r value of concrete

I had an argument with a friend. I told him that concrete has little or no r value if it isn't backfilled. Does anyone have the rating of straight 8" thick concrete?
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Mike wrote:

Dang, is there any way to insulate that with a sealing coat or insulating additive (to floor paint)?
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before back filling some folks are putting foam up. You can also insulate from the inside. Backfilling makes for great r value but it isn't a good idea to back fill right up to the siding ....
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M wrote:

It is a technical point I admit, but backfilling has no change to the R-value of the wall. It changes the delta-T that the wall sees, but it doesn't affect the resistance to heat transfer. If you are in a cold climate where the earth freezes for 3-4' in the winter, then the top half of the concrete wall will still lose a lot of heat. Adding foam does increase the R-value of the wall and will help a lot if in a location where the ground gets pretty cold in the winter ... or warm in the summer.
Matt
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