How to insulate basement interior (with 2″ XPS on the exterior)?
Hello. I am planning to finish my basement and I have a question regarding the interior insulation. The house was built in 2001 and is located in RI (Zone 5). The basement has poured cement walls (12″ thick), 8 feet tall. The below grade portion of the walls has 2″ XPS on the exterior and the above grade portion (about 2 feet) has no insulation.
Given that I have R-10 on the outside, my understanding is that in order to meet code
1. I only need continuous R-5 on the interior (1″ XPS or 1.5″ EPS) and then frame a 2×4 stud wall 0.5-1″ away from the rigid foam (no additional insulation in the stud bays).
2. Not use any rigid foam on the interior and only frame a 2×4 stud wall 0.5-1″ away from the bare concrete walls with R-15 Roxul in the stud bays.
I would prefer the second method for simplicity, however, I am a little concerned regarding possible condensation on the bare cement walls. Any thoughts?
A few other things:
If the bottom plate of the stud wall is PT, should I still include 1″ XPS or EPS as a capillary break between wall and floor? (There is 10 mil poly under the 4″ slab but no insulation). I am planning to finish the floor using glazed tile directly on the cement (probably without Ditra).
On the top of the foundation walls there is a double sill plate installed over the pink sill gasket (not sure if the sill plate wood is PT or not) if this helps.
It looks like HD and Lowes only carry faced EPS. Would this be a problem (trapping moisture in walls causing issues to sill plate)? I will need to check with the 2 reclaimed insulation places in MA and see if they carry unfaced EPS. My guess is the perm. rating of unfaced vs faced EPS is very different?
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