While I agree, I want more R-value. I have a local company that air sealed my new house (foam, caulk every crack and air doored it) and used high density cellulose in the walls, I have an R23-26 in the walls, with R-58 in the ceilings. The house has 2 air changes and hour, almost too tight, with the air door test. The bathrooms and range hood vents keep it from being too tight. And I had a 3500 sq ft home done for less that it would cost to spray foam the shop for way less r value but the same air sealing.IMO not doing it is underkill. I'm looking at using zip (maybe zip r if I'm feeling frisky) sheathing on my upcoming house build and that's the idea, seal it up nice and tight. With that alone, you quickly approach passive house standards.
Sooooo, I plan on 1.5" foam board between the girts and trusses, foamed, caulked and air sealed, I'll air door it to ensure no air leaks. Then possibly the same high density cellulose, as I am waiting on a qoute in case prices went sky high (possibly R-21 batts). I'll end up with R-25 plus walls and R58-65 ceilings. So I'll have more than double the R value of spray foam for way less the cost.
The air sealing is key, so alot of attention will be spent there.
I only have electric and propane available, and neither are cheap, so the better I can get it insulated, the better.
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