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Community and Q&A

Basement Wall Insualtion

CliffW | Posted in Energy Efficiency and Durability on

I had a French drain installed and the entire basement wrapped with a heavy vapor barrier.  Now comes  the framing for living space.

With the plumbing and other restrictions on one wall, the plan is to frame the wall about 2″ out from the foundation. 

I know I need to add insulation and was planning on using foam board between the studs.

My question is:  Should I secure the foam insulation directly to the vapor barrier (which is secured to the wall via special clips)  then frame the wall, which would create a gap between the insulaltion and interior wall,  or should I frame the wall then tighly place the insulltion between the studs, which will leave a gap between  the insualtion and the foundation wall?


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  1. Expert Member


    To prevent warm air condensing on the concrete walls, you need:
    - A continuous, air-sealed layer of foam.
    - No air-space between the concrete and the foam board.

  2. Expert Member
    BILL WICHERS | | #2

    Put the foam directly against the vapor barrier, then frame right over that. Don't leave any air gaps. You didn't mention your climate zone, but it's possible you might need more than 2" layer of foam to meet code for this insulation. In my CZ5 area, for example, you need R15 worth of insulation for a basement wall, which is 3" of XPS, just over 3.5" of EPS, or about 2.5" of polyiso. I would use polyiso here if you don't have any water issues to worry about.

    Instead of framing a full wall against the foam, try using 2x3s "on the flat" instead, then use 4" square electrical boxes (which are 1.5" deep for the regular ones) and mudrings for wiring. This will save you a little interior space, since you don't need to waste floor space with a full depth studwall here.


    1. CliffW | | #3

      Bill, this will work on all walls exept this one. I have a sewar main running along the wall and other piping. The easist thing would be to move the wall out a bit. I'm inCZ4. What is I used a roll insulation and packed it in?

      1. Expert Member
        MALCOLM TAYLOR | | #4


        I'm not a spray foam fan, but that looks like your best option.

        1. CliffW | | #5

          I think you may be right on this wall. Realistically, it's only about 25' x 7 high. The other 3 walls can all be donw with typical framing.

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