Stacking SIPs and nailbase for superinsulation
I have a passive house project in the Colorado Rockies and need heaps of insulation to make the numbers work (R-90 walls, R-120 roof). A local supplier has polyurethane SIPs that come in at R 6.66 /inch, however only to a dimension of 8.25″ thick for approx R-50 for the 8″ panel. I had thought about stacking nailbase SIP from the same manufacturer on top to achieve my R value, but my brain sounded alarm. There would be a layer of OSB that can’t “breathe”-this seems bad. However, being a passive house it is going to very air tight, so the probability for moisture carried into the wall system seems low. However moisture could still enter by diffusion, and then has no place to go. I am now thinking of cantilevering TJI’s ont he exterior of the SIP with cellulose to derive my desired R Value and allow that OSB skin to breathe, but I liked the simplicity of two systems (Load bearing wall system + SIPS) instead of three (Bearing Wall+SIPS+TJI’S).
I could omit the SIPS, but my wall would grow thick as cellulose is significantly less R per inch than polyurethane SIPS, and I would have to build custom 2’+ thick larsen trusses. Double framing does not seem to wrk as I have not found a good detail to avoid thermal bridging at the foundation interface. Anyone?
I know Thorsten up in Alaska is a fan of the remote wall system, and that got me thinking,
but I have never liked the idea of the moment all the siding puts on really long screws. (Sag?)
Thoughts, anyone…….? Really thinking up a storm here….
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