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Good day. My wife and I are up here in Middlebury, VT looking to build a SIP home. I was shocked yesterday to hear (from both an artchitect and the SIP manufacturer) that the State of Vermont "let's them get away with" (sounds like a red flag) R-22 panels because the issue of thermal break to the studs has been elliminated by the SIP.
This reeks of the scam used by the spray foam folks trying to sell more foam by saying 2" of foam is good as R-20 because it stops air leakage. Two separate issues.
Sure, with a SIP there is no thermal break issue at the studs, but they have taken away the extra insulation value between the studs, which is 90% or more of the wall!
If you built stick-frame and added 2" of XPS over an R-19 wall, you would have a thermal break of R-12 over the stud and R-31 over the wall cavity. So the R-value between the studs is R-31. How can you remove the R-19 part and say you have met code?
I believe this to be a bad precident, poor building practice and I am shocked to hear Vermont is getting away with it. If the IRC calls for a minnimum of R-38 in the walls, by all that is holy, put up R-38.