Housewrap under Roxul Comfortboard IS?
We are designing our new house in the PNW in a Marine 4 zone. The walls will be 2×6 with Rock wool batt insulation. We are planning to use plywood CDX sheathing taped or otherwise sealed as the air barrier. 2″ Comfortboard IS would go on the outside of the CDX with furring strips for a rain screen under the siding. Siding will either be clapboard or cedar shingles if I can figure out how to do the attachment efficiently to the furring strips (may have to have horizontal over vertical furring strips).
My first question is: do I need a house wrap type WRB between the plywood and the Comfortboard? Roxul insulation guide recommends it, but I don’t understand why. The vented rain screen and Comfortboad will keep the wind driven rain off of the plywood. The Comfortboard is supposed to be water resistant with a high vapor permanence to allow for drying of any liquid that would get behind the siding.
My second question is: what is the best technique for sealing around the windows and doors since one cannot tape to the Comfortboard? Perhaps this is ultimately the reason for the WRB, but then perhaps it should go on the outside of the Comfortboard.