Air permeability of wood-frame wall assemblies

Publisher’s version / Version de l'éditeur:

Home Builder Magazine, Jan./Feb., p. 16, 1992-01

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Air permeability of wood-frame wall assemblies

Rousseau, M. Z.

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Air pe rm e a bilit y of w ood-fra m e w a ll a sse m blie s

N R C C - 3 5 0 1 7

R o u s s e a u , M . Z .

J a n u a r y 1 9 9 2

A version of this document is published in / Une version de ce document se trouve dans:

Home Builder Magazine, Jan./Feb., pp. 16, January, 1992

The material in this document is covered by the provisions of the Copyright Act, by Canadian laws, policies, regulations and international agreements. Such provisions serve to identify the information source and, in specific instances, to prohibit reproduction of materials without written permission. For more information visit http://laws.justice.gc.ca/en/showtdm/cs/C-42

Les renseignements dans ce document sont protégés par la Loi sur le droit d'auteur, par les lois, les politiques et les règlements du Canada et des accords internationaux. Ces dispositions permettent d'identifier la source de l'information et, dans certains cas, d'interdire la copie de documents sans permission écrite. Pour obtenir de plus amples renseignements : http://lois.justice.gc.ca/fr/showtdm/cs/C-42

T

E

Oil

N

o

L

o

G

Y

Air Penlleabi'itr of Wood.Frame

Wall

_Assemblies

Spunbonded olefin filmon one face of a

25-mm glass fibre semi-rigid board+compatible

tape atjoints (with or withouttape atnail heads) 0.30 Spunbonded olefin film sand'Nicl1ed

between16x38-mmwoodstrapping@

406mm c/eand11·mmasphalt

impregnatedfibreboard 0.49 <0.005 <0.005 <0.005 <0.005 <0.018 <0.005 0.025 <0.005 <0.019 <0.006 <0.015 Air

PermealH1ity

LIs

per

m'

at

75

Pascals

38-mmextrudedpolystyrene insulation

... compatibletaPeat joints' (with or

without tapeatnailheads)

28-mmphenOlicfoam insulation ...

compatible lape at-jOintsandnail heads

Composite

WaD

Assembly

Syntheticstuccofinish on 51-mm expanded polystyrene insulation on 13-mrn exterior gypsum bOard 13·mm interior gypsumboardpainted

wrthtwo coats of latex paintwithjoint of papertaPeandjoint compound

O.15-mm (6-mil)polyethylenefilm

sandwiched between l1-mm plain

fibrebOardand13-mm interior gypsum board

11·mm asphalt impregnated fibreboard (with/Ointstaped)coveredwith 76-mm sprayed potyurethane foam on one side 9.S-mm sheathing grade plywood on

bothSideSof studs + subftoor adheSive

at the studs ... 64·mmglassfibre batt

insulatiOn in the cavity

9.5-mm sheathing grade pl'ywood on bOth

SideSof studS (one sheathing with two 51-mm

hOles) ...subflooradhesille atthestuds ... 64-mmglassfibre batt insulaloo in the cavity

28·mmphenolicfoam insulation+

compatibletapeat joints

dUl1lbility of the air barrier system.

For more information, refer to Building Science Insight

'86 •An Air Barrier for the Building Envelope", NRCC 29943. It can be purchased for 520 from IRC Client Services, Institute for Research in Construction, NRC, Ottawa, Ontario, KIA OR6. TeI.:(613)993·2463, fax:(613l954-5984. To obtain the IRC research report on the testing of wood-frame wall assemblies, fax your re-quest to Jacques Rousseau, canada Mortgage and Hous-ing Corpol1ltion, (613)748-2402. IS

11·mmasphalt impregnated fibreboard (with joints untaped) covered with 76-mm sprayed potyurethanefoam on one side 13-mm exterior gypsum bOard ... compatibletapeat joint

The Institute for Research in Construction was man-dated by CMHC to measure the air penneability ofa dozen wood-fl1lme wall assemblies. On the rightisacomparison of their air penneability rates.

The air penneability of building assemblies can be measured in the labol1ltory using accurate and reproduc-ible testing procedures. Typically, the sample occupies one large face ofan airtight box; the rate at which air flows through the sample is measured for various pressure differentials. In the follOWing table, air flow l1Ites are reported in Us per m' ofsample at an air pressure differ-ential of 75 Pascals (Pa). Keep in mind that these values represent the best performance possible. Tests were conducted in the protected environment of the laboratory with no outside weathering. The harsher conditions of actual installations would likely cause anincreasein air flow rates.

Fiveyears ago the Institute for Research in Construction

suggested maximum air flow rates per unit area of air .

harrier assembly according to indoor humidity levels. Starting with the American Industry guideline for the maximum allowable leakage for curtain wall (0.3 Us per m' at 75 Pal and estimating a 5(JOAJ funher reduction achievable in canadian construction, the levels suggested

were:

• 0.15 Us perm' at 75 Pa for buildings operated at indoor humidity levels up to 27%

• 0.1 Usperm' at 75 Pa for indoor hUmidity levels be-tween 270/0 and 55%

• 0.05 Us per m' at 75 Fa for indoor humidity levels

over

;5%

These values were only proposed for discussion and feedback on their adequacy for our climate, building types and variety of construction techniques. In 1990 Construction Specifications canada, in their document "Tek-Aid onAirBarriers" suggested using materials and assemblies that do not leak more than 0.1 Us per m' at 75 Pa. Obtaining this air flow rate via the air barrier assembly will not necessarily prevent all moillure damage

inall types of buildings in our canadian climate.

Nev-enheless, this target defutitely calls for improved design

and construction prae.tices.

Besides achieVing low air penneability, air barrier assemblies must alsc proVide the rigidity and strength necessary to transfer large air pressure loads (due to Wind, mechanical ventilation and stack effectl with little de-flection. Design and construction of interface details must ensure thaI rigidity and strengthareobtained in acontinuous fashion over the whole envelope. The air barrierｭｵｳｴ｡ｾｯ

be dUl1lble; the ovel1llI design of the wall (e.g., location of insulation, presence ofawind barrier, application of the rain screen principle), the ease of inspection and main-tenance of the air barrier assembly, as well as the potential for damage during se!Vice life, all have an impact on the

I I .

'1be

air

penneabillty

of

building assemblies can be

measured ... using accurate

and reproducible

procedures."

•

Madeleine L Rousseau, architect, NatimuU ResearchCouncil

,MadeleineZ. Rousseau iswith the Industr)' Liaison Branch at the National Research Council's Institute for Research inｃｯｮｳｴｮｬｃｾ

tion. She specializes in building envelope technology.

http://www.nrc-cnrc.gc.ca/irc

Air pe rm e a bilit y of w ood-fra m e w a ll a sse m blie s

N R C C - 3 5 0 1 7

R o u s s e a u , M . Z .

J a n u a r y 1 9 9 2

A version of this document is published in / Une version de ce document se trouve dans:

Home Builder Magazine, Jan./Feb., pp. 16, January, 1992

The material in this document is covered by the provisions of the Copyright Act, by Canadian laws, policies, regulations and international agreements. Such provisions serve to identify the information source and, in specific instances, to prohibit reproduction of materials without written permission. For more information visit http://laws.justice.gc.ca/en/showtdm/cs/C-42

Les renseignements dans ce document sont protégés par la Loi sur le droit d'auteur, par les lois, les politiques et les règlements du Canada et des accords internationaux. Ces dispositions permettent d'identifier la source de l'information et, dans certains cas, d'interdire la copie de documents sans permission écrite. Pour obtenir de plus amples renseignements : http://lois.justice.gc.ca/fr/showtdm/cs/C-42