Solar vapour drive a concern?
jchwang
| Posted in Green Building Techniques on
How risky is solar vapour drive in zone 6 toronto which experiences hot humid summers? And increasing occurences of severe thunderstorms? Have what I think is a non-resevoir cladding (2 metal skins with polyiso foamed in btw like a SIP but dependent on caulking at joints, over 2″ mineral wool, Tyvek Drainwrap, plywood, 2×6 with mineral wool batt, ? and drywall. Not sure of Tyvek and whether ? layer is needed. Thx.
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Replies
Jerry,
Your cladding (metal) is vapor-impermeable. You don't have to worry about inward solar vapor drive.
You also asked about Tyvek. Tyvek is a water-resistive barrier (WRB). Every wall needs a WRB, because it is required by code. There are many options, however; you don't have to choose Tyvek. For more information, see All About Water-Resistive Barriers.
I'm not sure what your "?" refers to, but I'm guessing that your question concerns interior polyethylene. While interior poly is still common in Canada, and is in fact sometimes required by local building inspectors, I don't recommend that you install any interior poly. If your building inspector insists on seeing a membrane that comes in a roll, I suggest that you install MemBrain -- a "smart" vapor retarder -- not poly.
For more information, see Do I Need a Vapor Retarder?
Thank you. Puts my mind at ease as I wasn't sure if moisture in the air inside my Roxul layer would be a problem.
And yes, my '?' was asking whether I needed any interior vapour barrier to stop interior moisture from getting into the 2x6 cavity, and if so, what should that layer be?
I was thinking MemBrain as well, but will read both articles you refer to. Thanks.