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frost wall/slab insulation

merrimacdave's picture

Hi: I live in the Northeast and am  adding a 12'x12' heated (fhw) mudroom on to the end of my home. The walls will be 10" thick and go down 4+ feet. I'll be filling in the hole and pouring a slab for my finish floor to sit on. I'm planning on putting down 2" thick styrofoam insulation under the slab but wondered if it was necessary to also put styrofoam insulation on the inside of the concrete walls before backfilling. Thanks for your input.  Dave

You won't get much extra (post #206996, reply #1 of 2)

You won't get much extra benefit from doing both. One or the other will perform well.

What's more important than doubling up is to be sure you create a thermal break between the slab and the wall.

Insulating a slab (post #206996, reply #2 of 2)

You must insulate whereever the outside meets the inside. We typically use 2" of XPS under our radiant floors here in Minneapolis. 

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