air tight per passivhaus = .60 ach at 50pa. if you don't know the terms or numbers, just know that this is extremely air tight. achieving this requires care and attention to detail, both in the design approach and in the execution.
our air barrier strategy is simple - use the exterior plywood roof and wall sheathing as the continuous air barrier. all seams, corners, and joints in the plywood are taped with SIGA wigluv tape.
the sill plate is taped to the concrete foundation (our 2x8 sill is cantilevered beyond the foundation). the concrete is first primed with SIGA dockskin primer to ensure adhesion. carefully apply tape. the result is an air tight joint. simple.
the plywood air barrier runs up the wall and over the roof. the joint is taped and then the parapet is framed on top. after seeing some tears in the tape we got nervous and taped the parapet too.
all roof and wall penetrations are sealed. we used SIGA wigluv for these too.
the tapes are super sticky, very flexible and easy to use. the paper backing is recyclable, which is good because there is a lot.
it's not inexpensive though, and we used far more than we originally thought. air sealing takes time too. it's worth it though.
SIGA tapes are available through small planet workshop.
another great exterior air sealing product is prosoco joint and seam filler (used at rough openings in combination with prosoco fast flash). more on that in the next post.