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Community and Q&A

Slab on grade footings – interior vs exterior

ArchitectJudge | Posted in Energy Efficiency and Durability on

Hello folks, 

I am building a new home in climate zone 4 (Marine, north of Seattle), slab on grade with R 20 below slab, 2×6″ R21 w/ R5 exterior insulation

I have read various articles on GBA about where to insulate a stemwall, but after talking with my concrete subcontractor, I am leaning toward insulating it on the interior. It is easier to build and I can save money by not buying a protection of the insulation.

I do not have a radiant slab, but was wondering if I need to worry about the small area of uninsulated slab. We will have a floating LVT floor. We dont wear shoes inside, but how often would we really stand so close to the exterior wall?

Has anyone installed the slab insulation on the inside and regretted it? 

Building the formwork as we speak!

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  1. Expert Member


    I'd suggest a third alternative, which would be not to insulate the stem-wall at all except at the edge of the slab. You already have more than adequate sub-slab insulation for your climate.

    Another thing to consider is moving your framing in so that the outside of the exterior wall insulation is flush with the outside of your stem-wall. That means you don't have to worry about protecting the bottom of the insulation, and the bottom plate can now help cover the slab-edge foam.

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