English: The air barrier for the building envelope was confused with the vapour barrier in the construction of buildings for decades. They are distinctly different from each other. In 1980, the author, a research officer of the Institute for Research in Construction of the NRCC, participated in a research project examining many types of commercial, residential, institutional and industrial buildings not performing as expected according to the architectural plans and specifications. During this 6 month project, the author discovered a fundamental flaw in the design of exterior walls, roof and other envelop components. Specifically, that air leakage control depends 1st on the structural properties of the air barrier and then the air permeance of the materials.
Air leakage occurs under an air pressure difference. An air pressure difference always results in a mechanical force on the building envelope. If air leakage is to be limited or controlled, the air pressure differences of wind pressure, stack effect and fan pressurization must be supported structurally to achieve air leakage control with an air barrier system. This article expand on this finding and development.
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