How risky is a single layer nailbase SIP over a single stud wall with sealed sheathing?
In the quest for a cost-effective, durable super-insulated wall, we’ve typically done double stud walls with dense pack cellulose, with the air barrier/vapor retarder on the inside behind the sheetrock (polyamide), and sometimes had the exterior sheathing (plywood or fiberboard, or a combination thereof) taped as the air barrier. We’ve also designed walls with a single stud wall and the exterior sheathing (typically OSB) sealed as the air barrier, and two layers of rigid foam sheathing to the exterior, with furring strips over the WRB over the foam, fastened through to the studs. This “single stud wall with foam sheathing” has the benefit of a rigid durable air barrier outboard of the wiring (and in some cases some plumbing and/or heat distribution), and the air barrier is pretty resistant to future tampering by homeowner renovation. However, builders in my area are not fond of installing two layers of foam followed by furring – it is a lot of labor time and hard to keep things square and plumb outside. I’m wondering if a single stud wall with one thick SIP nailbase panel is a good idea. This concept lets builders get a house framed in, and allows the air barrier to be carefully detailed and tested. If the nailbase panels are installed with sealant and minimally expanding foam between the joints, or maybe with a spline panel joint, how worried should I be about shrinkage or movement over time? I don’t want to lose the continuity of the thermal sheathing layer. Feedback? I’m in climate zone 7, so am thinking about a 2 x 4 wall with dense pack cellulose (roughly R-12) and a 7 3/4″ nailbase panel (R-28).
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