Uncontrolled air leakage increases the burden on heating or air-conditioning, and causes problems because air can transport large amounts of humidity. Consequently, the concept of an ‘air barrier material’ was formally introduced in the 1985 edition of the National Building Code of Canada (NBC). Building professionals adapted their designs to this new reality, but the appropriate choice and positioning of materials in assemblies brought new challenges, with the functions of air barrier and vapour barriers often misunderstood. Consequently, major failures such as mould growth in wall assemblies, rotting of structural materials, or bursting of water-saturated exterior cladding materials in winter were observed.
Starting in the mid-’90s, NBC prescribed a maximal air leakage rate for exterior wall assemblies, but did not indicate how to evaluate materials and systems to determine compliance. Interestingly, standards for air barriers appeared first at ASTM with the development of the E2178, Standard Test Method for Air Permeance of Building Materials, published in 2001. This standard rapidly became the reference for the determination of air leakage of building materials.
In Canada, the first standards related to air barrier materials and systems appeared several years later. CAN/ULC-S741, Standard for Air Barrier Materials-Specification, and CAN/ULC-S742, Standard for Air Barrier Assemblies-Specification, were published in 2008 and 2011, respectively. Some may say these are just Canadian versions of the ASTM E2178 and E2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies, because they reference their U.S. counterparts for test conditions. However, that is all they have in common.
To learn more about the differences, and overall approaches to air barriers, you can download the new, free Construction Canada e-book, “Barriers Against Air Leakage” at https://www.constructioncanada.net/download-the-new-free-e-book-on-barriers-against-air-leakage. The latest is a suite of sponsored e-books, this resource also includes magazine articles on curtain walls, insulating concrete forms (ICFs), and exterior insulation and finish systems (EIFS).