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I am working on a single family house in Climate Zone 5 in New York State.

The first floor is a suspended concrete slab with radiant heat over wood framing. The basement is totally buried with the exception of the top 6". It's covered in 2" of rigid insulation. It will be heated but to a lower temperature than the first floor.The only opening into the basement is a bilco door.

I had originally specified 1" white Dow to be used under the first floor joists but am wondering if I can specify instead one of the radiant barrier materials in the interests of economy. Thanks.

Asked by Linda Gatter
Posted Feb 7, 2013 5:08 PM ET


2 Answers

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If you install a radiant barrier instead of insulation, there will be more heat flow from the heated floor into your basement. Unless the basement is finished space -- and it doesn't sound like it is -- you probably don't want downward heat flow. So I advise that you install a layer of insulation.

If you want the best of both worlds, install a layer of foil-faced polyisocyanurate. Two inches would be better than 1 inch. The foil facing is a radiant barrier.

Make sure to install the rigid foam in an airtight manner. Tape the seams of the rigid foam with a high quality tape.

Incidentally, foil-faced polyisocyanurate is much easier to tape than white EPS foam.

Answered by Martin Holladay, GBA Advisor
Posted Feb 8, 2013 8:27 AM ET


Thanks......I meant to say 1" Thermax, which is polyiso. Sounds like I should stick with that and increase the thickness.

Answered by Linda Gatter
Posted Feb 8, 2013 10:39 AM ET

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