Fresh attic insulation in Zone 7
Hello!
I’ve recently gutted my attic of old fiberglass and spray-in styrofoam balls (not sure what the technical term is). I’ve had substantial mold issues in the interior due to leaking basement windows which may have worked its way up into the attic. The old insulation had mold/water stains, as does the deck sheathing.
The house was built in 1978 and has a vented attic (soffits and ridge vents when I put a new roof on).
I’m working to seal everything up tight with caulk and replaced the old recessed cans with new IC-AT cans that I’ve also caulked and will surround with foam. I will be blowing in cellulose up to R60 where there is space. Unfortunately it’s a low pitched roof with little space at the ends.
My first question is: should I spray vapor barrier paint in the attic on top of the drywall (the old fiberglass batts were foil faced). This approach was recommended to me but from my understanding it won’t do much good in Zone 7 if I have everything sealed up well already. Is there a better alternative? Is radiant foil better?
My plan is to install rigid xps at the ends near the vents and spray closed cell foam to seal up gaps. This seems to be the best way to get the highest possible R value in such a small space. Is this an acceptable method?
Thank you in advance.
-Dave
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Replies
Dave,
Q. "My first question is: should I spray vapor barrier paint in the attic on top of the drywall (the old fiberglass batts were foil faced)?"
A. No. A vapor retarder isn't required by building codes in this location, nor is it recommended by building scientists. If you pay attention to airtightness, you shouldn't have any attic moisture problems. For more information on this issue, see "Air Sealing an Attic."
Q. "Is radiant foil better?"
A. No. For more information on this issue, see "Radiant Barriers: A Solution in Search of a Problem."
Q. "My plan is to install rigid XPS at the ends near the vents and spray closed-cell foam to seal up gaps. This seems to be the best way to get the highest possible R-value in such a small space. Is this an acceptable method?"
A. The approach you suggest is often used, and if you are working from inside the attic, it's probably as good an approach as any. This problem -- not enough space in the attic near the eaves for code-minimum levels of insulation -- is a tough one, and the only good solution is to install a thick layer of rigid foam on the exterior side of the roof sheathing, and to convert the vented unconditioned attic into an unvented conditioned attic. Of course, installing exterior rigid foam means that you also need new roofing, so it's an expensive solution.
Thanks for the advice, Martin!