My contractor is using 2x6 construction, plywood, then tyvek for better water drainage, and then 1 inch xps foam blueboard on the outside with taped joints. I understand the permeability of blueboard is not technically impermeable but I believe it is close enough without the problems of cell phone reception that the foil face gives. I worry about using the tyvek behind the bluboard though. If it acts as a water barrier(not vapor) and traps water behind the foam then wouldn't that set up for mold growth. Just wondering? And what are ya'lls thoughts on roxul wool board sheathing. I would have to use a seperate vapor barrier with that I assume. And the smallest is over an inch would derail my current architect details. Thanks

I'm not sure how much drainage the Tyvek is going to get you sandwiched between sheathing and blueboard. There are products that can actually create a drainage plane there if necessary. Where are you that you have to have a foil faced barrier?

It was recommended because im having brick exterior and in Memphis TN the heat would drive the dew into the house every morning.

The best answer to the moisture driven inwards from a brick exterior is Greenguard DC14. You could possibly eliminate the Tyvec if you used a taped and lapped joint between the upper and lower DC14 (it is an approved WRB when used this way). The DC14 provides a drainage plane on both sides and it has relatively little moisture permeability. You'd probably still need the exterior foam as just plain insulation.