Research Highlights

Technical Series 98-109

Air Permeance of Building Materials

Introduction

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.

Research Program

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.

Results

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.

Implications for the Housing Industry

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.

Table 1:
Average Air Leakage Rates at 75 Pa

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
Glasswool Insulation 36.7327
Vermiculite Insulation 70.4926
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.

A 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.