You could put rigid foam on the inside of the studs, but it's harder to get continuous coverage through floors and ceilings. If you put the foam on the outside, you can span the rim joists. But you've got brick on the outside, so exterior foam is out of the question.

If you put foam inside the studs, it's probably silly to put open cell foam between the studs because XPS is less permeable than open cell. Use closed cell foam between the studs and skin a layere of rigid foam inside if you're really worried about thermal bridging. But in North Carolina, winter doesn't last that long -- even in the mountains, so my guess is that thermal bridging is less of a worry than say New England or Montana. Maybe a good compromise would be a strip of fanfold (3/8 in.) on the face of the studs (the first R is the biggest).

Hope that helps,

Dan
TheGreenBuildingAdvisors.blogspot.com