Insulating Basement Walls with Rigid Foam

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Joined: Mon Apr 17, 2017 1:35 pm

Insulating Basement Walls with Rigid Foam

Post by malimited » Mon Apr 17, 2017 1:40 pm

I live in North New Jersey (Zone 5) and I am going to be finishing my basement. My thought was to use the rigid polyfoam boards as the insulation.

Here is what I (think) I know.
1. Zone 5 has a code for R-13 insulation for basement
2. Rigid polyfoam boards have a rating of R-5 per inch.
3. That means that I will need 3" of rigid polyfoam board to meet code?

1. Are any of my assumptions, correct or incorrect?
2. Based on the previous, that means I would need a 3" rigid polyfoam, plus the studs, plus the drywall, which means I would lose 7" of space for every walls??? This doesn't seem right.

Does anybody know the codes for basement insulation. Is it absolutely required to have insulation, if so, what is the minimum rigid foam that will satisfy the code?

Please help, I've searched high & wide and I cant seem to find an answer.

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Re: Insulating Basement Walls with Rigid Foam

Post by Shannon » Mon Apr 17, 2017 2:47 pm

That is one way to do it but it takes more space away from the basement. I prefer to use 1" rigid foam against the concrete walls and then frame the walls and use bat or Roxul insulation in the stud cavities and poly vapour barrier under the drywall.This way you will only loose about 5 or 5-1/2" of space around the perimeter of the basement. Using the 1" rigid and Roxul insulation will leave you an R value of about R19 which is well above what you say your area requires.

All basements should be insulated but I do not know anywhere that requires you to use rigid foam.
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