I'm looking to convert an existing screened room into a sun room. Part of that process will be insulating the cathedral ceiling. Unfortunately I don't have a lot of space. Ideally I'd like to get R39 in less than 7 1/4" space. The only option seems to be impermeable spray foam for a hot roof. Any other options?

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    Polyiso foam board R-13.1 per inch. 2 layers of 2" with drywall over it...? Mar 30, 2021 at 22:34
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    Is insulating atop the roof deck an option? Also, what sort of ground snow loads do you get where you're at? Mar 30, 2021 at 23:21
  • Unfortunately insulating on top of the roof isn't an option. I'm in Howard County Maryland an it looks like snowloads are 35psf. I'll check out the Polyiso foam boards.
    – jonathan
    Apr 1, 2021 at 21:50


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