Air-Sealing Techniques From a Passive House Pro

The air barrier under the footing and slab is also a vapor retarder and radon retarder. Here 10-mil Stego Wrap was taped with Siga Rissan tape.

If the foundation wall is poured concrete, no separate air-barrier layer should be needed, as concrete is fairly airtight. Service penetrations must be sealed before they are inaccessible.

The top of the foundation wall is rarely flat enough for generic sill seal to fill the gap between the concrete and band joist, resulting in serious air leaks as well. In this Passive House, though, that connection wasn’t an issue.

Because the foundation air barrier ran up the outside of the foundation and was more or less in line with the air barrier running up the outside of the structural wall, there would be no J-bolts penetrating the air barrier or gaps between the top of the foundation wall and the mud sill to worry about.

The insulation curtain wall consisted of 16-inch vertical wood I-joists spaced 36 inches on-center filled with dense-pack cellulose.

The 6-inch-long HeadLok screws used to attach the I-joists would penetrate the air barrier, so the screw holes were pre-drilled in each joist while it was on the ground, and filled with Pro Clima’s permanently flexible caulk, Contega HF (OR-F). The screws cinched the joist tight to the DB and the caulking was compressed for a good seal.

The 3/4-inch plywood window bucks were set in place before the building was wrapped with DB .

The soffit framing on this Passive House was built on top of the insulation assembly, which was above the air barrier, so there were no framing penetrations to deal with.

The air barrier on the ceiling was the most important surface to completely seal. This roof assembly was designed to be both foam-free and unvented, utilizing the advanced moisture-controlling properties of Intello.

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