Technical Series 98-109
Resistance to air leakage is a key requirement of an air barrier system. The Institute for Research in Construction (IRC) of the National Research Council Canada has proposed the following levels of airtightness for air barrier systems:
|Air Leakage Classification||Air Leakage Rate (l/s-m2 @ 75 Pa)|
|Type 1||0.10 to < 0.15|
|Type 2||0.05 to < 0.10|
|Type 3||< 0.05|
In order to create an air barrier system that achieves the required overall air leakage rate, it is important that the materials composing the air barrier system be resistant to air leakage. In order to select materials to use in constructing an air barrier system that will meet the above guidelines, the designer needs to know the air leakage rates of building materials. This research project was conducted to give designers guidance in choosing materials appropriate for air barrier systems.
Since this study was conducted, the National Building Code (NBC) has been amended to require that materials forming part of an air barrier assembly should not exceed an air leakage rate of 0.02 l/s-m2 @ 75 Pa.
In this study, a test method was developed to determine the air leakage rate of common building materials. To conduct the test, the materials were first wrapped in polyethylene (zero air leakage) and sealed to the open side of a chamber. The air leakage rate through the chamber was then measured with the chamber exposed to various pressure differentials to determine the leakage, if any, of the test apparatus. The polyethylene was then removed from the sample, and the air leakage rate was again measured with the chamber exposed to various pressure differentials. The air leakage rate through the sample was determined by subtracting the air leakage rate of the chamber. The test procedure was validated using orifice plates and by comparison of results with those obtained from IRC.
A total of 36 building materials, in pieces measuring 1 metre by 1 metre each, were tested at static pressure differentials varying from 25 to 100 Pa.
Table 1 shows the average air leakage rates at a pressure differential of 75 Pa for the 36 materials tested. The table also indicates the ratings as per the IRC guidelines and the NBC. Twelve of the materials had a non-measurable air leakage rate. An additional seven materials complied with the National Building Code air leakage limit of 0.02 l/s-m2.
The testing determined that non-homogeneity could exist within some samples and from one sample to another for a specific material. The air leakage through building materials having an air flow rate less than 0.15 l/s-m2 was found to be mainly laminar.
As airtightness is a key requirement of an effective air barrier system, designers need to know the air leakage rate of building materials. The test method developed in this study can be used to determine the air leakage rate of a variety of building materials, including rigid, flexible or loose materials. The determination of air leakage rates provides helpful information to designers with respect to the selection of materials needed to construct a good air barrier system. Further, since the air leakage through building materials with low air leakage rates was found to be mainly laminar, designers can calculate air flow resistance through a composite system in the same manner as they calculate resistance to heat flow.
|Material||Air Leakage Rate (l/s-m2@75 Pa)|
|Smooth Surface Roofing Membrane, 2 mm||Non-measurable|
|Aluminum Foil Vapour Barrier||Non-measurable|
|Modified Bituminous Torch-On Grade Membrane, 2.7 mm, Glass Fibre Matt||Non-measurable|
|Modified Bituminous Self-Adhesive Membrane, 1.3 mm||Non-measurable|
|Modified Bituminous Torch-On Grade Membrane, 2.7 mm, Polyester Reinforced Matt||Non-measurable|
|Plywood Sheathing, 9.5 mm||Non-measurable|
|Extruded Polystyrene, 38 mm||Non-measurable|
|Foil Back Urethane Insulation, 25.4 mm||Non-measurable|
|Phenolic Insulation Board, 24 mm||Non-measurable|
|Phenolic Insulation Board, 42 mm||Non-measurable|
|Cement Board, 12.7 mm||Non-measurable|
|Foil-Backed Gypsum Board, 12.7 mm||Non-measurable|
|Plywood Sheathing, 8 mm||0.0067|
|Flakewood Board, 16 mm||0.0069|
|Gypsum Board (M/R), 12.7 mm||0.0091|
|Flakewood Board, 11 mm||0.0108|
|Particleboard, 12.7 mm||0.0155|
|Reinforced Non-Perforated Polyolefin||0.0195|
|Gypsum Board, 12.7 mm||0.0196|
|Particleboard, 15.9 mm||0.0260|
|Tempered Hardboard, 3.2 mm||0.0274|
|Expanded Polystyrene, Type 2||0.1187|
|Roofing Felt, 30 lb.||0.1873|
|Non-Perforated Asphalt Felt, 15 lb.||0.3962|
|Rigid Glass Fibre Insulation Board with a Spun Bonded Olefin Film on One Face||0.4880|
|Plain Fibreboard, 11 mm||0.8223|
|Asphalt Impregnated Fibreboard, 11 mm||0.8285|
|Spun Bonded Olefin Film (1991 product)||0.9593|
|Perforated Polyethylene, # 1||4.0320|
|Perforated Polyethylene, # 2||3.2307|
|Expanded Polystyrene, Type 1||12.2372|
|Tongue and Groove Planks||19.1165|
|Cellulose Insulation, Spray-On||86.9457|
Project Manager: Jacques Rousseau
Research Consultant: Air Ins.
Research Report: Air Permeance of Building Materials, 1998
A full report on this research project is available from the Canadian Housing Information Centre at the address below.
full report on this research project is available
from the Canadian Housing Information Centre.
The information in this publication represents the latest knowledge available to CMHC at the time of publication, and has been thoroughly reviewed by experts in the housing field. CMHC, however, assumes no liability for any damage, injury, expense or loss that may result from use of this information.
©1999 CMHC-SCHL. All rights reserved.