In the first post of this two-part series, I talked about a method for tying a foundation to the wall of a house built on a concrete-free slab. The result is an energy-efficient connection at the rim joist—an area notorious for air leakage. Here, I’ll explain detailing the transition from the wall to the roof system. As previously mentioned, both assemblies come from a certified Passive House build and they meet the zero-energy objective.
Starting with the wall
The wall itself is a 2×6 stud wall with intermediate framing with studs at 24 in. o.c. We sheath the wall with 1/2-in. CDX plywood with the seams taped using Siga Wigluv to continue the air barrier up the wall. The stud bays are insulated with dense-packed cellulose, blown in and tested to a density of 3-1/2 lb. per sq. in. to prevent any future settling. This makes the CDX plywood the least permeable part of our assembly at approximately 10 perms, therefore making it the vapor control layer. This is the layer we are most concerned about seeing condensation on the coldest stretches of the year and therefore we want to keep it warm enough to keep it safe.
To keep the sheathing warm, on the exterior of the wall we install 1-3/8-in. Steico wood-fiber rigid insulation board. We like this product because of its low embodied carbon and ease of installation with the tongue-and-groove profile that can be installed “off layout,” meaning the seams don’t need to line up with the studs to install it. Because this is a wood product being installed in a climate that sees 42 inches of rain on average per year, we install a mechanically attached water-resistive barrier (WRB) to…
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