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Is rigid foam necessary under concrete slab in Central Virginia?

rikard5150's picture

We are having a house built in Central Virginia. The builder uses a CMU stem wall and then pours a concrete slab. They isolate the slab from the stem wall with 1" XPS for R-5. This is all that the building authority requires. My question is it worth the extra cost to have the builder install R-5 on the entire stem wall and then 2" XPS or EPS under the slab for R-10?



I would insulate the entire (post #212923, reply #1 of 2)

I would insulate the entire stem wall and 4' in from edge of slab with rigid XPS. If you plan on any type of radiant heat integrateted into this floor, then I recommend insulating over the entire slab gravel subgrade with closed cell spray foam about 3-4" thick. If you're spraying foam, then keep in mind that your subgrade should be fully compacted, dry, and above freezing.

Thanks, that is what I was (post #212923, reply #2 of 2)

Thanks, that is what I was thinking.