The wall system shown here is an improved version of the system I used for the house I built in Knox, Maine, in 2011 (see "An Affordable Passive House," JLC May/12 and Jun/12). Since building that prototype house, I've switched to some advanced European materials for air-sealing and moisture management that weren't on the U.S. market back then.

We start with an inner 2x4 stud wall, sheathed on the exterior side with OSB (A); all joints and nail lines are sealed with Pro Clima Tescon Vana tape (foursevenfive). The OSB layer is airtight, and also braces the structure. Next, we fasten 11 7/8-inch wood I-joists to the outside of the walls, driving 4-inch GRK RSS structural screws through...

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