Should I use two layers of 1 inch or one layer of 2 inch closed cell rigid foam board on the exterior? Locally we have available foil-faced on both sides. My understanding is to have only the exterior side foil faced. If using two layers of 1 inch, then should the board against the stud be unfaced?
I've read the articles on rigid board insulation on the exterior and concerns of condensation. I live in a warmer part of zone 5B at 3,400 ft. elevation.
The existing 2x4 walls built in 1987 are insulated with a 7/8" open cell board in the inside with fiberglass batt insulation, the exterior wrapped in kraft paper with a redwood lap siding. The plans are to retain the 1/2" drywall and 7/8" open cell foam board. Working from the outsiide the fiberglass will be removed and replaced with closed cell spray in foam, then OSB, Tyvek house wrap, with 2" closed cell rigid foam board with metal siding.