Can I eliminate the water-resistive barrier and vapor barrier?
I am building a new float home in an area with high humidity and wind driven rain conditions. (Vancouver, BC)
I plan to use the following exterior rain screen wall construction method.
Hardie horizontal plank, with Hardie furring 3/4″ thick, over 1″ Styrofoam Weathermate taped, on braced 2X6″ frame construction. Stud space insulation will be high density closed cell, spray in place foam 3-4″ thick. Interior mold reistant 1/2″ drywall.
My question is, will this construction suffice to provide the indoor vapor barrier, the exterior water-resistive barrier and the air barrier without application of further building wraps and poly?
I plan to manage the indoor environment with an HRV unit.
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Replies
Jim,
1. Of course, you'll need to verify any proposed building details with your local inspector to be sure your plans meet Canadian code requirements. I know that coastal British Columbia has specific rainscreen requirements, but I am not familiar with all the details.
2. There is no need from a building science perspective (as opposed to a code perspective) for an interior vapor retarder when the stud cavities are filled with closed-cell spray foam. Closed-cell foam is a vapor retarder.
3. Some building science consultants recommend flashing details that allow the use of exterior foam sheathing as as WRB. Not all builders or inspectors agree with this method, however. Read more here:
https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/12284/do-i-need-house-wrap-under-exterior-wall-rigid-foam