The industry made further advancements in the field of envelope performance in the 1930s with the rise of insulation in framing cavities and attics (For more information, read the article, “Heat, Air and Moisture Control in Walls of Canadian Houses: A Review of the Historic Basis for Current Practices,” by M. The introduction of ‘building paper’ in the form of asphalt-impregnated felt-also known as sheathing membranes or weather-resistive barriers (WRBs)-represented an early effort to reduce wetting of wall assemblies and air leakage (Refer the 2017 book Building Materials: Product Emission and Combustion Health Hazards written by K. Initial attempts to increase the thermal comfort of occupants in modern North American wood-framed construction date back to the 1800s. In this regard, the term ‘air/vapor barrier’ is misleading and should be replaced with more appropriate terminology.Ī brief history Photo © As manufacturers introduce materials with new properties and attempt to push the boundaries of building envelope construction, it is crucial the industry agrees on terminology for communicating the specific functions and purpose of these materials to avoid confusion and costly errors. the vapor barrier is always on the inside and the air barrier is always on the outside). This lack of understanding of the functions of these assemblies has resulted in simplistic rules-of-thumb prone to misapplication ( e.g. Also, the consequences of installing these materials improperly can result in failures. Most building professionals know they are needed, but often struggle to locate them correctly within wall assemblies. The terms ‘air barriers’ and ‘vapor retarders’ (or ‘vapor barriers’) are perhaps some of the most poorly understood concepts in the construction industry.
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