Insulation
jam1030
| Posted in General Questions on
Have 2×10 floor joist. Located in zone 2a, would it be a bad idea to use R15 rockwool which is 3.5” thick pushed up to bottom of joists and then apply osb or polyiso to bottom of joist to seal and protect insulation?
Or just use 2” of closed cell spray foam?
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Replies
Hi Jam1030.
Air sealing this floor assembly is just as important as R-value. If you a couple inches of polyiso, detailed as an air barrier on the bottom of the joists, your R-value will likely meet the code in your area. Then, any insulation you put in the joist bays is a bonus. Again, pay close attention to air sealing.
The answer to your question depends in what is under your joists. If you have a basement or a sealed crawl space I think it is a bad idea.
If you are on piers I would not want to have polyiso exposed to the element.
Walta