Hadegord Moisture Control in Buildings Nrcc20752 1982

8/3/2019 Hadegord Moisture Control in Buildings Nrcc20752 1982

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N21d ! National Research Conseil national .2 . l a 63 'I Council Canada de recherches Canadac. 2

AIR LEAKAGE, VEN TILATION, AN DMOISTURE CONTROL IN BUILDINGSby G.O. Handegord

APSALYZED

Reprinted fromAmerican Society for Testing and MaterialsSpecial Technical Publication 779, 1p. 223 - 233

DBR Paper No. 1 063Division of Building Research

Price $1.25 OTTAWA NRCC 20752


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SOMMAIRE

Bien qu ' e l l e s so i e n t une cause ma jeure de s p r o b lh e s de condensat ione t p eu t- at re un f a c t e u r f a v o r i s a n t l a p e n et r a ti o n d e l a p l u ie , l e sf u i t e s d ' a i r on t to ujo urs S t6 consid 'erees cornme un moyen acce pta bled1 a6 ra t i on des bat iments . Malgr'e l ' ac ce nt r6cemment plac 'e su r l e sBconomies d ln ergi e , i n c i ta n t a rendre Stanches l e a ba t iments ,beaucoup pensent encore que, B un c e r t a in degr' e, le s f u i t e s d ' a i rs o n t i n di s pe n sa b le s e t q u ' i l f a u t e n t o u t p re mi er l i e u c h i f f r e r le sp e r t e s d l n e r g i e a ux q u el l es e l l e s do nn en t l i e u .On e t u d i e d a n s l e p r 'e se nt d ocument l e s e f f e t s p o s s i b l e s du v e n t , d e schemin'ees, d e s e v e n t s e t d e s v e n t i l a t e u r s s u r l e s f u i t e s d ' a i r , a i n s iq ue l ' i n f l u e n c e d e l 'em plac em ent e t d e l 'i m p or t an c e d e s f u i t e s s u r l ep r o f i l d e l a c i r c u l a t i o n de l ' a i r d an s l e s_ b 9t im e nt s . O n e penchep ar l a s u i t e - .s decondensat ion e 3desd e l i m i t a t i o n d el ' h d d i t ' e a d ete ch n iq ues dc mesd 1 6 t a n c h S i t g r e nd' Bconomtser e tpar prolongat - - - . - -- -.- - .


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Authorized Reorint fromSpecial Technical Publication 779CopyrightAmerican Society for Testing and Materials1916 Race Street, Philadelphia. Pa. 191031982

Air Leakage, Ventilation, andMoisture Control in Buildings

REFERENCES: Handegord, G. O., "Air Leakage,Ventilation, andMoiPture ControlinBddinp," Moisture Migration in Buildings. ASTM STP 779, M. Lieff and H. R.Trechsel, Ed., American Society for Testing and Materials, 1982, pp. 223-233.ABSTRACT: Aii leakage through the building envelope traditionally has been regardedas an acceptable means of ventilation, although it is a major cause of condensation prob-lems in buildings and can be a contributing factor to rain penetration. Recent concern forenergy conservation, promoting the need for air tightness, is still clouded by the notionthat some leakage must be provided and that the primary effort must be toward quantify-ing the resultant energy loss.

This paper discusses the possible effects of wind, stack effect, vents, and fans on airleakage, and the influence of air leakage openings and their location on the pattern of airflow through buildings. The possible extent and location of condensation in relation tothese patterns is considered, as well as methods of controlling moisture entry and removalof accumulated moisture. Effort toward the development of construction details, tech-niques, and standards to ensure air tightness in buildings and building components is ad-vocated as the primary means of achieving energy conservation through improvedbuilding performance and extended service life.

KEY WORDS: air leakage, moisture, humidity, condensation, vapor diffusion, heatingsystems, chimneys

Water vapor moves from inside buildings in winter by both diffusion andair leakage into exterior walls, ceilings, and roofs to condense as water orfrost on the colder, outer elements. Melting, collection, or absorption andrefreezing can result in deterioration or displacement of exterior masonrycomponents. If this moisture is not removed by drainage or evaporation itcan contribute to paint failures on exterior cladding, corrosion of metal con-nectors or cladding, or subsequent decay and deterioration of organicmaterials in milder weather.

The provision of a vapor barrier as a membrane or interior coating, even ifincomplete, can limit to acceptable levels the rate of diffusion of water vapor

'co ordina tor -~u ild in ~ echnology, National Research Council of Canada, Division ofBuilding Research, Ottawa, Ontario KIA 0R6, Canada.


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224 MOISTURE MIGRATION IN BUILDINGS

under a vapor pressure difference, but any existing or subsequent cracks,fissures, or holes in the vapor barrier or interior cladding will allow muchgreater rates of moisture transfer and accumulation under an air pressuredifference. This can be controlled best by ensuring in design and construc-tion that such air leakage openings are avoided wherever possible and thatany joints or locations where cracks or holes are likely to develop are coveredand sealed in such a way as to preserve the air tightness of the detail.

Indoor Humidity Levels in BuildingsThe moisture content of the air inside any heated building in winter

generally will be higher than that outdoors owing to the unintentional addi-tion of moisture by the occupants and the operation of moisture producingequipment. The actual level of humidity will depend on the balance betweenthe rate of moisture supplied and the rate of moisture lost by diffusion, airleakage, ventilation, and condensation.

Values for the rate at which moisture is supplied by the occupants andequipment can be estimated [ l , 2 ] . 2 he moisture lost by diffusion will de-pend on the water vapor permeance of the building envelope and the vaporpressure difference across it. The moisture lost through air leakage will de-pend on the air pressure differences across the envelope and the size, loca-tion, and characteristics of the leakage openings through the building fabric.Losses due to ventilation will depend on the performance characteristics ofvents, fans, and air-handling systems in the building and on the way in whichthey are operated. The dehumidification effect due to condensation on coldsurfaces exposed to the building interior normally will be small, and willeither be eliminated by improved thermal design of the enclosure element orby intentional lowering of indoor humidity.

Lowering of indoor humidity to minimize surface condensation on win-dows is one approach, but increasing the surface temperature of the windowby improving its thermal properties through multiple glazing is a moresatisfactory solution as far as energy conservation and occupant comfort areconcerned. Simply lowering the indoor humidity to avoid concealed conden-sation on the exterior sheathing or cladding of an insulated construction isnot likely to solve the problem nor satisfy the occupants. The temperature ofthe exterior sheathing and cladding of the building envelope will be close tooutside air temperature if even small amounts of thermal insulation havebeen used. Lowering the indoor dew-point to this level to avoid condensationon such surfaces would result in most cases in indoor relative humidities ofless than 10 percent.

The levels of relative humidity that are maintained in heated buildingsusually will be determined by the requirements of the occupants, but in some

he italic numbers in brackets refer to the list of references append ed to this paper.


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HANDEGORD O N AIR LEAKAGE AND VENTILATION 225

instances may be limited by visible condensation on surfaces exposed to theoccupied space. If improved thermal perform ance of th e envelope compo-nent in question is not possible, intentional sources of moisture such as hu-midifiers should be discontinued. If this does not suffice, moisture removalsystems should by considered. These might well involve dehumidifiers rathertha n increased ventilation rates if energy conservation is to be achieved.Humidity Levels in Houses

The moisture levels in houses in winter normally will be maintained by theoccupants up to the point where excessive window condensation is experi-enced. In houses without chimneys, such as electrically heated houses, the in-put from the occupants' normal activities may be sufficient to raisehumidities above such values. In fuel-fired heating systems, however, theventilation rate afforded by the chimney in conjunction with air inlet open-ings normally will be sufficient to m aintain relative humidity levels below th ewindow condensation poin t, particularly if multiple glazing is utilized.Relative humidities up to 40 percent can be maintained without excessivewindow condensation on double-glazed windows with outside temperaturesdown to -18OC and on triple-glazed windows with outside temperatures to-30C. In both instances some condensation may appear around the edge ofthe window perimeter, but it should disappear on a warming trend. Multipleglazing selected on the basis of the outside design temperature should ensurethat the window will remain clear most of th e time. This criterion m ight wellbe used to judge whether to install double or triple glazing to maintain thedesired humidity or whether to reduce humidity to avoid condensation dur-ing the coldest periods. [3] .Control of Indoor Humidity in Houses

The most direct approach to lowering indoor humidity is to eliminate orreduce obvious sources of moisture such as hum idifiers, attach ed green-houses and open sumps. Exposed soil surfaces in crawl spaces or cellars canrelease significant amounts of moisture and should be covered withpolyethylene film or other durable moisture resistant membranes held downby sand, gravel, or other suitable means.Th e occasional openin g of windows an d doors or other short-term ventila-tion procedures may lower the humidity momentarily, but it probably willrise to its original level as soon as ventilation is discontinued. Materials suchas wood, fabrics, paper, and rugs absorb water vapor from the air until theirmoisture content is at equilibrium with th e relative humidity. This is a slowprocess but it involves substan tia l quantities of water if all th e materials in-volved are considered. If the relative humidity is reduced, the absorbedmoisture slowly evaporates from t he material, b ut it may tak e several days or


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even weeks before a new, lower moisture content is established. This is thereason for higher "natural" relative humidities in houses in autumn [ 4 ] .

It is not likely that windows and doors will be held open very long in mid-winter because of the discomfort from cold drafts entering the occupiedspace. If windows are only "cracked open" discomfort may be reduced, butcondensation and icing may occur, and the window may become inoperable.For these reasons windows and doors are not always a satisfactory means ofventilation in very cold weather.

Houses with fuel-fired, forced warm-air systems can utilize an outside airintake duct with an adjustable damper for continuous ventilation as re-quired. The chimney acts as an exhaust outlet for indoor air as well as for theproducts of combustion. It is advisable to operate the furnace circulating fancontinuously with this intake duct arrangement in order to control thedistribution of outside air entering the system. A manual or an automaticallycontrolled damper in the outside air duct can be installed. The duct shouldbe insulated to avoid condensation on its surface in cold weather.

Although this system of ventilation can be very effective in controllinghumidity levels, it involves an expenditure of energy to heat the additionaloutside air required for humidity control, and is therefore not energy effi-cient. With closed combustion or condensing furnaces, heat recovery systemsin which the air being exhausted from the house is used to heat the incomingair can be employed. Domestic dehumidifiers also can remove moisture fromthe room air without loss in heat energy, but their moisture removal capacitymay be limited at relative humidities below 40 percent because of evaporatorcoil frosting.

Condensation in Wall and Roof Spaces of HousesThe higher moisture content of air within heated buildings in winter pro-vides a vapor pressure difference that causes water vapor to diffuse through

the interior cladding materials towards the outside. Incorporation of a vaporbarrier membrane in the construction or the application of coatings ofmoderate to low permeance to the exposed wall and ceiling surfaces canreduce this rate of flow considerably. A much more significant flow ofmoisture will occur through cracks, fissures, and holes in the constructionowing to an outward air pressure difference caused by wind, stack effect,chimneys, or mechanical air-handling systems.

There has been a general tendency to assume that leakage through thebuilding enclosures occurs primatily at doors and windows where visiblejoints occur. Studies undertaken on six houses in Ottawa, Canada, havedemonstrated that the leakage openings contributed by windows and doorsconstitute only about 20 percent of the total 151. Leakage cracks and open-ings in walls and ceilings are not so obvious as those around windows, butthey are more numerous and constitute a higher percentage of the total


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HAND EGORD ON AIR LEAKAGE AND VENT ILATION 227

leakage openings in most houses. Measurements indicate that as much as 70percent of the total leakage openings occur in walls and that about as muchcan occur through the ceiling, depending on the particular house. Measure-ments of the area of holes in upper plates used for wiring or plumbing sug-gest that these may contribute about one half of the total through the ceilingand that an equivalent leakage area may develop from shrinkage of the upperwall plates after construction. Substantial leakage openings also may occuras a result of wood shrinkage or cantilevering of floor constructions at thefoundation wall or second floor level, and where chimneys or plumbingstacks penetrate wall or roof construction. Poorly fitted nonweatherstrippedattic access hatches are also likely locations for air leakage. Unsealed jointsin ductwork and at duct penetrations or exhaust fan openings are also com-mon, and in the extreme case fans may be incorrectly installed, dischargingdirectly into the attic space.Not all cracks and openings in existing houses can be sealed, nor will it bepossible to ensure absolutely tight construction in new housing. But every ef-fort should be made to provide as tight an enclosure as possible in order toreduce the rate of air leakage and minimize the amount of condensation thatoccurs in walls and roofs. Such measures will make it possible to control ven-tilation and energy loss.Air Leakage in Houses

The direction and rate of air leakage through cracks and holes depends onthe direction and magnitude of the air pressure differences created bynatural forces such as stack effect and wind and by the action of chimneys,fans, and blowers. Most significant and least recognized is the stack effectdue to the difference in temperature between inside and outside air in winter.Warm inside air is lighter and more buoyant than cold outside air andtends to rise and flow outwards through cracks and openings in the upperwalls and ceilings of buildings. As it leaks outward, the warm inside air en-

I counters progressively colder surfaces, eventually contacting those below itsdew-point temperature so that condensation takes place. The magnitude ofthe pressures will depend on the height of the heated space and the inside-to-outside temperature difference.Air pressure differences created by wind may be of the same order ofmagnitude as those from stack effect for low buildings in cold climates.Pressures due to wind will a d inward over the height of windward walls andoutward over leeward walls and those parallel to the wind. Although suctionpressures generally will be created over all flat or sloped roofs, the sustainedpressure difference across the ceiling in a ventilated roof space will tend tobalance out near zero.For electrically heated houses or others with no operating chimney themid-winter pattern of pressure differences from a combination of average


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wind and stack effect will probably be similar to that shown in Fig. 1. Out-side air will leak inward through windward walls and room air will leak out-ward through the ceiling and leeward walls. The pressure acting upwardacross the ceiling will be due primarily to stack effect, and will act in thisdirection as long as the inside temperature is higher than that outside. Therethus will be a constant pressure acting to move moist indoor air up into coldroof spaces.

This upward air pressure difference is counteracted and may even bereversed by the action of the burner and chimney in houses with fuel-firedheating systems [ 6 ] .The stack effect of an operating chimney is greater thanthat of the house because the flue gases are at a much higher temperature.The chimney thus acts like an exhaust fan, lowering the air pressure insidethe house. The pressure difference across the ceiling therefore is reduced orreversed and the pressure difference acting inward is increased, acting over agreater total area of inlet openings, as indicated in Fig. 2. The total airchange rate is thus increased, with most or all of the room air exhaustingthrough the chimney with the flue gases rather than into the cold wall androof spaces.

The furnace chimney represents the most significant difference betweenelectrically and fuel-fired heated houses as far as air leakage and indoorhumidity levels are concerned. The chimney provides an exhaust systemwhen the furnace is operating and an air exhaust opening when the burner isoff.

Electric dehumidifiers provide a more energy efficient method of reducingthe humidity level than ventilation and may be particularly applicable in

FIG. I-Pressure differences in houses without operating chimneys.


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HANDEGORD ON AIR LEAKAGE AND VENTILATION 229

FIG. 2-Pressure differences in houses with operating chimney s or exhau st fans.

houses with electric baseboard heating systems. If problems of roof spacecondensation are experienced, however, simply lowering the humidity maynot be sufficient. If the house has been tightly built, or if it can be brought upto such a standard, a relatively small capacity exhaust fan will be capable ofreducing the pressure difference across the ceiling and the flow of moist in-door air into the roof space, If the house has a substantial number of inac-cessible leakage openings, a larger capacity fan will be required. This willresult in increased energy consumption to warm the replacement air leakageinto the house. Recovery of the heat in the air being exhausted could par-tially balance this loss while still maintaining the desired negative pressure inthe house. A small heat pump or adapted dehumidifier or air conditionercould be used to recover heat and moisture from the exhaust air.

Concealed Condensation in Larger BuildingsBuildings for human occupancy are usually humidified to a level of 30 to50 percent to satisfy the occupants. High-rise buildings that experience

substantial pressure differences as a result of stack effect and high windpressures must be built to higher standards of air tightness than houses ifenergy conservation, comfort, and condensation control are to be achieved.

Air leakage through hollow' concrete masonry walls is often much greaterthan normally assumed. Upward leakage in the cavity is not always ade-quately blocked and parallel random air flow passages occur between gyp-sum wallboard finishes and the block face.


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230 MOISTURE MIGRATION IN BUILDINGSIn commercial buildings the application of rigid insulation and built-up

roofing above the roof deck results in fewer openings from the interior of thespace into the roof/insulation system, but a critical location for air leakageand condensation in such buildings is a t the junction of the wall and roof[7,81. This may be aggravated further where dropped ceilings are providedfor service spaces and the exterior wall above the ceiling is left unplastered orinadequately treated with respect to air tightness. In some instances verticalservice shafts provide passages for unrestricted air flow to this critical loca-tion or into exterior walls.Air leakage through exterior walls also can occur where the structural sys-tem or services penetrate the air barrier, or where joints between dissimilarmaterials or components occur. Masonry cannot be instalIed tightly againststructural steel columns and beams. In some cases subsequent instaIlationsof anchors for precast cladding have left major holes through the wall [A.In principle it is preferable to have the structural frame of a building in-ward and separate from the exterior wall system. The waU can then incor-porate a continuous structural air barrier pmtected from the fluctuating eon-ditions of the weather by insulation on the outside [ 9 ] . Exterior cladding isbest applied following the two-stage weather-tightening system to controlrain penetration [IU].Consideration also should be given to providing accessto the interior wythe and air bamer for maintenance of the air seal andjoints.

The deterioration of exterior structural elements of a building and damageto the interior through air leakage and condensation have an important bear-ing on maintenance costs.

There is also merit in improving the air tightness of internal floors and par-titions, particularly in high-rise buildings. This will tend to redistribute thetotal pressure differences due to stack effect so that the pressure differenceacting across the exterior wail on each floor is reduced [ I l l . Such an ap-proach also will allow better control of the air distribution within thebuilding. It also should make it much easier to control smoke movement inbuildings during a fire, and permit a more equitable apportioning of energycharges for space heating from unit to unit in apartment buildings.

The degree of tightness attainable may well have economic limits, butthere is considerable evidence that many of the leakage openings existing inactual buildings result from holes cut either accidentally or deliberately in analready reasonably tight membrane or component. A specific example is thepenetration of services through specified air or vapor barriers or solid com-ponents. Other leakage openings in the exterior enclosure elements resultfmm changes in the dimensions or deflection of materials that may well bepromoted by either improper location within the wall or inadequate provisionof appropriate sealants or membranes to bridge the joints or cracks thateventually open up in the construction [12] .


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Removal of Condensed Moistare

With requirements to maintain reasonable relative humidity levels insidebuildings in winter and the difficulty of obtaining a complete air and vaporbarrier, some condensation inevitably will occur. In walls, drainage bygravity can provide the most effective means of removal, and all cavitiesshould be drained and flashed to the outside. Some consideration should begiven to carrying the flashing through to the vapor barrier if optimummoisture control is desired. Reversal of the temperature gradient due to solarheating can result in water vapor migration inward from absorptive claddingor sheathing materials or insulations in winter and resultant condensation onthe outer face of the vapor barrier or interior cladding. The alternatingmigration and condensation will act to dry out the construction gradually ifthe condensed moisture is allowed to drain to the outside.Sloped roofs over attic spaces have several advantages over flat roofs inwood frame construction. The water vapor that flows upward by air move-ment or diffusion through openings in the ceiling has an opportunity to mixwith the attic air and be exhausted or to condense in a more uniform patternover a large roof sheathing area. In flat wood frame roofs the condensation

will form immediately above the leakage opening in the ceiling vapor barrier,and on melting will drip from low points of the sheathing to find its way intothe house by virtue of the openings through which it passed upward initially.In cathedral ceilings localized condensation also will occur near leakageopenings, but it can drain to outside at the soffit on top of a vapor barrierthat has been applied to the slope in overlapping shingle fashion.Ventilation of roof spaces with outside air can provide an auxiliary meansof removing moisture by evaporation, but it becomes less and less effective atlow temperatures because of the small vapor pressure differences involved.Although increased roof sheathing temperatures and increased potential forsublimation and evaporation result from solar radiation, attic or roof spaceventilation is most effective at milder outside temperatures. In some caseswhere leakage openings in the ceiling vapor barrier cannot be sealed orreduced in number, closure of roof space vents and pressurization of the roofspace in cold weather could be considered [13].Ventilation of wall cavities may be a less effective means of removingmoisture than drainage but can provide added capability for evaporation ofaccumulated moisture in mild weather. Circulation of outside air throughporous insulation, through joints in the insulation, or through spaces be-tween the insulation and interior cladding or structural components, how-ever, can result in a significant reduction in thermal resistance and even incooling of interior surfaces below the indoor dew-point. The provision ofweep holes at the flashing at only one level in each exterior wall compartmentwill allow drainage and outward diffusion of moisture without promoting cir-


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culation of outside air to an unnecessary degree. With insulation having gooddrainage characteristics, air spaces could be eliminated as a requirement formoisture control. In any case, air tightness of the interior cladding and vaporbarrier is the most effective way to avoid concealed condensation in heatedbuildings.Achieving Air Tightness in Buildings

Specifications that simply call for a continuous air or vapor barrier are notlikely to achieve air tightness in actual construction. Practical details must bedeveloped that recognize the location of leakage paths, joints, and the poten-tial location of subsequent cracks in a particular construction. These oftenmay have to be developed for a specific building or type of construction, andmay require changes in practice or construction sequence to achieve success[12,14]. Their presentation in three dimensional format or to show the se-quence of construction may be necessary to ensure proper application.Pressurization or evacuation tests on small buildings or localized airpressure difference tests on assembled components in larger multi-storybuildings provide an extremely useful means of performance evaluation[1.5,16].Only relatively simple tests need be made to locate leakage paths andto provide an indication of whether the designer and the builder were suc-cessful in achieving the objective. The required level of tightness might wellbe based on what is possible with reasonable forethought and care. Ideally,the tightness requirement should equate to the allowable rate of moisturetransfer resulting from diffusion as defined in accepted vapor retarder (bar-rier) requirements in existing standards.

AcknowledgmentsThis paper is a contribution from the Division of Building Research, Na-tional Research Council of Canada, and is published with the approval of theDirector of the Division.

References[ I ] American Society of Heating, Refrigerating, and Air-Conditioning Engineers, A S HR A EHandbook and Product Directory. Equipment, 1979, Chapter 5 .(21 American Society of Hea ting, Refrigerating, and Air-Conditioning Engineers, A S HR A EHandbook; F undamentals. 1977, Chapter 25.[3] Wilson, A. G . , "Thermal Characteristics of Double Window s," Canadian BuildingDigest. No. 58.National Research Council of C anada, Division of B uilding Research, Ot-tawa, Canada, 1964.[ 4 ] Kent, A . D., Handegord, G . O ., and Robson, D . R . , ASHRAE Transactions. Vol. 72,Part 11. 1966, pp. 11.1.1-11.1.8.151 Tamura, G . T . , ASHRAE Transactions. Vol. 81, Part 1 , 1975, pp. 202-211.[6] Tamura, G . T . and Wilson, A. G . ,ASHRAE Journal. Vol. 5, No. 12, 1963, pp. 65-73.


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[ 4 Pemault, J. C. in Construction Details for Air Tightness. NRCC 18291, NationalResearch Council of Canada, Division of Building Research, Ottawa, Canada, 1980, pp.7-11.181 Turenne, R. G. in Construction Details for Air Tightness. NRCC 18291, NationalResearch Council of Canada, Division of Building Research, Ottawa, Canada, 1980, pp.25-29.

191 Hutcheon. N. B., "Requirements for Exterior Walls," Canadian Building Digest, No. 48,National Research Council of Canada, Division of Building Research, Ottawa, Canada.1%3.[lo] Garden, G . K., "Rain Penetration and Its Control," Canadian Building Digest. No. 40,National Research Council of Canada, Division of Building Research, Ottawa, Canada,1%3.[Ill Wilson, A. G., and Tamura, G. T., "Stack Effect in Buildings," Canadian BuildingDigest. No. 104, National Research Council of Canada, Division of Building Research,Ottawa, Canada, 1968.[12] Burn, K. N. in Construction Details for Air Tightness. NRCC 18291, National ResearchCouncil of Canada, Division of Building Research, Ottawa, Canada, 1980, pp. 13-19.1131 Tamura, G. T., Kuester, G. H., and Handegord, G. 0.. "Condensation Problems in FlatWood-Frame Roofs," Second International CIB/RILEM Symposium on Moisture Prob-lems in Buildings, Rotterdam, Paper No. 2.6.2, Sept. 1974.[I41 Quirouette, R. L. in Construction Details for Air Tightness. NRCC 18291, NationalResearch Council of Canada, Division of Building Research, Ottawa, Canada, 1980, pp.21-23.[ I S ] Om, H. W. and Figley, D. A., "An Exhaust Fan Apparatus for Assessing the Air LeakageCharacteristics of Houses," BR Note 156, National Research Council of Canada, Divisionof Building pesearch, Ottawa, Canada, March 1980.(161 Shaw, C. Y., ASHRAE Transactions. Vol. 86, Part 1, 1980, pp. 241-250.


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Hadegord Moisture Control in Buildings Nrcc20752 1982