Vapor Retarder or Not in Zone 6
I’m trying to get some additional opinions on a house I’m currently building. One of the comments back from my plan review highlights the following:
“R601.3 Vapor Retarder: Class I and II vapor retarders shall be installed on the interior side of framed walls in Zone 6A OR per code section exceptions”
My wall assembly is planned as a simple 2x6 with blown fiberglass and exterior ZipR3 sheathing.
I wouldn’t have considered a Class 1 retarder due to concerns with trapping moisture in the wall assembly but I’m equally concerned about no being able to dry out the wall or trapping moisture inside the assembly.
Anecdotally I know a few building science nerds in the area and they recommended not using an additional retarder on the interior side of the wall.
The ZipR has less than 1.0 perm rating so having another interior side perm rating for Class II. Less than 1.0 has me concerned.
Any additional thoughts would be appreciated. Above is a wall section detail from my plans.