Replies

1. Expert Member
   Dana Dorsett | Nov 11, 2019 07:14pm | #1

   And your IECC/DOE climate zone is...??

1. 
   Matt_Ohio | Nov 11, 2019 07:27pm | #3

   Dana,
   Would this wall assembly need a Poly vapor barrier on the inside prior to the drywall? I'm a bit confused on the CI, I believe I read that in Zone 5 you should have a minimum of R7 exterior, but due to multiple reasons that is not an option for this project.
   Thanks!

2. 
   Matt_Ohio | Nov 11, 2019 07:19pm | #2

   Zone 5

3. GBA Editor
   Brian Pontolilo | Nov 12, 2019 09:28am | #4

   Hi Matt.

   The international Residential Code calls for a class I (poly sheeting) or class II (kraft-faced insulation) interior vapor retarder in your area unless you meet one of two conditions. Those conditions are R-7.5 continuous insulation or a vented siding installation. You'll be meeting the second requirement, so you can choose to use a class III interior vapor retarder, which is essentially painted drywall.

   However, since you will not be meeting the R-value requirement with your continuous insulation, which is meant to keep water vapor from condensing on the inside face of the sheathing, I'd consider a smart vapor retarder on the inside, like the Intello membrane.

   I couldn't find the perm rating of the Thermo-Brace sheathing, but I don't think it matters, you'll want the most vapor open rainscreen assembly possible. Is there a reason why you are not considering a built system with furring strips?

4. 
   Jon_R | Nov 12, 2019 10:38am | #5

   Sounds like Thermo-Brace SIB is reversible - if so, put the foam to the exterior and then use below to verify the design.

   https://www.appliedbuildingtech.com/fsc/calculator

   IMO, not being forthcoming with perm values is a negative. Huber (Zip) also engages in this.