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Is there a better green method to frame a floor over a concrete slab?

GBA Editor | Posted in General Questions on

Turning a garage into a habitable room and we are installing a new wood sub floor (needs to be 5″ higher than the slab) over an existing concrete slab. We are presuming there is no membrane below the slab. In past jobs we have put down a 6mil membrane and floated PT 2xs with 3/4″ ply on top. I am wondering if there is a better method by which we didn’t use pressure treated wood. Any ideas are appreciated. Thanks.

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  1. Sean @ SLS Construction | | #1

    2" foam over slab
    2 x 4 sleepers tapconned into slab on 2' centers - foam inbetween
    2 - 3/4 T& G - gets you up to 5" & insulated & with no wood touching the slab

  2. Garth Sproule | | #2

    Just curious, why two layers of plywood? I would also recommend a layer of poly between the foam and the insurance to prevent vapor diffusion ...

  3. Garth Sproule | | #3

    Ah...just figured out that it is to get the floor up to 5"...I would think that an extra layer of 3/4" foam would work as well, and would add more R value for close to the same cost?

  4. Tom | | #4

    Like the answer but won't 2" foam compress over time?

  5. mike | | #5

    we've done the floating floor before...
    2" rigid, 2 layers of plywood, rotated 90deg for diaphragm, with t&g over.

    the plywood spreads the load, so the rigid shouldn't compress.

  6. Armando Cobo | | #6

    Installing wood floor on top of a non-vented floor assembly over concrete slab, w/o a moisture barrier under the slab, could be a recipe for disaster, especially if your job is in a high humidity area or high indoor humidity.

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