What is the right approach to vapour retarder/barrier for my assembly in Atlantic Canada (zone 6)?
None, 6-mil poly, smart (variable permeability) membrane, painted gypsum board, combination, something else? Does a smart retarder perform better/worse with/without a service cavity (separation from vs contact with wallboard)? Specific product type, brand, installation method/details? Can anyone recommend a business in Atlantic Canada where I can buy this type of stuff?
Right now the exterior wall assembly from outside to inside is as follows:
-new vinyl siding
-new doors and triple pane windows
-new house wrap (IPG NovaWrap Aspire) plus proper peel and stick flashing details around doors and windows
-original 1″ rough boards (lots of gaps)
-original rough 2×4 balloon frame studs
-minimum 3/4″ gap
-new 2×4 walls (not balloon framed, interrupted by second floor)
The new walls are plumb and straight whereas the 110-year-old walls are not so in some spots the gap gets bigger and that gives me at least an 8.25” deep cavity for insulation in a double-stud wall. There is no exterior insulation, no taped osb/plywood, no expensive membranes/tape yet.
The walls will be dense-packed with cellulose (should come out at R30+ I think) and the attic will be at least R60, maybe up to R80, of loose-fill cellulose.
Thanks,
Pat
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Replies
Pat,
You need two things:
First, and most importantly you need a good air-barrier. Ideally, with board sheathing, that would have been a self-adhered house-wrap, but it sounds like that ship has sailed. I would use a combination of the new house-wrap you have used (carefully sealed) and whatever interior vapour-barrier you end up using to stop air-leakage.
Canadian codes require an interior vapour-barrier, so nothing is not one of your options. Where that goes doesn't matter much as long as it is close enough to the interior not to attract condensation. Practically, directly under the drywall is probably the best place. A variable-perm membrane is one option, but in your climate poly works well too, That would be my suggestion. Trades are familiar with it and know how to detail joints and penetrations - and it is more robust than most membranes.
Thank you Malcolm.
Yes, unfortunately, the exterior ship has sailed. We had to finish the outside completely differently than we originally envisioned and had to get it done during some of the more difficult times since the spring of 2020. Vinyl siding and regular house wrap was what we could accomplish quickly. I did get a price for Siga Majvest and Wigluv and almost fell off my chair. Its price and my worries that I wouldn’t be able to get it to stick as well to the boards as it might to plywood (which also wasn’t an option at that time) made me think I might spend a lot more money and only get a little extra performance. I could be wrong.
I am doing all of the work myself (I am a carpenter for a renovation contractor and this is my personal house) and did the best I could with all of the details and sealing.
The location for the interior membrane will be the interior stud faces of my inner exterior wall and I might do a service cavity further inward of that but I won’t be placing the barrier/retarder in the middle of my double stud walls.
In the fantasy land of perfection, if I did the best that could be done with the exterior, if I do the best that could be done with whatever interior membrane I choose, and if I have a properly size and installed ERV, am I more likely to get moisture from the exterior and is this assembly good for drying to the exterior? Or is that something that can’t really be predicted?
Pat,
I think with the work you have done and propose to do the walls will perform very well. Between the moisture buffering of the cellulose, and good ability to dry to the exterior it should easily handle any moisture that gets into the walls from either direction. I wouldn't have any worries.