Wall assembly feedback
Hey folks,
after digesting lots of information on this site and reconciling that against local build codes this is the wall assembly we’re looking to use in our new build.
From the inside to outside we have
-Latex paint
-Drywall
– 6 mil polyethylene – class I vapour barrier
– 2×6 studs with batt insulation
– 7/16 OSB sheating
– 1″ – 1 1/2″ inches of exterior insulation. Currently looking at graphite infused EPS as it is at least a bit permeable
– Tyvek
– Rainscreen
– Exterior siding
我们的建筑区6。Windows将外windows. Everything will be properly flashed on the outside as it should obviously be. Regarding the interior vapour barrier, I understand that this goes against what many people oi this site would like to see but in reality, this is a strict building code requirement. Inspectors in my area will simply not allow you to forgo this.
Couple of questions for the community…
Any feedback you’d like to provide?
With respect to air sealing, provided that the interior vapour barrier is properly detailed, from the inside out, the house should be fairly tight. With that being said, is there any point with this type of assembly of taping joints on the outside sheathing? Or for that matter, the the exterior insulation?
Thanks all.
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Replies
Hi Eric,
I think there is value in detailing the sheathing as an air barrier. With fiberglass insulation it is best practice to air seal the stud bays on all six sides. Your project will benefit from as much air sealing as possible. And it is a good idea to test the effectiveness of the air sealing work with a blower door test.
Eric, from your description, the only thing you're doing that goes above code minimum is 1" to 1.5" of exterior foam and a rainscreen, but that's better than doing nothing. It's too bad about the class 1 vapor retarder but I know that's a hard requirement in a few behind-the-times locations. I agree with Brian; air sealing may be the most important thing you can do. I find that taping the sheathing is the easiest way to get a good air barrier, but with air-permeable insulation you need to make all sides airtight.
It would be better to use enough exterior insulation that you aren't putting yourself at risk of moisture accumulation. In CZ6, with R-21 in the walls, you need at least R-11 on the exterior, and more is better. You might be ok with the permeance of EPS or GPS (graphite-infused EPS) but I would either increase the thickness or use a more vapor-open material such as wood fiber insulation board or mineral wool to make sure the wall can dry easily to the exterior, since it's not going to dry to the interior at all.
Most builders find it easier and better to locate the WRB at the sheathing layer, rather than at the surface of the foam. But either way can work.
+1 on all of the above. Make sure that the foam insulation is > 1 perm (no impermeable facing). Other things what will improve the wall are plywood, cellulose and HydroGap WRB on the sheathing.
Note that Winter indoor humidity makes a huge difference - keep it just a bit lower and your wall will perform better than other designs (for example, more exterior foam).
Thanks for the feedback everyone. I'll put the effort into air sealing the outside of the walls for sure.
Eric you mention "batt insulation", which varies from basic fiberglass R-19 to high density fiberglass or mineral wool as high as R-23. Your nominal wall insulation could total R-24 to R-30, depending on your choices including thickness of exterior GPS/EPS (before deducting for thermal bridging). That's not a lot for such a cold climate.
Your insulation will last indefinitely, and won't be upgradable easily. 1.5" of exterior insulation would reduce the risks of condensation, mold and rot in your walls if your interior air & vapor barrier isn't perfect over the decades. Your comfort and lower utility bills would be better with insulation upgrades despite higher initial costs.