SECTION 07 2500 (07260) - WEATHER BARRIERS
Principal Changes, Fall 2007 Update:
- A new comprehensive checklist aids in specifying multiple applications and coordinating similar materials specified in other sections. Water-resistive barriers can be specified either in this section or in one of the sections where exterior stud walls and sheathing are specified: 054000 Cold-Formed Metal Framing, 061000 Rough Carpentry, or 092116 Gypsum Board Assemblies.
- New definitions were added to distinguish Air Barriers, Vapor Retarders, and Water- Resistive Barriers because the terminology is confusing.
- Two new articles were added in PART 2: Air Barriers and Water-Resistive Barriers. The existing main product article in PART 2 has been renamed Vapor Retarders, since all of the products in it were that type. The existing mastics and spray coatings were appended to the Vapor Retarders article, since they are also that type.
- PART 3 is almost entirely new.
- MF95 version title has changed from Vapor Retarders to Weather Barriers.
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.