Insulate an existing concrete floor slab?
I have an existing ADU (in-law suite) in Portland, OR (Zone 4C). It’s part of a garage structure, sharing the same concrete slab floor. The stem wall extends 18″ deep below grade, and rises about 12″ above the floor. I’m preparing to remodel the ADU including replacing the carpet with new finish flooring (probably laminate planks).
My question is: Should I insulate the floor slab while I have the concrete exposed? I’m thinking of laying down foam above the slab and floating a new subfloor above it, as has been aptly addressed on this site. Or do I just leave it alone? I’m more interested in energy efficiency than comfort, as this is a rental unit.
My thinking is that in this climate, there’s a trade-off between the cold floor heat loss in the winter, versus the benefit of having a cooler floor in the summer. Would perimeter insulation on the outside make more sense? If som complications include the stem wall above grade, a sidewalk abutting the foundation on one side, and the garage sharing the slab. Thanks.
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