Spray foam in a 2×6 wall : partially filled vs flash and batt vs full cellulose
Looking at my inside insulation options now, and I am waivering between flash and batt (2″ spray foam + 3.5″ kraft faced minerall wool batt), 3″ spray foam (leaving 2.5″ air cavity behind drywall) or seal the osb cavity with caulking and canned foam and just go full dense pack cellulose.
I already have 2″ of EPS foam on the outside of the OSB sheathing, so with 2″ of spray foam only I would technically meet the 2012 OBC requirements (R-23). The advantage of flash and batt with 2″ as I see it is the spray foam would not interfere with wiring too much, so I could have it done now and get the wiring done later. I could probably spend this winter without batt and drywall if needed.
3″ of spray foam would place me well over code, but should I be worried about the 2.5″ of air left behind the drywall?
Last option is probably the cheapest (full dense pack cellulose), but relies on me doing all the air sealing in each cavity before the insulation contractor comes. The only available contractor also uses cellulose with ammonium sulfate, whichIi want to avoid.
So, which option would you pick?
PS Zone 5, house is about 3000 squ ft net (windows and doors removed).
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