Firstly, I’d like to thank all the contributors on this forum.  You’ve expanded my knowledge base more than I can measure, and I offer all the gratitude that I can.  The background of our build is as follows:

We are building a 1.5 story home in the NC mountains (Zone 5) plus a walk-out basement.  Foundation walls are 12″ CMU, fully grouted, with 2×6 stud walls interior to the foundation.  We have 2″ of EPS foam between the stud walls and the CMU, and the stud walls will be insulated with Rockwool, for a combined R-value of approximately R-31.  The floor system is framed with 16″ open-web joists, sitting on double 2″x12″ plates, and we have 3/4″ fire blocking at the top of the gap between the CMU and the stud walls.  Exterior sheathing is 7/16″ ZIP, sill plates were caulked with acoustical sealant when installed, and then the sheathing to CMU connection further taped with SIGA Fentrim.  If air can get through this, well, I don’t know how it could.

My question is that since the basement is going to be fully finished living space, do I need to use EPS foam along the rim joist plus Rockwool, or can it simply be Rockwool?  I’m having a hard time understanding why this area should require a different approach than the transition between the 1st floor and 2nd floor of the house, which has essentially the same type of construction and “conditions”, namely that the area above, and below, and within will be fully conditioned space.

I’m willing to cut and cobble EPS foam up against the rim, with spray foam around the edges of each piece to make an air barrier from the inside, before installing mineral wool, but it seems like unnecessary overkill especially with the detailed air sealing I’ve already done from the outside.

Many thanks in advance for your sensible comments.