A. J. D. Ned Nisson responds: The three common options for foundation insulation are exterior foam, interior foam, and interior framed wall with fiberglass batts. Which approach is best depends on a few site-specific variables, including climate, soil conditions, and homeowner preference. Consider these questions when making your decision:
Is the basement heated? How cold are the winters? Heated basements obviously require higher R-value than unheated basements. Since exterior foam is practically limited to R-5 or R-10, interior insulation is more suitable, especially in very cold climates.
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