If I add 4” of spray foam to the exterior of a concrete block house, would it be better than a stick-built house? What kind of R-Factor could I expect?
Right out of the gate, I’m going to tell you that I love ICF buildings (Insulated Concrete Forms). Of course, ICF blocks are filled with concrete and have insulating foam on both sides, though. Are the existing blocks already filled? If not, it won’t be as effective; still, in my opinion, if you are planning to spray the exterior side with foam then sheath it with some type of siding, whether cement fiber board or vinyl, you can’t go wrong. The combination of concrete block and foam gives you a highly energy-efficient structure that is ultra-quiet, too. As far as the R-factor, it really depends on what type of foam you use. For most of the polyurethane foams, you’re looking at up to R-6.8 per inch. That would put your walls near an R-27. Not too shabby! But just remember, no matter how well insulated your walls are, you need to make sure ample insulation is in the attic space. And, the biggest source of heat loss/gain is going to be in your windows and doors. If you’re tacking on an additional 4-inches of girth around the exterior of the house (even more when you add siding), you might as well plan on replacing doors & windows with energy-efficient models.
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