Hello, in my quest to work out kinks in this basement in terms of vapor retarders and barriers, I have discovered another scenario that isn’t clear to me with regard to where one places vapor retarders on an exterior wall. The home in question is in zone 6 (WI).

This situation involves a bathroom, and this bathroom has one wall that is an exterior wall.  This exterior wall is half below grade and half above. The half below grade has 1-1/2″ XPS glued to the foundation wall. There is a 3/4″ gap between the wall XPS and 2×4 stud wall, and this stud wall is filled with fiberglass and extends to the ceiling in part of the room.

Now…where would we want to provide VR? I have come to understand (or think I do) that it’s generally not recommended to use VR on inside walls below grade. I think it will be not that easy to somehow “separate” or seal off the below- and above-grade sections of this wall.

Is there a typical way to handle something like this? Does it make any sense whatsoever to install VR on upper part of the wall only, and leave the bottom open, even though the stud cavities run from floor to ceiling?

Thank you.