Sub-Slab Insulation for Garage
I’m in Climate Zone 6 (Lakes Region of NH). I’m building a two-car garage with a 740 sq. ft. apartment above. In a separate post, I inquired about perimeter insulation, which I’m definitely going to do. I’m wondering if I should also insulate under the slab? After asking my foundation guy several times, he said insulating under the slab isn’t needed, but I’m questioning that advice. How much of a difference will it really make over and above the perimeter insulation? XPS or EPS? More details: I have perimeter drains around the foundation footings. At the moment, my dirt guy has filled up to the bottom of the slab mark with clean, compacted fill, compacted in 1 foot lifts. There will be about eight inches of foundation wall above the top of the slab when it’s poured. Would vertical insulation also be needed in addition to the horizontal insulation?
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