History of changes for Section 07 2500 (07260) - Weather Barriers


Principal Changes, Fall 2007 Update:

This section covers supplementary air barriers, vapor retarders, and water-resistive barriers, primarily for exterior walls. This section uses the following definitions: - Air Barrier: Retards air passage, is water vapor permeable, and is liquid moisture resistant. Air barriers are assumed to be vapor permeable because they are commonly installed on the cold side of exterior walls where a vapor retarder might be inadvisable. If a vapor retarder is appropriate in such a location, don’t call it an air barrier, even though it does perform that function. Air barriers offered are mechanically fastened sheets ("housewraps") and spray or roller applied coatings. An air barrier can function as a water-resistive barrier (see below). - Vapor Retarder: Retards passage of both air and water vapor. Must be sealed at joints and penetrations. Vapor retarders are used on the "warm" side of walls to preclude condensation inside the wall or insulation. Vapor retarders offered are mechanically fastened sheets, self-adhesive sheets, mastic and spray coatings. - Water-resistive barrier: Neither air barrier nor vapor retarder but is liquid moisture resistant. Water-resistive barriers only protect the construction from damage due to precipitation. (The term "water-resistive barrier" is from the ICC International Building Code, 1404.2, which requires a minimum of one layer of No. 15 asphalt felt behind exterior wall veneer, unless other conditions are met.) Water-resistive barriers offered are No. 15 asphalt felt, waterproof Kraft building paper, and "housewrap" sheets installed lapped but not sealed. An air barrier can be used as a water-resistive barrier.

Many other materials and components specified in other sections can make up part of the entire "weather barrier". This section does not contain any provisions that define the air or vapor performance of those other materials.