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
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