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Community and Q&A

Rigid foam stacking in basement wall

thegiz | Posted in General Questions on

Im not a professional builder so maybe someone can explain this to me.  I was wondering what would be the cons of using rigid foam (internal) against a basement wall, then building a 2×4 wall and stacking rigid foam between studs and sealing both layers (not a vapor barrier but tape and spray foam) Would that not be a poor mans version of closed spray foam?  I know if you meet a certain thickness of rigid foam based on climate zone you can then fill bays with fiberglass batts but why even take risk of mold at all.  Is stacking rigid foam not cost effective, a fire hazard, or too time consuming?  Does it actually lead to a poorly built wall?  Just trying to figure why I have never seen this done or suggested at all.  This is for a future project.

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  1. Expert Member
    BILL WICHERS | | #1

    There is no reason you can’t do that, but it’s a lot of work and very time consuming. It’s much easier to just use thick enough rigid foam directly against the foundation wall for vapor control, then use batts (or nothing at all) inside the stud bays.

    As long as you drywall over the studs, which I assume is your plan, you’re ok for fire code either way.


  2. Expert Member
    Michael Maines | | #2
  3. thegiz | | #3

    Read both articles which are great. Yes thick enough foam in a basement and you can install batts in bay or nothing at all. I think in this case I would still stack foam for extra r value and to be guaranteed mold free for lifetime. I have seen batts turn into black mold before.

    In a detached garage, if you are insulating a wall or ceiling (not roof).would there be a reason to use exterior foam as a precaution against animals and critters eating insulation, or even moisture. I mean would you treat a garage the same as your home insulation.

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