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Community and Q&A

Alternative basement floor

jimdt50 | Posted in Green Building Techniques on

Finished building our house last year and now I want to update the basement floor. I used Superior prefabricated foundation walls for the entire house. 9′ basement walls with a walkout. I didn’t want a concrete slab for the basement floor, so I did a wood floor using 2×6’s on top of 8″ of crushed stone and a plywood subfloor on top of that. I would now like to take the plywood up lay treated 2x4s across the 2x6s spaced 16″ on center and then 1 1/2 inch eps foam board between the 2x4s. A vapor barrio on top of all that then some kind of cement board. Does anyone see any problems with this. The exterior walls have a perimeter tile and a sump pump inside the basement. Also has natural drainage¬† for the tile.

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  1. Jon R | | #1

    Consider draping a vapor barrier across the 2x6s (treated I assume), then plywood, then continuous (no thermal bridging through 2x4s) taped EPS, then cement board. The assembly will dry to the interior.

    Don't trap the plywood in moist conditions (below a vapor barrier).

    1. jimdt50 | | #2

      The plywood is coming out. I'm thinking about filling the space between the 2x6s with stone, to help support the EPS foam board.

  2. Expert Member
    Peter Engle | | #3

    Unless your 2x6's are rock-solid, any cement board and/or tile floor will crack and fail. Also, cement board by itself is not strong enough to provide a subfloor.

  3. GBA Editor
    Brian Pontolilo | | #4

    Hey Jim,

    The two things that you need to consider managing here are moisture and radon. To manage moisture, there is typically a vapor barrier below the basement floor (a common assembly is rigid foam insulation, vapor barrier, concrete). To manage potential radon, there is typically a system installed below the floor and the basement floor and walls should be as air tight as possible to allow the system to work.

    You didn't say why you don't want a concrete floor, but with all the work you are about to do, perhaps you'd reconsider. And I agree with Peter, your assembly will not be a great substrate for rigid flooring materials like cement board or tile. Here are some articles that may be helpful:

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