I'm working with a general contractor who is building my house. I also work as a builder. Our wall system is drywall, 2x6 spruce, 1/2"cdx, 4" XPS, ?, sheathing, white cedar shingles treated with bleaching oil. My builder wanted to put tyvek over the inner sheathing, which I talked him out of. He also would like to create a drain plane between the foam and the outer layer of sheathing, and then use felt or building wrap under the cedar. I'm wondering if we could skip the furring over the foam and then use a draining housewrap, (which I've never used, and it's not generally available in this area)between the sheathing and the shingle back. Any thoughts or advice?