Air barrier location speaks to where to locate air barriers, why use air barriers, types of air barriers.
The fact that air barrier materials can be located anywhere in an assembly as long as they form an interconnected airtight system.
At the inside surface of a building enclosure, the Airtight Drywall Approach and Simple Caulk and Seal are barrier systems consisting of gypsum wallboard combined with caulks, sealants and gaskets to seal leakage paths around wallboard penetrations and between underlying framing members.
These systems are relatively easy and inexpensive to install, making them especially popular for residential construction. They are less favoured for commercial building types where frequent changes to interior partitions, finishes and wiring make it unlikely that the continuity of a system depending on the careful detailing of these elements will be maintained over the life of the building.
Plastic sheeting, frequently used as a vapour retarder behind gypsum wallboard, also has a low permeance and can act as an air barrier. However, difficulty in sealing plastic sheet seams and penetrations, as well as a tendency for the plastic to stretch and deflect between supporting framing, limit this material’s suitability in air barrier systems, especially for taller buildings or wherever else high air pressure differentials are expected.
Toward the outside of the building enclosure, air barrier materials are frequently installed over sheathing in framed construction or on the exterior face of masonry or concrete backup walls. Building wraps, plywood or gypsum board sheathing panels and fluid applied or fully adhered sheet membranes may all be used in combination with various sealing sealing and taping materials.
In this location, air barrier materials are easy to install, with a minimum of complex intersections. Where penetrations occur for the anchoring of cladding or sheathing, they are easily sealed to ensure airtightness.
Where air barriers fall to the exterior side of the building insulation, they can also protect against wind washing, in which exterior air currents within the assembly reduce insulation effectiveness. However, materials close to the exterior side of a building assembly must be especially durable and able to perform satisfactorily while exposed to the effects of penetrating rainfall and large temperature fluctuations over the life of the building.
In taller buildings, systems consisting of liquid applied or sheet membranes that are fully adhered to rigid substrates are fully adhered to flexible sheets with such as building wrap. As noted earlier, loose sheet materials can be compromised by tearing or excess deflection. Exterior side air barrier materials also frequently play an important role in keeping liquid water out of the building enclosure, forming water resistant drainage surfaces behind the outer cladding.
Unlike a vapor retarder, there is no harm in installing multiple air barriers within one assembly. Multiple air barriers can provide the particular advantages of each type of system and can also provide redundancy, lessening the chance of a flaw in one material compromising a building’s overall leakage performance.
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