Which insulation option with Zip R
I am in Ohio Zone 5 and my building envelope I have 2×6 walls with Zip R-9. I have a couple different insulation options that I have bids for. Both contractors would be doing blown in cellulose in the attic. One contractor does damp spray cellulose Nu-wool for the walls and would use Nu-wool batts for around the rim board. That bid is $10.4k. The other contractor does spray foam and would do a quick flash coat of 2lbs closed cell on the walls and R-19 fiberglass batts. They would then do 2″ around the rim board. This bid is right at $13k. My third option would be to use the damp spray cellulose contractor and then have the spray foam contractor come for the rim board and that would be around $11.5k.
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Replies
I don't see an advantage to flash and batt (a thin layer of spray foam with the rest batts) gains you much over strategic air sealing with canned foam and caulk/tape where needed. You do need vapor impermeable insulation over the rim joist though, unless the Zip R9 panel will come down and cover the exterior of the rim joist and not just the studwall part of the structure. If the Zip R9 covers the exterior of the rim joist, then you can insulate that as you would the walls, otherwise you need vapor impermeable insulation there to avoid moisture issues, so closed cell spray foam. That would make your middle option your best choice here.
Bill
Bill,
Or insulate the rim-joists with sealed foam board, and avoid having spray foam anywhere.
I have found that sometimes it's difficult to seal all the different pieces when going that route, although that is what I did in my own home: I sealed in EPS panels into each joist bay using canned foam.
Bill
Yes, my Zip R covers the rim joist.
Then you should be safe using batts on the interior. I would use mineral wool batts here myself, mostly because they are more likely to self support and stay in place on their own. I'm not familiar with "Nu-wool", but if it can self support too, it'd probably be fine.
Bill
I am using foam board on the walls. A combination of EPS R-Tech where I am finishing a couple areas and putting up a stud wall and cavity insulation. Unfinished areas I have the The Dow Thermax so it can be left exposed. Spray foaming the rim joist would tie the top in. Or I could can foam the top edge of the foam board on the wall and still do batts in rim joist.