What kind of foam board should I use to insulate rim joists in Wisconsin?
My home was built in 1927 and at some point fiberglass was used to insulate the rim joists. I've started to remove it because its become a home to mice in some places, and just plain not working in others. But what to replace it with?
I'm leaning toward 4" of polyiso, with a <25 fire spread. It won't work as well at low temps and will lose some R value over time but I think I'm properly compensating by installing 4". (2x 3" layers) It seems that XPS would be the alternative but I'm concerned with fire code rating. While XPS has a lower fire spread rating its not suitable for exposed inside walls. It would need a layer of sheet rock. Thoughts?