Air barrier

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Air barriers control air leakage into and out of the building envelope. Air barrier products may take several forms:

Air barriers are divided into air barrier materials, air barrier accessories, air barrier components, air barrier assemblies and air barrier systems.

Air barrier material – Building material that is designed and constructed to provide the principal plane of airtightness through the environmental separator and which has an air permeance rate no greater than 0.02 L/(s•m²) at a pressure difference of 75 Pa when tested in accordance with ASTM E 2178. Air barrier materials meet the requirements of the CAN/ULC S741 Air Barrier Material Specification. The air barrier materials are typically the "big" pieces of material used in an air barrier assembly.

Air barrier accessory – products designated to maintain air tightness between air barrier materials, assemblies and components, to fasten them to the structure of the building, or both (e.g., sealants, tapes, backer rods, transition membranes, nails/washers, ties, clips, staples, strapping, primers) and which has an air permeance rate no greater than 0.02 L/(s•m²) at a pressure difference of 75 Pa when tested in accordance with ASTM E 2178. Air barrier components are used to connect and seal air barrier materials and/or air barrier assemblies together.

Air barrier components – pre-manufactured elements such as windows, doors and service elements that are installed in the environmental separator and sealed by air barrier accessories and which has an air leakage rate no greater than 0.20 L/(s•m²) at a pressure difference of 75 Pa when tested in accordance with ASTM E 2357.

Air barrier assemblies – combination of air barrier materials and air barrier accessories that are designated and designed within the environmental separator to act as a continuous barrier to the movement of air through the environmental separator and which has an air leakage rate no greater than 0.20 L/(s•m²) at a pressure difference of 75 Pa when tested in accordance with ASTM E 2357.

Air barrier system – combination of air barrier assemblies and air barrier components, connected by air barrier accessories, that are designed to provide a continuous barrier to the movement of air through an environmental separator and which has an air leakage rate no greater than 2.00 L/(s•m²) at a pressure difference of 75 Pa when tested in accordance with ASTM E 779 or CAN/CGSB 149.10 or CAN/CGSB 149.15.

Air barriers and water vapor[edit]

Some air barriers may be water vapor permeable, while others perform the function of a vapour barrier. This is because water fits through narrower pores than the other main constituents of air, oxygen(O2) and nitrogen[citation needed].

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