Insulating a Sauna
Hi there –
I live in Minnesota and there is a large sauna building community here. Specifically, mobile sauna’s are becoming increasingly popular. Currently, I have an order in from a reputable mobile sauna builder for one of these mobile sauna units. They are 7×12 (think sauna in a ice house trailer). The builder frames up the trailer, insulates it, and then provides all the cedar and materials to finish out the inside.
Here is my question:
These units are insulated with 2 inches of closed cell spray foam. Admittedly, spray foam in a sauna makes me a bit nervous due to the lack of research around long term off gassing, especially at elevated temperatures (manufacturer states it is safe at 200+ degrees). I’ve been doing research and trying to come up with alternative solution for insulation. The conundrum is that the spray foam provides much needed rigidity and air seal to the trailer structure itself (it is framed with 16 oc aluminum framing with 090 aluminum sheet panels on the outside).
Here is my proposed solution for the wall envelope of the trailer to both reduce off-gasing concerns and ensure long-term rigidity of the unit: 090 aluminum sheeting>1 inch of closed cell spray foam>1 inch of Rockwool mineral wool batting (AFB), foil vapor barrier, T&G cedar.
This is basically a “flash and batt” method for a trailer (replacing 1 inch of the spray with 1 inch of mineral wool). My hope is that this will greatly reduce the heat that the spray foam is exposed to (which is my biggest concern with the SPF).
I am not a builder or architect. Does this envelop make sense? Would there be any of the common condensation issues with the 1 inch spray foam in MN winters (climate zone 6a). Again this is for a trailer that only has a wall thickness of 2 1/4 inch, so not sure if the dew point issue is relevant as with other “flash and batt” applications.
If I should avoid spray foam all together, what else would provide rigidity to the trailer (would also like to avoid pink rigid foam board)?
Any advice would be greatly appreciated by the sauna community here in Minnesota!
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