Leaky homes waste a lot of energy, so most building codes now include requirements calling for floors, walls, and roofs to be sealed against air leakage.
Builders can detail a house’s air barrier in several ways. By taping sheathing seams, the air barrier can be established at the exterior wall and roof sheathing. Using spray foam, the air barrier can be established inside the wall and ceiling cavities. Or the air barrier can be located on the house’s interior by using polyethylene sheeting or by implementing the airtight-drywall approach. Building scientists now realize that in all but the coldest climates, interior polyethylene causes more problems than it solves, so builders who favor interior air barriers usually choose the airtight-drywall approach.
Developed in Canada during the early 1980s, the airtight-drywall approach uses ordinary drywall as the chief air barrier. To achieve a high level of airtightness, you must pay close attention to potential leakage points at the perimeter of the drywall. Although air can’t leak through drywall seams sealed with paper tape and drywall compound, it can easily leak through cracks wherever drywall is screwed to framing lumber. The airtight-drywall approach relies on caulk and gaskets to seal these cracks.
If you climb into the attic of an average house during the winter and pull aside the insulation above a partition, you’ll discover warm air rising through the visible crack between the drywall and the top plates. Air usually enters partition walls through cracks at electrical boxes. The airtight-drywall approach addresses these cracks, as well as others.