Making Air Barriers that Work:
Why and How to Tighten Up Buildings

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Air leaks may not be as dramatic as water leaks, but they cause plenty of problems. When a new LEED-certified building in New York formed icicles and ice dams, the owners brought in building-science consultant Terry Brennan of Camroden Associates to investigate. “The detailing of the air barrier was actually pretty good,” he says. The rafters are sealed with rigid-foam insulation taped at the seams, and the walls are sealed with gypsum board and a polyethylene vapor barrier. “But where they came together there was nothing in the drawings and nothing in the specs,” he told EBN, “so it’s got this crack.” With an eighth-inch (3-mm) crack running along the eaves, that gap leaks a lot of heated air, melting snow and causing ice buildup while creating the potential for leaks and moisture damage.

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