|Conceptual Reference Database for Building Envelope Research||
AIR: This is considered the mixture of gases that make up the earth's atmosphere. The principal gases that compose dry air are Nitrogen (N2) at 78.09%, Oxygen (O2) at 20.946%, Argon (A) at 0.93%, and Carbon Dioxide (CO2) at 0.033%. One of the most important constituents of air and most important gases in meteorology is water vapor (H2O).
Air barriers reduce the infiltration and exfiltration through the envelope. This serves as two purpose. One is to reduce the air exchange of the house. The other, more important, is to reduce the masses carried with the air flow. In the latter regard, the moisture carried by air flow through the envelope is of major importance. It is critical for the moisture control.
See An Air Barrier for the Building Envelope in Building Science Insight '86.
Exterior Air Barriers
Exterior air barriers are products that keep infiltration of exterior unconditioned air from entering the building. These products are impermeable to air flow but permeable to moisture flow. Moisture travels through them to increase the drying potential of the building's shell, but air does not pass through it. Foam boards also serve the same purpose but all joints must be taped.
Non-Permeable Air and Vapor Barriers (source: Henry BES): "non-permeable air and vapor barriers perform the function of air barrier, vapor barrier and rain water barrier all in one product. These products essentially help create an environmental separation within the building envelope between the exterior climatic condition and the interior building conditions. Since these membranes can perform as the vapor barrier, their position within the wall assembly is critical in avoiding potential condensation problems. Regions are typically separated into two climate categories: Cold Climate or Hot and Humid Climate... Typically, in cold regions, the non-permeable air and vapor barriers are positioned on the outside of the interior wythe but still on the warm-in-winter side of the primary insulation. In hot and humid climates, the positioning could be reversed such that the insulation is installed on the inside of the membrane. Refer to our graphics below for an illustration of a typical wall assembly."
Henry Vapor Permeable Air Barriers (source: Henry BES):
"...vapor permeable air barrier systems ... provide continuous air tightness and water protection, while remaining permeable to the passage of vapor... used as a transition membrane to span gaps between dissimilar surfaces in key areas such as wall-to-window frames, wall-to-slab, wall-to-roof junction, etc. ... their position would not interfere with the vapor diffusion of the wall assembly. Because of their high vapor permeance, vapor permeable air barriers can essentially let the wall "breathe" and are considered "breather type membranes". "
Airtight Drywall, and Simple Caulk and Seal for Air Movement Control
ADA is to seal any seams and joints where the foundation, sill plate, floor joist header, and sub-floor meet. The spaces between floors, the sub-floor, rim joist, and plates are also sealed. The wall-framing plates are sealed to the lower sub-floor and the upper rim joist. Gaskets are often used at the top and bottom wall plates (between the drywall and framing) and between ceiling drywall and attic joists. Airtight electrical boxes (or standard electrical boxes sealed with caulk) complete the air barrier. Holes where pipes and cables pass through also need to be sealed before the wall and ceiling finishes are applied. After all this has been done and the perimeter drywall seams have been finished, the room is effectively sealed from expensive and uncomfortable drafts. -- http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11310
There are differences between the air barrier and the vapor barrier, see E-34
Also called "house wraps" as known in the industry, Tyvek in the late 1970s introduced by DuPont and other co.
Two basic categories: perforated (are either woven polyethylene, woven polypropylene, spun bonded polypropylene, or laminated polypropylene film) or non-perforated (are either spun bonded polyethylene or fiber-mesh-reinforced polyolefin.
ADA Airtight Drywall Approach: Use drywall with gaskets to create an interior air barrier. (Vapor retarder is still required (foil-backed drywall, or polyethylene
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