Quote:
Originally Posted by mrd
Earth has a low R-value, something like 1 per foot...
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Dry earth with R-1 per foot would mean R-0.083 per inch. That's really not so much.
Pink XPS has an insulating factor of R-5.4 per inch.
This would imply that heat loss into the earth would be (5.4/.083) or about 65 times the rate of heat loss through XPS.
I think I would consider the money well spent, if I insulated under my slab.
In addition, the time lag to heat up or cool down an insulated slab is shorter than with an uninsulated slab.
-AC_Hacker
P.S.: I've heard tales of the radiant slabs that were in the homes that were built in Levittown, New York. They were put in without any insulation, as you describe. The residents were able to grow flowers all through the winter in the garden beds around the edges of their houses.
Pretty good thing if you like flowers in January.
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