Insulate attic floor with rigid foam board under flooring.?

Apr 30

I am going to finish off some attic space and need to insulate the floor. I will use thick rolled in insulation but was wondering if I could use rigid dow foam board under the floorboard? Is there a foam board that works under the floor and would it provide additional sound insulation?

Dow Styrofoam is sold in a variety of types. Hit their website to see. I would suspect that a Type IV product handle the compressive strength for a residential attic. I would not use their Type X product, which has little compressive strength. It will help with sound, esp. where the joists are.

Given that, though, I’d be asking if its neccessary. You are adding to the thickness of the floor.

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Filed under: Rigid Foam Insulation

3 Responses to “Insulate attic floor with rigid foam board under flooring.?”

  1. DIYpro, on April 30th, 2009 at 10:27 am Said:

    Either way will work, but I would go with fiberglass insulation. Much easier to work with and cheaper as well.
    References :
    http://www.icanfixupmyhome.com/Insulation_For_Energy_Efficiency.html

  2. barrbou214, on April 30th, 2009 at 11:11 am Said:

    i think the foam board would give to much when walked on and distort the top of the finished flooring. what you could do is install 6 mil poly over the rafters then roofing felt then install the finished flooring.
    have fun and good luck.
    References :

  3. TOM W, on April 30th, 2009 at 11:49 am Said:

    Dow Styrofoam is sold in a variety of types. Hit their website to see. I would suspect that a Type IV product handle the compressive strength for a residential attic. I would not use their Type X product, which has little compressive strength. It will help with sound, esp. where the joists are.

    Given that, though, I’d be asking if its neccessary. You are adding to the thickness of the floor.
    References :

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