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Community and Q&A

Existing basement framing against concrete

tyman00 | Posted in Green Building Techniques on

We are looking to insulate our concrete basement foundation walls and the 18″ wood framed area between the foundation top and the bottom of the floor above it that includes the sill plate. We are settling on closed cell spray foam.

When the house was built the framing for the exterior basement walls were set up against the concrete foundation. There is anywhere between 0 to 1/4″ between the studs and the concrete depending on the studs and the texture of the concrete forms.

I understand that ideally there should be a 1-2″ gap between the concrete and studs, but it just isn’t there. In order to do so we would have to cut out what exists and reframe it. Some of it is either load bearing or will interfere with load bearing interior walls.

If we sprayfoam it as it is, are we asking for trouble?

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  1. Expert Member
    Michael Maines | | #1

    Tymanoo, assuming your foundation is like most and is somewhat damp, what you propose is somewhat risky, because moisture will always be trying to get from the foundation to the basement interior. (Even if the foundation appears dry, it likely holds moisture.)

    If you don't want to reframe, the next best option would be to include a vapor barrier between the studs and the concrete. I'm not sure what materials would be best under sprayed foam; regular 6-mil poly sheeting might work, but the foam may not stick well and/or may melt the plastic under the heat of reaction.

  2. tyman00 | | #2

    Thanks Michael,

    Most spots there is nothing touching, but it is 1/8" away. I'm not sure how far the foam will penetrate or block moisture transfer. I'll talk with the insulation crew and see if they have any suggestions for a compatible moisture barrier.

  3. GBA Editor
    Martin Holladay | | #3

    This is a judgment call. The existing situation isn't ideal, but my guess is that if your basement has no evidence of moisture entry, and you go ahead and install closed-cell spray foam in the existing stud wall, the wall will probably last for decades.

    That said, the best approach would be to take out the studs and reframe the wall farther from the concrete.

  4. tyman00 | | #4

    Thanks Martin. I believe we will go this route since there hasn't been any sign of moisture entry anywhere.

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