell be to leave alone for the present, apart fromcarrying out normal maintenance to keep out rainor frost. But this is a difficult decision to take whenthere is any element of doubt, and it is importantthen that any works undertaken do really increasesafety and the expectation of life.

Structural interventions have been made in thepast for a variety of reasons, and not always withdesirable results. Among the most regrettable havebeen a number of later additions of tall towers andspires to the crossings of Gothic cathedrals, whichhave subsequently resulted in major collapses. Theoutstanding example of this was at Beauvais in thesixteenth century. Many buildings have also beenstructurally weakened by being cut into to providemore light or space, to open a new entrance, toaccommodate new furniture, or for some other sim-ilarly non-structural reason. Others, like St Irene inIstanbul, have had columns removed for re-useelsewhere. In this case smaller columns were sub-stituted without apparent damage to the structure.More surprisingly, the entire nave arcades of S. Apollinare Nuovo in Ravenna were lifted, with-out apparent damage to the clerestory walls, whenthe floor was raised on account of a rise in theground level outside.

If we consider only past interventions that havehad a primarily structural motive, they can bedivided into additions of props, ties or infills; recti-fications of leaning walls or columns; consolidationof masonry, partial renewal of facings and patchingof decayed timber; and more extensive renewals orrebuildings including partial reconstructions afterlocal collapses. If this list is read as referring only towork above ground, we should add to it consoli-dation of foundations and underpinning works.Few major historic buildings can have escaped anysuch attention, and many have achieved their pres-ent form only as a result of the later addition of but-tresses or ties or as a result of partial rebuilding.This is particularly true of buildings which wereinnovatory in form or scale, either in an absolutesense or in terms of the experience of theirbuilders. The church of St Sophia in Istanbul is pos-sibly the outstanding example, but many largeRomanesque and Gothic buildings are good exam-ples also. Wherever it is true, it is a factor that must

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be taken into account when assessing the signifi-cance of present apparent deformations.

Can we learn anything further from these pastinterventions? I think that we can draw a few gen-eral conclusions, although undoubtedly we couldlearn more if we were better informed, particularlyabout the less successful interventions. One lesson,relevant to buildings in continued use, is that visi-ble additions or modifications are not necessarilyaesthetically detrimental. It is partly due to the addi-tion of flying buttresses to structures that initiallylacked them that we owe the definitive form of theGothic cathedral. It is also partly due to a series ofadditions and modifications and a partial recon-struction to a slightly different design that we owethe unique spatial qualities of St Sophia. A morepractical lesson that is relevant to all buildings isthat props and ties will not restrain further move-ments as effectively as they might, unless steps aretaken to transfer load to them without prior furtherdeformation. Inserted ties were usually fitted withwedge-shaped keys or turnbuckles for this pur-pose. But buttresses were often simply built againstthe wall they were intended to prop. They couldthen do more harm than good, if they were effec-tively bonded to it, by themselves tilting as theground beneath consolidated, and thereby pullingthe wall further over. In a somewhat similar way,the simple selective replacement of cracked orspalled facings in a wall could merely lead to thecracking or crushing of other blocks, because allload was initially thrown on these other blocks. Afurther lesson is that the execution of remedialworks that involve any cutting away of the existingstructure is, in itself, hazardous. A striking demon-stration of this hazard was the collapse of the maineastern arch and part of the original dome of St Sophia, not during the earthquakes of A.D. 556and 557 that both damaged it, but in May 558 whilerepairs were in progress.

The most desirable action in any particular casetoday must always be a matter for individual deci-sion and will probably differ according to whetherthe building is to be preserved only as an historicmonument or to be given a further lease of life inactive use. In the former case, the minimum inter-ference with the ‘original’ or ‘definitive’ form seemshighly desirable. In the latter case, additions ormodifications may be justifiable.

Given, as the primary objective, the assurance ofthe continued existence of the structure for a further period, I should look first (after taking stepsto remove any obvious causes of excessive weather-ing, rot, etc.) for means of limiting further increasesin deformation that did not involve any major struc-tural changes. These might include internal consol-idation of inhomogeneous and therefore weakmasonry; repairs to weak members and joints oftimber trusses; and the limited introduction of newties. In consolidating weak masonry cores, it wouldbe important to ensure the bonding of the core tothe facing and to bear in mind the effects ofchanges in relative stiffnesses if the consolidationwas done selectively. Both in repairing joints in tim-ber and in introducing new ties it would be import-ant to bear in mind that some cyclic movementsare inevitable as a response to changes in temper-ature and humidity and that, unless the building isturned into the equivalent of a pre-stressed mono-lith, some cracks and other similar freedoms arenecessary in the absence of deliberately formedexpansion joints. This, of course, is also relevant tothe treatment of cracks generally. Externally theyare undesirable because they provide an entry forwater. But filling should preferably be with some-thing of low elastic modulus because, otherwise, itwill accelerate the process whereby cyclic move-ments gradually add to permanent deformations. Ishould undertake the rectification of leaning wallsor columns, partial reconstructions and any othermajor interferences with the existing form only as alast resort, because I think that they destroy part ofthe historic value of the building. There are cer-tainly cases, however, where there would be mer-its, both to reveal what is of chief historic value andto relieve the structure of unnecessary and undesir-able weight or mass, in removing later accretions tothe original form. Reducing the mass near the topof the building might even be desirable at somesacrifice of the original structure where there is aserious risk of earthquake.

This is really tantamount to a personal plea forrespecting the structural as well as the architecturaland historical integrity of the building, and there-fore for getting to know it as fully as possiblebefore presuming to do anything to it. This know-ledge can only be gained in the first place by making a meticulous visual inspection.

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Principles

The conservation architect will find himself facedwith many practical problems relating to security.

As with fire, security poses difficult problems forthe designer. Blind application of the building regu-lations produces aesthetic disasters so the reason-ing behind the regulations has to be understoodand trade-offs made in order to find reasonablecompromises. Much therefore depends on the qual-ity of the fire service and the architect or surveyor.The fire audit procedure should prove useful. Withsecurity one is dealing with a wide range of impon-derables and there are no regulations. It is all a mat-ter of judgement for the owner or administrator ofthe building. Very little has been written on the subject—possibly for security reasons—yet, it isone of which the historic architect must be aware.This Appendix has been added in order to dealwith the subject more fully than in the first edition.

Standards for fire prevention and means ofescape are continually being raised, so that securityis becoming more and more difficult to maintain to the standards required by insurance companies,and conflicts which have to be resolved by thedesigner are becoming more noticeable.

Security is concerned with the prevention ofcrime, particularly the theft of valuables in thebuilding and prevention of damage to the fabric ofthe building. There can be conflict between thedesired requirements of ‘means of escape’ for the public and security precautions for valuables—one interest requiring the door to be open and theother shut and securely locked. So it is necessary totreat each case on its merits. First, all possible risksmust be identified and the following factors relatingto site, construction and equipment should bereviewed.

The site

(1) Climatic hazards such as wind, flood and earth-quake.

(2) The environment, pollution, noise, the flightpattern of a nearby airport, military over-flying,sonic bangs.

(3) Access for foot traffic, motor vehicles and theirparking locations. Is off street parking available?

(4) Layout, both internal and external. Utilizationof spaces, reception areas, visitor control. Notetoilet areas are vulnerable. Planning to reduceunnecessary movement and access by carefulassignment. Security should increase withdepth of access, but escape routes and doorscreate problems.

(5) Political situation. Incidence of street crime,civil and religious unrest, terrorism, arson.

Construction

Roof structures, walls, partitions, ceilings, floors,doors and locks, ducts, windows and ledges atground floor and first floor levels where bombsmight be placed should be studied. Glazing can betoughened and made bullet resisting. Are curtainscapable of stopping flying broken glass? Externalshutters are useful to protect windows against civilunrest and storms.

Equipment Consider the use of car park barriers,locks and grilles. Review the benefits of combinedfire alarm and security systems with computer con-trol to monitor internal movement patterns and thework of security guards, and review the alarms forfire, plant malfunctions, lift breakdowns, and panicalarms for occupants.

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In principle there are three types of lock security:

(1) To prevent people entering the building.(2) To prevent the wrong people entering a room

or space.(3) To protect valuables stored inside furniture.

All valuables should be protected by physicalbarriers of one type or another including bulletresistant glass.

To overcome the conflict between security andfirefighting, one master key for all doors is ideal,but this is easier said than done.

Keys issued by a supervisor must be signed for—however exalted the recipient. Every so often (sayat five year intervals) it is desirable that the locks bechanged so as to eliminate the number of ‘illegal’keys which come into use in the course of time.The mechanism of the locks should be capable ofseveral arrangements to enable these renewals tobe done easily and at low cost. This renewal ismuch easier with electronic coded locks.

Detection systems

The wide range of detection systems available forprotection against theft and damage, can be dividedinto three main groups: (see also Table 1)

(1) localized point detection applied to objects(a) fixed to a wall(b) free standing(c) contained in a showcase

(2) perimeter detection(3) volumetric detection.

An electronic alarm system consists of four elements; a detector, a control box, an alarm sig-naller, and the wires joining them all together. Thesystem is like a chain, it is only as strong as itsweakest link; therefore it must be protected againstintentional neutralization by cutting of wires,against mechanical or electrical destruction, againstmasking or changing the alignment or position ofthe detector, against involuntary neutralization suchas by power failure or breakdown.

Good detectors and detector monitoring systemsinclude electronic protection measures to sense anytampering with the detectors, such as cutting ofpower supply and/or signal lines, and which willalso sense mains power failures. Since the technol-ogy is readily available and the risk of tamperingreal, such safeguards should be specified as a mat-ter of course. If an alarm system is monitored by acentral station it should signal automatically when a

disaster occurs or if it is intentionally or accidentallydisconnected or disabled.

Protection systems are generally designed to givedaytime protection based on localized and linearsystems, supported at night by volumetric detec-tion. Window and door bars give greater protectionif they are wired to anti-tampering devices. Morethan one complementary system gives greater security against premeditated theft. Control boxesshould have a reserve supply of electricity in caseof power failure. Alarms can be sirens, flashinglights, closing of doors automatically, tapedannouncements, and telephone links to the policestation via a central station using either the publictelephone network or dedicated lines. The mal-function of a sophisticated alarm system can occurat least ten times for one real alarm. Because of thenuisance that these alarms cause, there is a dangerthat indolent staff may switch them off.

Security personnel

The difficulties of an old nightwatchman dealingwith intruders should not be minimized. At night, inaddition to electronic alarms, the building shouldbe patrolled by a trained able-bodied person.Uniforms confer some additional authority. Themulti-toned internal communication system (bleep)while not being as good as a two-way radio, is ahelp for internal security when combined with theefficient internal telephone system which may alsobe linked by direct line to the police station.

One of the easiest ways for an intruder to gainaccess is via builder’s ladders and scaffolding. So,ladders should be removed and locked at night and scaffolding made unattractive by liberal use ofbarbed wire and sticky paint or grease on the lowerparts. Permanent illumination is also another aid tosecurity as any night time intruder would benoticed or anyway run that risk.

The public, who visit historic buildings in everincreasing numbers, produce a range of problemsbecause of carelessness and in particular, illicitsmoking and even deliberate arson. Vandalism iscommon, including name cutting, removing smallobjects, throwing things from galleries and roofparapets and breaking windows. Rowdyism andaggressive and uncontrollable behaviour arebecoming more frequent, particularly with gangs ofyouths from any distant part. There are problemswith unfortunate down-and-outs, methylated spiritsdrinkers, and would-be or actual suicides; alsobomb scares may involve a thorough check of pub-lic parts of the building by police and staff. Goodinternal security reduces these problems.

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Table 1 Types of Theft Detection System

Type of detector False alarms Remarks

LOCALIZED POINT DETECTORS:Mechanical contact No Local range of alarm. Cheap installation easyMagnetic contact No Can be used on doors, windows, etc. A small piece of detector

must be fixed to the object and this may cause difficulties. Easy toinstall.

Capacitive system Yes Prevents cutting of paintings or tapestries and can deter vandalismif the alarm is sufficiently frightening. Easy to install.

Contact mat No Inexpensive. Good for keeping visitors at a distance without usingtraditional barriers. Useful for protecting works consisting ofseveral pieces. Good ‘trap’ protection if placed in passages wherethieves might walk, but also easily avoided if location is known orsuspected. Easy to install.

Variable pressure wire Invisible when wires are placed directly behind or under theobject.

Radio alarm Can be used with any of the above detectors and avoids the use ofvulnerable wires, but the battery must be charged regularly.

Vibration sensor Yes Detects attempts to break glass and, as sensitivity can be regulated,can be used to protect walls, ceilings and doors. If too sensitivecauses false alarms. Subject to corrosion.

Glass cutting sensor Few More expensive than the vibration sensor. The sensor is glued tothe glass.

PERIMETER DETECTORS:Photoelectric cell Few Inexpensive. The light source may overheat and blow out thus

setting off a false alarm. Can be bypassed using a torch or cigarettelighter. A mirror system makes the beam zigzag and can make itmore difficult to pass.

Laser barrier invisible No Based on laser diodes, a low cost technology. The detector cannotpulsed emission be bypassed by supplying another emission source.

Passive infra-red detection, Few Reliable. Not sensitive to atmospheric disturbance or radio waves.sensitive to rapid changes Screens an area 14 m (46 ft) in front of a work but does not detectin temperature gradual movement. Can be bypassed by using an insulating cloth

as a screen. Also effective for volumetric protection as they areinexpensive in this category.

VOLUMETRIC DETECTORS:Ultrasonic detector Some Movement in the detector’s field of action causes variations in the

frequency transmitted and that received. Does not affect materialsand can be used in showcases. Solid proven construction. Rangelimited to 12–15 m (40–50 ft) because false alarms increase as therange becomes greater. Lightning, bells, supersonic booms, aircurrents and ventilation can lead to false alarms. Low frequency,16–40 kHz.

Microwave detector Few Works at high frequencies, 1–10 GHz, and is therefore notdisturbed by lower frequencies. The detection zone can extendto 100 m (328 ft) and can be regulated exactly. High sensitivity canbe obtained without risk of false alarms, even by insects.Microwaves penetrate wood, glass and other building materials,so location of the apparatus must be chosen carefully.

PERIMETER PROTECTION Line sensing to surround a building or single exhibit, using fibreoptic pressure sensing cables or metal wire fencing that can detectvibrations. Many systems available.

CLOSED CIRCUIT TELEVISION Cameras covering vulnerable areas relaying back to monitors inthe security guard office. Intrusion at night can be detected byinfra-red illumination.

The advantages of having able-bodied men todeal with uncontrolled behaviour are considerable.The entrance to a building should be supervised bya uniformed man at all times, for by firm and politeaction they can often prevent rowdyism. Thefts ofvaluables or souvenirs cause a great nuisance, theonly antidote being constant supervision; however,pairs of experienced thieves can, by workingtogether, put supervisors off their guard. One his-toric house has equipped its host guides withwhistles to blow the alarm and alert companions toclose external exits.

The risk of theft by bogus workmen is consider-able, this can be reduced by a system of recordingand checking credentials. In historic buildings,workmen generally have to be supervised continu-ously and this can be a severe problem for the cus-todial staff.

Additional points on security measures

The U.K. Fire Protection Association provides datasheets intended as an aide-memoire for those whohave the responsibility for the protection of prem-ises and to help them achieve cost effective secur-ity measures. Some of the points that they make aregiven below.

Control equipment

Controls for alarm systems can usually be operatedby non-technical staff and should be contained in aunit within the ‘alarmed’ area and protected againsttampering and have their own detection circuit.

Systems should be divided into zones to assist inidentification of devices which have triggered andalso for early diagnosis of fault conditions.

Alarms normally operate at 12 volts produced viathe mains, with standby batteries in case of powerfailure. Short circuiting the system will result in analarm being given.

There should be a maintenance and serviceagreement with equipment manufacturers. Recordsof previous inspections, false alarm calls, changesof key holder and servicing should be kept by theuser as this can be of considerable use in diagnos-ing faults.

Wire free systems

Systems using radio transmitters with receivers ortransceivers are simple to install but their range is lim-ited. Signals to remote centres are sent conventionally

by telephone. Their advantage is that they avoidunsightly wiring and damage to the fabric.

Detection devices

Detection devices need careful siting in historicbuildings with large volumes and variable internalair movements, which should be studied usingsmoke tests. Multiples of a device or differentdevices in combinations should be used accordingto circumstances. Wiring for devices and their sitingshould be supervised to prevent tampering.

The insurer and a fire engineer or security expertshould be consulted to advise on the most suitablesystem.

Surveillance

The effectiveness of patrols and observers can beenhanced by the use of electronic surveillance.Strategically placed, remotely controlled TV cam-eras improve surveillance possibilities. Movementdetectors can be used to activate cameras and security lighting, so alerting the operator. Lenses capable of producing images at extremely low levels of light are available. A further developmentis the use of infrared light and television cameraswhich can read the movements of an intruder.

Access control

Access control is fundamental to security. Peopleare now used to control procedures which involvea body check as well as a baggage check.

Electronic access control systems enable entry tobe gained to a secure area by a holder inserting orpassing an electric coded card through a reader to a locked door. An electronic lock will be operatedallowing entry. Fitting of such locks should not beallowed to spoil the appearance of the door.

Complex facilities to regulate access are possibleincluding:

Individual code numbersVoice recognitionSignature recognitionRetina recognitionHand, finger or thumb prints.

Perimeter protection

Regardless of their height, most walls and fences,whether topped with barbed wire or other

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enhancements, can be breached or climbed byintruders within a few minutes. Nevertheless, theypresent a formidable obstacle for the less deter-mined trespasser. Topping materials on walls andfences must not be so positioned as to be able toinjure pedestrians or users of adjacent land. Wallsare often perceived as being effective, but are lesshelpful than fences because they screen buildingsfrom passersby.

When considering walls with a security function:

They should be at least 2.4 metres high.Avoid providing toe holes.They should maintain their height throughout theirlength, regardless of undulating ground.Be 3 metres from buildings, structures or trees.Have strong gates and doors of the same heightand topping without significant gaps at groundlevel or between top and keystone if inset.Deny the use of fall pipes and similar climbing aidsby fixing spiked metal collars.The local fire prevention officer should be con-sulted before adapting fire escapes and fire doorsfor security purposes.Avoid recesses and hidden doorways.

Fences

Many of the requirements which apply to wallsapply equally to fences. Only nominal protection isafforded to premises by a standard wire mesh orchain link fence. As wire can be cut or dismantled,additional deterrents including electronic detectorsor security lighting may be needed. Welding meshfences, palisade fencing, reinforced concrete panelsand rolled steel palisades improve perimeter secur-ity, but will probably spoil the environment of ahistoric building. Great care must be taken with thequality of any fencing.

Vehicle barriers

In many instances it is important to keep vehiclesaway from the immediate vicinity of historic build-ings, especially at night. Protective measuresinclude, lifting poles, slewing poles, one wayplates, and rising steps.

Security lighting

Lighting, unless well planned, installed and main-tained may not hinder an intruder but help to lighthis way or provide shadows in which he can hide.Security lighting should complement physical andelectronic security, illuminate the intruder on his

approach, conceal a defender from the intruder,completely illuminate protected premises, operatefrom dusk to dawn and be mounted out of reach ofvandals and protected against missiles. It may notbe easy to meet all these conditions in a suitablemanner. By night, if it is activated by an intruderalarm it is the most effective deterrent as it alsogives general alert to staff.

Perimeter lighting

Environmental considerations apart, the aim ofperimeter lighting should be to illuminate bothsides of a perimeter, especially if it is a wall, with-out shadows being cast along its length. Columnscarrying flood lighting need careful spacing if themaximum benefit is to be obtained. High intensityluminaires providing low level glare towards aperimeter prevents a potential intruder seeingbeyond the light, making any intrusions more haz-ardous. However, it may well be found that peri-meter lighting spoils the environment of a historicbuilding.

Vandalism

The potential for vandalism and arson rises ifgroups are able to gather in unsupervised areas.Extra precautions to safeguard vulnerable areas,such as isolated fuel tanks and flammable stores,need to be considered. Open spaces, e.g. yards, carparks and cleared sites, can be attractive toteenagers for ball games, cycling and similar activ-ities, which can lead to avoidable damage.

Doors

When supervision is at a minimum doors becomevulnerable to attack in a number of common ways,such as body pressure, using an instrument,drilling, spreading and removal of panels. Criminalsare resourceful and will go to great lengths to forcedoors which impede them, for example:

Ramming doors with a vehicle.Using a vehicle to pull a door out.Sawing through exposed hinges.Drilling holes to release a panic bar.Applying torque to a cylinder knob set.

Vulnerability can be reduced by fitting hinge bolts,good rebates, outward opening doors and fittingsolid core doors. Quality locking devices at morethan one point, such as mortise bolts in the top and

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lower third, reduce vulnerability whilst glazingincreases the risk of a break in.

Locks and keys

Specifications for thief resistant locks, provide fordesign requirements such as five levers giving atleast a thousand ‘differs’, end pressure resistance onbolt, hardened steel rollers inset in bolt.

Key security is essential. They should be formallycontrolled and their whereabouts always cata-logued, only be copied as a last resort, labelled byreference to a coded list, issued according to needand not status. High security areas should beexcluded from key suites.

The architect should understand the merits anddead latches, rim and mortice locks, padlocks andsystems of master key suiting and combinationlocking. Some locks provide thousands more ‘differs’ plus unique key designs which reduce therisk of unauthorized copying., The most commonpin tumbler lock cylinder night catch has little secu-rity value. Tumbler locks are more resistant to pick-ing but vulnerable to torque pressures. There areavailable unorthodox cylinder locks operated bykeys for which blanks are not readily obtainableexcept from the manufacturers.

Master key suiting

A system of locks allowing all to be opened by amaster, some to be opened by a sub-master andsingle doors by their individual keys, is often con-venient, but master keying considerably reducesthe security of the system.

Combination locking

Combination locking is conveniently used onstrong rooms and security cabinets or safes.Sometimes they are combined with key locks. Timelocks permit opening only at pre-determined times.On safes and strongrooms they supplement con-ventional locks.

Windows

It has been observed that large panes are not asoften attacked as small ones. Intruders prefer togain access through an open light rather than a broken window. Secluded windows are most at risk.

Leaded lights and puttied panes can be removedwithout shattering the glass. Windows and skylightsaccessible from flat roofs, fire escapes and fall pipesneed protection. Alternative glazing of polycarbon-ate or laminated glass having resistance to impact,or toughened glass, although susceptible to pointedobjects, may be considered. Acrylic glazing isunsuitable, being flammable.

Anti-bandit glazing

Anti-bandit glazing and bullet resistant glazing areintended to provide protection for staff handlingcash or other valuables. It normally consists of lam-inations of glass and plastics and should be sup-plied and installed by specialist contractors.

Although windows are not usually part of anescape route, consultation with the fire authoritybefore fitting protective bars and grilles is advisable.

In many cases simple window locks fitted toopening lights and their frames can be a sufficientdeterrent, but it should be borne in mind that thekeys used in many window locks are easilyobtained or duplicated.

Steel bars should be fitted internally, firmlygrouted into surrounding masonry or brickwork.Distances between the bars should not exceed127 mm and the steel rod should not be less than19 mm in diameter. Tie bars should be fitted atintervals not exceeding 610 mm to prevent spring-ing. Prefabricated welding mesh can be substitutedfor bars. Proprietary shutters and grilles can also befitted. The importance of non-return screws, mush-room headed bolts and hidden fixings should benoted when choosing pre-formed protection.

Conclusion

Security is a complex subject ranging from macroconsiderations to careful attention to detail; it mustbe studied to be cost effective as any system is onlyas strong as its weakest link.

Security experts tend to play on our fears and soincrease the demand for expensive guards.However, only the owner or full time occupant ofa historic building can make a realistic assessmentof the risks. The key element is the alertness andvigilance of the caretaking team.

I would like to acknowledge the considerablehelp received from Mr Stewart Kidd of the FireProtection Association and Dr E. C. Bell of the LossPrevention Council Technical Centre in preparingthis Appendix.

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This extract from Dr David Watt’s book, BuildingPathology, published by Blackwell, 1998, is grate-fully acknowledged. Due to the limitations of eachdifferent technique, it is advisable to consult a spe-cialist expert as to whether a proposed techniquecan and will produce the desired information.

Less than ten per cent of the fabric of a buildingwill usually be available for direct observation andassessment during a survey, whilst the structure and other parts of the fabric remain hidden belowground, within the construction or covered by fin-ishes and decorations.

In certain cases it is necessary to investigatebeneath the surface in order to understand the con-struction and identify actual or potential defects.Aside from physically opening up parts of thebuilding, it is possible to employ non-destructivetechniques to provide a level of information, basedeither on direct penetration into the fabric or indirect/remote imaging techniques, that will aidassessment.

The term ‘non-destructive survey’ covers a col-lection of techniques that may be used to inspect orobserve materials or elements of construction inplace without causing alteration, damage ordestruction to the fabric of the building. Each tech-nique is able to provide a specific set of measure-ments or data in response to known or suspectedconditions. This may be for the analysis of materialproperties, detection of hidden aspects of construc-tion or sub-surface anomalies, or the evaluation ofperformance in use.

As with all forms of investigation, success reliesupon the correct selection of the technique or com-bination of techniques that are most appropriate for the particular task, and skilled interpretation ofthe collected data in order to reliably inform the decision-making process.

Radiography

Penetrating X-rays or gamma rays are used to seeinside a wide range of materials and elements ofconstruction to detect discontinuities, cracks, voids,density variations, hidden details, foreign objects orchanges caused by deterioration. Materials such asplaster and wood are easily penetrated to showembedded fixings and structural members, but withdenser materials, such as masonry and concrete, amore powerful radiation source is required.

Surface penetrating or impulse radar

A pulse of radio energy transmitted into the groundor solid material along a pre-determined survey lineis reflected by internal surfaces and objects, identi-fying boundaries, thicknesses and defects such ascracking of stone or concrete. Examples of its usewith buildings include determining the materialthickness, moisture content, and locating voids andembedded metalwork.

Microwave analysis

The strength and direction of projected energy thatis reflected back from surfaces and changes within amaterial can record inconsistencies, discontinuities,faults and hidden details. This technique has beenused successfully on mass constructions, such asramparts and redoubts found in military architecture.

Thermography

The measurement of infrared energy, in the form of waves radiated from the surface of building

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elements, is commonly used to detect and quantifyheat losses and temperature variations throughroofs and walls. It can also be used to detect sub-surface details, such as the presence of embeddedtimber-frame members, voids, inconsistencies, anddeterioration in timber members.

Infrared photography

Based on the same technology as thermography,photography using infrared film, together withappropriate filters, can indicate subtle variations insurface colour that might, for instance, result from an increased moisture content or sub-surfacedeterioration.

Acoustic testing

Various techniques have been developed for build-ing and engineering applications that make use ofthe sound wave to detect inconsistencies within testmaterials. Sonic transmission and sonic echo testinguses transducers on both sides of the material orstructure, to detect differences in time and fre-quency response.

Ultrasonic testing uses high frequency soundwaves to detect and locate hidden details, voids,faults, cracks and cavities, and measure thicknessand density. This technique is particularly useful indealing with homogeneous materials, such asceramics, metals and masonry, rather than with lessuniform forms of construction.

Magnetometry

The measurement of an induced magnetic field can,through distribution patterns, identify and locatemagnetic features buried within non-magneticmaterials such as wood, concrete, brick and stone.Cover meters are commonly used to locate andidentify reinforcement within concrete construc-tions, but can also be used to detect metal cramps,armatures and fixings within masonry or timber,and buried pipes, conduits, flues and ducts. Certainnon-magnetic materials and sub-surface anomaliescan also be detected due to changes in magneticfields induced by stimuli such as heat. Simple metaldetectors are also widely available for use in thehome to locate hidden cables, pipes and fixings.

Geotechnical surveying

The term ‘geotechnics’ describes an array of tech-niques and procedures used in investigating ground

conditions, either in response to a defect or inadvance of new development. These includedestructive techniques such as sampling and testingusing trial pits and boreholes, penetration testing,plate testing, as well as site and laboratory testing and monitoring of soils, rocks and contam-inated landfill. Non-destructive techniques are alsoused, such as impulse radar for detecting cavitiesand obstructions below ground level.

Geophysical surveying

Archaeological prospection using non-destructivegeophysical techniques can be used to detect sub-surface features that may have an importance inunderstanding a building or relevance to anyplanned works.

Resistivity surveying is based on the resistance ofan electric current passing through the ground rela-tive to its moisture content. Sub-surface variationsin this resistance can be interpreted to indicate fea-tures such as ditches, walls and built-up surfaces.

Magnetic surveying, or magnetometry, is used todetect changes in the magnetised iron oxides in theearth caused by the fires and cultivation associatedwith occupation of a site. Magnetic anomalies canassist in the identification of industrial sites, hearths,kilns and filled pits.

Surface-penetrating radar is also being used todetect sub-surface features, often at depths of sev-eral metres, and is likely to become a more familiartechnique as interpretation improves.

Detection of sub-surface features can also comefrom direct probing, percussion variations knownas bosing, by using metal detectors and dowsing.

Remote sensing

Remote sensing is the general name given to the acquisition and use of data about the earth from sources such as aircraft, balloons, rockets andsatellites.

Many of the techniques used in this field areapplicable to the non-destructive surveying ofbuildings, and a number of photographic tech-niques have been employed in ground-basedremote sensing to identify and record surface andsub-surface anomalies.

Rothound® search dogs

The detection and subsequent monitoring of dry rot (Serpula lacrymans) has traditionally been

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undertaken by periodic opening up and directinspection of suspect timbers. Rothound® dry rotsearch dogs are capable of detecting the scent ofthe metabolites produced by living dry rot, thus dis-criminating between living and dead outbreaks,and indicating the extent of an infestation Gas sam-pling technology, probably in combination withmicro-drilling (see below), may similarly provide ameans of detecting fungal decay and possibly thepresence of beetle infestations through the gasesgiven off by faecal pellets.

Dowsing

Dowsing can be used to discover buried features aswell as its more common role in discoveringunderground water.

Close-circuit television surveying

Remote CCTV or video inspection and tracking ofdrain runs, flues, ducts and other concealed voidscan provide direct information on condition, block-ages and defects, and allow record drawings to beprepared for later use.

Micro-drilling

The rate of penetration of a fine drill probe (1 mmdia.) into timber can be used to identify and locatefaults and variations due to decay and otherdefects, and inform later localised repair or treat-ment. Entire structural members may be sampledby regular drilling and the condition of concealedtimber members, such as lintels, assessed bydrilling through overlying plaster.

Fibre-optic surveying

Direct penetration into cavities or voids within thefabric of a building using a fibre-optic probe canprovide useful information on aspects of construc-tion, or the condition of specific elements or com-ponents. The probes may be either endoscopes,which are flexible tubes filled with bundles of opti-cal fibres that can illuminate and view remoteobjects, or boroscopes, which are rigid tubes, againwith fibre bundles, that deliver illumination to thesubject and carry the image back to the eye-piece.Both systems can be used to inspect and photo-graph hidden or obstructed details through existingcracks or openings, or small drilled holes.

Liquid penetrant testing

Application of a light oil impregnated with dye onto the surface of non-porous materials will providea visual indication of cracks and fissures by theconcentration of the dye in the defects. Dyed water(or smoke) may also be used to check pipe anddrain runs, and also to detect leaks.

Load testing

Applying load to an individual member or assemblyallows its behaviour to be assessed. The technique isuseful in assessing damage following a fire or explo-sion, or establishing the efficacy of a repair. With thistechnique it is important to consider carefully thesafety of the personnel undertaking the tests and theeffects the tests might have on the building.

Monitoring defects

Most defects are progressive in nature and can bemonitored over a period of time. In order to pro-vide evidence as to the nature and timing of thedefect, monitoring usually includes a level ofabsolute or relative measurement.

Early techniques of monitoring were simple, limited by the available resources and relativelyundemanding user requirements. Increased sophis-tication has stemmed, in part, from a growing needto understand and, where possible, quantify the causeof a building defect rather than just the effects itwill have on the fabric.

In addition to monitoring current defects, it isimportant to appreciate the opportunities for com-paring present defects with the state of the propertyin the past. In this respect the use of earlier photo-graphs and other visual material may assist in con-firming and quantifying levels of decay, deteriorationor disrepair.

How monitoring is performed depends on thedifficulties of access, the overall condition of thefabric, the need to obtain a standard and continualsequence of information, and available finance.Accuracy will typically increase with complexityand cost. The reasons for monitoring must also beconsidered, whether it be to record progressiveconditions, or detect certain changes or conditionsbefore damage is sustained.

Structural distortion and movement

Monitoring of structural distortion and movementcan take many forms, depending on the underlying

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cause and how it has manifested itself in the fabricof the building (BRE Digest 343, 1989; Digest 386,1993 and Digest 344, 1995).

Cracking and in-plane deformation of masonrycan be undertaken using crack width gauges orrulers, calibrated tell-tales (such as those producedby Avongard™), vernier gauges and fixed studs,demountable strain gauges, or electronic sensorsconnected to data loggers.

The deflection of a structural member, which typi-cally implies either flexure under increased load ormovement as a result of material deterioration, canbe monitored by levelling, inclinometers or elec-tronic level gauges, whilst vibrations can be moni-tored by laser interferometry or with sensors anddata loggers.

Distortion of vertical surfaces, such as leaning orbulging walls, may be monitored using simpleplumb-bobs or spirit levels, plumbed offsets or,more accurately, an optical plummet or by theodo-lite intersection.

Material deterioration and decay

Understanding how and why materials deteriorateand decay requires a detailed understanding of theparticular material and the various agencies andmechanisms that can act upon it. Assessing theseverity of such action with regard to defined criteria(such as aesthetics and structural considerations)may require initial and subsequent testing, whetheron the actual material or on appropriate replicates,and monitoring to take account of varying condi-tions (such as time, temperature and humidity).

Tests have been established to determine keyqualities and characteristics of common buildingsmaterials (such as durability, porosity, waterabsorption and salt crystallisation), but it is alsonecessary to be able to assess performance in thecontext of a particular building, environment orapplication.

The diagnosis of particular defects may requiremonitoring over time, and this can be undertakenusing various simple or sophisticated methods.Surveyors may, for instance, use specific diagnosticinstruments, such as moisture meters, wall surfacethermometers and salt detectors, to establish mois-ture levels in wood and other building materials,dew point temperatures, the risk of surface con-densation and the presence of hygroscopic salts, orundertake simple on-site tests to determine, forinstance, moisture content (carbide meter), thepresence of lead paint, or the alkalinity of concrete(phenolphthalein indicator solution).

Generally, however, it will be necessary to usecompetent laboratory services in order to obtaindata (qualitative and quantitative) to inform thediagnosis and prognosis of a particular defect oraspect of decay. Such services may include the following:

● laboratory and site testing● diagnosis and analysis● statistical analysis

Chemical and physical testing may be undertakento identify particular materials, and measure levelsof deterioration and decay. These include:

● timber (e.g. moisture content, preservative treatment)

● mortars (e.g. aggregate:binder ratios, cement con-tent, aggregate grading)

● concrete (e.g. carbonation, strength) (BS 1881:Part 201: 1986)

● metals (e.g. composition, thickness of coatings,corrosion, fractures)

● asphalt and bituminous products (e.g. composi-tion, bitumen content, hardness)

● glass (e.g. composition, surface discoloration)● plastics (e.g. composition, compatibility)● moisture analysis (e.g. carbide meter, gravimetric

tests) salt analysis (e.g. carbonates, chlorides,nitrates, sulphates)

Testing is also being undertaken at national and inter-national levels to determine the responses of materi-als to varying environmental conditions. Thisincludes the National Materials Exposure Programme,and its international counterpart, which is investi-gating the effects of pollution on building materialsaround the country. Such tests have been able todetermine relationships between atmospheric con-ditions and the degradation of specific buildingmaterials, and so predict future patterns of materialdecay.

Research into the mechanisms of decay and treat-ment of historic building materials is similarly beingundertaken by English Heritage. Projects include:

● Smeaton project on historic mortars durability● masonry consolidants● floor wear and tile pavement decay● polishable limestone decay● sandstone decay● anti-graffiti barriers● structural fire protection● lime and lime treatments● underside lead corrosion

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● timber decay and moisture ingress● masonry cleaning● fire safety in cathedrals● terracotta decay and conservation● stained glass● stone slate roofing● mosaic clad concrete● national sand and aggregates library● earthen structures

Environmental conditions

The three environmental conditions that have thegreatest effect on built fabric are temperature(ambient and surface), humidity (absolute and relative) and sunlight (lux and ultraviolet). Each canbe measured and monitored to provide necessaryinformation for corrective measures or suit-able protection. Consideration may, in addition,

have to be given to air movement and atmosphericpollution.

As with all monitoring, it is important to establisha pattern of readings over a period of time to takeaccount of such variables as seasonal, diurnal andnocturnal differences; times and levels of occu-pancy; movement of caretaking, security and clean-ing staff; and use of service installations.

On-site measurement may be undertaken usingsimple diagnostic instruments, but for more accu-rate measurement and monitoring the surveyor maybe required to use or commission specific instru-mentation:

● manual (e.g. thermometer, whirling hygrometer)● mechanical (e.g. thermohygrograph)● electronic (e.g. various humidity and temperature

meters)● remote (e.g. sensors, data loggers and radio

telemetry systems).

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A society coming before the public with such aname as that above written must needs explainhow, and why, it proposes to protect those ancientbuildings which, to most people doubtless, seem tohave so many and such excellent protectors. This,then, is the explanation we offer.

No doubt within the last fifty years a new inter-est, almost like another sense, has arisen in theseancient monuments of art; and they have becomethe subject of one of the most interesting of stud-ies, and of an enthusiasm, religious, historical, artis-tic, which is one of the undoubted gains of ourtime; yet we think that if the present treatment ofthem be continued, our descendants will find themuseless for study and chilling to enthusiasm. Wethink that those last fifty years of knowledge andattention have done more for their destruction thanall the foregoing centuries of revolution, violenceand contempt.

For Architecture, long decaying, died out, as apopular art at least, just as the knowledge of medi-aeval art was born. So that the civilised world of thenineteenth century has no style of its own amidst itswide knowledge of the styles of other centuries.From this lack and this gain arose in men’s mindsthe strange idea of the Restoration of ancient build-ings; and a strange and most fatal idea, which by itsvery name implies that it is possible to strip from abuilding this, that, and the other part of its history—of its life that is—and then to stay the hand at somearbitrary point, and leave it still historical, living,and even as it once was.

In early times this kind of forgery was impossi-ble, because knowledge failed the builders, or per-haps because instinct held them back. If repairswere needed, if ambition or piety pricked on tochange, that change was of necessity wrought inthe unmistakable fashion of the time; a church of

the eleventh century might be added to or alteredin the twelfth, thirteenth, fourteenth, fifteenth, sixteenth, or even the seventeenth or eighteenthcenturies; but every change, whatever history itdestroyed, left history in the gap, and was alivewith the spirit of the deeds done midst its fashion-ing. The result of all this was often a building inwhich the many changes, though harsh and visibleenough, were, by their very contrast, interestingand instructive and could by no possibility mislead.But those who make the changes wrought in ourday under the name of Restoration, while profess-ing to bring back a building to the best time of itshistory, have no guide but each his own individualwhim to point out to them what is admirable andwhat contemptible; while the very nature of theirtask compels them to destroy something and tosupply the gap by imagining what the earlierbuilders should or might have done. Moreover, inthe course of this double process of destruction andaddition, the whole surface of the building is nec-essarily tampered with; so that the appearance ofantiquity is taken away from such old parts of thefabric as are left, and there is no laying to rest inthe spectator the suspicion of what may have beenlost; and in short, a feeble and lifeless forgery is thefinal result of all the wasted labour.

It is sad to say, that in this manner most of thebigger Minsters, and a vast number of more hum-ble buildings, both in England and on theContinent, have been dealt with by men of talentoften, and worthy of better employment, but deafto the claims of poetry and history in the highestsense of the words.

For what is left we plead before our architectsthemselves, before the official guardians of build-ings, and before the public generally, and we praythem to remember how much is gone of the

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religion, thought and manners of time past, neverby almost universal consent, to be Restored; and toconsider whether it be possible to Restore thosebuildings, the living spirit of which, it cannot be toooften repeated, was an inseparable part of that reli-gion and thought, and those past manners. For ourpart we assure them fearlessly, that of all theRestorations yet undertaken, the worst have meantthe reckless stripping a building of some of its mostinteresting material features; whilst the best havetheir exact analogy in the Restoration of an old pic-ture, where the partly-perished work of the ancientcraftsmaster has been made neat and smooth by thetricky hand of some unoriginal and thoughtlesshack of today. If, for the rest, it be asked us to spec-ify what kind of amount of art, style, or other inter-est in a building makes it worth protecting, weanswer, anything which can be looked on as artis-tic, picturesque, historical, antique, or substantial:any work, in short, over which educated, artisticpeople would think it worth while to argue at all.

It is for all these buildings, therefore, of all timesand styles, that we plead, and call upon those whohave to deal with them, to put Protection in the placeof Restoration, to stave off decay by daily care, toprop a perilous wall or mend a leaky roof by suchmeans as are obviously meant for support or cover-ing, and show no pretence of other art, and other-wise to resist all tampering with either the fabric orornament of the building as it stands; if it has becomeinconvenient for its present use, to raise anotherbuilding rather than alter or enlarge the old one; infine to treat our ancient buildings as monuments of abygone art, created by bygone manners, that modernart cannot meddle with without destroying.

Thus, and thus only, shall we escape thereproach of our learning being turned into a snareto us; thus, and thus only can we protect ourancient buildings, and hand them down instructiveand venerable to those that come after us.

(Written by William Morris, 1877)

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The Venice Charter

Imbued with a message from the past, the historicmonuments of generations of people remain to thepresent day as living witnesses of their age-old traditions. People are becoming more and moreconscious of the unity of human values and regardancient monuments as a common heritage. Thecommon responsibility to safeguard them for futuregenerations is recognized. It is our duty to handthem on in the full richness of their authenticity.

It is essential that the principles guiding thepreservation and restoration of ancient buildingsshould be agreed and be laid down on an interna-tional basis, with each country being responsiblefor applying the plan within the framework of itsown culture and traditions.

By defining these basic principles for the firsttime, the Athens Charter of 1931 contributedtowards the development of an extensive interna-tional movement which has assumed concrete formin national documents, in the work of ICOM andUNESCO and in the establishment by the latter of the International Centre for the Study of thePreservation and the Restoration of CulturalProperty. Increasing awareness and critical studyhave been brought to bear on problems whichhave continually become more complex and var-ied; now the time has come to examine the Charterafresh in order to make a through study of the prin-ciples involved and to enlarge its scope in a newdocument.

Accordingly, the IInd International Congress ofArchitects and Technicians of Historic Monuments,which met in Venice from May 25th to 31st 1964,approved the following text:

Definitions

ARTICLE 1. The concept of an historic monumentembraces not only the single architectural work but

also the urban or rural setting in which is found theevidence of a particular civilisation, a significantdevelopment or an historic event. This applies notonly to great works of art but also to more modestworks of the past which have acquired cultural sig-nificance with the passing of time.

ARTICLE 2. The conservation and restoration of mon-uments must have recourse to all the sciences andtechniques which can contribute to the study andsafeguarding of the architectural heritage.

Aim

ARTICLE 3. The intention in conserving and restoringmonuments is to safeguard them no less as worksof art than as historical evidence.

Conservation

ARTICLE 4. It is essential to the conservation of monu-ments that they be maintained on a permanent basis.

ARTICLE 5. The conservation of monuments is alwaysfacilitated by making use of them for some sociallyuseful purpose. Such use is therefore desirable butit must not change the lay-out or decoration of thebuilding. It is within these limits only that modifi-cations demanded by a change of function shouldbe envisaged and may be permitted.

ARTICLE 6. The conservation of a monument impliespreserving a setting which is not out of scale.Wherever the traditional setting exists, it must bekept. No new construction, demolition or modifica-tion which would alter the relations of mass andcolour must be allowed.

ARTICLE 7. A monument is inseparable from the his-tory to which it bears witness and from the settingin which it occurs. The moving of all or part of amonument cannot be allowed except where thesafeguarding of that monument demands it or

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where it is justified by national or internationalinterests of paramount importance.

ARTICLE 8. Items of sculpture, painting or decorationwhich form an integral part of a monument mayonly be removed from it if this is the sole means ofensuring their preservation.

Restoration

ARTICLE 9. The process of restoration is a highly spe-cialised operation. Its aim is to preserve and revealthe aesthetic and historic value of the monumentand is based on respect for original material andauthentic documents. It must stop at the pointwhere conjecture begins, and in this case moreoverany extra work which is indispensable must be dis-tinct from the architectural composition and mustbear a contemporary stamp. The restoration in anycase must be preceded and followed by an archae-ological and historical study of the monument.

ARTICLE 10. Where traditional techniques prove inad-equate, the consolidation of a monument can beachieved by the use of any modern technique forconservation and construction, the efficacy ofwhich has been shown by scientific data andproved by experience.

ARTICLE 11. The valid contributions of all periods tothe building of a monument must be respected,since unity of style is not the aim of a restoration.When a building includes the superimposed workof different periods, the revealing of the underlyingstate can only be justified in exceptional circum-stances and when what is removed is of little inter-est and the material which is brought to light is ofgreat historical, archaeological or aesthetic value,and its state of preservation good enough to justifythe action. Evaluation of the importance of the ele-ments involved and the decision as to what may bedestroyed cannot rest solely on the individual incharge of the work.

ARTICLE 12. Replacements of missing parts must inte-grate harmoniously with the whole, but at the sametime must be distiguishable from the original so thatrestoration does not falsify the artistic or historic evidence.

ARTICLE 13. Additions cannot be allowed except in sofar as they do not detract from the interesting partsof the building, its traditional setting, the balance ofits composition and its relation with its surroundings.

Historic sites

ARTICLE 14. The sites of monuments must be theobject of special care in order to safeguard their

integrity and ensure that they are cleared and pre-sented in a seemly manner. The work of conserva-tion and restoration carried out in such placesshould be inspired by the principles set forth in theforegoing articles.

Excavations

ARTICLE 15. Excavations should be carried out inaccordance with scientific standards and the rec-ommendation defining international principles tobe applied in the case of archaelogical excavationadopted by UNESCO in 1956.

Ruins must be maintained and measures neces-sary for the permanent conservation and protectionof architectural features and of objects discoveredmust be taken. Furthermore, every means must betaken to facilitate the understanding of the monu-ment and to reveal it without ever distorting itsmeaning.

All reconstruction work should however be ruledout a priori. Only anastylosis, that is to say, thereassembling of existing but dismembered parts canbe permitted. The material used for integrationshould always be recognisable and its use shouldbe the least that will ensure the conservation of amonument and the reinstatement of its form.

Publication

ARTICLE 16. In all works of preservation, restorationor excavation, there should always be precise doc-umentation in the form of analytical and criticalreports, illustrated with drawings and photographs.

Every stage of the work of clearing, consolida-tion, rearrangement and integration, as well as tech-nical and formal features indentified during thecourse of the work, should be included. This recordshould be placed in the archives of a public insti-tution and made available to research workers. It isrecommended that the report should be published.

The following persons took part in the work ofthe Committee for drafting the International Charterfor the Conservation and Restoration of Monuments:

Mr. PIERO GAZZOLA (Italy), ChairmanMr. RAYMOND LEMAIRE (Belgium), ReporterMr. JOSÉ BASSEGODA-NONELL (Spain)Mr. LUIS BENAVENTE (Portugal)Mr. DJURDJE BOSKOVIC (Yugoslavia)Mr. HIROSHI DAIFUKU (U.N.E.S.C.O.)Mr. P.L. DE VRIEZE (Netherlands)Mr. HARALD LANGBERG (Denmark)Mr. MARIO MATTEUCCI (Italy)

Guidelines on education and training in the conservation of monuments, ensembles and sites

363

Mr. JEAN MERLET (France)Mr. CARLOS FLORES MARINI (Mexico)Mr. ROBERTO PANE (Italy)Mr. S.C.J. PAVEL (Czechoslovakia)Mr. PAUL PHILIPPOT (International Centre for the

Study of the Preservation and Restoration ofCultural Property)

Mr. VICTOR PIMENTEL (Peru)Mr. HAROLD PLENDERLEITH (International Centre for

the Study of the Preservation and Restoration ofCultural Property)

Mr. DEOCLECIO REDIG DE CAMPOS (Vatican)Mr. JEAN SONNIER (France)Mr. FRANÇOIS SORLIN (France)Mr. EUSTATHIOS STIKAS (Greece)Mrs. GERTRUD TRIPP (Austria)Mr. JAN ZACHWATOVICZ (Poland)Mr. MUSTAFA S. ZBISS (Tunisia)

Guidelines on education and training in the conservation of monuments,ensembles and sites

The General Assembly of the International Councilon Monuments and Sites, ICOMOS, meeting inColombo, Sri Lanka, at its tenth session from July 30to August 7, 1993;

Considering the breadth of the heritage encom-passed within the concept of monuments, ensem-bles and sites;

Considering the great variety of actions and treat-ments required for the conservation of these her-itage resources, and the necessity of a commondiscipline for their guidance;

Recognizing that many different professions need tocollaborate within the common discipline of conser-vation in the process and require proper educationand training in order to guarantee good communi-cation and coordinated action in conservation;

Noting the Venice Charter and related ICOMOS doc-trine, and the need to provide a reference for theinstitutions and bodies involved in developing training programmes, and to assist in defining andbuilding up appropriate standards and criteria suitable to meet the specific cultural and technicalrequirements in each community or region;

Adopts the following guidelines, and Recommendsthat they be diffused for the information of appro-priate institutions, organizations and authorities.

Aim of the guidelines

1. The aim of this document is to promote theestablishment of standards and guidelines for

education and training in the conservation ofmonuments, groups of buildings (“ensembles”)and sites defined as cultural heritage by the WorldHeritage Convention of 1972. They include his-toric buildings, historic areas and towns, archae-ological sites, and the contents therein, as well ashistoric and cultural landscapes. Their conserva-tion is now, and will continue to be a matter ofurgency.

Conservation

2. Conservation of cultural heritage is now recog-nized as resting within the general field of envir-onmental and cultural development. Sustainablemanagement strategies for change which respectcultural heritage require the integration of con-servation attitudes with contemporary economicand social goals including tourism.

3. The object of conservation is to prolong the lifeof cultural heritage and, if possible, to clarify theartistic and historical messages therein without the loss of authenticity and meaning. Conservationis a cultural, artistic, technical and craft activitybased on humanistic and scientific studies andsystematic research. Conservation must respectthe cultural context.

Educational and training programmes and courses

4. There is a need to develop a holistic approach toour heritage on the basis of cultural pluralismand diversity, respected by professionals,craftspersons and administrators. Conservationrequires the ability to observe, analyze and syn-thesize. The conservationist should have a flexi-ble yet pragmatic approach based on culturalconsciousness which should penetrate all practi-cal work, proper education and training, soundjudgement and a sense of proportion with anunderstanding of the community’s needs. Manyprofessional and craft skills are involved in thisinterdisciplinary activity.

5. Conservation works should only be entrusted topersons competent in these specialist activities.Education and training for conservation shouldproduce from a range of professionals, conserva-tionists who are able to:(a) read a monument, ensemble or site and

identify its emotional, cultural and use sig-nificance;

(b) understand the history and technology ofmonuments, ensembles or sites in order to

define their identity, plan for their conser-vation, and interpret the results of thisresearch;

(c) understand the setting of a monument,ensemble or site, their contents and sur-roundings, in relation to other buildings,gardens or landscapes;

(d) find and absorb all available sources ofinformation relevant to the monument,ensemble or site being studied;

(e) understand and analyze the behaviour ofmonuments, ensembles and sites as com-plex systems;

(f) diagnose intrinsic and extrinsic causes ofdecay as a basis for appropriate action;

(g) inspect and make reports intelligible to non-specialist readers of monuments, ensemblesor sites, illustrated by graphic means such assketches and photographs;

(h) know, understand and apply Unesco con-ventions and recommendations, and ICO-MOS and other recognized Charters,regulations and guidelines;

(i) make balanced judgements based on sharedethical principles, and accept responsibil-ity for the long-term welfare of cultural heritage;

(j) recognize when advice must be sought anddefine the areas of need of study by differ-ent specialists, e.g. wall paintings, sculptureand objects of artistic and historical value,and/or studies of materials and systems;

(k) give expert advice on maintenance strate-gies, management policies and the policyframework for environmental protectionand preservation of monuments and theircontents, and sites;

(l) document works executed and make sameaccessible.

(m) work in multi-disciplinary groups usingsound methods;

(n) be able to work with inhabitants, adminis-trators and planners to resolve conflicts and to develop conservation strategiesappropriate to local needs, abilities andresources;

Aims of courses

6. There is a need to impart knowledge of con-servation attitudes and approaches to all thosewho may have a direct or indirect impact oncultural property.

7. The practice of conservation is interdiscipli-nary; it therefore follows that courses should

also be multidisciplinary. Professionals, includ-ing academics and specialized craftspersons,who have already received their normal qualifi-cation will need further training in order tobecome conservationists; equally those whoseek to act competently in historic environment.

8. Conservationists should ensure that all artisansand staff working on a monument, ensemble orsite respect its significance.

9. Training in disaster preparedness and in meth-ods of mitigating damage to cultural property,by strengthening and improving fire preventionand other security measures, should beincluded in courses.

10. Traditional crafts are a valuable culturalresource. Craftspersons, already with high levelmanual skills, should be further trained for con-servation work with instruction in the history oftheir craft, historic details and practices, and thetheory of conservation with the need for docu-mentation. Many historic skills will have to berecorded and revived.

Organization of education and training

11. Many satisfactory methods of achieving therequired education and training are possible.Variations will depend on traditions and legis-lation, as well as on administrative and eco-nomic context of each cultural region. Theactive exchange of ideas and opinions on newapproaches to education and training betweennational institutes and at international levelsshould be encouraged. Collaborative networkof individuals and institutions is essential to thesuccess of this exchange.

12. Education and sensitization for conservationshould begin in schools and continue in univer-sities and beyond. These institutions have animportant role in raising visual and culturalawareness—improving ability to read and under-stand the elements of our cultural heritage—andgiving the cultural preparation needed by can-didates for specialist education and training.Practical hands-on training in craft work shouldbe encouraged.

13. Courses for continuing professional develop-ment can enlarge on the initial education andtraining of professionals. Long-term, part-timecourses are a valuable method for advancedteaching, and useful in major population cen-tres. Short courses can enlarge attitudes, butcannot teach skills or impart profound under-standing of conservation. They can help intro-duce concepts and techniques of conservation

Appendix V: ICOMOS Charters

364

in the management of the built and naturalenvironment and the objects within it.

14. Participants in specialist courses should be of ahigh calibre normally having had appropriateeducation and training and practical workingexperience. Specialist courses should be multi-disciplinary with core subjects for all partici-pants, and optional subjects to extendcapacities and/or to fill the gaps in previouseducation and training. To complete the educa-tion and training of a conservationist an intern-ship is recommended to give practicalexperience.

15. Every country or regional group should beencouraged to develop at least one compre-hensively organized institute giving educationand training and specialist courses. It may takedecades to establish a fully competent conser-vation service. Special short-term measuresmay therefore be required, including the graft-ing of new initiatives onto existing programmesin order to lead to fully developed new pro-grammes. National, regional and internationalexchange of teachers, experts and studentsshould be encouraged. Regular evaluation ofconservation training programmes by peers is anecessity.

Resources

16. Resources needed for specialist courses mayinclude e.g.:(a) an adequate number of participants of

required level ideally in the range of 15 to25;

(b) a full-time co-ordinator with sufficientadministrative support;

(c) instructors with sound theoretical knowl-edge and practical experience in conserva-tion and teaching ability;

(d) fully equipped facilities including lecturespace with audio-visual equipment, video,etc., studios, laboratories, workshops, sem-inar rooms, and staff offices;

(e) library and documentation centre providingreference collections, facilities for coordi-nated research, and access to computerizedinformation networks;

(f ) a range of monuments, ensembles and siteswithin a reasonable radius.

17. Conservation depends upon documentationadequate for understanding of monuments,ensembles or sites and their respective settings.Each country should have an institute for

research and archive for recording its culturalheritage and all conservation works relatedthereto. The course should work within thearchive responsibilities identified at the nationallevel.

18. Funding for teaching fees and subsistence mayneed special arrangements for mid-career par-ticipants as they may already have personalresponsibilities.

The Draft ICOMOS UK Charter for theConservation of Buildings and Sites

Preamble

This Charter was written in 1998 against the back-ground of the whole history of the built environ-ment and the almost entirely man-made andman-influenced landscape of the United Kingdomand its constituent parts, and of changing attitudesto its exploitation and conservation, from the earli-est times to the present day.

Definitions

Article 1. For the purposes of this Charter:

1.1 Conservation is action to secure the survivalor preservation for the future of buildings, cul-tural artefacts, natural resources, energy or anyother thing of acknowledged value.

1.2 Design of a building or artefact is the abstractconception, on the basis of which it was made.A design may exist in the mind or imagination,on paper, or it may be realised and representedin the building or artefact itself. The design ofan unaltered building will be pure, that of amuch altered building composite, made up ofseveral designs overlaid one upon the other.

1.3 Fabric is the physical material of which abuilding or other artefact is made. Its state atany particular time will be a product of theoriginal design and of everything to which ithas been subject in the course of its history,including deliberate alterations based on wellconsidered secondary or subsequent designs,careless changes, the effects over time ofweather and use, damage and decay.

1.4 Archaeology is the scientific study and inter-pretation of the past, based on the uncovering,retrieval, recording and interpretation of infor-mation from physical evidence. Archaeologicalevidence in buildings is as likely to be visibleor concealed in the superstructure as below

The Draft ICOMOS UK Charter for the Conservation of Buildings and Sites

365

ground archaeological investigation may bedestructive.

1.5 Reconstruction is more appropriately usedwith reference to the design, than with refer-ence to the fabric of a building or artefact. Adesign may be reconstructed on the basis ofdocumentary or physical evidence, or a com-bination of the two. Depending on the strengthof the evidence, such a reconstruction, like thatof a crime or historical event, may be provenor, to a greater or lesser extent, hypothetical.

1.6 Maintenance is the routine work necessary tokeep the fabric of a building, the moving partsof machinery, grounds, gardens or any otherartefact in good order.

1.7 Repair is work to the fabric of a building orartefact, to remedy defects, significant decay ordamage caused deliberately or by accident,neglect, normal weathering or wear and tear,the objective of which is to return the buildingor artefact to good order, without alteration orrestoration. It is in the nature of repairs thatthey are irregular and beyond the scope of nor-mal routine maintenance. They may occasion-ally be required in response to a specific event,such as a storm or accident, and be unpre-dictable. Usually, however, they should beanticipated and planned.

1.8 Alteration is work to the fabric of a building orartefact, which is neither maintenance nor repair,the objective of which is to change or improveits function, or to modify its appearance.

1.9 Restoration of a building, part of a building orartefact, which has decayed, been lost or dam-aged, or is thought to have been inappropri-ately repaired or altered in the past, isalteration, the objective of which is to make itconform again to its design or to its appearanceat a previous date.

2.0 Conversion of a building or artefact is alter-ation, the objective of which is a change fromone type of use to another.

2.1 Intervention is any action which has a physi-cal effect on the fabric of a building.

2.2 Preservation of a building or artefact is simplyits survival, whether by historical accident orthrough a combination of protection and activeconservation. Preservation is a state or anobjective, not, in a technical sense, an activity.

2.3 Protection is the provision of legal restraintsor controls on the destruction or damaging ofbuildings, artefacts, natural features or systems,sites or areas or others things of acknowledgedvalue, with a view to their survival or preserva-tion for the future. Any intervention or worklikely to affect a building or its character, land,

or anything which is legally protected, wouldnormally require a consent to be obtainedthrough a procedure established by the rele-vant legislation.

2.4 Rebuilding or remaking are the appropriateterms when a building, part of a building, orartefact which has been irretrievably damagedor destroyed is built or made again on the basisof an existing or reconstructed design.

2.5 Replication is the making of an exact copy, orcopies, of a building or artefact.

2.6 Reversibility is the concept of carrying outwork to a building, part of a building or artefactin such a way that it can be reversed at somefuture time, with only minimal damage havingbeen done to the fabric.

Conservation principles

Article 2: Good conservation practice should bebased on a clear perception of conservation theoryand principles, such as those set out in this Charter.

Article 3: Good conservation requires sound deci-sion making, on the basis of appropriate and bestreasonably ascertainable knowledge and understand-ing of the building or site.

Article 4: Good conservation should be based ona clear perception of the objectives of such conser-vation, both general and specific, with regard to theparticular building or site.

Article 5: The objectives of conservation should beholistic, not ‘tunnel-visioned’, and should normallyhave regard to economic and environmental, aswell as purely cultural criteria.Notes: (a) The conservation of artefacts and the man-made environment closely parallels the conservationof resources and the natural environment. The under-lying and ultimate objective of both is to ensure thatthe long-term interests of future generations are notcompromised by short term considerations.

(b) Only in the case of ‘monuments’ which mightbe said to have little or no demanding economicuse or environmental significance should the objec-tives of conservation be predicated on cultural criteria alone.

Article 6: Conservation should be sustainable.Notes: (a) Any conservation process should have areasonable chance of success in the long term, sub-ject to good management, maintenance and furtherinterventions.

(b) There should be a reasonable prospect thatany such management, maintenance or furtherinterventions necessary for sustained conservationwould be forthcoming.

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(c) No conservation process should cause unrea-sonable collateral damage, whether cultural, envir-onmental or to human health or safety.

(d) When there are choices, the preferred optionis likely to be that which maximises the cultural,environmental and economic benefits and min-imises the impacts and costs.

Article 7: The Conservation Policy appropriate to abuilding or site should be determined on the basisof a Statement of Values, in which all the variousvalues of the building or site are assessed andstated, and an Analysis of Objectives, in which theeconomic, environmental and cultural benefits tobe derived from conservation are laid out.

Article 8: The Statement of Values, Analysis ofObjectives and Conservation Policy should be incor-porated into a Conservation Plan which should beagreed in advance of any intervention and whichshould be the standard against which all subse-quent decisions are judged.

Article 9: “Prevention is better than cure” and “Astitch in time saves nine”. The lowest appropriatelevel of intervention should normally be preferred.Good management and housekeeping, carefulmaintenance and considered repair when necessaryare the primary processes of conservation.Notes: (a) Conservation measures should includeappropriate procedures to minimise the risk ofdamage from fire and disaster.

(b) It may be beneficial for continuous care to bemanaged on the basis of a quinquennial cycle.

(c) It may be beneficial for continuous care to bebased on a Conservation Manual, which should bea permanent and accessible document containingessential information about the building, guidanceon appropriate management, maintenance andhousekeeping procedures, essential health andsafety information and reference to the constraints towhich any proposed intervention should be subject.

(d) It may be beneficial for a Log Book to bemaintained as part of the ongoing record of thebuilding or site.

Article 10: More substantial interventions may incertain circumstances be necessary and/or desirablefor the sustainable conservation of the building orsite. Alterations, to achieve an improvement or

change of function may amount to conversion.Alteration, often in association with repair, toimprove the construction or appearance of a build-ing or site may amount to restoration.Notes: (a) Original or significant fabric of a buildingor site should always be treated with respect andthe minimum appropriate intervention should nor-mally be preferred (see Article 9).

(b) There is a presumption against restoration inthe UK, particularly in the English tradition, whichshould be maintained.

(c) Interventions should wherever possible bereversible or at least repeatable.

(d) Interventions should be carried out withregard to the “Salvage and Recycling Protocol”.

(e) Interventions should always be preceded byappropriate research, investigation and recording.

(f ) Conservation records should always be maintained, kept with the documentation of thebuilding or site and deposited in an appropriatearchive.

Article 11: Conservation should be directed andundertaken by people of appropriate knowledge,experience and skill, including all the relevant dis-ciplines. (See ICOMOS Guidelines for Training.)

Article 12: Conservation should always be basedon appropriate research and physical investigation,which should, as far as possible, be non-destruc-tive. All aspects of the significance of the buildingor site, with regard for work of all periods andphases of development, should be considered andbalanced, without inappropriate emphasis on oneaspect or period at the expense of another.

Article 13: Conservation should always haveregard to the need to maintain the appropriate set-ting of a building or site.

Article 14: Fixtures, fittings, contents or other arte-facts associated with a building or site shouldalways be treated with respect and the associationmaintained wherever possible.

Article 15: The organisations and individualsresponsible for decisions made should be clearlyidentified and recorded, with reasons where appro-priate. Such records should be kept with the docu-mentation of the building or site and deposited inan appropriate archive.

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For ease of reference the Bibliography has been arranged under the various chapter headings of this book.The following list is an explanation of the abbreviations that occur within the Bibliography.

General

Ashurst, J. (1983). Mortars, Plasters and Renders inConservation, A Basic Guide, London EcclesiasticalArchitects’ and Surveyors’ Association. A comprehensiveguide to the history, production, use and specification.

Ashurst, J. and Ashurst, N. (1988) Practical BuildingConservation, Gower Technical Press, Aldershot, England.Vol. 1. Stone Masonry.Vol. 2. Brick Terracotta, Earth.Vol. 3. Mortars, Plasters, Renders.Vol. 4. Metals.Vol. 5. Wood, Glass, Resins, Bibliography.

Ashurst, J. and Dimes, F.G. (1984). Stone in Buildings its Useand Potential Today, The Stone Federation, London.

Ashurst, J. and Dimes, F.G. (1990). Conservation of Buildingand Decorative Stone, Butterworth-Heinemann, London. Acompendium in 2 volumes by several authoritative writers.Gives a comprehensive description of building and decora-tive stones, introduced by a summary of the history of stoneconservation. An explanation of the weathering and decay ofmasonry is followed by guidelines on treating structural andsuperficial problems.

Bates, W. (1984) Historical Structural Steelwork Handbook,British Constructional Association, London. A guide to factorsto be considered in assessing load bearing capacity of 19thand early 20th century cast iron, wrought iron, and steelframed buildings. Information on properties of materials,profiles, loads and stresses.

Bernard, J. (1972). Victorian Ceramic Tiles, Cassell, London. Adetailed guide to Victorian tiles.

Bowyer, J. (1981). Handbook of Building Crafts inConservation, Hutchinson, London. A reprint of a large portion of The New Practical Builder and Workman’s

Bibliography

369

AIA American Institute of ArchitectsAIC American Institute for ConservationAMS Ancient Monuments SocietyAPT Association for Preservation TechnologyASCE American Society of Civil EngineersASCHB Association for Studies in the Conservation of

Historic BuildingsBISRA British Iron and Steel Research AssociationBRE Building Research Establishment (UK)CCI Canadian Conservation InstituteCIB Conseil International du BâtimentCOSIRA Council on Small Industries in Rural AreasDoE Department of the Environment (UK)DSIR Department of Scientific and Industrial ResearchFPA Fire Protection Association (UK)GLC Greater London CouncilHMSO Her (or His) Majesty’s Stationery Office (UK)IoAAS Institute of Advanced Architectural Studies

(formerly the York Institute of Architectural Study)ICCROM International Centre for the Study of the

Preservation and the Restoration of CulturalProperty

ICE Institution of Civil Engineers (UK)ICOM International Council on MuseumsICOMOS International Council of Monuments and SitesIIC International Institute for ConservationI.Mech.E. Institution of Mechanical EngineersIOB Institute of Building (now Chartered—CIOB) (UK)I.Struct.E. Institution of Structural Engineers (UK)LDA Lead Development Association (UK)NPL National Physical Laboratory (UK)RIBA Royal Institute of British ArchitectsRICS Royal Institution of Chartered Surveyors (UK)RILEM Réunion Internationale des Laboratoires d’Essais

et de Recherches sur les Matériaux et lesConstructions

RSA Royal Society of Arts (UK)SPAB Society for the Protection of Ancient Buildings

(UK)TRADA Timber Research and Development

Association (UK)UNESCO United Nations Educational, Scientific and Cultural

OrganisationVAG Vernacular Architecture Group (UK)

Companion by Peter Nicholson, 1823, probably the bestknown book of its kind, to which articles by modern specialistson brickwork, carpentry, joinery, slating, plastering, leadwork,glazing and painting have been added. These give informationon the methods which should be used for conservation.

Brereton, C. (1991). The Repair of Historic Buildings; Advice onPrinciples and Methods, English Heritage, London. A wideranging statement on the policy of English Heritage on main-tenance and repair. Covers general principles, day-to-daymaintenance and repair techniques related to the principalmaterials and features of historic buildings. It also advises onsituations where reinstatement is necessary rather than repairand where lost original features should be replaced.

Brett, L. 4th Viscount Esher (1968). York; A Study inConservation, HMSO, London.

British Standards Institution, BS 5937: 1981, Trees in Relation toConstruction, British Standards Institution, London. A conciseintroduction to a wide ranging topic.

British Standards Institution, BS 6270: Part I: 1982, Cleaningand Surface Repair of Buildings; natural stone, cast stone,and clay and calcium silicate brick masonry, BritishStandards Institution, London.

British Standards Institution, BS 8210: 1986, Building MaintenanceManagement, British Standards Institution, London.

British Tourist Authority (1980). Britain’s Historic Buildings; APolicy for their Future Use (Montague Report), British TouristAuthority, London.

Brunskill, R.W. (1970). Illustrated Handbook of VernacularArchitecture, Faber & Faber, London.

Brunskill, R.W. (1985). Timber Buildings in Britain, VictorGollancz in association with Peter Crawley, London.

Brunskill, R.W. (1990). Brick Building in Britain, VictorGollancz in association with Peter Crawley, London.

Building Research Establishment (1992). Recognising Wood Rotand Insect Damage in Buildings, Building ResearchEstablishment, Watford. A well illustrated handbook to assist

with recognition on site with the major wood destroyingfungi and insects found in building timbers and appendiceson remedial treatment, preservatives including health andsafety aspects.

Building Research Establishment, WatfordDigests:

‘Decay and conservation of stone masonry’, Digest 177, 1975.‘Painting walls’, Digest 192, 1982.‘Increasing fire resistance of existing timber floors’, Digest

208, 1988.‘Selection of natural building stones’, Digest 269, 1983.‘Cleaning external surfaces of buildings’, Digest 280, 1983.‘Influence of trees on house foundations in clay soil’, Digest

298, 1985.‘Dry rot; its recognition and cure’, Digest 299, 1985.‘Corrosion of metals by wood’, Digest 301, 1985.‘Prevention of decay in external joinery’, Digest 304, 1985.‘Identifying damage by wood boring insects’, Digest 307,

1986 (rev. 1992).‘Insecticidal treatment against wood boring insects’, Digest

327, 1987 (rev. 1992).‘Repairing brick and block masonry’, Digest 359, 1991.‘Control of lichens, moulds and similar growths’, Digest 370,

1992.Butterworth, B. and Flitz, J. (1981). Dictionary of Building Terms,

English/French, French/English. Construction Press, London.

Charles, F.W.B. and Charles, M. (1984). Conservation of TimberBuildings, Hutchinson, London. A description of varioustypes of timber structures and their repair, including detailedcase studies.

Charles, F.W.B. and Charles, M. (1987). Conservation of TimberBuilding, Stanley Thornes.

Chitham, R. (1985). The Classical Orders of Architecture,Butterworth-Heinmann, Oxford.

Clifton-Taylor, A. (1972). The Pattern of English Building, 3rdedition, Faber & Faber, London.

Clifton-Taylor, A. and Ireson, A.S. (1983). English StoneBuilding, Victor Gollancz, London. A well illustrated bookdescribing the use of stone from early times to the present,including recent developments and conservation work.

Coad, J. (1985). The Royal Dockyards 1690–1850; Architectureand Engineering Works of the Sailing Navy (Scolar Press,Aldershot). An authoritative and extensive account of RoyalNavy buildings in the UK and abroad. Well illustrated.Bibliography.

Condit, C.W. (1968). American Building Materials andTechniques from the First Colonial Settlements to the Present,Chicago University Press, Chicago.

Construction Industry Research and Information Association(1986). Structural Renovation of Traditional Buildings,Construction Industry Research and Information Association,London. Structural aspects of renovating 18th, 19th, andearly 20th century buildings.

Crafts Council (1982). Science for Conservators, Crafts Council,London.1 Materials2 Cleaning3 Adhesives and CoatingsA series intended to introduce those with no previous knowledge of science to the scientific principles which lieunder conservation.

Curl, J.S. (1993). Encyclopedia of Architectural Terms, DonheadPublishing, London.

Cutler, D.F. and Richardson, J.B.K. (1989). Tree Roots andBuildings, Longman Scientific and Technical, Harlow. Themost extensive study into tree roots and buildings in the UKbased on an analysis of over 12 000 trees and shrubs, initi-ated by Kew and completed by Cutler and Richardson. Givesdetails of 16 major deciduous species, brief reference to 13 lesser species and 6 conifers.

Davey, N. (1961). A History of Building Materials, Phoenix,London (also published in Italian, 1965, Storia del Materialeda Construzione, Il Saggiatore, Milan).

Department of the Environment (1991). Environmental ActionGuide, HMSO, London. A guide, following up the 1990Environmental White Paper, to assist those involved in commissioning works or managing property and ancillaryservices in dealing with the implications of their activities.

Edinburgh New Town Conservation Committee (1980). Careand Conservation of Georgian Houses. A MaintenanceManual, Architectural Press, London. After explaining theunique qualities of a New Town and the efforts being madeto maintain it, the book identifies the weak spots in Georgianconstruction, which need regular attention. A very usefulpublication, largely applicable to Georgian Houses elsewhere.

Gimpel, J. (1961). The Cathedral Builders, Evergreen Books,London.

Gray, A.S. (1985). Edwardian Architecture, A BiographicalDictionary, Wadsworth Editions, London. An extensive, well-illustrated production describing the work of over 300 architects and artists of the period. Contains a usefulintroduction to building at that time.

Harvey, J. (1972). Conservation of Buildings, John Baker, London.Hewitt, C.A. (1980). English Historic Carpentry, Phillimore,

London. Describes the development of carpentry from theSaxon period to the end of the 19th century. Assists in dating timberwork from framing techniques, jointing methods, and mouldings.

Historic Scotland, Technical Advice Notes:1 Preparation and use of lime mortars2 The conservation of plasterwork3 Performance standards for traditional sash and case

windowsHistoric Scotland, Edinburgh.

Innocent, C.F. (1916). The Development of English DomesticBuilding Construction, Cambridge University Press,Cambridge, rev. repr. 1971, David and Charles, Newton Abbot.

Insall, D.W. (1972). The Care of Old Buildings Today.Architectural Press, London.

Insall, D. (1974). Historic Buildings, action to maintain theexpertise for their care and repair, European ArchitecturalHeritage Year Study Series 3, Council of Europe, Strasbourg.

Insall, D.W. and Associates (1968). Chester; A Study inConservation, HMSO, London.

Institution of Civil Engineers (1983). Conference proceedings onthe engineering aspects of the repair of historic and recentbuildings, Thomas Telford, London.

Institution of Structural Engineers (1980). Appraisal of ExistingStructures, Institution of Structural Engineers, London.Describes factors involved in investigating, appraising, andreporting on existing structures. Gives information on natureof and methods of testing structural materials and ways ofassessing defects. Useful to architects and surveyors as wellas engineers.

Knoop, D. and Jones, G.P. (1933). The Medieval Mason,Manchester University Press, Manchester.

Lead Sheet Association, Lead work, Technical Notes 1–10, LeadSheet Association, London. Lead Sheet Technical Notes onimportant developments.

Lead Sheet Association (1990–2) Lead Sheet Manual Vol. I, Vol.II Lead Sheet Coverings to Roofs, Lead Sheet Association,London. A complete revision of the previous standard work.

Leary, E. (1983). Building Limestones of the British Isles,Building Research Establishment, Watford. Gives informationon limestone from British quarries stating quantities avail-able, sizes, and test results.

Leary, E. (1986). Building Sandstones of the British Isles, BuildingResearch Establishment, Watford. Gives information on sandstones from 78 quarries including amount available, blocksize, and test results. Also lists buildings where stones can beseen.

Lee, R. (1987). Building Maintenance Management, 3rdEdition, Collins, London. Building maintenance described ina systematic way including the use of computers.

Bibliography

370

Mainstone, R.J. (1975). The Development of Structural Form,Allen Lane, London.

Martin, D.G. (1970). Maintenance and Repair of StoneBuildings, Council for the Repair of Churches, London. Abooklet on stone repair.

McKay, W.B. (1963). Building Construction, Volumes 1–3,Longmans, London. The basic building construction textbook dealing principally with traditional construction. The4th and earlier editions are the most relevant to the con-struction of buildings in need of conservation.

Michell, E. (1988). Emergency Repairs to Historic Buildings,English Heritage, London. A guide to temporary repairswhich can be carried out easily and at the minimumexpense until permanent repairs are possible. Also coverssecurity protection of empty buildings. Includes case studies.

Nash, W.G. (1986). Brickwork, Repair and Restoration, AtticBooks, Eastbourne. A practical guide to the maintenance ofbrickwork, covering the selection of materials, craft techniques,methods of planning and scheduling work, and description ofthe precise standard of craftsmanship required.

National Audit Office (1991). Upkeep of Historic Buildings on theCivil Estate, HMSO, London. A report to the House ofCommons on the conditions of buildings on the Civil Estatemaking recommendations for their maintenance byDepartments.

Nature Conservancy Council for England (1991). Bats inRoofs—A Guide for Surveyors, Nature Conservancy Council,Peterborough. A leaflet describing the legal protection forbats and guidance on surveying and carrying out workwhere bats may be present.

Newmarkkay Gersil (1992). Mechanical and Electrical Systemsfor Historic Buildings, McGraw-Hill, Maidenhead.

Parnell, A.C. (1987). Building Legislation and Historic Buildings,Architectural Press, London. Covers Building Regulations1985, Public Health Acts, Fire Precautions Act, and HousingAct. Examines the legislation in relation to historic buildingsand procedures for relaxation. Describes case studies.

Powys, A.R. (1981). Repair of Ancient Buildings, Society for theProtection of Ancient Buildings, London. A reprint of the1929 publication with additional notes and appendices totake account of advantages in technology and provide extrainformation. It describes methods of repair in accordancewith the principles of the Society.

Purchase, W.R. (1987). Practical Masonry, Attic Books, BuilthWells (1987 reprint of 1985 publication). Describes practicalmasonry skills and is also useful to those specifying andsupervising work.

Riden, P. (1987). Record Sources for Local History, Batsford, London.Royal Commission on the Historic Monuments of England and

English Heritage (1990). Revised Thesaurus of ArchitecturalTerms, London.

Royal Society of Arts (1987). The Future of the Public Heritage,Royal Society of Arts, London. Verbatim report of a conferencein 1986 on the future policy for Government owned historicbuildings.

Rykwert, J. (ed.) (1955). Ten Books on Architecture by LeoneBattista Alberti, Trans. J. Leoni, London, 1776. Facsimile edn,Tiranti, London.

Salaman, R.A. (1975). Dictionary of Tools used in Woodworkingand Allied Trades c. 1700–1900, Allen & Unwin, London.

Schwicker, A.C. (1972). International Dictionary of BuildingConstruction, Technoprint International, Milan; McGraw-Hill,New York; Dunod, Paris.

Scottish Civic Trust (1981). New Uses for Older Buildings inScotland. A Manual for Practical Encouragement, HMSO,Edinburgh. Gives general guidance on possible new uses,describes case studies, and provides information on technicaland financial aspects of conversions.

Scottish Conservation Bureau (1991). Edinburgh; HistoricScotland. A comprehensive guide to organisation: whosework relates to the conservation of historic objects andbuildings.

Scottish Natural Heritage (1988). An Inventory of Gardens andDesigned Landscapes in Scotland. In 5 volumes availablefrom the Scottish Natural Heritage, Battleby, Redgoston,Perth PH1 3EW.

Smith, L. (1985). Investigating Old Buildings, Batsford, London.Describes materials and methods of construction of post-medieval buildings and techniques for recording them.

Smith, R.J. (1990). A Dictionary of Specialist Crafts for Architectsand Builders. Robert Hale, London. A classified directory of firmsand individuals practising the various professions, trades, andcrafts required in conservation of buildings and their contents.

Society for the Protection of Ancient Buildings, BasicInformation Leaflets:IN/1 How to make limewashIN/2T Timber Treatment—A Warning about De-frassingIN/3 Surface Treatment of Timber Framed BuildingsIN/4T The Need for Old Houses to BreatheIN/5 Removing Paint from Old BuildingsSociety for the Protection of Ancient Buildings, London.

Society for the Protection of Ancient Buildings, TechnicalPamphlets:Ashurst, J. Cleaning of Stone and BrickBrockett and Wright Care and Repair of Thatched RoofsHunt, A. Electrical Wiring in Old BuildingsMacGregor, J. Outward Leaning WallsMacGregor, J. Strengthening Timber FloorsParnell, A. and Ashford, D. Fire Safety in Historic BuildingsThomas, A. Treatment of Damp in Old BuildingsWilliams, G. Chimneys in Old BuildingsWilliams, G. Pointing of Stone and Brick WallingSociety for the Protection of Ancient Buildings, London.

Stagg, W.D. and Masters, R. (1983). Decorative Plasterwork, ItsRepair and Restoration, Orion Books, Eastbourne. An intro-duction to assist craftmen and supervisors in plastering intraditional materials and methods and to guide architectsrestoring decorative plasterwork.

Stone Federation, Handbook and Directory of Members (revisedannually) Ealing Publications, Maidenhead. Includes tables ofmembers engaged in quarrying, stone supply, and cleaning.

Stone Federation Natural Stone Directory (published everythree years), Ealing Publications, Maidenhead. Lists membersengaged in quarrying giving details of stone produced.

Suddards, R. (1988). Listed Buildings; The Law and Practice(2nd Edition), Sweet and Maxwell, London. A detailed exam-ination of the Law relating to Historic Buildings, AncientMonuments, and Conservation Areas.

Thompson, M.W. (1981). Ruins, Their Preservation andDisplay, British Museum, London. An exploration of the careof ruined buildings—retrieval of remains, preservation ofmasonry, laying out for display, representation of missingparts, restoration of ancillary parts and interpretation.

Viollet-le-Duc, E.E. (1854–68). Dictionnaire raisonné de l’archi-tecture française du XIe an XVIe siecle (The analytical diction-ary of French architecture from the 11th to the 16th century), 10 vols, Bance, Paris (see trans. article ‘Restauration’ in Vol. 8).

Viollet-le-Duc, E.E. (1875). On Restoration, trans. CharlesWethered, Sampson Low, Marston, Low and Searle, London.

Warland, E.G. (1986). Modern Practical Masonry, Stone Federation,London (reprint of 1929 publication by Pitman Books). This wasthe standard work on masonry. It illustrates the methods used inthe early twentieth century for cladding steel framed buildingswith stone which are now causing trouble in some instances.

Weaver, M.E. (1993). Building Conservation. Guide toTechniques and Materials, Wiley, New York, USA. A scien-tific study which also defines the work of conservators.

Introduction to architectural conservation(chapter 1)

Australia ICOMOS (1981). The Burra Charter. Pamphlet.

Bibliography

371

Batra, N.L. (1996). Heritage Conservation: Preservation andRestoration of Monuments, New Delhi.

Beggs, C. (2002). Energy Management & Conservation,Architectural Press, London.

Birdwood, G. (1880). Industrial Arts of India, London.Bowyer, J. et al. (1981). Handbook of Building Crafts in

Conservation, Hutchinson & Co., London.Brown, P. (1942). Clark, K. (2001). Informed Conservation,

English Heritage, London.

Collingwood, R.G. (1938). The Principles of Art, Oxford.Committee on Historic Resources (1983). Preservation Practice,

AIA Handbook, C-1, American Institute of Architects,Washington, D.C.

Coomaraswamy, A. (1909). The Indian Craftsman, London.Coomaraswamy, A. (1974). The Dance of Shiva, New Delhi.Curl, J.S. (1997). Encyclopaedia of Architectural Terms,

Donhead, Dorset.

Dimes, F.G. and Ashurst, J. (1998). Conservation of Building &Decorative Stone, Architectural Press, London.

Doxidias, A.C. (1963). Architecture in Transition, London.

Earl, J. (1996). Building Conservation Philosophy, Reading.English Heritage (1986). Public Sources of Grant Aid for the

Repair, Adaption and Reuse of Historic Buildings andMonuments. Historic Buildings and Monuments Commissionfor England, London.

Erder, C. (1986). Our Architectural Heritage fromConsciousness to Conservation, UNESCO, Paris.

Fawcett, J. (ed.) (2001). Historic Floors: Their Care andConservation, Architectural Press, London.

Fitch, J.M. (1982). Historic Presentation. CuratorialManagement of the Built World, McGraw-Hill, New York.

Fletcher, Sir Banister (1996). A History of Architecture, 20th edn.(ed. Cruickshank D.), Architectural Press, London.

Fram, M. (1988). Well-preserved: The Ontario HeritageFoundation’s Manual of Principles and Practice forArchitectural Conservation, The Boston Mills Press, Extractsfrom ‘The Inheritance’ and ‘Careful Conservation’, Erin Ontario.

Havell, E.B. (1913). Indian Architecture: its Psychology,Structure and History, from the First Muhammadan Invasionto the Present Day, London.

ICCROM (1982). International Meeting of Co-ordinators ofTraining in Architectural Conservation. UNESCO Rome.

ICOMOS (1966). The Venice Charter (1966), InternationalCharter for the Conservation and Restoration of Monumentsand Sites. Paris.

ICOMOS (1984). Florence Charter for Historic Gardens andLandscape, Paris.

ICOMOS (1987). Washington Charter for the Conservation ofHistoric Towns and Urban Areas, ICOMOS/INFORMATION,April/June, Paris.

ICOMOS (1990). Lausanne Charter for Archaeological Heritage,Paris.

ICOMOS (1993). Guidelines for Education and Training forConservation of Monuments, Ensembles and Sites, Paris.

Inocent, C.F. (1916) (1999). The Development of EnglishBuilding Construction, Donhead, Dorset.

Insall, D. (1972). The Care of Old Buildings Today,Butterworth-Heinemann, Oxford.

Jokilehto, J. (2002). History of Architectural Conservation,Architectural Press, London.

Kain, R. (ed.) (1981). Planning for Conservation: AnInternational Perspective, London.

Langston, C. (ed.) (2001). Sustainable Practices in the BuiltEnvironment, Architectural Press, London.

Larsen, K.E. and Marstein, N. (2000). Conservation of HistoricTimber Structures, Architectural Press, London.

Litchfield, M.W. (1982). Renovation a Complete Guide, J. Wiley,New York.

Lynch, G. (1994). Brickwork, History, Technology & Practice(2 vols.), Donhead, Dorset.

Maddex, D. (1985). All About Old Buildings. The WholePreservation Catalog. The Preservation Press, Washington D.C.

Marshall, J. (1923). The Conservation Manual, ASI, New Delhi.Miller, H. et al. (1986). Skills Development Plan for Historical

Architects in the National Park Service. US Department of theInterior (NPS), Washington D.C.

Pasley, C.W. (2001). Practical Architecture (facsimile 1826),Donhead, Dorset.

Pearson, S. and Meeson, B. (ed.) (19XX). Vernacular Buildings ina Changing World, Council for British Archaeology, London.

Pevsner, N. (1990). An Outline of European Architecture,London.

Philippot, P. (1972). Restoration, Philosophy, Criteria, Guidelines,ICCROM, Rome.

Powys, A.R. (reprint 1981). Repair of Ancient Buildings, Societyfor the Preservation of Ancient Buildings, London.

Powys, A.R. (1995). Repair of Ancient Buildings, third edition,Guildford.

Robson, P. (1999). Structural Repair of Traditional Buildings,Donhead, Dorset.

Ruskin, J. (1849). The Seven Lamps of Architecture, London.

Sebestyen, G. and Rudnay, J. (2002). New Architecture &Technology, Architectural Press, London.

Smith, J. (1978). A Critical Bibliography of BuildingConstruction, Mansell, London.

Snowden, A.M. (ed.) (1990). Maintenance of Brick and StoneStructures, E. & F.M. Spon, London.

Thompson, M.W. (1981). Ruins, their Preservation and Display,Colonade Books, British Museum Publications, London.

Tiesdell, S.A., Oc, T., Heath, T. (1996). Revitalising HistoricUrban Quarters, Architectural Press, London.

Tillotson, G.H.R. (1989). The Tradition of Indian Architecture:Continuity, Controversy & Change since 1850, London.

Tschudi, M.S. (1976). Restoration and Anti-Restoration (2ndEdition), Universiteforlaget, Oslo.

UNESCO World Heritage Convention (1985). Conventions andRecommendations of UNESCO Concerning the Protection ofCultural Heritage, UNESCO, Paris.

UNESCO (1968). The Conservation of Cultural Property,UNESCO, Paris.

Vyas, H.K. (2000). Design: The Indian Context, Ahmedabad.

Warren, J. (1998). Conservation of Brick, Architectural Press,London.

Warren, J. (1999). Conservation of Earth Structures,Architectural Press, London.

Watt, D. (1999). Building Pathology: Principles & Practice,Blackwell Publishing, Oxford.

Watt, D., Swallow, P. and Ashton, R. (1993). Measurement &Recording of Historic Buildings, Donhead, Dorset.

Watt, D., Swallow, P. and Ashton, R. (1996). Surveying HistoricBuildings, Donhead, Dorset (has an excellent bibliography).

Worthington, J. (1998). Context: New Buildings in HistoricSettings, Architectural Press, London.

Structural actions of historic buildings(chapter 2)

Beckman, P. (1977). ‘Structural Analysis and Recording ofAncient Buildings’, in papers on the Seminar on Structuresin Historic Buildings, ICCROM, Rome, also Arup J. 7 (2) 2–5,July 1972, London.

Building Research Establishment (1988). ‘New Site Tool forTesting Masonry Strength’, in BRE News of ConstructionResearch, Watford.

Bibliography

372

Fitchen, J. (1986). Building Construction before Mechanization,MIT Press, Cambridge MA USA.

Innocent, C.F. (1971). The Development of English BuildingConstruction (Cambridge University Press, 1916, reprint),David and Charles, Newton Abbot, England.

Jandl, H. Ward (ed.) (1983). The Technology of HistoricAmerican Buildings, Foundation for PreservationTechnology, Washington, D.C.

Lemaire, R.N. and Van Baless, K. (eds) (1988). Stable—Unstable? Structural Consolidation of Ancient Buildings(24 lectures), Leuven University Press, Leuven.

Reid, E. (1984). Understanding Buildings; a MultidisciplinaryApproach, Construction Press, London.

Robson, P. (1991). Structural Appraisal of TraditionalBuildings, Donhead, Dorset.

Society for the Protection of Ancient Buildings (SPAB) (2001).‘Technical Pamphlets & SPAB Guides, SPAB, London

TP5 Pointing Stone & Brick WallingTP8 The Control of Damp in Old BuildingsTP9 Electrical InstallationsTP10 The Care & Repair of Thatched RoofsTP11 Panel Infilling to Timber-Framed BuildingsTP12 The Repair of Timber Frames & RoofsTP13 Repair of Wood WindowsTP15 Care & Repair of Old FloorsTP16 Care & Repair of Flint Walls

Information Sheets, SPAB, LondonIN1 Basic LimewashIN2 Timber TreatmentIN4 The Need for Old Buildings to ‘Breathe’IN5 Removing Paint from Old BuildingsIN7 First Aid Repair to Traditional Farm BuildingsIN8 Tuck Pointing in PracticeIN9 An Introduction to Building LimesIN10 Patching Old FloorboardsIN11 Rough-Cast for Historic BuildingsIN12 Into to Repair of Lime-Ash & Plaster FloorsIN13 How to make Beeswax PolishIN14 Is Timber Treatment Always Necessary?

Torraca, G. (1982). Porous Building Materials. Science forArchitectural Conservation, ICCROM, Rome.

Viollet-le-Duc, E.E. (1881). Lectures on Architecture, 2 Vols,translation, Sampson Low, Marston, Searle and Rivington,London.

Structural elements I: Beams, arches,vaults and domes (chapter 3)

Baer, N.S., Fitz, N.S. and Livingston, R.A. (ed.) (1998).Conservation of Brick Structures, Donhead, Dorset.

Burn, S.B. (2001). Masonry, Bricklaying & Plastering (facsimile1871).

Courtney, L.T. (ed.) (1997). Engineering of Mediaeval Cathedrals,Ashgate Variorum Studies in the History of Civil Engineering.

Cowper, A.D. (1998). Limes & Lime Mortars (facsimile 1927),Donhead, Dorset.

Fitchen, J. (1961). The Construction of Gothic Cathedrals; a Studyof Medieval Vault Erection, Oxford University Press, Oxford.

Heyman, J. (1966). ‘The Stone Skeleton’, Int. J. Solids &Structures 2, 249–279, Pergamon Press, Oxford.

Heyman, J. (1967). ‘Spires and Fan Vaults’, Int. J. Solids andStructures, 3, 243–257, Pergamon Press, Oxford.

Heyman, J. (1969). ‘The Safety of Masonry Arches’, Int. J. Mech.Sci., 11, 363–385, Pergamon Press, New York.

Heyman, J. (1976). ‘The Strengthening of the West Tower of ElyCathedral’, Proc. Inst. Civ. Engrs. pt. 1. pp. 123–147, London.

Heyman, J. and Threfall, B.D. (1972). ‘Two Masonry Bridges: (1) Clare College Bridge, (2) Telford’s Bridge at Over’, Proc.Inst. Civ. Engrs, 52, 319–330, London.

Hill, P.R. and David, J.C.E. (1996). Practical Stone Masonry,Donhead, Dorset.

Howe, J.A. (2001). The Geology of Building Stones (facsimile1910), Donhead, Dorset.

Lynch, G. (1990). Gauged Brickwork, Donhead, Dorset.

Macgregor, J.E.M. (1973). Strengthening Timber Floors(Technical Pamphlet 2), Society for the Preservation ofAncient Buildings, London.

Pasley, C.W. (1997). Observation on Limes (facsimile 1838),Donhead, Dorset.

Ruddock, T. (2000). Masonry Bridge & Viaducts, AshgateVariorum Studies in the History of Civil Engineering.

Vicat, L.J. (1997). Mortars & Cements (facsimile 1837),Donhead, Dorset.

Viollet-le-Duc, E.E. (1854–68). Dictionnaire raisonné de l’architecture française du XIe au XVIe siecle, Paris, 10 vols. Translation of the article ‘Construction’ inHuss, G.M. (1895), Rational Building, Macmillan, New York.

Yeomans, D. (ed.) (1999). The Development of Timber as aStructural Material, Ashgate Variorum Studies in the Historyof Civil Engineering.

Structural elements II: Trusses andframes (chapter 4)

Bailey, M.W. (1961). The English Farmhouse and Cottage,Routledge and Kegan Paul, London.

Bennet, F. and Pinion, A. (2000). Roof Slating & Tiling(facsimile 1948), Donhead, Dorset.

Brunskill, R.W. (1970). Illustrated Handbook of VernacularArchitecture, Faber & Faber, London.

Charles, F.W.B. (1984). Conservation of Timber Buildings,Hutchinson, London.

Charles, F.W.B. and Charles, M. (1995). Conservation of TimberBuildings, Donhead, Dorset.

Fletcher, J. (ed.) (1978). Dendrochronology in Europe, 139–161,BAR International Series 51.

Goodall, H. and Friedman R. (1980). Log Structures.Preservation and Problem Solving, American Association forState and Local History, Nashville, USA.

Hewett, C.A. (1969). The Development of Carpentry 1200–1700,David and Charles, Newton Abbot.

Insall, D. (1973). The Care of Old Buildings Today,Butterworth-Heinemann, Oxford.

Rempel, J. (1980). Building with Wood (revised edn),University of Toronto Press, Toronto.

Tokyo International Research Institute of Cultural Properties(1983). The Conservation of Wooden Cultural Property.Internal Symposium on Conservation and Restoration ofCultural Property Nov. 1982. Tokyo and Saitma. TokyoNational Institute of Cultural Properties, Veno Park, Tokyo.CALMSC.

Weaver, L. (2002). English Leadwork, Its Art & History (facsimile1948), Donhead, Dorset.

Bibliography

373

Structural elements III: Walls, piers andcolumns (chapter 5)

Ashurst, J. (1983). Mortars, Plasters and Renders inConservation, Ecclesiastical Architects and Surveyor’s Assoc.,London.

Ashurst, J. and Ashurst, N. (1988). ‘The Repair andMaintenance of Cob, Chalk Mud, Pisé and Clay Lump’, inPractical Building Conservation, English Heritage TechnicalHandbook, Vol. 2, Brick, Terracotta and Earth, GowerTechnical Press, Aldershot.

Blankart, G. (2002). The Art of the Plasterer (facsimile ed. of1908), Donhead, Dorset.

Building Research Establishment (1983). The Selection ofNatural Building Stone, Digest 269, HMSO, London.

Knoop, D. and Jones, O.P. (1933). The Medieval Mason,Manchester University Press, Manchester.

Millar, W. (1998). Plastering, Plain & Decorative (facsimile1897), Donhead, Dorset.

Pearson, G.T. (1992). Conservation of Clay & Chalk Buildings,Donhead, Dorset.

Ross, K.D. and Butlin, R.N. (1989). Durability Tests for BuildingStone, Building Research Establishment, Watford.

Schaffer, R.J. (1985). The Weathering of Natural Building Stones,Building Research Establishment Special Report No 18,Garston BRE (1932) (facsimile reprint), HMSO, London.

Schofield, J. (1985). Basic Limewash, Information Sheet No: 1,SPAB, London.

Simpson, J. and Brown, S. (2002). Conservation of Plasterwork,Historic Scotland, Advice Note No. 2, Edinburgh.

Verall, W. (2000). The Modern Plasterer (facsimile 2 vol.),Donhead, Dorset.

Williams-Ellis, C. (1999) Buildings in Cob Pisé & StabilisedEarth (facsimile 1919: 1947), Donhead, Dorset.

Wingate, M. (1985). Small Scale Lime Burning, IntermediateTechnology Publications, Rugby.

Structural elements IV: Foundations(chapter 6)

Aboricultural Journal, (1985). A series of articles:Pryke, F.S. ‘Trees and Buildings’Biddle, P.G. ‘Trees and Buildings’Coutts, M.P. ‘Tree Root Damage to Buildings’Flora, T. ‘Physiological Characteristics of Tree Root Activity’Flora, T. ‘Trees and Building Foundations’The series covers arboricultural aspects with some

thoroughness.

Bowen, R. (1984). Geology in Engineering, Elsevier AppliedSciences Publishers, London.

Dowrick, D.J. and Beckman, P. (1971). Paper 74155, YorkMinster Structural Restoration, ICE, London.

Dunham, C.W. (1962). Foundations of Structures, McGraw-Hill,New York.

Schultze, E. (1970). Techniques de conservation et de restaura-tion des monuments, terrains et foundations (Techniques forconservation and restoration of historic buildings, soils andfoundations). Publication No. 3, ICCROM, Rome.

Climatic causes of decay (chapter 7)

Addleson, L. (1982). Building failures (non structural); aGuideline to Diagnosis, Remedy and Prevention,Butterworth-Heinemann, Oxford.

Allen, W. (1997). Envelope Design for Buildings, ArchitecturalPress, London.

Building Research Establishment (1971). An Index to DrivingRain, BRE Digest 127, 2nd ser., HMSO, London.

Building Research Establishment (1976). Roof Drainage, Digests188–9, HMSO, London.

Building Research Establishment (1982). The Durability of Steel inConcrete, Parts I, II, III. Digests 263, 264, 265, HMSO, London.

De Angelis d’Ossat, G. (1972). Guide to the Methodical Study ofMonuments and Causes of their Deterioration, ICCROM,Rome.

Holmström, I. and Sandström, C. (1975). Maintenance of OldBuildings, Document D 10, National Swedish Institute ofBuilding Research, Stockholm.

Kendrew, W.G. (1963). Climate of Continents, 5th edn,Clarendon Press, Oxford.

Mather, J.R. (1974). Climatology; Fundamentals andApplications, McGraw-Hill, New York.

Plenderleith, H.J. and Werner, A.E.A. (1971). The Conservationof Antiquities and Works of Art, 2nd edn, Oxford UniversityPress, Oxford.

Simpson, J.W. and Horrobin, P.J. (eds) (1970). The Weatheringand Performance of Building Materials, Medical andTechnical Publishing, Aylesbury.

Smith, B.J. and Warke, P.A. (ed.) (1996). Processes of UrbanStone Decay, Donhead, Dorset.

Thomson, G. (1974). The Museum Environment, Butterworth-Heinemann, Oxford.

Historic buildings in seismic zones(chapter 8)

Anon. (1976). Guidelines for Disaster Prevention, Office of theUnited Nations Disaster Relief Co-ordinator, United Nations,Geneva.Vol. 1 Pre-disaster Physical Planning of Human Settlements.Vol. 2 Building Measures for Minimising the Impact of

Disasters.Vol. 3 Management of Settlements.

Anon. (1978). Disaster Prevention and Mitigation; aCompendium of Current Knowledge, Vol. 3, SeismologicalAspects, Office of the United Nations Disaster Relief Co-ordinator, United Nations, Geneva.

Cestelli, G.C. et al. (1981). Salient Aspects of the Behaviour ofBuildings under Seismic Shaking, Associazione ItalianaTecnico Economica del Cemento, Rome.

Dowrick, D.J. (1977). Earthquake Resistant Design—a Manualfor Engineers and Architects, Wiley, London.

Feilden, B.M. (1987). Between Two Earthquakes, ICCROM withGetty Conservation Institute, Rome/Marina del Rey, USA.

McDonald, R. (2002). Rebuild in the Aftermath of a Disaster,Architectural Press, London.

Pichard, P. (1984). Emergency Measures and DamageAssessment after an Earthquake, UNESCO, Paris.

UNESCO (1985). Earthquake Risk Reduction in the BalkanRegion, Final Report, Sofia.

UNESCO (1985). Building Construction under SeismicConditions in the Balkan Region & Post-Earthquake DamageEvaluation and Strength Assessment of Buildings underSeismic Conditions; Seismic Design Codes, United NationsDevelopment Programme, Vienna.

Bibliography

374

Botanical, biological and microbiologicalcauses of decay (chapter 9)

Allsopp, D. and Seal, K.J. (1986). Introduction to biodeteriora-tion, E. Arnold, London.

Building Research Establishment (1985). Dry Rot. ItsRecognition and Control. Digest 299, HMSO, London.

Insects and other pests as causes of decay(chapter 10)

Bletchly, J.D. (1967). Insects and Marine Borer Damage toTimber and Woodwork, Forest Products Research Laboratory,HMSO, London.

Bravery, A.F., Berry, R.W., Carey, J.K. and Cooper, D.E. (1992).Recognising Wood Rot and Insect Damage in Buildings,Building Research Establishment, Watford.

Building Research Establishment (1980, rev. 1992). Reducingthe risk of pest infestation: design recommendations and liter-ature review, Digest 238, HMSO, London.

Building Research Establishment (1986). Controlling DeathWatch Beetle, Information paper 19/86, BRE, Garston,Watford.

Building Research Establishment (1986, rev. 1992). IdentifyingDamage by Wood-boring Insects, Digest 307, BRE, Garston,Watford.

Building Research Establishment (1987, rev. 1992) InsecticidalTreatments against Wood-boring Insects, Digest 327, BREGarston, Watford.

Leigh, J. (1972). Bats, Birds, Bees, Mice and Moths; the Controlof Occasional Pests in Church Buildings, Council for Placesof Worship, London.

Ridout, B. (2000). Timber Decay in Buildings: The ConservationApproach to Treatment, E&FN Spon, London.

Man-made causes of decay (chapter 11)

Ashurst, N. (1994). Cleaning Historic Buildings (2 vol.),Donhead, Dorset.

Building Research Establishment (1989). Brickwork: Preventionof Sulphate Attack (Design), DAS 128, BRE, Garston, Watford.

Building Research Establishment (1990). Damage to Structuresfrom Groundborne Vibration, Digest 353, BRE, Garston,Watford.

DoE Building Effects Review Group (1990). The effects of acidDeposition on Buildings and Building Materials, HMSO,London.

Kapsa, I. (1971). Protection of Housing Estates againstUnfavourable Effects of Traffic, Research Institute forBuilding and Architecture, Prague.

Steffens, R.J. (1974). Structural Vibration and Drainage, BRE,Garston, Watford.

Thompson, G. (1994). The Museum Environment, 2nd edn,Butterworth-Heinemann, Oxford.

Webster, R.G.M. (ed.) (1992). Stone Cleaning, Donhead, Dorset.

Internal environment of historic buildings (chapter 12)

Brommelle, M., Thomson, G. and Smith, P. (eds) (1980).Conservation within Historic Buildings, IIC, London.

Building Research Establishment (1949). Pattern Staining inBuildings, Digest 4, 1st ser., BRE, Garston, Watford.

Building Research Establishment (1951). The Principles of NaturalVentilation in Buildings, Digest 34, 1st ser., HMSO, London.

Buys, S. and Oakley, V. (1996). Conservation and Restorationof Ceramics, Architectural Press, London.

Cunnington, P. (1984). Care for Old Houses, Prism Alpha,Sherborne, Dorset.

Department of the Environment (1970, 1971). Condensation inBuildings, pt. I ‘Design Guide’; pt. II ‘Remedial measures’,HMSO, London.

Faber & Kell (2001). Heating and Air Conditioning forBuildings, 9th edn., Architectural Press, London.

Gill, K. and Eastop, D. (1998). Upholstery ConservationPrinciples and Practice, Architectural Press, London.

Hughes, P. (1986). The Need for Old Buildings to ‘Breathe’,SPAB Information Sheet No 41, London.

Keene, S. (2002). Managing Conservation in Museums,Architectural Press, London.

Kite, M. and Thomson, R. (2003). Conservation of Leather andRelated Materials, Architectural Press, London.

Leiff, M. and Trechsel, H.R. (eds) (1982). Moisture Migration inBuildings, Symposium Philadelphia Oct 1980. ASTM SpecialTechnical Publication 779, American Society for Testing andMaterials, Philadelphia, USA.

Plenderleith, H.J. and Werner, A.E.A. (1971). The Conservationof Antiquities and Works of Art, 2nd edn, Oxford UniversityPress, Oxford.

Straaten, J.F. van (1967). Thermal Performance of Buildings,Elsevier, Amsterdam.

Thompson, G. (1994). The Museum Environment, 2nd edn,Butterworth-Heinemann, Oxford.

Vinney, N. and Rivers, S. (2002). Conservation of Furniture,Architectural Press, London.

Webb, M. (2000). Lacquer, Technology and Conservation,Architectural Press, London.

Multi-disciplinary collaboration projectsin the UK (chapter 13)

Horie, C.V. (1987). Materials for Conservation, ArchitecturalPress, London.

Hughes, H. (ed.) (2002). Layers of Understanding: SettingStandards for Architectural Paint Research, Donhead, Dorset.

Inspections and reports (chapter 14)

Becker, N. (1980). The Complete Book of Home Inspection,McGraw-Hill, New York.

Beckman, P. (1972). Structural analysis and recording of ancientbuildings. Arup J. 7 (2) 2–5, Arup and Partners, London.

Beckmann, P. (2003). Structural Aspects of BuildingConservation, Architectural Press, London.

Bowyer, J. (1970). Guide to Domestic Building Surveys, 3rdedn, Architectural Press, London.

Building Research Establishment (1972). Condensation, Digest110, BRE, Garston, Watford.

Building Research Establishment (1976). Site use of the theodo-lite and surveyors level, Digest 202, BRE, Garston, Watford.

Building Research Establishment (1986). Rising Damp in Walls;diagnosis and treatment, Digest 245, BRE, Garston, Watford.

British Research Establishment (1989). Simple measuring andmonitoring of movement in low rise buildings, Digest 343,BRE, Garston, Watford.

Bibliography

375

Building Research Establishment (1991). Why do buildingscrack ? Digest 361, BRE, Garston, Watford.

Burnay, S.G., Williams, T.L. and Jones, C.D. (1988).Applications of thermal imaging, Adam Hilgar, Bristol.

Carson, A. and Dunlop, R. (1982). Inspecting a House; A Guide forBuyers, Owners and Renovators, General Publishing, Toronto.

CBA Research Report 126 (2001). Vernacular Buildings in aChanging World, York.

Collings, J. (2002). Old House Repair and Care, Donhead,Dorset.

Council for the Care of Churches London (1980). A Guide toChurch Inspection and Repair, CIO Publishing, London.

Davison, S. (2002). Conservation and Restoration of Glass,Architectural Press, London.

De Angelis d’Ossat G. (1972). Guide to the Methodical Study ofMonuments and Causes of their Deterioration, Issued jointlyby ICCROM and the School of Architecture, Rome University,Rome (text in English and Italian).

Ecclesiastical Architects and Surveyors Association (1985).Quinquennial Inspections: notes for Members undertakingquinquennial inspections of Churches and Church premisesand for the preparation of reports on such inspections,Newcastle upon Tyne.

Hart, J.M. (1990). A Practical Guide to Infra-red Thermographyin Building Surveys, BRE Report 176, Garston, Watford.

Mainstone, R. (2001). Developments in Structural Form, 2ndedn, Architectural Press, London.

Mainstone, R.J. Evaluation of Actions in the Field of Protectionand Restoration of Cultural Monuments 1960–85, UNESCO,Paris.

Oxley, R. (2003). Survey and Repair of Traditional Buildings,Donhead, Dorset.

Seeley, I.H. (1985). Building Surveys, Reports andDilapidations, Macmillan, London.

Smith, L. (1985). Investigating Old Buildings, Batsford, London.

Research, analysis and recording (chapter 15)

Beckamn, P. (1972). Structural analysis and recording of ancientbuildings, Arup J. 2, 2–5, Arup and Partners, London.

Borchers, P.E. (1978). Photogrammetric Recording of CulturalResources, US Department of the Interior (NPS),Washington D.C.

Bray, R.S., Dale, W., Grainger, W. and Harrold, R. (1980).Exterior Recording Training Manual (rev. edn), ParksCanada (CIHB), Ottawa.

Buchanan, T. (1983). Photographing Historic Buildings, HMSO,London.

Building Research Establishment (1971). Devices for DetectingChanges in Width of Cracks in Buildings, Information sheetTIL5, BRE, Garston, Watford.

Busch, A. (1987). The Photography of Architecture, VanNostrand Reinhold, New York.

Chambers, J.H. (1973). Rectified Photography and PhotoDrawings for Historic Preservation (draft), US Department ofthe Interior (NPS), Washington D.C.

Chitham, R. (1980). Measured Drawings for Architects,Architectural Press, London.

Colvin, H.M. (1954). A Biographical Dictionary of BritishArchitects 1600–1840, revised edn, 1978, John Murray, London.

Falconer, K. and Hay, G. (1981). The Recording of IndustrialSites. A review, Council for British Archaeology, London.

Fladmark, K. (1978). A Guide to Basic ArchaeologicalFieldwork. Procedures, Simon Fraser University, Burnaby.

Fleming, J. et al. (1991). The Penguin Dictionary ofArchitecture, 4th edn, Penguin, Harmondsworth.

Hart, D.M. (1975). X-ray Examination of Historic Structure,Office of Archaeology and Historic Preservation, NationalPark Service, US Dept. of Interior, Washington D.C.

Harvey, J.H. (1974). Sources for the History of Houses, BritishRecords Association, London.

McDowall, R.W. (1980). Recording Old Houses; A Guide,Council for British Archaeology, London.

Poppeliers, J.C. et al. (1983). What style is it? PreservationPress, Washington D.C.

Salzman, L.F. (1952). Building in England down to 1540; adocumentary history, Clarendon Press, Oxford.

Smith, J.T. and Yates, E.M. (1974). On dating English Housesfrom external evidence (reprint), E. W. Classey Ltd,Faringdon, Berks.

Teutonico, J.M. (1986). Laboratory Manual for ArchitecturalConservators, ICCROM, Rome.

Preventive maintenance of historic buildings (chapter 16)

Anon. (n.d. late 1940s). The Treatment of Ancient BuildingsDamaged in Wartime, SPAB, London.

Anon. (1985). Proceedings of symposium on building appraisal,maintenance and preservation, University of Bath,Department of architecture and engineering, Bath.

Anon. (1986). Wood decay in Houses and How to Control it,rev. edn, US Department of Agriculture, Washington D.C.

Architect’s Journal (1976). ‘Damp Proof Courses. In Handbookof Housing Rehabilitation, Repair and Maintenance’,Information Sheet No. 2, 21 July pp. 139–141, London.

Ashley-Smith, J. (1999). Risk Assessment for ObjectConservation, Architectural Press, London.

Ashurst, J. (1977). Cleaning Stone and Brick, Technical pamphlet4, Society for the Preservation of Ancient Buildings, London.

Beard, G. (1975). Decorative Plasterwork in Great Britain,Phaidon, London.

Beard, G. (1983). Stucco and Decorative Plasterwork in Europe,Thames and Hudson, London.

Brereton, C. (1991). The Repair of Historic Buildings (Advice onPrinciples and Methods), English Heritage, London.

Building Technology Standards (1975). Graffiti Removers; evaluation and preliminary selection criteria, MB SIR75–914, Division of Energy, Washington D.C.

Building Research Establishment (1962–88). Garston, WatfordAdvisory papers:‘Diagnosis of rising damp’, TIL29, 1977.‘Electro osmosis damp proofing’, TIL35, 1975.‘Rising damp: advice to owners considering remedial work’,

TIL47, 1976.Digests:‘Condensation’, Digest 110, 1972.‘Drying out buildings’, Digest 163, 1974.‘Failure patterns and implications’, Digest 176, 1975.‘Preventing decay in external joinery’, Digest 304, 1985.‘Rising damp in walls’, Digest 27, 1962.Current papers:‘Protection of buildings against water from the ground’, CP

102/73Information papers:‘House inspection for dampness. A first step in remedial

treatment for wood rot’, IP 19/88.Building Research Advisory Service (1985). Diagnosis of

Dampness, BRE, Garston, Watford.

Central Council for the Care of Churches (1960). Bats andBirds; damage by; notes on its preservation and cure. 14thrept, Central Council for the Care of Churches, London.

Central Council of Church Bell Ringers (1966). A Handbook ofthe Installation and Repair of Bells, Bell Frames and Fittings,6th edn, Council for the Places of Worship, London.

Bibliography

376

Central Council of Bell Ringers (1973). The Towers and BellsHandbook, Brackley Smart & Co. for the Council, London.

Chambers, J.H. (1976). Cyclical Maintenance for HistoricBuildings, U.S. Department of the Interior, Washington D.C.

Clements, R. and Parker, D. (1965). Manual of MaintenanceBuilding Services, Business Publications, London.

Clutton, C. (1951). The Parish Organ, 11th rept, Central Care ofChurches, London.

Council for the Care of Churches (1951). The Treatment andPreservation of Monuments in Churches, 11th rept, Councilfor the Care of Churches, London.

Council for the Care of Churches (1957). Church Timberwork,Books and Fabrics: Damage and Repair, A special report.Council for the Places of Worship, London.

Council for the Care of Churches (1962). The Care ofMonuments, Brasses and Ledger Slabs in Churches, Councilfor the Places of Worship, London.

Council for the Care of Churches (1963). Damage to Organsthrough abnormal Atmospheric Conditions, Council for thePlaces of Worship, London.

Council for the Care of Churches (1970). Church Organs,Council for the Places of Worship, London.

Council for the Care of Churches (1970). How to look after yourChurch, Church Information Office, London.

Council for the Care of Churches (1971). Church Clocks,Maintenance and Repair, Church Information Office, London.

Council for the Places of Worship and Monumental BrassSociety (1973). Monumental Brasses and Brass Rubbing,Church Information Office, London.

Davey, A., Heath, B., Hodges, D., Milne, R. and Palmer, M.(1978). The Care and Conservation of Georgian Houses; aMaintenance Manual for the Town of Edinburgh, Paul HornsPublishing, Edinburgh.

Department of the Environment (1972). R & D Bulletin:Building Maintenance, HMSO, London.

Department of the Environment (1972). Efflorescence andStains on Brickwork, Advisory Leaflet N 75, HMSO, London.

Department of the Environment (1976). Current Informationon Maintenance, pt F, ‘Preservation and Restoration ofBuildings, a Bibliography’, 2nd edn, Library Bibliography,Property Services Agency Library, London.

Department of the Environment (1977). Current Informationon Maintenance, pt. B ‘Design and Maintenance, a bibliogra-phy’, 3rd edn, Library Bibliography, 140, Property ServicesAgency Library, London.

Gayle, M., Look, D. and Waite, J.G. (1980). Metals in America’sHistoric Buildings, Uses and Preservation Treatment, HeritageConservation and Recreation Service, Washington D.C.

Gettens, R.J. and Stout, G.L. (1966). Painting Materials—aShort Encyclopedia, Dover Publications, New York.

Grimmer, A.E. (1988). Keeping it Clean. Removing ExternalDirt, Paint Stains, Graffiti from Historic Buildings, USDepartment of the Interior, Washington D.C.

Harley, R.D., (1982). Artist’s Pigments c. 1600–1835, 2nd edn,Butterworth-Heinemann, Oxford.

Holmström, I. and Sandström, C. (1975). Maintenance of OldBuildings, Document 10 D, National Swedish Institute forBuilding Research, Stockholm.

Hurst, A.E. and Goodier, J.H. (1980). Painting and Decorating,9th edn.

Hutchinson, B.D., Barton, J. and Ellis, N. (1975). Maintenanceand Repair of Buildings and their Internal Environment,Butterworth-Heinemann, Oxford.

Insall, D. (1972). The Care of Old Buildings Today: A PracticalGuide, Architectural Press, SPAB, London.

Insall, D. (1974). Historic Buildings: actions to maintain theexpertise for their Care and Repair, Council of Europe,Strasbourg.

Locke, P. (1986). The Surface Treatment of Timber FramedHouses, SPAB Information Sheet No. 3, Society for thePreservation of Ancient Buildings, London.

Locke, P. (1986). Timber Treatment, SPAB Information Sheet No.2, Society for the Preservation of Ancient Buildings, London.

London, M. (1988). Masonry: How to care for old historic brickand stone, National Trust for Historic Preservation,Washington D.C.

Massari, G. and Massari, I. (1974). Risanamento Igienico delLocali Umidi (Hygienic Improvement of Humid Buildings),4th edn, Hoepli, Milan (English Translation ICCROM, Rome).

Michell, E. (1988). Emergency Repairs for Historic Buildings,English Heritage, Butterworth, London.

Mills, Edward, D. (1994). Building Maintenance andPreservation, 2nd edn, Butterworth-Heinemann, Oxford.

Mora, P., Mora, L. and Philippot, P. (1984). Conservation of wallpaintings (English translation), Butterworth, London.

Newton, R. and Davidson, S. (1989). Conservation of Glass,Butterworth-Heinemann, Oxford.

Newton, R.G. (1982). The Deterioration and Conservation ofPainted Glass: a Critical Bibliography, Oxford UniversityPress, Oxford.

Oxley, T.A. and Gobert, E.G. (1984). Dampness in Buildings:Diagnosis, treatment, instruments, Butterworth-Heinemann,Oxford.

Richardson, B.A. (1980). Remedial Treatment of Buildings,Construction Press, Lancaster.

Sandwith, H. and Stainton, S. (1984). The National TrustManual of Housekeeping, Allen Lane, London.

Saunders, M. (1987). The Historic House Owner’s Companion,B.T. Batsford Ltd, London.

Schofield, J. (1984). Basic Limewash, Pamphlet available fromthe Society for the Protection of Ancient Buildings or theCouncil for the Care of Churches.

Stagg, W. and Pegg, B. (1976). Plastering: A Craftsman’sEncyclopedia, Crosby Lockwood Staples, London.

Stahl, F. (1984). A Guide to Maintenance, Repair andAlteration of Historic Buildings, Van Nostrand Reinhold,New York.

Stambolow, T. and Asperen de Boer, T.R.J. van (1972). TheDeterioration and Conservation of Porous Building Materials inMonuments. A Literature Review (rev. 1975), ICCROM, Rome.

Sugden, A.V. and Edmonson, J.L. (1925). A History of EnglishWallpaper 1509–1914, Batsford, London.

Thomas, A.R. (1992). Control of Damp in Old Buildings,Technical pamphlet 8, Society for the Preservation of AncientBuildings, London.

Torraca, G. (1981). Porous Building Materials. MaterialsScience for Architectural Conservation, ICCROM, Rome.

Webster, R.G.M. (ed.) (1992). Stone Cleaning and the NaturalSoiling and Decay Mechanisms of Stone, Donhead, London.

Wingate, M. (1985). Small Scale Lime Burning, IntermediateTechnology Publications, London.

Wright, A. (1986). Removing Paint from Old Buildings, SPABInformation Sheet No. 5, Society for the Preservation ofAncient Buildings, London.

Fire (chapter 17)

Allen, N.L. (1988). Protection of Churches against Lightning,Council for the Care of Churches, London. A booklet whichgives guidance on protection from lightning with referencesto BS 6651: 1985 ‘Protection of Structures against lightning’.

Anderson, H. and McIntyre, J.E. (1985). Planning and disastercontrol in Scottish libraries and record offices, NationalLibrary of Scotland, Edinburgh.

Building Research Establishment (1987). Digest 320. Fire Doors,HMSO, London.

Butcher, E.G. and Parnell, A.C. (1979). Smoke Control inFire Safety Design, E & FN Spon, London. Explains theprinciples governing the behaviour of smoke and its controlin building design.

Bibliography

377

Butcher, E.G. and Parnell, A.C. (1983). Designing for FireSafety, John Wiley, Chichester. Describes the nature of fire,and the precautionary measures to be taken in the design ofbuildings.

Council of Europe (1986). The Protection of Cultural Heritageagainst Disasters, Doc. 5624E, Strasbourg.

Department of the Environment (1992). Fire Standard E. 13.Department of the Environment, Fire Branch, ConstructionPolicy Directorate, HMSO, London. Provides guidance togovernment departments in the precautions to be takenagainst fire in historic buildings.

Department of the Environment (1991). Guidance for theDesign of Government Buildings, HMSO, London. Providesimportant guidance to departments on the design of newbuildings and the alterations to existing buildings and theconsultants.

Department of the Environment (n.d.). Standard FirePrecautions for Contractors, HMSO, London. Revised periodically. Fire precautions which should be applied to allbuilding contracts by government.

Fire Protection Association (1981). Fire Safety Bibliography(Fire and the Architect; Fire Protection Design Guide), FPA,London.

Fire Protection Association (1990). Fire and Historic Buildings,FPA, London.

Jones, B. (1986). Protecting Historic Architecture and MuseumCollections from Natural Disasters, (ed.) B.G. Jones,Butterworth, London.

Kidd, S. (ed.) (1990). Heritage under Fire, Fire ProtectionAssociation, London.

National Fire Protection Association (1985). RecommendedPractice for the Protection of Libraries and Collections, NFPA,Quincey, MA USA.

National Fire Protection Association (1985). RecommendedPractice for the Protection of Museums and MuseumCollections, 911, NFPA, Quincey, MA USA.

Parnell, A. and Ashford, D. Fire Safety in Historic Buildings, Part1, Technical Pamphlet 61, Society for the Preservation ofAncient Buildings, London.

Withers, M. (1975). Fire Protection of Panelled Doors, BathPreservation Trust, Bath.

Presentation of historic buildings (chapter 18)

Alderson, W.T. and Low, S.P. (1976). Interpretation of HistoricSites, AASLH, Nashville, USA.

Bosselman, F.P. (1978). In the Wake of the Tourist. TheConservation Foundation, Washington D.C.

Brown, C. (1983). The Mechanics of Sign Control, AmericanPlanning Association, Chicago.

Denhez, M. (1978). ‘Heritage in Action; A Case Study’, inHeritage Fights Back, pp. 184–277, The Heritage CanadaFoundation, Ottawa.

Fitch, J.M. (1982). Two Levels of Interpretation. HistoricPreservation; Curatorial Management of the Built World,McGraw-Hill, New York.

Kerr, J.S. (1982). The Conservation Plan: A Guide to thePreparation of Conservation Plans for Places of EuropeanCultural Significance, The National Trust of Australia, Sydney.

Longstreth, R. (1987). The Buildings of Main Street; A Guide toAmerican Commercial Architecture, Preservation Press,Washington D.C.

Serageldin, I. (1986). Financing Adaptive reuse of CulturallySignificant Areas; The Challenge to our Cultural Heritage;

Why Preserve the Past? (ed. Yudhishthir Raj Isar),Smithsonian Institution Press and UNESCO, Washington D.C.

Worskett, R. (1969). The Character of Towns; An Approach toConservation, Butterworth-Heinemann, Oxford.

Cost control of conservation projects(chapter 19)

Davey, K.J. (1992). Building Conseravtion Contracts and GrantAid—A Practical Guide, E & FN Spon, London.

Thorncroft, M.E.T. (1975). The Economics of Conservation,RICS, London.

Rehabilitation of historic buildings (chapter 20)

Advisory Council on Historic Preservation (1976). AdaptiveUse: a survey of construction costs. Report, special issueIV(4), Advisory Council on Historic Preservation, WashingtonD.C.

Advisory Council on Historic Preservation (1979). Assessing theEnergy Conservation Benefits of Historic Preservation, USGovernment Printing Office, Washington D.C.

Advisory Council on Historic Preservation (1979). TheContribution of Historic Preservation to Urban Revitalization,US Government Printing Office, Washington D.C.

Aldous, T. (1990). New Shopping in Historic Towns. TheChesterfield Story, English Heritage, London.

Benn, B., Karma, D. and Denhez, M. (1979). How to Plan forRenovations, Heritage Canada Foundation, Ottawa.

Benson, J. and Stone, E. (1981). Restoring Victorian Houses, andturn-of the-century Structures, Architectural Press, London.

Cantacuzino, S. (1975). New Uses for Old Buildings, ArchitecturalPress, London. Old buildings are categorized and severalexamples of new uses are given for each category.

Cantacuzino, S. and Brandt, S. (1980). Saving Old Buildings,Architectural Press, London. Describes nearly 100 projects forconverting old buildings to a wide range of new uses inEurope and the United States.

Chudley, R. (1981). The Maintenance and Adaption ofBuildings, Longman, London.

Council for the Places of Worship (1972). Lighting and Wiringof Churches, revised, Church Information Office, London.

Cunnington, P. (1988). Change of Use, Alpha Books, A. Black,London.

Department of the Environment (1971). Aspects of Conservation1. New Life for Old Buildings, HMSO, London.

Fellows, R. (1999). Edwardian Civic Buildings, ArchitecturalPress, London.

Heritage Conservation and Recreation Service (1979). FederalTax Provisions to encourage Rehabilitation of HistoricBuildings, US Department of the Interior, Washington D.C.

Hunt, A. (1985). Electrical Installations in Old Buildings,Technical Pamphlet 9, Society for the Preservation of AncientBuildings, London.

Latham, D. (2000). Creative Re-use of Buildings, 2 Vols,Donhead, Dorset.

Levitt Bernstein Associates (1978). Supervisor’s Guide toRehabilitation and Conservation, Architectural Press, London.

Long, H. (2001). Victorian Houses and their Details,Architectural Press, London.

Lumsden, W.K. et al. (1974). Outdoor lighting Handbook,Gower Press, Epping, London.

Markus, T.A. (ed.) (1979). Building Conversion andRehabilitation: Designing for Change in Building Use,Butterworth-Heinemann, Oxford.

Bibliography

378

Mitchell Harris (1982). How to Hire a Contractor, CMHC, Ottawa.

Royal Institute of Chartered Surveyors (1976). The Economics ofConservation, RICS, London.

Sabnis, G. (ed.) (1985). Rehabilitation, Renovation andPreservation of Concrete Masonry Structures Symposium,American Concrete Institute, Detroit.

Thompson, E.K. (1977). Recycling Buildings, Renovations,Remodelings, Restorations, and Reuses, McGraw-Hill,New York.

US Department of the Interior (1983). The Secretary of theInterior’s Standards for Rehabilitation and Guidelines forRehabilitation of Historic Buildings, revised 1983, USDepartment of the Interior, Washington D.C.

US National Park Service (1982). Respectful Rehabilitation.Answers to your questions about old Buildings, ThePreservation Press, Washington D.C.

Special techniques of repair and structural consolidation (chapter 21)

Anon. (1972). ‘Moving House after 350 Years’, ContractJournal, February, London.

Beard, G. (1975). Decorative Plasterwork in Great Britain,Phaidon, London.

Beckmann, P. (1974). Flatjacks and some of their Uses. Arup J.9(3), 10–14, Arup and Partners, London.

Borchelt, J.G. (ed.) (1982). Grout for Reinforced Masonry,Symposium Orlando, Dec. 1980, ASTM Special TechnicalPublication 778, American Society for Testing Materials,Philadelphia.

Bowen, R. (1981). Grouting in Engineering Practice, AppliedScience Publishers, London.

Braun, H. (1954). The Restoration of Old Homes, Faber & Faber,London.

Building Research Establishment (1944–46). Repair of DamagedBuildings series, Notes 1–24, BRE, Garston, Watford.

Building Research Establishment (1945). Shoring and OtherPrecautions against the Collapse of Damaged Buildings andAdjacent Property, Repair of Damaged Buildings series, Note17. BRE, Garston, Watford.

Hayden, R.S. and Despont, T.W. (1986). Restoration of theStatue of Liberty 1984–86, Harper and Row, New York.

Lizzi, F. (1982). The Static Restoration of Monuments, Sagepeditrice, Genova.

MacDonald, S. (2001). Preserving Post War Heritage, Donhead,Dorset.

Mill, E.D. (1996). Building Maintenance & Preservation, ReedEducational & Professional Publishing Ltd.

Peterson, S. et al. (1980). Mortars, Cement, Grouts used in theConservation of Historic Buildings, Symposium, Rome, ICCROM, Rome.

Simpson, J.W. and Horrobin, P.J. (eds) (1970). The Weatheringand Performance of Building Materials, Medical andTechnical Publishing, Aylesbury, England.

Stumes, P. (1979). The WER System Manual, APT, Ottawa.Sutherland, R.J.M. (ed.) (1997). Structural Iron 1750–

1850, Ashgate Variorum Studies in the History of CivilEngineering.

Thorne, R. (ed.) (1997). Structural Iron & Steel 1850–1900, Ashgate Variorum Studies in the History of CivilEngineering.

Zander, G. (1971). Methods of Consolidation (Text in Italianand English), ICCROM, Rome.

Non-destructive survey techniques (Appendix III)

British Standards Institution (1986). Testing Concrete: Guide tothe Use of Non-Destructive Methods of Test for HardenedConcrete. BS 1881: Part 201. London: BSI.

Building Research Establishment (1989). Simple Measuring andMonitoring of Movement in Low-Rise Buildings – Part 1:Cracks. Digest 343. Garston: BRE.

Building Research Establishment (1990). An Introduction toInfra-Red Thermography for Building Surveys. InformationPaper 7. Garston: BRE.

Building Research Establishment (1993). Monitoring Buildingand Ground Movement by Precise Levelling. Digest 386.Garston: BRE

Building Research Establishment (1995). Assessment of Damagein Low-Rise Buildings. Digest 251. Garston: BRE.

Building Research Establishment (1995). Simple Measuring andMonitoring of Movement in Low-Rise Buildings – Part 2:Settlement, Heave and Out-of-Plumb, Digest 344. Garston:BRE.

Bibliography

379

Principal magazines and periodicals in conservation and restoration

Conservation

Archaeometry, Oxford University, EnglandBollettino dell’Istituto Centrale del Restauro, RomeBulletin de L’Institut Royal du Patrimoine Artistique, BrusselsBulletin du Laboratoire du Musée du Louvre, ParisDenkmalpflege in Baden-Württemberg, StuttgartDeutsche Kunst und Denkmalpflege, Munich-BerlinJournal for Architectural Conservation, Donhead SherbourneJahrbuch der Bayerischen Denkmalpflege, MunichMaltechnik, MunichMonuments Historiques, ParisOsterreichische Zeitschrift für Kunst und Denkmalpflege, ViennaRestauro, NaplesStudies in Conservation, LondonTechnical Studies in the Field of the Fine Arts, Harvard, Boston, Mass.Technische Mitteilungen für Malerei und Bildpflege, MunichUrbes Nostrae, AmsterdamZeitschrift für Schweizerische Archaeologie und Kunstgeschichte, Zurich

Text

1. Convention for the Protection of Cultural Property in theEvent of Armed Conflict (The Hague), 1954

2. Recommendation on International P’rinciples applicable toArchaeological Excavations, adopted by the GeneralConference at its Ninth Session, 1956

3. Recommendation concerning the most effective means ofrendering Museums accessible to everyone, 1960

4. The Organization of Museums—practical advice, Museumsand Monuments, IX, 1960

5. Recommendation concerning the safeguarding of the beautyand character of landscapes and sites, 1962

6. Recommendation on the means of prohibiting and preventingthe illicit export, import and transfer of cultural property

7. Recommendation concerning the preservation of culturalproperty endangered by public or private works, 1968

8. The Conservation of Cultural Property, Museums andMonuments, X, 1958

9. Convention on the means of prohibiting and preventing theillicit export, import and transfer of cultural property

10. Convention concerning the protection of the World culturaland natural heritage, 1972

11. Recommendation concerning the protection, at nationallevel, of the cultural and natural heritage, 1972

12. Preserving and Restoring Monuments and HistoricBuildings, Museums and Monuments, XIV, 1972

13. Recommendation concerning the international exchange ofcultural property, 1976

14. Recommendation concerning the safeguarding and contemporary role of historic areas, 1976

15. The Manmade Landscape, Museums and Monuments, XVI,1977

16. Recommendation for the protection of movable culturalproperty, 1978

17. Introduction to Conservation, by B.M. Feilden

18. Conservation Standards for Works of Art in Transit and onExhibition, Museums and Monuments, XVII, 1979

Bibliography

380

Cover

Definitions of cultural property, protective action and rules formilitary authorities in the particular case of armed conflict

Definitions, extensive statements of principle and guidelines onarchaeology

Definitions, statement of principle and guidelines on themuseum in the community

Wide-ranging coverage of museum practice

Definitions, statements of principle and guidelines on landscapes, natural sites, parks, reserves, etc.

Definitions of cultural property, legal and institutional arrangements

Definitions of cultural property, wide-ranging guidelines onadministrative, technical measures, etc.

Wide-ranging coverage of conservation practice—some aspectsnow out of date or inaccurate

See 6 above

Definitions of ‘cultural and natural heritage’, institutionalarrangements

Definitions, guidelines on practice and institutional, legalarrangements

Wide-ranging coverage of building conservation practice; certain elements out of date

Definitions of cultural property, general institutional arrangements for exchange

Definitions of historic areas, general principles and guidelines forplanners and conservators, institutional and legal arrangements

Wide-ranging coverage of landscaping principles

Definitions of movable cultural property, general principles,institutional and legal arrangements

Wide-ranging introductory explanations of basic principles ofconservation

Self-explanatory

N.B. A collection of international and national legislative texts has appeared in French: La protection du patrimoine culturel mobilier, 1979.

Restoration

Annual Report of the Society for the Protection of Ancient Buildings, LondonAnnual Reports of Ancient Monuments Society, Civic Trust, Georgian Group, Society for the Protection of Ancient Buildings and

Victorian Society, LondonBulletins and Newsletter of Association for Preservation Technology, OttawaTransactions of the Association for Studies in the Conservation of Historic Buildings, London

Principles and norms for the protection of movable and immovable cultural property: relevant UNESCO statements and definitions

UNESCO documents which contain statements of principles concerning the above are listed below. Many legal textscontain definitions of what is meant by cultural property, some of which overlap considerably, but generally speak-ing the Conventions do not contain very much statement of what is ethically or technically desirable since their mainemphasis is the provision of legal cover.

381

Abu Simbel, Egyptian Nubia, 12, 19, 33,269

Algeciras Market Hall, Spain, 44Apollodorus of Damascus, architect to the

emperor Trajan, 34Arbil, N. Iraq, 143Arch of Constantine, Rome, Italy, 262Arch of Titus, Italy, 262, 269Aswan High Dam, Egypt, 12, 79, 115, 269

Babylon, Iraq, arched culvert, 33Bage, 19th cent. inventor of cast iron

beams, 34Baia, Italy, Temple of Mercury, dome, 34Baker, late 19th cent. engineer, designer of

Forth Bridge, Scotland, 34Basilica Vicenza, Verona, N. Italy, 34Baths of Caracalla, Rome, Italy, 33Baths of Diocletian, Rome, Italy, 40, 277Beauvais Cathedral, France, 28, 62Beckmann, P., engineer for York Minster,

England, author, 147, 189, 330Beverley Minster, Yorkshire, England, 65Borobudur, Indonesia, 19Brunelleschi, architect of the dome of

S. Maria del Fiore, Florence, Italy, 42, 45

Buildwas, England, cast iron bridge, 34

Capri, Italy, Villa Jovis, 93Chain arch bridges, Yangtze Delta, China,

34Charles, F.W., architect, expert in timber

framed buildings, 55Chauvim Huamtar, Peru, 115Chesterfield, England, 277Cisman river bridge by Palladio, N. Italy, 51Coleman, C.R., timber preservation expert,

141Cologne Cathedral, Federal German

Republic, 28, 221Colosseum, Rome, Italy (Flavian

Amphitheatre), 38, 161Coremans, P., scientist, head of IRPA

Brussels, Belgium, 94Coulomb, early 18th cent. engineer, father

of soil mechanics, 80Craigellachie, Scotland, UK bridge by

Telford, 34Crockett, J., vibration expert, 226Crown Hall, Illinois Institute of

Technology, Chicago, USA, 52Cusco, Peru, Convento San Bernardo, 121

Dowrick, D., engineer to York Minster,England, earthquake expert, 118

Dulles Airport, Washington D.C., USA, bySaarinen, Ammann and Whitney, 47

Duomo, Florence, Italy, S. Maria del Fiore,45

Eiffel, 19th cent. engineer, designer of irontruss bridge at Garabait, Portugal, 34

Euston Station, London, England, 51

Fairburn, engineer, designer of MenaiBritannia tubular bridge, N. Wales,UK, 34

with Hodgkinson, Liverpool StreetStation, London, England, 51

Falerii Novi, arched Roman bridge, Italy,33

Florence, Italy, flood, 115, 116Forth Bridge, Scotland, UK, by Baker, 34Freeman Fox, Forth, Severn and Humber

suspension bridges, England, 47Friday Mosque, Isphahan, Iran, 42Fukien stone bridge, China, 32

Garabait, Portugal, bridge by Eiffel, 34Gizeh, Pyramids of Cheops, Egypt, 19, 33Guatemala Antigua, Guatemala, Church of

La Merced, 122, 146

Hall of Justice, Rouen, France, 34Hennebique, engineer, inventor of

reinforced concrete (1897), 37Heyman Jacques, Professor of

Engineering, Cambridge, England, 28,37, 62

Horie, C.V., conservation scientist, 179House, M.E., vibration expert, University

of Southampton, England, 160

Innocent, C.F., author, recording Englishvernacular, 33

Insall, D., conservation architect, author,19

Iraq, domical structures, 33Iron Bridge, Coalbrookdale, England, 328

Kapsa, L., author of Czechoslovakvibration report, 160

Kerbala, Iraq, holy shrines, 71, 83, 163Kolaric, M., Jugoslav engineer, 129

Leaning Tower of Pisa, Italy, 31, 32,81, 273

Leningrad, USSR, 319Leonardo da Vinci, Italian genius of late

Renaissance, 109Lime Street Station, Liverpool, England, 51Lion Gate, Mycenae, Greece, 33Liverpool Street Station, London, 51Los Angeles, USA, 169

Machu-Picchu, Peru, 69Mainstone, R.J., engineer, author, 19, 25,

35, 45Mark, R., American Professor of

Engineering, 28

Massari, G. and I., humidity experts,authors, 330

Mausoleum of Theodoric, Ravenna, Italy,315

Menteumhet El Assraf, tomb arches, 33Mercalli, author, earthquake intensity

scale, 4, 121, 122, 123Mies Van der Rohe, architect of Illinois

Institute of Technology, USA, 51, 332Milan Cathedral, Italy, 28, 32, 64, 83, 162Mohenjodaro, Pakistan, 79, 83Mora, P., chief conservator, Instituto di

Restauro Centrale, Rome, Italy, 152Mori and Arai, Japanese conservation

science experts, 136, 146Morris, William, designer, poet, author,

236Mycenae, Greece, Treasury of Atreus, 59Mylne, Robert, Surveyor to St Paul’s

Cathedral, fl. 1750, Scottish architect,mason, 64

Nara, Japan:timber pagoda, 34, 51Toruji temple, 34, 51

Needham, J.R., author, 72Neresheim, German Federal Republic,

Baroque vaults, 40Nervi, Italian engineer, domes in Rome

(1960), 44Newcomen, inventor of the steam

pumping engine, 162Norwich Cathedral, England, 28, 65, 66,

109, 305, 322

Ospizio di San Michele, Rome, Italy, 18, 19

Ove Arup & Partners, firm of Britishengineers, 28, 225, 313

Palladio, 17th cent. Venetian architect, 51Pantheon, Paris, France, 37Pantheon, Rome, Italy, 42Parthenon, Athens, Greece, anastylosis of,

266, 268Perronet, engineer for multispan stone

bridges, 30Persepolis, Iran, 97Petra, Jordan, Qasr el Bint, 120Plenderleith, H.J., first director of

ICCROM, 90Poleni, Italian mathematician, fl. 18th

cent., 19Polygonal walls, Delphi, Greece, 33Pompeii, S. Italy, baths, dome, 34Pont du Gard, S. France, 33Pont St Martin, Aosta, M. Italy, 33Pope, engineer, 37Powys, A.R., author, secretary of SPAB, 71,

81

Index to buildings, persons and places

Raleigh Arena, USA, by Norwicki andSeverad, 47

Ross, Norman, York Minster residentengineer, 313

Saarinen, Ammann and Whitney, TWAterminal, New York City, USA, 44, 47

St Catherine, Mount Sinai, Egypt, 51St Clement’s Church, Norwich, England,

51St Denis, Paris, France, 221St Giles, Edinburgh, Scotland, UK, 169St John, Ousegate, York, England, 161St John’s College, Oxford, England, 242St Louis, USA, gateway arch, 34St Martin-in-the-fields, London, England,

truss, 51St Paul’s Cathedral, London, England, 18,

29, 30, 42, 45, 47, 160, 162, 290St Peter’s, Rome, Italy, 18, 42

Constantinian church, 313St Sophia, Istanbul, 45

dome, 42Salisbury Cathedral, England, 28, 109San Lorenzo, Turin, Italy, ribbed dome,

4, 42Santa Maria del Fiore, Florence, Italy, 45Scaperia, Tuscany, Italy, 113

Schultze, E., foundations expert, 80, 86, 229

Sheldonian Theatre, Oxford, England,Wren’s truss, 51

Sydney Opera House, Sydney, Australia, 4, 44

Tacoma Narrows, USA, suspension bridge,47

Taj Mahal, Agra, India, 169Telford, Thomas, engineer and designer of

bridges in cast iron at Buildwas inEngland and Craigellachie, Scotland,UK, 34

Tintern Abbey, South Wales, UK, 307Tiryns, Greece, arched bridge, 33Torraca, G., chemist and deputy director,

ICCROM, 171Torroja, Spanish engineer pioneering

reinforced concrete, Market Hall,Algec̀iras, Spain, 44

Trajan’s Column, Rome, Italy, illustratingbridge over Danube, 34

Tredgold, author of 19th cent. manual oncarpentry, 34

Utzon, original architect for the SydneyOpera House, Australia, 44

Venice, Italy, 10, 34, 80, 102, 116,162, 275

Versailles Palace, France, 62Villa Farnesina, Rome, Italy, 162Villa Jovis, Capri, Italy, 93Viollet le Duc, architect, great restorer and

author, 28, 29, 42Vitruvius, 1st cent. B.C. Roman architect

and author, 2, 178

Weaver, M., archaeologist and conservatorof historic buildings, 153

Wells Cathedral, England, 11, 66Westminster Abbey, London, England,

177Westminster Hall, London, England, 34, 70Wilkinson, engineer, 37Williamsburg, Virginia, USA, 149, 271Wren, Sir Christopher, 17th cent. architect,

designer of St Paul’s Cathedral,London, England, 42, 45, 51, 109

Yangtze Delta, China, chain arch bridges,34

York Minster, England, 18, 21, 28, 29, 31,40, 62, 65, 79, 81, 86, 98, 113, 162,221, 227, 229, 252, 273, 300, 303, 305,313, 314

Index to buildings, persons and places

382

383

Absolute movements, 79Absorption capacity, 105Absorptivity, solar, 95Abstraction of groundwater, 79, 162Abutments to arches, firmness, 39Accelerograph, 132Access:

by intruders, 350for fire fighting, 279for maintenance, 240

Acetic acid, 171Acoustic testing, 354Acoustics, 290

characteristics of historic buildings, 293

consultant, 158, 290, 293Additions to historic buildings, 9Administrators/owners, 191Adobe 72, 122, 124Aerosols, 101, 111Aging of a building by traffic vibration,

158, 160Air conditioning, 179, 264, 285, 290Air movement, 174, 177–8Alarm systems, fire detection, 258Albedo, 95Algae, 133Ambient Air Quality Standards (USA), 168Ambrosia beetles, 141American National Conservation Advisory

Council, 13Ammonia toxic wash, 134Ammonium phosphate, for fireproofing,

255Ampelopsis veitchii (Boston ivy), 133Analytic studies of historic buildings, 224Anastylosis, 10, 31, 268

scaffolding for, 296Ancaster stone, 170Animal damage, 133Anobium punctatum (furniture beetle),

139, 141, 151Anti-bandit glazing, 352Arcades, 341Archaeological excavations, 221, 233

maintenance of, 77Archaeological levels, 221Archaeologists, 21, 126, 191, 263Arches, 38, 339

abutments to, 38, 39bridge, 39chain, 34construction of, 33cracks in, 39deformation in, 29pseudo-, 33repair of, 40rubbed brick, 71strength of, 38timber, 34

Architects, 12, 127, 192, 235, 262, 277, 282–5Architectural conservation, 1Architectural conservator, 6, 13, 17, 243

work of, 21Architectural historian, 193Armature for synthetic stone, 70

decorative plaster, 214Arris, 98Arsenic pollutant, 170Art historian, 129, 193, 261Artists, 274Ashlar, 62

wall repair, 69Atmospheric pollution, 8, 18, 21, 93, 157,

164–72, 341bacterial decay, 169carbon dioxide, 167carbon monoxide and nitrogen dioxide, 169chlorides, 169, 330combating, 171–2ozone, 168sulphur dioxide, 167wet and dry deposition, 165

Axle weight, 158

Bacteria, 133, 169Balloon frame timber construction, 52Bankia (molluscan marine borer), 141,

151Barrel vaults, 41, 339–41Base shear, 131Battens, 82Batter, internal, 65Beams, 37, 67, 68, 320, 337, 338

cast-iron, 34Beetles, 52, 59, 139, 140

inspection for, 151Bending stresses, 25Biological causes of decay, 133Bird damage, 155Blowlamps, use of, 259Bonding new masonry work to old, 67–9Boston ivy (Ampelopsis veitchii), 133Bostrychidae (powder post beetles), 141Botanical causes of decay, 133Box timber frame construction, 54Boxed heart timber, 55Brick walls, repair of, 70Bridge arches, 39Broken timber joint, repair of, 55Buckling, 25Budgets for maintenance, 240

authority for work, 275contingency fund, 275quarterly reports, 275separate categories, 241

Buffer material, 174, 185Builder, 193Building craft skills, 13

Building economist, 199Building methods, 221Building regulations, 13, 256, 280, 281Building repairs, 22Building Research Establishment, 161Building style, 221Buildings as environmental systems, 172,

185, 237, 281, 283Bulges:

piers, 64, 95walls, 64, 65weak masonry, 64

Bulging masonry, 77, 97Buttresses, 66

flying, 28, 42, 343

Calcareous sandstones, 170Calcium carbonate, 107Calcium nitrate, 107Calcium sulphate, 107Camponotus (carpenter ants), 141, 145Canary Island ivy, 133Canvas linings, 214Capillary attraction, 73

rise, 101rise in moisture, 76transport of salts, 76, 210

Capping of mud bricks, 76Carbon dioxide, 167Carbon monoxide, 167, 170Carbonic acid, 167, 171Carcassing timber, 150Carpenter ants, 141, 145Cast-iron arches, 340Cast-iron beams, 34Catenaries, 25, 37, 47Cathedral Architects’ Conference, 242Cathodic protection, 331 Causes of decay, 92–118 (see also Decay of

cultural property)CCTV surveying, 355Ceilings:

armatures, 214inspection of, 214

Cement grout, 31, 40Central heating, 180, 184Chain arch, 34Chemical stabilization of ground, 32Chimney:

inspection of, 210parging of, 210tall, 125

Chromated copper arsenate, insecticide,152, 154

Civil engineer, 195Clay lump, building, 64, 72Claylime plaster, 73Clean Air Act (UK) 165Cleaners of historic buildings, 236, 239Cleft timber for repairs, 56

Subject index

Clerid (Korynetes caeruleus), insectpredator, 139

Clerk of works, 242, 244Climatic causes of decay, 20, 93–114Climatic data, 3Clipsham oolitic limestone, 170Cob, rammed earth building material,

72, 75Codes of Practice, building, 315Cofferdam, 86Cohesive soils, 79, 159Coke oven emission, 170Colour:

brickwork, 70masonry, 40, 66, 239re-pointing, 70

Column and beam temples, 338Columns, 63, 64Combating pollution, 171–2

chimneys and fuels, 171choice of materials for repairs, 171preventive measures, 171removal of pollutants in the internal

environment, 172Combustibility of materials, 252Combustion, spontaneous, 259

detectors, 258Compressed air equipment for drilling,

307, 314Compression, 25Compressive cracking, 62Concrete:

reinforced, 37roof tiles, 312

Condensation, 101, 266, 268, 270heating flues, avoidance of, 281in Iraq, 74interstitial, 176spots, 210surface, 176trays under windows, 211wood joints, 52

Coniophora cerebella (cellar fungus), 136Conservation:

architect, 12cost of, 6crafts, 17, 244definition of, 3emotional values of, 23, 261laboratory, mobile, 129object of, 8, 263preparatory procedures, 7principles of, 6, 278

Conservation officer, 194Conservationist, 9Conservator, 195, 244Consolidation, 9

chemical, 295–325of ruins, 266–8structural, 31

Contractor, 193Contractions, seasonal, in masonry, 100Contracts for conservation work, 275, 276

pricing of, 274Control:

carpenter ants, 145crowds, 262deathwatch beetles, 145draughts, 177drywood termites, 149–50ground termites, 147–9humdity, 184pollution, 157

Control systems, 274

Copper, 144, 154Coptotermes (termites), 146Cores, 65Corrosion, 266

embedded iron cramps, 165Cost, 116

comparative, 276control, 21maintenance, 238

Cracking of materials, 30under compression, 62

Cracks in:arches, 39beams, 37domes, 42, 45extent of, 212plaster, 159treatment of, 31walls, 31, 62, 64, 98, 225, 226

Cradling, 64, 65, 86Craftsman, 17, 242, 244, 266, 274

skilled, 17, 18, 276, 278Creep:

masonry, 98wood, 52

Creepers, 133Creosote, 152, 153–4Crime prevention, 262Critical water content, 102Crowd control, 262Crushing of materials, 30Cryptotermes (termites), 147Cultural values in conservation, 6, 261Curator, 201Curved membrane buildings, 37Cyclic movements in historic building

fabrics, 31Cyclone, 115

Damage:animals and birds, 154–5chlorides, 330earthquakes, 120electricians and plumbers, 213light, 179pile-driving, 158, 161

Damping, 131Dampness, 176Datum, 227Dead loadings, 25Deathwatch beetle (Xestobium

rufovillosum) 55, 139, 141, 145attack, 145control of, 145, 209smoke treatment, 145

Decay of cultural property, causes of,92–118

atmospheric pollution, 157,164–71

biological, 133, 134botanical, 133climatic, 93–114earthquakes, 119–32entomological, 139–54floods, 115, 116frost, 107, 109lightning, 116man-made, 157mining subsidence, 162moisture, 101–7piling, 158, 161, 162salts, 107sand, 111, 112smoke, 111

snow, 107, 109solar radiation, 93, 94, 97thermal movement, 96–101tornadoes, 115traffic vibration, 159–61water abstraction, 162wind, 109, 111, 112

Decoration:layers of colour, 214–15previous, 214

Defects, by heating, 181Deformations, 25, 29, 30, 341

reporting, 46, 65, 225–6, 240‘Demec’ strain gauge, 213, 226Dendrological studies, 224Detection systems:

control equipment, 350localized, 349perimeter, 349volumetric, 349

Detectors:combustion gas, 258fire, 258flame, 258heat, 258ionization, 258ultrasonic and laser, 258visible smoke, 258

Deterioration:agents of, 3prevention of, 9

Determinate structures, 25Dew point, 101, 176De-watering, 31, 32Diagnosis, 203Differential settlements, 31, 79, 341Disaster action:

emergency action, 130emergency inspection, 131emergency protection, 131

Disodium octaborate tetrahydrate, 154Dissolved salts, 107Documentation, 7, 8, 127Domes, 34, 42–7, 79, 334, 342, 385, 386

causes of stress in, 45repair of, 47

Domical structure prototypes, 33Doors:

inspection of, 211locks and keys, 352

Dovetail stitches, 67Dowsing, 355Drains, 32

inspection of, 216rainwater, 133

Draughts, 177, 184, 283Drawings:

isometric, 222measured, 282orthogonal, 222survey, 222

Drift in masonry, 30, 100Drilling, 345

diamond core, 65, 66equipment, 289–95, 307–13techniques, 295, 305, 315

Drip step in gutter, 302Dry rot fungus:

control, 136detection, 135walls, 62

Duckboards, 109Dust, 95, 111, 113Dynamic loads, 25

Subject index

384

Earth, rammed, 116, 120Earthquakes, 21, 25, 119–32

glossary of terms, 131ground acceleration, 121, 122hazard, 122magnitude and intensity, 121return period, 122Skopje and Montenegro, 279risk, 122vulnerability, 122

Eccentric loads on foundations, 28Efflorescence due to capillary action, 77Electrical installations:

causes of fire, 251, 254design, 285equipment for drilling, 307inspection services, 285obsolescence, 215, 237supply inadequate, 285tests, 285

Electrolytic action, 210Entomologist, 207Environment, internal, 173–84, 282Environmental conditions, 357Environmental Protection Agency (USA),

168Epoxy resin, 38, 64, 69, 70

grouting, 314, 325mortar, 70, 125

Ernobius mollis (wood-boring beetle), 141Erosion, mortar, 107Estimates, 273

approximate, 220final, 203initial, 220, 273

Ethanol, 76Ethics of conservation, 6Ethyl silicate, 76Euophryum confine (wood-boring

weevil), 139, 141Evaporation, 101

wind, 161, 256Excavations, archaeological, 221, 239Expansion, thermal, 139–44External conditions:

changes, 221modification by building, 175

Falseworks in construction, 40Fees and expenses of professionals, 220Fibre-optic surveying, 355Field survey measurements, 223Fire:

causes of, 254compartmentation, 256, 258detectors, 258drills, 253prevention of, 252protection:

active, 258passive, 258

Fire prevention officer duties, 252Fire Protection Association, 253, 259, 348Fire retarding paints, varnishes and

polishes, 255Fittings and fixtures, 215Flame detectors, 258Flashings, abutments, 210, 213Flat jacks, 66, 68, 86, 88, 303, 305Flight holes, insects, 139–41Flint walls, repair of, 70Floods, 115, 120, 135, 163Floors, heating, 283Flying buttress, 28, 42, 341

Flying shores, 66Focus of an earthquake, 130Footing of foundations, 88, 181Formalin toxic wash, 134Foundations, 79–90, 125

consolidation, 83, 84decay of, 82defects in, 81failure in earthquakes, 130inadequate, 337investigation of, 80–3repair of, 88settlement, 80, 81unequal loadings, effect of, 81

Fourier spectrum, 131Fractures, repair of, 67Framed structure, 51Frames, 51–60

portal, 25space, 52three-hinge, 25

Frass, 139, 141, 144, 150Frost:

changes, 107resistance, 109unexpected, 115

Fumigation, 129against termites, 150

Fungal decay in wood, 135, 136Fungi, 134

inspection for, 225Fungicides, 136Furniture beetle (Anobium punctatum),

139, 141

Gas heaters, 281Gel, silica, 185, 345Geodetic survey, 227Geodometer, 227Geological:

background, 32fault, Scarperia, Italy, 115movements, 79seismic spectrum, 120

Geometry of a structure, 337Geophysical surveying, 354Geotechnical surveying, 354Glass, laminated, 127Gothic:

churches, 343vaults, 40

Gravity, 18grouting, 323

Grit, 244Ground failures, 79

conditions, 120temperature changes, 109

Ground moisture transportation, 93Ground movement, 79Ground water:

abstraction of, 80levels of, 213replenishment, 86

Ground-dwelling termites, 147–8control of, 148shield, 148

Grouting, 31, 40, 64, 66, 123, 295, 315, 322compressed air, 323gravity, 323hand pump, 323mixes, 322protection during, 322records, 325vacuum, 323

Halation in photographs, 222Half-timbered work, 77

repair of, 71Hammer drill, 315Handymen for maintenance work, 244Heat:

detectors, 258pump, 281shield, 259solar energy, 281transfer, 174

Heating, 175background, 280, 281building factors, 281condensation in flues, 281continuous, 237defects caused by, 181distribution systems, 281floor, 282intermittent, 180, 181, 184local radiant, 281open fires, 181, 184plant factors, 237, 281radiators, 282replacement, 281

Hedera canariensis (Canary Island ivy), 133Heterotermes (tropical ground termites),

146Hips, roof, 210Historic buildings:

acoustics of, 293definition of, 1fire audit, 252fire hazards, 251fire regulations, 256fire resistance, 257in seismic zones:

architects role, 124foundation risks, 130improvement of seismic resistance, 119mechanical plant, 130seismic safety plan, 123site investigation, 126strengthening, 124, 127structural investigation, 126vulnerability, 123

uses for, 277Historic gardens conservator, 197Historical research, 203House longhorn beetle (Hylotrupes

bajulus), 139, 140Humidity:

control of, 264limits, 184measurement of, 103rapid changes, 184relative, 173, 184

Hurricane, 115Hydrangea petiolaris (a climbing

hydrangea), 133Hydraulic jacks, 86, 130, 303, 305Hygroscopic salts, 102, 173Hylotrupes bajulus (house longhorn

beetle), 139, 140Hyphae (dry rot), 135

Impulse radar, 353Inclinometers, 82Indeterminate structures, 25Infrared photography, 354Insecticides, 153–4Inspection of historic buildings, 7, 18, 21

legal aspects of, 205regular, 127, 203–20, 239, 274

Subject index

385

Insurance against disasters, 118Internal environment of building, 21International Centre for the Study of the

Preservation and Restoration ofCultural Property (ICCROM), 116

Intervention, degree of, 8Inventory of cultural property, 7Isometric drawings, 222Isostatics, 37

Jacks:flat, 133, 305hydraulic, 86, 130, 303, 305

Japanese architecture, 59Joints:

details of, 56open, 59trusses, 52worn, 63

Junction boxes, 215

Key, lock systems, 350, 352Key of plaster, 289Knapped flint, 70Korynetes caeruleus (clerid), 139

Laboratory, mobile for earthquakes, 129Labour contracts, 275Lacunae, 21, 262

treatment, 262, 263Laminated glass, 127Landslide, 115, 120Landscape architect, 197Larvae of insects, 139Laser fire detectors, 258Lateral restraint, 99Lateral thrusts, 70‘Least bad solution’ philosophy, 12, 262, 278Legislation, 203, 205Lichens, 133Light, 95

artifical, 180, 227natural, 179ultraviolet, 96

Lightmeters, 180Lightning, 116–18, 255

conductors, 116, 117Lime mortar, 30, 31, 62, 63, 66, 100, 122Limewash, 68Limnoria (crustacean marine borer),

141, 151Linings:

canvas, 214flues, 300

Liquid penetrant testing, 355Load testing, 355Loadings, 25

active, 25dead, 25eccentric, 28increased, 279

Lock security, 348Log book, 239, 242, 243Longhorn beetle:

house, 139tropical, 146

Lyctus (powder post beetle), 139, 141,143, 151

Lyctus africanus, 146

Macrotermes (termites), 146Magnesium silicofluoride, 136Magnesium sulphate, 107Magnetometry, 354

Maintenance:annual routine of, 243archaeological excavations, 77budgets, 240categories of, 241cost of, 238, 241cyclical, 240emergency, 239general, 235–49log book, 239, 241, 242mud brick, 72plan, 21, 203, 236policy, 239preventive, 9, 21, 121, 130, 236programme, 241, 244responsibility for, 238routine for, 242–4standard, 239

Management precautions:fire drills, 253during building operations, 259hot work permit, 259

Man-made causes of decay, 157–71Mandrel for drilling, 311Marine borers, 151Masonry:

grouting, 141joints, worn, 63tensile resistance, 62walls, 69, 211–13

Master craft worker, 198Mastotermes (termites), 147Masutitermes (termites), 147Materials:

in buildings, 32–5scarce, 276strengths of, 34

Material deterioration and decay, 356Materials scientist, 198Measuring pollution, 164Mechanical services engineer, 196Mercalli Scale of earthquake intensity,

120–1Mercury, pollutant, 170Methodology of conservation, 203Methyl bromide fumigant, 150Microbiological causes of decay, 133Microcerotermes (termites), 147Microclimate, 93, 184Microdrilling, 355Micrometer, 213, 226Microwave analysis, 353Mildew, 134Mining subsidence, 77, 162Moisture:

action, 101, 102condensation, 101, 211content, 30, 135excess, 102material absorption, 107meter, 213movement, 213precipitation of, 103vapour, 237

Monitoring defects, 355Mortar, 31, 63, 66, 100, 122

joint, 62Mosaics, 108

floor, 344wall, 346

Moss, 133Mould, 134Mud brick, 72

decay, 73

repair, 76, 77surface treatment of, 76

Mullions, window, 69Museum:

design, 292environment, 168

Nacerdes melanura (wharf-borer), 140Natural disasters, 3, 4, 130Needling, 66Nitrates, 107Nitrogen dioxide, 168, 170Noise, 158, 185Non-destructive survey techniques, 353–57

Odontotermes (termites), 147Oemidagabani (longhorn beetle), 146Oil heaters, 281Openings in walls, 33Opticial plummet, 227Orthodichlorobenzene, 151Osmophilic fungus, 136Ozone, 95, 168, 169Paint:

fireproof, 255layers, previous, 214

Parging of chimneys, 210Participation factor, 131Patina, 21, 357

preservation of, 263Pentarthrum buttoni (wood-boring

weevil), 139, 141Perspex model, 212Pest-borne infection, 154Pesticides, 152–4Phellinus megaloporus (wet rot fungus), 136Photoelastic analysis, 28Photogrammetry, 119, 127, 223Photographs, use of, 222Piers, 63, 64Piezometer, 82, 163Pile-driving damage, 158Piling vibration, 158, 161, 162Pipe runs, 283Pisé, 72, 75Planking and strutting, 86, 295Plaster key, 158, 214Plenum air heating, 290Plumb bob, 81, 224, 227

optical, 82, 227Plumbing, faulty connection, 215Pneumatic test for drains, 215Pointing:

brickwork, 70masonry, 40, 66, 68, 170, 239

Pollutants effect on building materials:aluminium, 171bricks, roofing tiles and terracotta, 170copper, 171ferrous metals, 170glass, 170lead, 171mortars, renderings, cement and

concrete, 170non-ferrous metals, 170stone, 169wood, 169zinc, 170

Polluted atmosphere, 21, 101, 157, 164–72Polyester resin grouting, 125Pooria vaillantii (wet rot fungus), 136Poplar trees, 133Porosity of stone, 69, 102Porous masonry, 101

Subject index

386

Portal frames, 25, 52Portland cement, 31, 33, 66, 70, 72, 76,

100, 239disadvantages of, 72

Portland stone, 247, 249Potassium nitrate, 107Potassium sulphate, 107Powder post beetle, 139, 141, 143, 151Power electrical engineer, 196, 197Pozzuolana, 33, 72, 315Presentation of historic buildings, 21, 261–9

of ruins, 266policy, 261–4vandalism, 259

Preservation, 9, 28, 29St Paul’s Preservation Act, 161, 162

Preservatives, 152, 153Project manager, 201Protection systems:

closed circuit television, 349perimeter, 349perimeter lighting, 351perimeter wall of fences, 350

Pseudo-arches, 31Psychrometer, 174Ptilinus pectinicornis (wood-boring

insect), 140Pulverized fly ash, 315Purlin joints, 54Pynford stool, 88

Quantity surveyor, 199Quoins, 68

Radiation, solar, 93, 95Radiators, 285Radiography, 353Radiometer, 95Rainfall, 93, 105

data on, 103Raking shore, 66Rammed earth, 73, 76Re-alkalisation, 332Rebuilding walls, 69Reconstruction, 11, 28, 32, 221, 266–71Recording, 203, 221, 222Regulations:

buildings, 279fire, 279hygiene, 279scaffolding, 296

Rehabilitation, 10, 32, 277–93economic criteria, 278

Reiher Meister Scale of Human Perception,159

Reinforced concrete, 37, 66, 123, 328Remote sensing, 354Repairs:

arches, 40beams, 37brickwork, 70domes, 47flint walls, 70foundations, 88half-timbered work, 71mud brick, 74, 76timber-framed structures, 54–9walls, 66–77window mullions, 69

Re-pointing:brickwork, 70masonry, 40, 66

Reports, 203–220final, 233

Reproduction works, 11Research Institute for Building and

Architecture (Czechoslovakia), 160Resin:

epoxy, 64, 69, 70, 125polyester, 125

Resonance, vibration, 159Restoration, 9Reticulitermes (termites), 147Reverberation time, 185, 290Ribs, 40, 342Richter Scale (earthquakes), 121Ridge in lead roof, 307Risk in fixed price contracts, 274Roofing:

carpentry, 54inspection, 208

Rotation settlements, 32Rothound search dogs, 354Rotting beams, 63Rubbed brick arches, 71Rubber sealing, timber repair, 55Rubble wall repair, 68, 69Ruins, 61, 266–8Rusting, of reinforcements, 38

St Paul’s Cathedral Preservation Act (1935),83, 161

Salt spray, 101Salts, dissolved, 107Sand, 66, 111Sash windows, 325Scaffolding, 66

erection of, 224design of, 296, 298maintenance of, 242planned use of, 299

Scarfing joints, 56Scissor scarf joint, 56Security, 239–44

access control, 350detection devices, siting, 350detection systems, 348lighting, 351lock security, 348personnel, 348principles, 347site factors, 347surveillance, 350

Seiches, 132Seismic sea waves (tsunamis), 131Seismic shocks, 119

spectrum, 132Seismograph, 132Seismometer, 132Serpula lacrymans (dry rot fungus), 135, 136Settlements, 30–2

absolute, 31differential, 30, 31foundation, 31, 80, 81rotation, 32

Sewage effluent, 83Shake (crack in timber), 55Shear cracks, 62Shearing force, 25Shear-panel analysis, 28Sheet metal roofs, 210Shores, 66, 86, 127Shoring, 300

jacking of, 303Silica, 107

gel, 185Silicon dioxide, 107Slabs, 37

Slurry of mud, 76, 115Smoke, 111, 112, 244

detectors, 258emission, 170test for drains, 216treatment against insects, 145

Smoking, fire risk, 259, 283cause for dismissal, 259

Snow, 107Society for Protection of Ancient

Buildings, 236Sodium:

chloride, 101, 107nitrate, 107pentachloride, 134, 136sulphate, 107

Soil:cohesive, 126condition, 32mechanics, 80, 86, 229stress, 79structure, 81

Solar radiation, 93, 95absorptivity, 136heat gain, 95, 97

Solder repairs failures, 210Sound reinforcements, 185Spalling, 60, 64Sparge pipe, 65Spatial environmental system, 173, 185,

237, 279, 297Specifications, 205, 276Sphaeroma (crustacean marine borer), 151Spore of fungus, 135Squinch under dome, 342Stack effect, 177Stainless steel wire, 70Stefan effect, 101Stiffness of structures, 25, 34, 120, 337Stone beams, 32Stone, substitutes, 69Stonecrop, 133Strain gauge, Demec, 213, 226Strengthening of masonry, 122, 123, 174Stresses:

arches, 38beams, 37calculation of, 28tensile, 31thermal expansion, 99

Stripping paint, 341Structural:

actions, 18, 34analysis, 18–21, 203, 225consolidation, 31damage, 159developments, 328elements, 34improvement of foundations, 83, 84

Structural distortion and movement, 355Structural engineer, 195Structures, classification of, 35Strutting, 88, 127, 129, 282, 295, 300Subsidence, mining, 79, 162Suction wind, 111Sulphur dioxide, 167, 245, 246Sulphuric fluoride, 150, 171Sunlight, 179Supersonic aircraft vibration, 159Surface penetrating radar, 353Survey:

drawings of buildings, 222geodetic, 227legal limitations of, 205

Subject index

387

Surveyor, 200Symbolic values in conservation, 6, 261Synthetic stone, 69

Tannic acid, 171Tax relief for rehabilitation, 279Tectonics, 121, 122Television, provision for, 285Telltales (plaster, etc.), 226Tellurometer, 227Temperature:

daily changes, 96, 100differential, 97ground, 109internal, 173seasonal changes, 100

Temples, 336Tenon in wood, 55Tension loads, 25Teredo (molluscan marine borer), 141, 151Termites, 146–51

control of, 151dry wood, 149feeding habits, 150fumigation, 150ground dwelling, 148

Theodolite, 82, 208, 223, 224, 226Thermal expansion, 96–101Thermal insulation, 175Thermal mass, 97, 184Thermal movement, 29, 30, 39, 65, 98,

101, 122Thermography, 353Thermohygrograph, 174, 339Throat, water check, 325Thrusts, 339, 341Tidal wave, 115Timber, 32

decay, 37jointing, 268roof, 63shakes in, 55structural systems, 32trusses, 51, 52

Timber-framed structures:dismantling, 59earthquake resistance, 121repair, 54–6, 59rot at ground level, 59

Toilet bowls (W.C. pans), 215Tornado, 111, 115Torsion, 25Town planner, 200Town planning, 12, 162Toxic washes, 134Toxicity of pesticides, 153, 154Tracery in stone, repair, 69

Traffic vibration, 8, 18aging, 160loadings, 25removal of, 162

Tree damage, 133Tropical insects, 146Trullo dwelling, Italy, 32Trusses, 25, 51–60, 337

American, 51development of, 51roof, 341

Tsunamis (seismic sea waves), 115, 120

Tunnellings, 79Typhoon, 115Typology of action areas, 278

Ultrasonic detection of voids and cracks, 65

Ultrasonic fire detectors, 258Ultraviolet light, 95,

179, 180Underdrainage, 80, 162, 163Underpinning, 86, 88United Nations Disaster Relief

Organization, 3Urban infrastructure, 279US National Ambient Air

Quality Standards, 168US National Parks Service, 271

Vacuum impregnation of stone, grout, 325

Vandalism, 261Vapour:

barriers, 175, 185moisture, 237pressure, 174transfer, 174

Varnishes, fire-resisting, 255Vaults:

barrel, 42, 337Gothic, 46groined, 42ribbed, 342thrusts, 343

Vehicles, heavy, 158Venice, 33, 240Ventilation, 177, 178Vibration, 62–4

damage, 337measuring, 159protection from, 161research, 160

Vinylchloride, 169Voids, 65, 99, 315Volcanic eruptions, 115

Walls, 61–3ashlar, 69brick, 70cracks in, 62, 64defects in, 64, 65flint, 70foundations, 82inspection of, 211–14load-bearing, 62mud, 72opening in, 67repair of, 66–75rubble, 68stone-faced, 62

Water:abstraction, 79, 162capillary rise of, 101content of soils, 120extraction, 32penetration of porous materials, 101table, 82, 83, 120, 162vapour, 95, 174, 237

Wattle and daub, 77, 125Waves, tidal, 115Weathering, 31, 213, 289Welding operations, 259Wet rot, 136, 184White ant, 150Wind, 25

erosion by, 111evaporation by, 111exposure, 105pressure, 105, 177speed, 109suction, 111turbulence, 177

Window:anti-bandit glazing, 352design, 177, 178general, 111inspection of, 211mullions, 69ventilation, 176, 177

Wolfson Unit for Noise and VibrationControl, 160

Wood:detection of fungus, 137fatigue, 52movements, 101piles, 82, 163

Wood-boring weevils, 139, 141Workmanship, 17, 18, 37, 120, 244

Xestobium rufovillosum (deathwatchbeetle), 55, 139, 141, 144, 145

Zinc silicofluoride toxic wash, 134

Subject index

388