Insulating basement walls - CT

Old 12-30-14, 03:28 PM
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Insulating basement walls - CT

i have been doing a lot of research on this and figured that other than spray foam insulation (too expensive) is to use rigid extruded poly boards. The catch is that code asks for R-15 and in order to get that (without using FG - no no in basements due to mold) is with a 2" and 1" boards of rigid foam. There doesn't seem to be anything on the market that is R-15.

Any ideas? Do I just glue the 2 boards together? One over the other?

Old 12-30-14, 03:42 PM
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That may depend on the rest of the plan. What I mean by that is if you intend to have everything up to code, finished basements are a funny bird when it comes to building codes. So, let's say that the insulation is up to code but you have a bedroom there which is against code almost everywhere, it won't matter. None of if may matter until you try to sell the house. Keep it all in mind as you proceed.
Old 01-03-15, 06:48 PM
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How do you plan on attaching the foam board to the walls? If using mechanical fasteners, just run them through both boards back to back. I am surprised that R15 has to be code although I see that you are in CT.
So you're gonna have three inches of foam board to fasten? I'm in NJ and am using just the 2" R10
Old 01-23-15, 10:02 PM
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Worried about that 3" just being too thick, or having to deal w/ layering it (e.g. taping seams twice)?

You could always put the 2" against the wall, then frame in front of it, then cut the 1" into 14.5" wide strips and put that in the joist space. yeah, kind of a pain but it will get the job done.
Assuming the 2" is sealed well, you can just stuff the second layer in there w/o it having to be a perfect seal, since its just there for insulation and not a vapor retardant (already handled by the outer layer).

Yeah a little surprised you're required to have R15 below grade.

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