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Spray foam vs rigid board in my 40ft high cube, foam won by a mile
I spent 3 weeks last fall debating insulation for my Texas build. Rigid board looked cleaner and I could DIY it, but the thermal bridging at the steel ribs was killing my numbers. I bit the bullet and paid $2,400 for closed cell spray foam from a crew in Austin. The interior temp swing dropped from 18 degrees to 4 degrees between noon and midnight. Board would have needed furring strips and still left gaps at every corrugation. Anyone else deal with condensation issues on the metal frame before insulating? I caught rust on my door posts early and that's what pushed me over.
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blair_dixon16d ago
Appreciate the writeup but the 18 to 4 degree drop isn't really the foam doing all that. A 40ft high cube has a ton of thermal mass in those steel walls, so you're mostly seeing the lag from the mass itself, not just the R value. Rigid board done right, taped seams and all, plus furring strips to break the bridge, gets you close to the same numbers and you can still pull panels later if you need to get at a rib or run wire. Spray foam does kill the condensation though, that part you nailed, because it seals the air and no warm moist air hits the cold steel. Condensation on those posts is an air leak problem more than a foam vs board problem.
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