A. Paul Fisette, director of Building Materials and Wood Technology at the University of Massachusetts Amherst and a JLC contributing editor, responds: In a warm climate, it would make sense to use impermeable rigid foam to insulate the exterior of the building, because it would place the vapor barrier in the right position and make the mass of the block wall available to help modulate internal heat gain.
But in a cold climate such as yours, the most economical approach would be to insulate on the inside, particularly since you're reframing anyway. It would be a good idea to apply masonry dampproofing to the inside surface of the block. Then space a 2x3 wall away from the inside of the masonry wall by 3 inches (more or less depending on your...
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