Insulating variable depth basement stud bays
I’m working on a gut rehab of a basement in Chicago. The basement walls are about 3 feet of stone foundation with about 4 feet of 3 wythe brick on top. I framed out studs at least an inch from the stone foundation and then had 2″ of closed cell spray foam applied to the stone and brick. (with some dimple matt leading to an interior french drain). My question is how to deal with the variance of stud bay depth that is caused by the stone foundation being thicker than the brick portion of the wall. At the bottom of the wall the foam enters and covers about an inch of the stud but at the top of the wall there is a gap from the stud to the foam. I was looking at filling the remainder of the bay with mineral wool bats. Should I attempt to seal the top of each stud with canned foam? Should I worry if there is an air gap in the assembly and if the an air gap is ok would it be better to have space between drywall and mineral wool or mineral and spray foam?
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Replies
2" of cc SPF is pretty good R value already. There extra insulation doesn't hurt but it might not be worth the cost. There is some value to add in batts to the above grade section and rim joist area. Make sure you push the insulation against the SPF to prevent convective loops, it is fine to have a gap on the drywall side.
Assuming the rim joist area was also sprayed at the same time, the SPF seals up foundation you don't really need another air control. You can just install your batts/drywall and call it a day.