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Community and Q&A

Basement floor insulation

Chris_Kizzy | Posted in Energy Efficiency and Durability on

Situation: I am currently finishing a walk out basement in Cincinnati OH.

The foundation does have 3-4 inches of sub slab insulation. I have insulated the walls with 2 inch rigid foam insulation, stud cavities will also get fiber glass insulation.

Flooring will be carpet in living spaces, tile in bathroom, and laminate in a small kitchenette area. We tend to get cold easy so floor warmth is key.

Question: Do I still need to worry about summer time condensation on the floor enough to insulate the floor with rigid foam before laying flooring?  Additionally, any suggestions on how to keep laminate more comfortable (warm)? It will be in direct contact with the concrete if I don’t insulate the floor.

More Situation: The basement has never had any condensation/moisture issues but with the addition of more air flow (added HVAC ducts), I am not sure if this creates new opportunity for condensation.The basement already had vents but we have added 3 vents (total of 5 now) in the basement.

I also ran a dehumidifier all year round b/c this is what the builder instructs all their customers to do out of precaution I guess. I have had intervals where I turned off the dehumidifier, I saw no issues with moisture.


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  1. GBA Editor
    Martin Holladay | | #1

    If your slab has a continuous layer of horizontal sub-slab insulation, relax. Everything will be fine.

    The only insulation I would recommend would be vertical insulation (rigid foam) at the edge of the slab on the walk-out side of the basement. This vertical insulation should be 2 feet wide, and should extend vertically downward from the top of the slab. You'll need to dig a trench to accommodate the rigid foam, of course, and you'll need to install Z-flashing at the horizontal seam between the top of the rigid foam and the bottom course of siding.

    Protect the above-grade portion of the insulation with pressure-treated plywood, metal flashing, or stucco.

  2. Chris_Kizzy | | #2

    Thanks for the response Martin. I'm glad I posted the question here before buying materials to insulate the floor.

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