Hello, I am re-doing my attic and have removed the old fiberglass blown in insulation. I am replacing it with Rockwool and would also like to add rigid foam on top of the joists. Will this create any problems? Thanks

Hi All, Our house has a crawlspace, about 3-4 feet tall, with a concrete slab floor. A few years ago, we had the crawlspace walls professionally foam-sprayed with ~2" of closed cell foam ("Lapolla Foam Lock"), to an R-value of 13. Therefore, the crawlspace is (I think) now part of our conditioned space. I was down in the crawlspace the other day and realized that portions of the crawlspace ceiling still have some of the fiberglass insulation between the joists. I have read two competing theories: One is that there should be insulation between the ceiling joists (i.e., under the subfloor of our first floor above) even for such a conditioned space, in order to account for coldness coming up through the concrete floor. The second theory is that there should be no insulation between the joists because it is a conditioned space (it would be similar to putting insulation in the ceiling between my first and second floors, which I obviously just wouldn't do). Anyone have any thoughts? I know cold air doesn't rise, but the "stack effect" is something I've never really understood and don't know how it would affect this. Thanks in advance for any advice!