Building a Simple Passive House, Images 18-27

To provide added insulation with minimal thermal bridging, 2x4 sleepers were laid edgewise on the roof sheathing, staggered between rafters, and allowed to extend past the plane of the walls to form wide overhangs.

Foil-faced foam is cut to fit tightly between sleepers.

The foam slightly overhangs the sheathing.

It is sealed to the exterior wall insulation board with spray foam.

A second layer of 1/2-inch plywood was installed over the sleepers in a bead of spray foam.

To provide a caulkable surface for sealing the drywall to the framing, backing plates fashioned from scrap lumber and plywood were fastened to the edges of framing members.

The plates were also fastened across rafter and stud bays.

Although three-gang airtight electrical boxes were not available commercially, the crew made their own by cutting pieces of U-shaped plywood (C), caulking them to the box, and fastening the corners to the framing with finishing nails.

The wires were sealed with acoustical caulk.

The drywallers applied painter's caulk to the plates, backers, and rough openings as they hung the wallboard, using two cases of caulk for the 750-square-foot structure.

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