Q:
I am in the process of renovating my home and would like to add insulation without tearing out interior walls. I will be replacing the exterior siding, and I can expose the back side of the drywall. Is it possible to spray foam insulation into the wall cavities from outside? I live in Hawaii, where the average temperatures are in the 80s.
Alan Borman, Honolulu, HI
A:
Contributing writer Scott Gibson replies: Polyurethane foam fills cracks and crevices more effectively than batt insulation, and with R-values as high as 6 per in., it’s a highly effective thermal insulator. And yes, you can spray foam into wall cavities from the outside.
Even in your cooling climate, insulating the roof and exterior walls will make your house more comfortable. Spray foam, however, is expensive. No doubt because of the mild climate, the state of Hawaii recommends exterior walls to be insulated only to R-11. Even in a 2×4 wall, a full thickness of closed-cell foam would be far greater than that. If you’re looking for something more affordable, you might consider dense-pack cellulose or blownin fiberglass. Just keep in mind that with these alternatives, you’ll need to use separate airsealing measures.
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