Hello. We are in the process of building a new home and are making enhancements to the envelope. What we have done is add 2" of EPS (Amvic Silverboard with seams taped) directly on the OSB sheathing. Walls are 2x6 studs w/fibreglass insulation in between. I want to make sure I don't run into future moisture/mold issues, so my question has to do with what needs to be done to allow the wall to dry if it gets wet. My understanding is the 2" of EPS should significantly reduce the chance of any interior moisture condensating because in the winter it keeps the OSB above the dew point (we are building in Niagara Falls, Canada). I also believe that although EPS is permeable, my safest option is to allow walls to dry to the interior should it get wet. Is this correct? If so, could I accomplish this by not installing the interior vapour barrier? Thank you.

It looks like Silverboard is substantially less permeable than unfaced EPS. Cellulose works better than fiberglass. Plywood works better than OSB. IMO, a smart interior vapor barrier (like MemBrain) works better than either poly or nothing. Adequate roof overhangs and rainscreen gaps help too.

EPS will breathe. I believe 2" is (from memory) 1.5 perms @ 1 inch so likely just under a perm at 2"? Well, it depends is your EPS type 1 or type 2?

As jonr said, and what I'm doing, is to use a smart vapor barrier (intelloplus or membrain). MemBrain for me (Chicago) is impossible to find for some reason even though it is a CertainTeed product. I plan to get IntelloPlus online delivered to my site. I am using 1.5" XPS on my exterior.

Thanks for the advice. I will talk with my builder to see if his insulator has a smart vapour barrier product.

Hello Again, I'm still struggling with whether or not a smart vapour barrier is necessary and/or worth the additional cost. Can anyone provide me with the pros/cons for either scenario (no vapour barrier vs smart vapour barrier)? My biggest concern is allowing my walls to dry to the interior should moisture accumulate. I am not concerned that the moisture will enter the wall due to a leak from the exterior/roof, I am focussing on moisture as a result of interior air. The house has an HRV and the 2" Silverboard foam should drastically reduce the chance of the OSB sheathing from getting so cold that humid air condensates when it comes in contact with it. Any information or past experience will be very helpful. Thank you.