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  1. #1
    Join Date
    Jan 2008
    Posts
    3

    Question Insulating walls inside CMU exterior walls?

    This is a fresh thread to follow along where this thread left off:

    http://advice.thisoldhouse.com/showthread.php?t=3060

    We've got a 1947 house that has cinderblock exterior walls, and 1x4" vertical furring strips on the inside to hold the lath & plaster (only the original lath wasn't really wood lath, it was early drywall that contained wood dust and was perforated to accept & hold the plaster.

    The problem is that there's really no insulation. There's really no getting inside the cinderblock to put expando foam in there, so our only options that I can see are to either frame out new walls inside the cinderblock walls, which opens up all sorts of issues with the top & bottom plates, floors, etc, or to just use a 3/4" insulating board between furring strips and deal with the heat-loss.

    I have perused framing & construction books seemingly to no end, but have not found any good solution.

    We cannot be the only people to have run into this situation, so I'm hoping maybe someone has some advice in this regard.

    Any ideas?

    Thanks!

    -Clint

  2. #2
    Join Date
    Jan 2008
    Posts
    3

    Default Re: Insulating walls inside CMU exterior walls?

    One other idea that we had come up with was to rip 2x4's down to about 1-1/2" (about 2x2 size), matching the somewhat uneven profile of the furring strips, and then insulating with Dow rigid foam board between the 2x2 "studs" and then sheetrocking on top of that. But what to do with the top & bottom plates and the "floating floor"?

    -Clint

  3. #3
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Insulating walls inside CMU exterior walls?

    I'm guessing there will have to be some compromise made for comfort and efficiency.

    One method may be covering the cinder block entirely with sheets of rigid foam insulation. Then using 2x3 framing with bat insulation in each stud bay. While the bat insulation may only provide about R9 for a 2x3 depth the foam insulation will provide a continuous thermo break plus added insulation value.

    But what to do with the top & bottom plates and the "floating floor"?
    I'm not sure what the concern is here.
    The top plate would be fastened to the ceiling joists and the bottom plates would be fastened to the sub floor or joists.
    The "floating floor" would be trimmed accordingly for the new walls.

    Is there the possibility for adding insulation to the exterior?

    Hope this helps.

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