Vapour barrier vs retarder in wall assembly
We are mid build in climate zone 6 (Bancroft, Ontario) and the more reading I do on vapour barriers the more confused I get.
We have R5 silverboard HD XS (micro perforated) on the exterior with taped seams and siliconed at the top, with 2×6 walls and R20 fiberglass. The 1″ R5 isn’t enough to ignore a vapour barrier, and our code requires it.
So the first question is, am I going to regret regular 6mil poly? I’m not sure we can afford the upgrade to something like Membrain, but were we to, is there any need to use it on the ceilings? It was my understanding that a big part of why a retarder is recommended instead of poly was because of the R5 foam, so maybe the ceilings can be regular poly? Does the micro perforation change anything?
My head hurts…haha
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The assembly simply works, it has been build in Canada for a long time. As long as you detail your rough openings properly to limit bulk water issues, you won't have problems.
https://effectiver.ca/calculator/wall.php?id=7073
Since you are using somewhat permeable exterior insulation, the wall can dry to the exterior which does help.
With the silly cost of Membrane up here in the great white north, it is simply not worth it.