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Sustainable Cities and Society 6 (2013) 57–67
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Sustainable Cities and Society
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ow carbon construction systems using prefabricated engineered solid woodanels for urban infill to significantly reduce greenhouse gas emissions
teffen Lehmann ∗
d+b Research Centre, University of South Australia, GPO Box 2471, Adelaide SA5001, Australia
r t i c l e i n f o
eywords:ulti-storey infill housing
ow carbon constructionolid wood panel systems
a b s t r a c t
Low-carbon prefabricated modular construction systems, using prefabricated engineered solid woodpanel construction systems, such as load-bearing cross-laminated timber panels, and ‘design for disas-sembly’ principles will offer significant opportunities for greenhouse gas emission reduction and wasteavoidance, among other benefits. However, introducing such innovative and sustainable constructionsystems to the Australian construction industries and housing markets has its challenges.
This paper explores the opportunities offered by an innovative low carbon construction system usingcross-laminated timber (CLT, also known as cross-lam) panels to improve the design and delivery of urbaninfill housing of the Australian construction market. CLT construction has been developed around 1996in Europe, mainly in Austria and Germany: thick layers of timber boards are glued crosswise in differentdirections to increase loadbearing capacity. This article describes a multi-disciplinary research project
into engineered timber panels which aims to transform the Australian construction and developmentindustry, involving a range of key partners. This project aims to introduce CLT panels as a way to buildwith a lightweight prefabricated low-carbon construction system that is advantageous for urban infilland residential buildings in the range of 4–10 stories height. The challenges, research questions andadvantages of this new engineered timber system are explained, and a research methodology for furtherresearch is presented.
The traditional model of greenfield housing development inustralia and the U.S. is unsustainable because of the quantity ofnergy, materials and water used, land consumed, waste generated,nd the greenhouse gas emissions that result from high consump-ion and inefficiencies. The flow of raw materials through the urbanystem has not received adequate attention because the topic ofrban waste is unglamorous albeit extremely important. Reducinghe consumption of materials in the construction sector is essen-ial and even more important than recycling of building materials,s the construction of buildings and neighbourhoods using currentethods require vast amounts of energy generated by fossil fuels
nd are based on linear one-way throughput of non-renewableaterials (Lehmann, 2011).Rethinking the way we deal with material flows and changing
ehaviour in regard to waste streams and waste avoidance, is likely
o deliver significant improvements and curb the threat of environ-
ental degradation and global warming. But how does this affecthe construction sector? The research the Sustainable Design and
Behaviour (sd+b) Research Centre is involved with explores a widerange of topics around consumption and waste of materials, mate-rial flows, and solutions for better management of resources forurban development. The university understands itself as a plat-form for the exchange of knowledge and ideas in these areas,bringing together representatives from academia with industry,government and local communities.
We have borrowed from the planet for a long time, exceedingits carrying capacity, and if our society and economy are not trans-formed we risk descent into unhealthy urban conditions, loss ofprecious biodiversity, and depletion of virgin materials. Our currentmodel of economic and urban growth is driving this unhealthy sys-tem, and, as a consequence, we have passed the limits of our planet’scapacity to support us. Over the last 20 years, the amount of wasteAustralians produce has more than doubled, and it is likely that thisamount will double again between 2011 and 2020: the amount ofwaste generated in Australia grows currently by around 6–7 percent per year (National Waste Report, 2010).
The notion of ‘waste’ is based on the assumption that energyand materials, having once served the construction sector’s imme-
diate purposes, simply cease to exist in any functional sense,and that the only possibility is dumping these ‘mis-allocatedresources’ in landfills. Or, to borrow a word from Mumford (1961),current construction methods are ‘paleotechnic, representing
nsustainable behaviour based on primitive, exploitative tech-ologies’ rather than regenerative ones. However, the re-use ofuilding components and construction materials would not onlyeduce the amount of waste created, but also allow for recyclingnd retrofitting of entire neighbourhoods or districts, once require-ents have changed (Lattke & Lehmann, 2007; Zaman & Lehmann,
011).Timber, arguably the original building material, retains its
rime importance within the construction industry because of itsersatility, diversity and aesthetic properties. Brick, steel, glass,lasterboard, concrete and particularly aluminium, all use morenergy in their production than timber, thus contributing consid-rably to CO2 emissions (Lyons, 2010).
Prefabricated engineered solid wood panel construction sys-ems can sequester and store CO2. Modular cross-laminated timberCLT, also called cross-lam) panels form the basis of low-carbon,ngineered construction systems using solid wood panels thatan be used to build residential infill developments of 10 storeysr higher. Multi-apartment buildings of 4–10 storeys constructedntirely in timber, such as recently in Europe, are innovative, butheir social and cultural acceptance in Australia and North Amer-ca is at this stage still uncertain. Commercial utilisation is onlyossible if there is a demand and user acceptance.
Wood is an important contemporary building resource due to itsow embodied energy and unique attributes. The potential of pre-abricated engineered solid wood panel systems, such as CLT, as austainable building material and system is only just being realisedround the globe. Since timber is the only material that has theapacity to store carbon in large quantities over a long period ofime, solid wood panel construction offers the opportunity to turnuildings into ‘carbon sinks’. Thus the historically negative envi-onmental impact of urban development and construction can beurned around with CLT construction on brownfield sites.
One cubic metre of wood stores around one tonne of CO2, mak-ng timber the only construction material that can impact positivelyn the environment. Generally, timber buildings require less pri-ary energy consumption (‘primary energy’ is the energy form
hat has not been subjected to any transformation process; it isnergy contained in raw fuels and other forms of energy receiveds input to a system; it can be non-renewable or renewable) andave a lower Global Warming Potential (GWP) than concrete orteel buildings (the difference can be 25 per cent or more). Ideally,houldn’t our buildings be like trees and our cities like forests?
Wegner and his colleagues noted that ‘the energy budgets ofroducts and buildings made of wood show that they may use lessnergy over their total life cycle (manufacture, use, maintenancend disposal) than can be recovered from the waste products ofheir production and from their recycling potential at the end ofheir life cycle: they are energy-positive. No other construction
aterial is so comprehensively energy-efficient and therefore cli-ate effective as wood’ (Wegener, Pahler, & Tratzmiller, 2010, p.
).This paper describes a multi-disciplinary research project into
ross-laminated timber (CLT) panels which aims to transform theustralian construction and development industry and involves aange of key partners. This project will introduce cross-laminatedimber panels as a way to build with a lightweight prefabricatedow-carbon construction system that is advantageous for urbannfill and residential buildings. The challenge, research questionsnd advantages of this system are explained below.
.1. Why transforming the current system of over-consumption is
We are a wasteful nation. For instance, 40 per cent of all foods not eaten, it is thrown out; it is neither used for composting to
nd Society 6 (2013) 57–67
return nutrients to the soil, nor in a biogas plant to generate energy(George, 2009). Our resources are limited and endless consumptionand growth is impossible. If we cut down more trees than we grow,at some point we run out of trees. Passing the limits has conse-quences, as we see in increasing global warming, changing weatherpatterns, and a change in the way the whole system of ‘SpaceshipEarth’ (Buckminster Fuller, 1969) behaves.
Topics such as food security (is the solution urban farm-ing?), water scarcity (stormwater harvesting?), rising energy costs(decentralised energy production on solar roofs and facades?),depletion of virgin materials (closing the loop of material cyclesand resource recovery?), and traffic congestion (strong investmentin public transport?) have emerged as major concerns. Researchersare looking into better ways for us to live together in the future,in more liveable and sustainable cities. Behaviour change hasfrequently been listed as the number one hurdle to reducingconsumption towards a more energy- and material-efficient low-carbon future. If we could only plan better cities and design betterbuildings and products that needed less energy, water, materialsand other resources (during production and operation), we couldgenerate less waste and facilitate behaviour change simply throughgood design. For instance, enabling people to be less dependent onair-conditioning, or car driving could significantly reduce green-house gas (GhG) emissions (Lehmann & Crocker, 2012).
Extended Producer Responsibility (EPR) is an approach thatseeks to designate responsibility for the impacts of products (orurban development) throughout their whole lifecycle. Applyingthis idea not only to mobile phones and appliances but also tothe construction sector means when a building is made, the con-sequences of its use and demolition (entire lifecycle until ‘grave’,disposal) must be already considered during its design. Adoptingthis approach across various industries would help to minimisewaste and improve the efficiency of the resources used.
Homes of the 1950s Australian suburbs have mostly been builtin traditional fibro and timber sticks method, which is material andlabour intense and only suitable for maximum two storeys; whilethe 1960s houses were usually constructed in crème-coloured brickveneer construction. None of these methods is particularly materialefficient and limited to maximum two storeys in height. Things aregoing to change in the construction sector too, as we must makeevery effort to future-proof the built environment by designingmore resilient urban systems to cater for low-consumption, low-carbon lifestyles (this is, not air-condition dependent), and increasethe longevity of buildings. We will increasingly learn from nature’scomplex ecosystems and natural ordering principles, redefiningour industrial ecology and changing the way we design, produceand re-use products. As environmental activist Paul Gilding pre-dicts, ‘we will break our addiction to growth, accept that morestuff is not making our lives better and focus instead on what does’(Gilding, 2011).
1.2. Urban development and CLT panel systems for infill
Residential building construction is about to change. Mid-riseinsertions within the existing urban fabric are gaining in popular-ity and will help to reduce unsustainable suburban housing builton greenfield sites. Increasing urban density means building oninfill lots. Demographical trends show that younger people, ‘emptynesters’ (these are down-sizing retirees), students and companyexecutives who are keen to walk to their offices, are opting to set-tle in the city centre where they can be closer to cultural activities,mass transit, more contemporary lifestyles, and other like-minded
people. The inner-city residential buildings of tomorrow will havea focus on weight reduction by using lightweight construction sys-tems and cladding; these low carbon construction systems willuse high performance timber panels. Building more mid-rise infill
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ith timber will become essential, as carbon sequestered in treess stored in wood products for the duration of the products’ usefulife. This can offer the potential to turn buildings into ‘carbon sinks’,
hile increasing resource efficiency.Only recently there is more research on sustainable forest man-
gement, the lifecycle of wood products and the use of timbern construction in regard to CO2 emission cuts. For instance, newesearch reports that instead of keeping the wood to grow in forestsor hundreds of years, it is beneficial if it the wood is regularly har-ested and used in construction to replace concrete or steel thatonsumes more fossil fuel during manufacturing; in this way, aulti-fold level of carbon dioxide can be removed from the atmo-
phere (Lippke, 2011). The analysis has identified a number ofossibilities for the use of wood to replace concrete and steel prod-cts that utilise fossil fuel resulting in one-way generation of carbonioxide. According to Lippke, sustainably managed forests practi-ally offer two-way flow of carbon dioxide: they absorb the carbonioxide during their growth and when the tree dies and decays,alls back or burns, the carbon goes back to the atmosphere, thusemaining carbon neutral. Therefore, the researchers recommend
quicker growth of trees and cropping of the wood before the treesecome less active, to utilise them in place of steel or concrete inonstruction; or to use wood as biomass to produce energy or bio-uels, replacing fossil fuels. A detailed evaluation of each forest haso be done, as older forests slowdown in the absorption of carbonioxide, however, some continue to offer a number of other eco-
ogical benefits. Research has to use detailed lifecycle analysis toompare the carbon footprint of engineered timber construction:or instance, the use of engineered wood joists weighing aroundne tonne (replacing steel floor joists) approximately cuts downround 10 tonnes of carbon dioxide. In another example, the usef wood flooring in place of concrete slab flooring brought downhe carbon dioxide level to the tune of 3.5 tonnes for every tonnef wood utilised (Lippke, 2011).
Over three-quarters of Australians live in its 18 major cities withver 100,000 people and the population of these major cities is pre-icted to grow (Commonwealth of Australia, 2010). Urban designnd low carbon technologies have a key role in shaping the futuref our cities. Planning strategies for Australian cities require a highercentage of new housing to be in existing urban areas—as anxample, the 30 Year Plan for Greater Adelaide estimates a growthf 560,000 people by 2040, requiring 70 per cent of new devel-pment to cater for this growth to be urban infill (Government ofouth Australia/DPLG, 2010). The Australian government throughhe Council of Australian Governments (COAG) is taking a muchreater interest in the mechanisms whereby housing can be pro-ided that is sustainable, focussing on its affordability, accessibilityo services, and carbon emissions during construction and occupa-ion. In Australia, the residential and commercial building sectorsroduce 23 per cent of the nation’s GHG emissions, indirectly, as
result of materials used in construction, waste disposal, mate-ial inefficiencies and ongoing energy use (Green Building Councilustralia, 2011). In addition, increasing cost of energy in Australia isriving the property and construction sector to look towards morenergy-efficient products (Green Building Council Australia, 2011).
. Introducing multi-storey prefabricated timberonstruction systems to Australia
It is time to scale up our scholarship in low-carbon solutions toatch the challenges we are facing in the construction sector – one
f the most wasteful – and to support policy development. Improv-ng collaboration across the sector is critical, as is guiding researchgendas and legislation. At the same time it is important to educateommunities to encourage a groundswell of support for this type
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of construction and hence influence the developers to build whatpeople want. Our researchers are collaboratively working towardsdeveloping a responsive plan for the transformation of Australiancities as an important part of the solution. These efforts must sup-port long-term planning and research in line with agreed nationalpriorities, for holistic whole-of-lifecycle approaches. We thereforefacilitate, support and continually evolve interdisciplinary, collab-orative research and development capability in architectural andurban design and in sustainability knowledge for resilient urbansystems and construction methods.
Low-carbon prefabricated modular construction systems, usingload-bearing cross-laminated timber panels (such as those sys-tems currently manufactured in Europe, Canada and New Zealand)and ‘design for disassembly’ principles will offer significant oppor-tunities for carbon reduction and waste avoidance, among otherbenefits. Introducing such innovative construction systems to theAustralian construction industries and housing markets has itschallenges. Hence this multi-disciplinary research project has beendeveloped, involving researchers at the Barbara Hardy Instituteand the Research Centre for Sustainable Design and Behaviour.The project’s partners include: the South Australian (SA) govern-ment’s Department of Communities and Social Inclusion; HousingSA; the Integrated Design Commission and Government Architect(Department of Premier and Cabinet); the Land Management Cor-poration, the government’s developing body; Zero Waste SA, agovernment agency; two city councils; a local construction com-pany; the Property Council of Australia; two architectural firms;and one of Australia’s wood product supplier. The compositionof these partner organisations will ensure a broad impact of theresearch project. In terms of introduction of CLT construction toAustralia, a 10–15 per cent market penetration within five years isseen a feasible by the team.
Timber has recently been used in a much more sophisticatedway than previously. In recent years, approaches to timber con-struction in Central Europe have undergone innovative changes.In construction technology, we generally need to differentiatebetween wood, timber and lumber. Definitions used in this chapterare (Dehne & Krueger, 2006):
• Wood: the hard, fibrous, lignified substance lying under the barkof trees. It consists largely of cellulose and lignin. Wood is a nat-ural material and is irregular by nature.
• Timber: the wood of trees cut and prepared for use as buildingmaterial (e.g., beams, posts).
• Lumber: timber cut into marketable boards, planks or other struc-tural members of standard or specified length.
Traditional approaches, such as block and half-timberedconstructions and the balloon-frame and platform-frame construc-tions seen in North America, have given way to today’s differenttypes of construction: frame, skeleton (GLT, LVL), or solid panelCLT constructions. The main difference between these systems lieswithin the hierarchy of the load-bearing elements of the buildingstructure as selective or linear elements. These constructions arecharacterised by the method of assembling prefabricated structuralelements and the structure of the facade (envelope). General build-ing systems consist of similar wall and ceiling elements, thoughthese elements can also be used in combination to form a buildingstructure; for example, the application of solid wood elements inceilings of framework structures.
Modern methods of construction including prefabrication of CLTpanels have gained attention in Europe, Canada and New Zealand.
CLT panels are fabricated by bonding together timber boards (usu-ally manufactured from spruce, larch, pine, or douglas fir) withstructural adhesives to produce a solid timber panel with eachlayer of the panel alternating between longitudinal and transverse
60 S. Lehmann / Sustainable Cities and Society 6 (2013) 57–67
Fig. 1. (a and b) Prefabricated cross-laminated panels are engineered load-bearing jumbo panels, consisting of a series of layers, bonded together timber boards (usuallyspruce, larch or pine) with structural adhesives, forming a solid timber panel with each layer of the panel alternating between longitudinal and transverse lamellae. CLTp
anels can be up to format 3.2 m × 16 m (approx. 10 ft × 45 ft) in size.
hotos: Carter Holt Hardy, Australia, 2010.
amellae (Timber Development Association of NSW, 2011). The CLTanels are compatible with digital design and precision cuttingechniques, enabling delivery of a prefabricated wall, floor or rooflement for rapid on-site assembly; implementation shows thathe system cuts construction times by more than half (Kaufmann,011; Waugh & Thistleton, 2011). Prefabricated CLT panels offer
number of advantages to delivering more sustainable buildingsncluding modular, rapid on-site assembly (substantially faster andafer) which reduces cost, construction activity impacts and wasteLee, 2011; Lehmann, 2010; Lehmann & Crocker, 2012). In Newealand, research has also highlighted the opportunity that tim-er structures, assembled on-site through bolt fixings, provide for
ntegrating ‘design for disassembly’ principles (John, Nebel, Perez, Buchanan, 2009). Such principles are said to allow reuse of loadearing timber panels and entire components on alternate sites athe end of the building’s useful life (see: Fig. 1a and b).
The presence of radiata pine softwood plantations in the ‘Greenriangle’ in the South East of South Australia (SA), close to urbanommunities in South Australia and Victoria, led to a recent scop-ng study by the Zero Waste SA Research Centre for Sustainableesign and Behaviour at University of South Australia (Lehmann &amilton, 2011). The purpose of the scoping study was to identify
he key factors preventing or enabling the adoption of CLT con-truction systems for infill development in South Australia and todentify the priority areas for research.
Designing timber buildings requires more careful detailingnd precise planning than other construction methods. Gener-lly, condensation can occur where moist air comes into contactith a surface of a lower temperature. Air always contains water
apour in varying quantities; its capacity to do so is related to itsemperature—warm air holds more moisture than cold air. When
oist air comes into contact with colder air or a colder surface (e.g., timber element), the air is unable to retain the same amount ofoisture and the water is released to form condensation in the ele-ent. The moisture from condensed water causes timber to decay,
s the damp causes wet rot inside the walls. This is often hard toetect and may not be noticed until mould growth or rotting ofaterial actually occurs.Consequently there is a need for a precise, correctly layered and
igh-quality construction envelope to protect the timber struc-ure from rain and water condensation. Only correct detailingill protect it from humidity and solve the question of surface
reatment—to keep maintenance low and to ‘pre-design’ the ageingrocess and the appearance of the surface.
The thermal properties of CLT panels depend on the timber used;
ensity is usually around 500 kg/m3 and has a thermal conductivityalue of 0.13 W/m K.
The project will introduce cross-laminated timber (CLT) panelso the Australian construction sector. These panels are lightweight,
prefabricated, modular, produced off-site, recyclable and highlymaterial-efficient. In addition, this construction method has signif-icantly less embodied energy and enables ‘design for disassembly’principles—buildings can be disassembled or adapted more easilyas use dictates. CLT panels are a ‘value-added’ timber product thatcan substitute for concrete or steel, which are both very carbon-intensive. As layers of timber boards are glued crosswise (width ofwood stripes usually varies between 80 and 240 mm, with thick-ness between 10 and 40 mm), the loadbearing capacity of CLTpanels in different directions is increased for taking up compres-sion loads, while the shrinkage and swelling as a result of humidityvariations is eliminated. It allows for a high level of prefabrica-tion, where buildings can be erected rapidly as openings for doorsand windows are already included in the factory cutting process(KLH, 2011). The project partners are committed to up-scaling theapplication (from prototyping to full-scale demonstration) and aninner-city pilot project will deliver useful preliminary information.
2.1. The future: a recyclable construction system with potentialfor carbon reduction
To identify holistic approaches, such as principles for disas-sembly and reusability of entire building components, requiresresearchers in disciplines including economics, design and mate-rials, to work together to enable the systemic environmentalrestructuring of consumption and provision in energy, water andwaste systems. In the context of this change process, designers –architects, urban planners, industrial, interior or product designers– play a major part. To advance design knowledge one has to engagein designing. In Sustainable by design, Walker (2006) outlines anew understanding of the complexity and potential of sustainabledesign, extolling the contribution of design to the creation of a moremeaningful material culture.
Prefabricated modular CLT panels, when manufactured inAustralia, should be available in sizes up to 16 m × 3.2 m(length × width), and thicknesses from 50 mm to 250 mm, even upto 500 mm. These panels are made from three, five or seven thicklayers of solid wood planks glued together in alternating direc-tions for strength. Recently new adhesives have been developedthat resolve the previous fire and off-gassing (VOC) issues, whichare on polyurethane basis. The CLT panels suit a wide range ofprefabricated floor, floor-to-floor high wall and roof applicationsfor both commercial and residential buildings. Utilising specialisedcomputer-controlled machinery, these panels are manufactured,factory cut, bored and grooved to suit any end use, and deliv-
ered just in time for assembly on-site. CAD and CNC computerisedtechnology delivers perfect precision and allows building design-ers to interface directly with production. Manufacturing elementsfor mass customisation of buildings (e.g., using a ‘kit of parts’)
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ill develop a manufacturing assemblies industry similar to theutomotive industry, using digital fabrication and systems designf components, realising prototypes and demonstration projects.pplied research and development in CNC-cutting technology will
urther drive this off-site fabrication. Findings from the author’sesearch activities show that the extent of factory prefabricationramatically reduces construction time on-site. The panels can besed as:
a complete construction system (modular and demountable);components in conjunction with complementary engineeredtimber products, such as glue-laminated timber and laminatedveneered lumber (GLT and LVL); andhybrid structures in combination with concrete and steel.
Material in architecture is the means of implementation as wells the means of expression. Architectural design and material arentrinsically intertwined. Engineered timber systems allow for a
ore systemic approach to architectural design. Timber panelsanufactured from reconstituted and waste wood are possible and
dd further to the efficient use of resource. However, about halfhe total of timber waste arises from building construction andemolition. According to the Timber Research and Developmentssociation (TRADA, 2009), the UK, for instance, generates approx-
mately 11 million tonnes of timber waste annually of which 80 perent enters landfill sites. Not only is this a costly waste of resources,ut it also generates methane as the timber degenerates in these
andfills with time. Of the 20 per cent of timber waste which is cur-ently recovered, only 16 per cent is recycled and 4 per cent usedor energy production.
A main concern with multistorey construction systems is fireehaviour. Timber is an organic material and therefore com-ustible; however, despite its combustibility, timber particularly
n larger sections performs better in a fire than the equivalent sec-ions of exposed steel or aluminium. The rate of charring of timberanges between 30 mm and 50 mm/h/surface exposed, dependingn the timber density (Lyons, 2010).
Design models of timber structures in fire usually take intoccount the loss in cross-section due to charring of wood. Whileome information is now available on charring of CLT panelsand their adhesives for bonding), a recent extensive testing pro-ramme on the fire behaviour of CLT panels has been conducted inwitzerland, and results are very promising (Frangi, Fontana, Hugi,
Joebstl, 2009). For instance, the spread of flame and therefore fireafety is comparable to other established construction methods.uilding designs for timber structures require fire engineering to bembodied in the architectural and structural design concepts fromhe beginning—to ensure integrated solutions that are cost effec-ive and meet the requirements of the building code and regulatoryuthorities.
To protect timber from insect attack, a wide range of effectivereservatives are commercially available for use under controlledonditions.
Using resources more efficiently through CLT constructioneduces the embodied carbon in materials and structures fromround 550–300 kg CO2/m2, compared to conventional materialssed for such construction. This is achieved by using a prefabri-ated timber construction system with lightweight facades withow-impact finishes. Timber is a significantly lower-impact mate-ial than steel or concrete, as it produces less GHG emissions, isully recyclable and regrows sustainably. CLT panels have a high
aterial efficiency, using around 0.75 m3 of CLT per m2 of apart-ent. Using local timber will allow the entire supply chain to be
ontrolled, developed, and its impacts minimised across the wholeifecycle of a building.
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2.2. The project challenge and policy context
The transformation of production processes, green infra-structure and systems includes concepts of resource efficiency(especially material efficiency), decoupling (material use decoup-led from urban growth), clean technologies, and design forsustainability, industrial ecology and lifecycle analysis. Industrialproduction and the construction sector as a whole have to be trans-formed. In their seminal book Natural capitalism: the next industrialrevolution, Hawken, Lovins, and Lovins (2000) described the pathwe must take to ensure the future prosperity of our civilisationand our planet. The book rocked the business and manufacturingcommunities with its authors’ innovative approach—which fusedecological integrity with business acumen via the radical conceptof ‘natural capitalism’.
This project aims to develop systems and designs in timberto tackle the negative environmental impact of buildings throughinnovative uses of wood technology that offer new ways of con-structing efficient and affordable structures that demand less ofthe environment while maintaining functionality and aestheticappeal. This innovative study has the potential to transform theconstruction sector and change the way we design, build, main-tain and recycle inner-city infill projects in Australian cities. Oncecarbon accounting is in place, existing building materials’ carbonlifecycles will be assessed, underpinning future government policyinitiatives in the construction sector. High carbon intensity mate-rials (such as steel, aluminium and concrete) have already beenidentified, and the Federal Government’s low carbon legislationwill motivate industry to develop low-carbon, high-performancealternatives and systems. Hence, there is an increasing importanceof research in recycled construction materials.
Legislation is already pointing this way, and South Australia’sdeclining manufacturing industries could instead assemble greenkit-buildings. A recent Thinker in Residence report published bythe SA government’s Integrated Design Commission (2011) recom-mends:
Manufactured assemblies for mass customisation of buildings.Expertise in the design and manufacturing of ‘green’ assembliesfor mass customisation of buildings by transforming non-viablemanufacturing industries into eco-innovation industries for diverselocations, populations and purposes in South Australia.
Therefore, the research project combines:
1. low-carbon materials with low embodied energy;2. design of prefabricated buildings: digital fabrication of modular
floor-to-floor high elements;3. initiating behavioural change in the construction sector to sup-
port a more sustainable style of living in new urban districts.
The project explores modular prefabrication and integratedsolutions, using low-carbon materials and lightweight constructionsystems for sustainable buildings to significantly reduce con-struction waste and the consumption of resources and materials.The developed ‘workplace and living’ prototypes and guidelineswill take passive and active solar principles into account, includ-ing international best practice for cross-ventilation and lifecycleassessment criteria. Today, digital design allows for ‘digital prefab’,which can lead to a new form of ‘sustainable prefab’. The buildingof today is designed with digital tools and is produced by meansof digitally controlled production. This might lead to a revolution
in the conception, design and realisation of multistorey apartmentbuildings. Moreover, it prompts a whole new debate about whatis appropriate in architecture: zero-waste construction becomes areality.
6 ities a
sorted into metals, timber, general waste and cardboard to opti-
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A paradigm shift has taken place, from architecture basedn mass production to architecture based on industrially pro-uced made-to-measure components. Simultaneously, the role ofhe architect, or, to be precise, the expert formerly known ashe ‘architect’, is changing as the context for development hasntirely changed. This project aims to develop a better under-tanding of these changes and to help design professionals andecision-makers develop better models for Australia’s transit-riented developments (TODs) and urban infill with residentialultistorey buildings.
.3. Exploring initial research questions
This project’s questions go far beyond the simple one ofecycling building components in the construction sector. John Till-an Lyle notes:
. . . among the most serious difficulties with waste management inthe industrialised nations is the immense quantity of materials to bedealt with. The industrial economies’ high emphasis on productivitynecessarily results in large volumes of waste, which is the essenceof the throughput system (Lyle, 1994).
It became clear at early stage that the project should explore aide range of issues, including:
How can we quickly introduce this technology in Australia?Will timber construction apartments be embraced by con-sumers?Given existing building codes, how can we get approval for inner-city residential buildings in the range of four to eight storeys (i.e.,resolving issues around fire and acoustics)?How can we ensure local supply chains, sourcing of appropri-ate timber (South Australian pine), investment and skills to buildwith timber?
The research team is now working to answer these questionsnd address the issues over the next two years.
Prefabrication ideas are, of course, not new (witness the ground-reaking systems research carried out by German architect Konradachsmann in the U.S. in the 1950s; or the prefabricated self-builtood frame kit houses by Swiss architect Walter Segal in the UK
n the 1970s), but with digital fabrication and advances in Buildingnformation Modelling (BIM) it has returned in an innovative wayhat will avoid endless repetition of the same element; the systemllows for individual mass customisation (Ward, 2007).
Literature shows that testing of new materials has always beenssential to architects. Although architects are keen to try outew energy-saving low carbon systems and construction materi-ls, these systems require significant testing to ensure that buildersre equally keen, standards can be met, and that the materials andenefits will last the lifecycle of the building and to avoid litigation.s a result, university research centres are now partnering withroject developers and contractors to build demonstration projectss test beds (with sensor-filled buildings that log the indoor cli-ate, energy performance of new materials and equipment, etc.),
or instance, measuring the effects of new insulation material, con-tructing test bed projects that track all performance aspects of newystems, and so on. There are now countless collaborations goingn in this field with the result that we can be hopeful to see somennovative changes in the construction sector.
.4. The main advantages of the new engineered timber system
The research team is working towards low-carbon constructionolutions that offer new ways of constructing affordable housing,
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which will benefit from the many advantages CLT panels offer. Theadvantages of CLT panels include:
• over 50 per cent reduction of construction time, significantly min-imising construction costs;
• high material-efficiency, zero-waste construction is becoming areality;
• less weight (lightweight, better handling on-site, smaller foun-dations. Timber has a weight of 500 kg/m3, compared to concretewith 2450 kg/m3);
• more safety (less dangerous manoeuvres on-site and less timeon-site);
• independent of weather, made under high quality control in anoff-site factory;
• significantly less noisy construction, convenient in urban centres,due to prefabrication off-site;
• earthquake resistant (ideal for all cities on fault lines);• strong and durable, locally sourced, leading to distinctive archi-
tecture;• thermally efficient, with low embodied energy;• healthy, dry construction method, quick readiness for occupancy;• simple construction techniques, easy to up-skill workforce, offer-
ing a complete system approach or components with highdimensional accuracy (see Fig. 1);
• lightweight, suitable for sites with poor foundation conditionsand narrow lots (as urban infill), with slim load-bearing construc-tion elements;
• recyclable and biodegradable, made from an abundant and fullyrenewable wood resource (sustainably harvested pine plantationforestry);
• adding economic value by processing our raw timber into spe-cialised components;
• improving cash flow mechanisms for developers, while prefabdelivers more security to financing banks; and
• negative net carbon emissions (the carbon storage capacity islikely to be recognised by government for carbon sink benefits),sourced from sustainably grown and harvested forest stock (usingplantation timber that is replanted in a 12-year cycle). Wood isthe only material with a negative CO2 balance; each cubic metreof wood sequestrates an average of 0.8–0.9 tonnes CO2.
European experiences of CLT construction over the last decadewill allow for significant technology transfer. Timber’s flexibilitymakes it much more affordable to saw-cut a large piece of CLT panelinto a particular geometry or complex shape, compared to laser-cutting a comparable piece of steel. The precision is impressive, aswell as the speed on construction site: modular repetition is highand the elements are light-weight in comparison to concrete. Forthe 9-storey ‘Stadthaus’ project in London, the engineers estimateda 17 weeks’ time saving (Waugh & Thistleton, 2011).
Further advantages of prefabricated modular, multistorey hous-ing systems include integrated waste management, which is asignificant factor in the design and delivery process, enhanced as aconsequence of building in a factory environment where one canachieve reduced site waste and environmental impact by:
• designing to standard building material dimensions to minimisewastage (e.g., if a sheet comes in at 1.2 m wide, the product isdesigned at intervals of 1.2 m or 0.6 m, rather than 1.0 m and0.5 m);
• continuously recycling and streaming waste (factory waste is
mise recycling opportunities);• minimisation of travel or transport emissions; and• zero-waste construction and fast assembly on-site using mechan-
ical jointing systems.
S. Lehmann / Sustainable C
Engineers have calculated a reduction of CO2 emissions by0–55 per cent compared to conventional construction methodsArup Research & Development, 2008). Timber stores 0.8 tonnes ofO2 within 1 m3 and is a replenishable material. In comparison, theroduction of concrete, aluminium and steel are one-way energy-
ntensive processes that release large amounts of CO2 into thetmosphere (see AGO, 2002; BEIIC, 2010; DCCEE, 2011; McKinseynd Company, 2008). CLT panels can be easily demounted for re-se, or used as an energy source at the end of the building’s life.verall, this technology offers construction systems for urban infillnd narrow lots, where there is no or little storage space, thereforedeal for four-to-eight storey buildings.
. Research strategy for low-carbon products andonstruction techniques
Research in the field related to CLT buildings has so far fre-uently been part of a broader focus on examining the low carbonroperties of timber buildings, their structural performance, theirre performance and how forest and wood products, includingecent innovations in engineered wood products, may be used moreidely in the construction of multi-storey buildings. A major focus
f timber building research compares the environmental impactsf timber with that of steel, concrete and masonry. A 55 per centeduction in GHG emissions (carbon dioxide) is reported to bechievable by using timber, compared to steel and concrete (Head,008), confirming that timber provides a lower carbon solution. Forulti-storey buildings specifically, Sathre and Gustavsson (2009)
ompared two functionally equivalent four storey buildings, oneramed in timber, the other framed in reinforced concrete, find-ng that the timber framed building used 28 per cent less primarynergy for materials and emitted 45 per cent less carbon than inhe concrete framed building.
Research in Australia (Carre, 2010), where radiata pine is widelysed for timber framing, concluded that single detached housingonstructed in timber uses less embodied energy than steel or con-rete construction. CSIRO have developed an environmental impactssessment module (called eCO2) for AccuRate which allows thembodied CO2 in a proposed house design to be assessed, althoughhis module does not apply to residential (Class 2) multi-storeyuildings (Woodsloutions, 2011). It has been estimated that therowth and processing of timber in Australia also stores carbon,stimated to be 0.83 tonnes carbon dioxide (CO2) per cubic metref timber (Bootle, 2006; NSW Department of Primary Industries,008).
Researching the systematic retrofitting of existing buildingtock and entire districts is increasingly important, because theajority of carbon emissions and environmental impact comes
rom existing buildings. In the very near future, new low-carbonroducts and construction techniques will be developed and com-ercialised with industry partners to help industry reduce lifecycle
arbon content and minimise embodied energy. The required mar-et transformation will only be achieved when new governmentolicy is implemented, underpinned by research into lifecycle car-on and the optimisation of local supply chains. This will transformhe building construction, material supply chain, infrastructurend property development markets, such that there is consumeremand for low-carbon products and services, removing identifiedarriers (Garnaut, 2008; PMEETF, 2010). The ability of governmentt all levels to adopt new policy and planning settings will be vital
o the success of these market transformations. It will also buildhe capacity and capability of industry such that the building andnfrastructure design and construction industry is able to deliverhe necessary low-carbon products and services.
nd Society 6 (2013) 57–67 63
The project focuses on appropriate uses of innovative andsustainable construction materials from a holistic standpoint ofstructural and environmental performance. Consequently, linkswith other university research centres are very important, espe-cially in the field of building physics and construction management.
4. Three recent European case studies to be analysed
Since the late 1990s, construction with CLT panels in Europehas resulted in some ground-breaking demonstration projectswhich have been extensively analysed (Lattke & Lehmann, 2007;Lehmann, 2010). The measured insulation (R-value) and acousticcharacteristics of the Austrian built cases are impressive: a R-value0.45 W/m2 K for external walls are easily achievable with CLT con-struction, and a superior acoustic value for external and internalwalls, achieving sound proofing values of Rw 50 dB-A (Kaufmann,2011), suggesting that CLT will perform well in terms of acousticaland general environmental functions. Here a brief description ofthree European cases:
Project 1: Svartlamoen multi-apartment building in Trondheim,Norway, 2005 (Architects: Brendeland and Kristoffersen, Trond-heim). This is one of the most remarkable timber constructionsin Europe. Two buildings with an overall area of around 1000 m2
were built. The main five-storey building, which measures6 m × 22 m, also contains rooms that can be used commercially,and the four upper floors contain units of 120 m2. The entireconstruction was made out of solid CLT boards and clad with Nor-wegian larch. The untreated timber surfaces of the load-bearingelements are exposed on the inside. The use of prefabricated ele-ments reduced total construction time significantly, to 9 months(about half the usual time). The efficient assembly of the timberelements allowed four workers to erect the main structure in just10 working days.Project 2: Am Muehlweg residential development in Vienna,Austria, 2005–2006 (Architects: Hubert Riess and Hermann andJohannes Kaufmann, Schwarzach/Vorarlberg Region, Austria). Onehundred public-sector apartments were built on three intercon-necting sites, with the emphasis on the optimum exploitation ofthe ecological and economic benefits of timber and mixed con-structions. Terraced houses and an L-shaped building surroundan internal courtyard, creating a communal area. The three-storeysuperstructures made from prefabricated CLT panels built on top ofthe concrete basement were constructed in 15 months (see Fig. 2aand b).Project 3: Holzhausen multi-apartment building in Steinhausen,Switzerland, 2006 (Architects: Scheitlin-Syfrig and Partner,Luzern). The new fire protection standard in Switzerland,introduced in January 2005, permits the construction of timberbuildings of up to six storeys with a 60-min fire-resistance capa-bility. This is Switzerland’s first six-storey timber building, witha four-storey CLT panel construction on top of a concrete base.Each floor accommodates two spacious apartments of 150 m2 and166 m2.
As a next step, actual performance data will need to be gatheredand the exact thermal performance and embodied carbon in thesecases to be calculated, assessed and compared to get more reliabledata on the potential of engineered solid timber panel systems toreduce carbon emissions.
4.1. Australia’s first CLT residential high-rise in Melbourne
In Australia, only a few CLT buildings have been designed andsubmitted for development approval so far. Construction costs
64 S. Lehmann / Sustainable Cities and Society 6 (2013) 57–67
F iveredT hitect
ig. 2. (a and b) Prefabricated cross-laminated panels, up to 16 m in length, are delhe 4-storey built CLT quarter in Vienna, Am Muehlweg, shows that a very high arc
hotos: the author, 2010.
or apartment buildings are still significantly higher than costsor houses; however, CLT construction has the capacity to changehis situation in the coming years. The 10-storey residential towerForté’ at Victoria Harbour (Docklands) in Melbourne, with 23 apart-
ents, is the first demonstration project recently completed (inctober 2012). Nine storeys in CLT construction sit on-top of a con-rete ground floor podium structure. Another development in theydney area (MacArthur Gardens in Western Sydney), and three indelaide (the 4-storey Sturt Street housing project in the city cen-
re; an 8-storey student housing project on top of an existing carark in Currie Street; and a 8-storey apartment building at Bowdenrban Village) propose CLT buildings, although the designs are stillnly in concept form at the time of writing.
Forté is a landmark project for the whole timber industry inustralasia. The ground floor concrete podium will be used for retailpace. The developer (Lend Lease) anticipates that 30–50 per centf their residential projects could be executed in CLT in the nextears, and expect the system also to be used in other applications,ncluding educational, community and commercial buildings.
The advantages of CLT are particularly relevant to the Dock-ands location and the Victoria Harbour precinct, as its reduced
eight generated substantial below-ground savings and the fastuild suited the compact site. By using engineered timber panels,orté will reduce carbon emissions by more than 1400 tonnes ofO2, compared with building in concrete and steel. The advantages
ontinue for residents too: the 23 apartments will require 25 perent less energy to heat and cool than a similar apartment built inonventional concrete or steel method. The building will be carboneutral after 32 years, for at least ten years.
Fig. 3. (a and b) The 10-storey ‘Forté’ apartment building in Bourke
ource: Woodsolutions/C. Philpot, 2012; S. Lehmann, 2012.
just in time for assembly on-site; image of a European project under construction.ural quality can be achieved even for public housing.
Construction of the building took only from February to October2012, constructed from 760 CLT panels, which were shipped fromAustria to Australia in 25 containers (panel length limited to 12metres due to container size). The developer decided that the build-ing would be fully sprinklered to make it look safe, although thiswas not requested by the Fire Department (see Fig. 3a and b).
5. Research methodology and next steps
This research initiative is timely and significant, addressing thelack of research in this field. The presence of a source of CLT pan-els in the Asia-Pacific region will increase the need for Australianregulators and building certifiers to develop knowledge, skill andcapacity to assess CLT building designs to ensure that this con-struction technology is not unduly disadvantaged compared totraditional construction systems or other modern methods of con-struction based on steel and concrete prefabricated panels. In thiscontext, research to address the key gaps in knowledge that restrictthe broader uptake of the CLT construction system in Australia isbecoming increasingly urgent.
The actual research methodology applied will further addressthree significant environmental problems: material consumptionof common construction methods is contributing to (i) growingresource scarcity, (ii) pollution in the form of GhG emissions andinefficiencies, adding to (iii) a growing waste problem in Australia.
In an analysis of barriers identified by stakeholders to usingCLT construction systems, Lehmann and Hamilton (2011) noted anumber of aspects related to the lack of reference CLT in perfor-mance standards in building codes and regulations in Australia.
Street, Melbourne Docklands, under construction (July 2012).
S. Lehmann / Sustainable C
ne aspect relates to the permitted height of timber buildingsenerally, reflecting the expected performance of timber framedonstruction rather than engineered CLT construction. The Nationalonstruction Code (NCC) also focuses on the combustibility of tim-er, classifying buildings constructed in timber as Type A. There areo deemed to satisfy provisions relating to CLT products or perfor-ance standards for these products, requiring expert opinion likely
o be based on destructive testing. The NCC and its building codesre performance based and are similar to codes adopted in mosturopean countries. A recent review of building regulations forulti-storey timber buildings in Europe (Östman & Källsner, 2011)
dentified and analysed five building requirements: fire safety;coustics and vibrations; stabilisation; seismic design; and durabil-ty design. They found that the main limitations from a regulatoryerspective to the increase in use of wood for multi-storey build-
ngs in Europe were fire and acoustic performance requirements.stman and Källsner (2011) noted that issues raised by BRE (2004)ere still being resolved in Europe in 2011. These issues relate to:
regional differences in building regulations in some countries;a lack of codes and standards for many wood products, result-ing in costly and time-consuming certification procedures fortechnical performance of these products;limited use of Euro Codes, although familiarity was increasing;uncertainty and lack of in-depth knowledge of regulations rele-vant to timber construction;limited external use of wood or wood products due to height ofthe building and distance between adjacent buildings—related toexternal spread of fire; andvariation in the maximum number of storeys permitted.
While timber is combustible, it is predictable in fire and has high degree of fire resistance; CLT panels are resistant to ini-ial combustibility. The results of recent fire performance testingf CLT has provided sufficient evidence to force a review of Euroodes and an update of building codes at a country level (Östman
Källsner, 2011). In respect of fire performance of CLT, the mostnfluential fire research to date has been undertaken by Frangi et al.or the WoodWisdom-Net project in Europe. Their study found thathe integrity of the CLT panels tested is reliant on both the rate ofre spread and speed with which the layer burns, and the type ofdhesive used.
In the next step, the project will outline policy directions toefine guidelines for urban infill and CLT construction in the nearerm (3–5 years), mid-term (10–15 years) and long term (beyond0 years). It is planned that at least six cases of recent 4–7 storeyLT buildings in Europe (in Vienna/Austria, Berlin/Germany, Lon-on/UK, Trondheim/Norway and Steinhausen/Switzerland) andanada (UBC Vancouver) will be analysed in-depth to betternderstand the factors affecting building standards adopted, the
nfluence of urban design features, suitable surrounding land-uses,ocation and community acceptance. Social and cultural acceptancelays a vital role during the implementation of any technology
nnovations. A detailed post-occupancy evaluation will be con-ucted for all cases, to develop an indicator matrix that allowsecommending future standards for CLT buildings and their socialcceptance, most suitable for an introduction of the technology inustralia (Lehmann & Fitzgerald, in press).
. Conclusion and further research
New research agendas are emerging in response to the needs ofur society to become sustainable. Conducting research is essentialn the change process, as it will deliver more and better solutionso curb global warming. Universities are leading the search for
nd Society 6 (2013) 57–67 65
solutions. In his seminal essay ‘The metabolism of cities’, HerbertGirardet notes that:
the linear model of urban production, consumption and disposalis unsustainable and undermines the overall ecological viability ofurban systems, for it has the tendency to disrupt natural cycles. Inthe future, cities need to function quite differently (Girardet, 2004).
Transforming the construction sector’s building methods is anessential part of moving towards a better model with reducedmaterial consumption, higher efficiencies, and carbon storage abil-ities. Timber is a wholly sustainable construction material for thedeveloped world, as it re-grows, can be sustainably harvested, isfully recyclable, and stores carbon. Using certified wood ensuresthat the timber is supplied from sustainable forestry, and not fromdeveloping countries, where precious ‘old-growth’ forests are ille-gally logged.
No doubt, CLT can become an interesting alternative construc-tion method in rapidly expanding, urbanising cities such as inthe Asia-Pacific region (e.g., in China), where there is a need forinner-city apartment buildings and rapid low carbon constructiontechnology. It also shows good performance against earthquakes(Ceccotti, 2008). Significant savings during the construction stageare achievable, as well as reduced CO2 emissions in compari-son with concrete or steel. The integration of sustainability inhousing, combined with holistic problem solving, is of crucialimportance for the development and re-development of all urbanareas. When combined with innovative technological solutions formodular prefabrication, this drive for sustainability could lead tomore affordable housing, if the advantage of repetitive modules isfully explored. This is particularly important for Australian cities;a recent international study ranked no Australian urban area as‘affordable’ and 25 of Australia’s 28 urban areas as ‘severely unaf-fordable’ (Demographia, 2011).
In conclusion, cross-laminated timber panels are a productextremely well suited for multi-storey urban infill buildingsbecause of its versatility and many outlined advantages comparedto concrete and steel. With lengths up to 16 m and the possi-bility of extending with mechanical joints or glued connections,widths of up to 3.2 m and thicknesses up to 500 mm, almost anynecessary shape of element can be manufactured on the markettoday. Innovative possibilities and new applications using CLT arefar from being exhausted. So far, the highest CLT building is the‘Stadthaus’ in London Hackney, a 9-storey apartment tower (wherealso the elevator shaft is made of CLT panels); but there is poten-tial for wood-concrete hybrids, composite structures, combiningCLT elements with a concrete core and structural outriggers as astructural system for much higher buildings, e.g., using CLT struc-tural wall elements in the facades in combination with a concretecore (Van de Kuilen, Ceccotti, Zhouyan, & Minjuan, 2011): verytall timber towers (up to 40 stories) have recently been devel-oped by various architect plus engineer teams, e.g., in Europe byKaufmann and TZG (TU-Munich), in the UK by Ramage and Ram-boll (with the University of Cambridge), in Austria by Winter (atthe TU-Vienna), and in Canada by Michael Green et al. However,for the time being these remain academic challenges, as long asfire safety and earthquake performance are still in research stage.In real construction, CLT has already proven to be very mate-rial efficient for multi-storey buildings in the range of 4–8 storiesheight; hence, ideal for the urban density Australian cities arerequiring.
In conclusion, such research in low carbon, zero waste construc-tion systems with a focus on construction waste avoidance, willdevelop low-carbon-lifecycle building construction components
for inner-city housing applying ‘design for disassembly’ and modu-lar prefabrication principles, thereby enabling significant emissioncuts. The low carbon construction materials and systems of the
6 ities a
6 S. Lehmann / Sustainable C
uture will have green supply chains, less environmental impactver their entire lifecycle, be light-weight to reduce embodiednergy, be fully recyclable/re-useable, and allow for off-site prefab-ication and prototyping. The construction industry of tomorrowill favour materials and systems with low embodied energy that
an easily be recycled and re-used, based on sustainable sup-ly chains. However, the influence of embodied energy on the
ifecycle balance is by many architects still not well understoodWackernagel & Rees, 1996). ‘Zero waste’ means maximum mate-ial efficiency and resource recovery, without any constructionaste to landfill; it also means that buildings are fully demount-
ble and fully recyclable at the end of their lifecycle. This researchroject aims to evolve timber designs and manufacturing systemso reduce buildings’ negative environmental impact through inno-ative uses of wood technology that offer new ways to constructfficient and affordable structures that demand less of the environ-ent, while maintaining high functionality and aesthetic appeal.
he research team aims to report findings in a forthcoming bookublication planned for 2013, so that an effective contribution tohe advancement of knowledge can be delivered. The project’sndings will apply to the lifecycle of sustainable multi-apartmentousing projects, help ensure long-term viability of buildings,udge the behaviour of stakeholders towards more sustainableutcomes, reduce resource consumption, and increase re-use ofaste and building components. There is no CLT manufacturing inustralia yet (New Zealand and Canada have started manufactur-
ng CLT panels in 2011). However, it is only a question of time, ashe demand for CLT products in Australia and the U.S. are likelyo reach the level to justify the investment in a domestic man-facturing plant; U.S.-architects have also become interested in
ntroducing this new way to build and have designed first demon-tration projects using CLT construction (such as the recent projecty Mark Mack Architects from San Francisco for a 4-storey multi-partment building).
This paper has outlined why CLT construction systems are a rel-vant topic within the context of the current environmental debatend the use of sustainable materials and construction methods.his technology might even turn urban infill developments into
carbon sinks’. Timber, the construction material of the past, isgain re-considered as the construction material of the future; as aigh-performance, low-carbon construction material, adequate forultistorey residential buildings even in an urban setting.
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