Masonry Magazine June 2005 Page. 30
AIR BARRIERS
By designing and constructing an "airtight" building envelope, the risk of moisture problems are minimized.
Gy efficiency requires that all critical details have to be airtight. The generally accepted level based on National Building Code of Canada requirements is 0.02 L/(s-m²) at 75 Pa pressure (0.004 cfm/ft² at 1.57 psf).
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26
Masonry
June 2005
While many common building materials like plywood and gypsum wallboard meet this standard, a sheathed wall assembly will not perform well as an air barrier unless the joints are treated with an air barrier material. The sheathed wall assembly with treated joints then becomes an air barrier sub-system of the total building envelope air barrier system. The total building envelope air barrier system consists of all the interconnected air barrier materials-for example, CMU backup with joint treatment, roof membrane, foundation waterproofing, windows and doors, and the air barrier connection materials between them.
Types of Air Barriers
ONE CHOICE is a new category in the market, a fluid-applied waterproofing/air barrier. Fluid-applied waterproofing/air barriers for wall assemblies have actually been manufactured in North America for more than 25 years. Only recently has their use increased as air leakage has become recognized as a potential source of moisture accumulation in walls, and some of their unique benefits have been realized.
Fluid-applied waterproofing/air barriers are rolled or sprayed onto masonry substrates or CMU backup and become part of the structural wall. Because of the way they are applied, there are no fastener holes where water penetration may occur, and there is no potential for mislapping or tearing, as with many sheet goods. During construction, a fluid-applied barrier will cover the substrate completely, and does not have to be covered immediately with a cladding, as many of them are UV-resistant.
Another important distinction of a fluid-applied waterproofing/air barrier in wall assemblies is that it can mitigate or eliminate one of the major forces that causes water infiltration into walls: pressure difference. A fluid-applied waterproofing/air barrier, in combination with venting and compartmentalizing, enables the pressure behind the cladding material to equalize with the pressure outside. This prevents rainwater penetration caused by pressure differentials. This pressure equalizing effect is only possible when the air barrier is structural, as is the case with fully adhered fluid-applied waterproofing/air barriers. Also, by designing and constructing an "airtight" building envelope, the risk of moisture problems-mold growth, decay, corrosion, loss of insulation value and Indoor Air Quality (IAQ) problems-that can occur because of air leakage and condensation are minimized.
Another type of air barrier is a house wrap, or sheet good product. These materials are usually applied under a home or
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