Replies

1. Expert Member
   BILL WICHERS | Feb 01, 2021 09:15pm | #1

   A vapor retarder is usually a safer choice than a vapor barrier on the interior when such a thing is required by code.

   Don't waste spray foam in a wall. While it's true spray foam gives a high R per inch number, the thermal bridging of the studs in a wall negate much of that advantage. Closed cell spray foam is especially bad here because it won't be filled to the full depth of the studs -- you'll have an air gap of around 1/2 to 1 inch on the interior side, which is around R3-R6 worth of performance reduction compared to what a full stud depth worth of spray foam would be. I would use mineral wool batts in the wall myself, along with a smart vapor retarder (Membrain, Intello, etc.) on the interior.

   I wouldn't use vinyl strips "for drying" here. I'd either allow for drying to the interior side only (which would be the case with mineral wool and a vapor retarder, for example), and I'd put the rigid foam directly against the sheathing. If you want more drying potential for the sheathing, use EPS instead of XPS -- EPS is more vapor open.

   Rain screens help a LOT with exterior drying, so you're good in your final exterior layers.

   Bill

1. 
   Malcolm_Taylor | Feb 04, 2021 06:35pm | #4

   Bill,

   Unfortunately the BC code requires an interior vapour barrier.

2. 
   johnwtaylor | Feb 04, 2021 05:28pm | #2

   Hi Bill

   Thank You for the response

   The 1/8" x 1 vinyl has been installed. This was done because the building inspector (who has now moved on) required a vapor barrier on the inside.

   It vinyl will reduce the effectiveness of the 1" XPS but I would guess it's similar to using mineral wool.

   Thank You
   John

3. 
   Malcolm_Taylor | Feb 04, 2021 06:34pm | #3

   John,

   Are you removing the cladding on the first floor, or do you hope to do all the work from the inside?

1. 
   johnwtaylor | Feb 04, 2021 09:29pm | #5

   Hi Malcom
   Cladding and Shiplap will be removed. The engineer wants the 2x4 balloon framing reinforced and sheer walls.

   It's hit and miss regarding air/water barriers. Our inspector said we have to have a vapor barrier. What he didn't tell us is we don't need a vapor barrier or even a vapor retarder if an Envelope Engineer gives the OK.

   Thanks
   John

1. 
   Malcolm_Taylor | Feb 04, 2021 11:45pm | #7

   John,

   If you build both the old and new walls with the assembly you have suggested (rain-screen and exterior foam), with batt insulation in the stud bays, an interior vapour-barrier, and drywall, you are reproducing (minus the rain-screen) what is now the standard wall assembly in Ontario. From all accounts it performs very well.

4. Expert Member
   BILL WICHERS | Feb 04, 2021 09:39pm | #6

   I think that's a code requirement for most, it not all, of Canada, correct? My brother in law is a builder outside of Toronto, and I remember when I first saw some of his projects I was surprised with the poly detailing EVERYWHERE. I didn't realize the OP was in Canada.

   Have you ever been able to use a smart vapor retarder instead of the poly vapor barrier? Have any inspectors been ok with that?

   Bill

1. 
   Malcolm_Taylor | Feb 04, 2021 11:51pm | #8

   Bill,

   It seems that with small amounts of exterior foam in the Canadian climate, poly vapour-barriers - as opposed to a vapour-retarder or variable-perm membrane - help improve the resiliency of the wall - or certainly do no harm. I think it was Jon who linked to a BSC article on the topic.