Siding Over Rigid Foam

1. Fasten the Foam: Apply foam to the wood-sheathed wall using cap nails. If the foam will function as your drainage plane, tape all seams carefully (no harm done even if you plan to add housewrap).

2. Strap the Wall: At the top and bottom of the wall, apply strips of a corrugated vent product such as Cor-A-Vent, wrapped with screening to keep the bugs out. Then strap the wall with 1x3 strapping. It's best to line the strapping up with the wall studs, and fasten it with ring-shank nails long enough to get through the foam and into the studs. (For thicker foam, long screws work best.)

3. Detail the Flashing: Flashing behind the lowest course of siding directs water from the face of the clapboards out over the wall base trim. Incidental water reaching the housewrap drainage plane can escape through the Cor-A-Vent behind the trim.

4. Apply the Siding: Wood clapboards are best nailed by hand using stainless steel 5d or 6d siding nails. Break the clapboard joints at the strapping, and remember to end-prime the boards.

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