Does closed spray foam installation require a separate air barrier?
user-914555
| Posted in Energy Efficiency and Durability on
It sounds like spray foam in the wall cavity initial seals and prevents air leakage. But as a house “settles” and lumber dries it would seem that the rigid cured spray foam would lose its air sealing benefits. Should an additional air barrier also be installed? Similarly, couldn’t vapor also move through these same small crevices, which would seem to call for some additional vapor retarder? Under the strategies and details tab it seems the basis assumption is that the cavity insulation is fiberglass or cellulose not foam.
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Replies
David,
A home's air barrier system includes many components. In most homes, the air barrier system includes elements of the poured concrete foundation, window glass, gaskets, caulk, and many other components.
It's possible to use spray foam insulation as one component in an air barrier system. But it is highly unlikely that spray foam will form the entire air barrier of your house. Wherever your spray foam stops, another component of your home -- a stud, a joist, a top plate, drywall, glass, or concrete -- becomes part of the air barrier. If there is a crack between the spray foam and the adjacent component, that crack must be addressed in order to achieve air barrier continuity.
Small cracks and defects do not appreciably affect the performance of a vapor retarder. A vapor retarder with holes covering 2% of its area is still 98% effective.