I’m installing 1/2″ Owens Corning XPS before I reside with FC. I was using 3/4″ t&G but thought I’d get better results with the siding with thinner foam. I’m about halfway through 1 wall and I notice that the O-C 1/2″ has a film on both sides, unlike the 3/4″. They note that this is to increase strength while installing. I’m concerned that, unlike the 3/4″ unfilmed XPS, the thinner foam will be a vapor barrier (versus a vapor retarded) and in which case I’d have two vapor barriers and a mold machine.
Should I remove the film on the 1/2″ xps? I was on the O-C website and they make no mention of this issue.
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Where do you live. (No profile to tell us.)
North of Minneapolis/St. Paul
In theory, you might be creating a problem, but I'm thinking that by the time you've driven a few thousand siding nails through the foam you're giving plenty of opportunity for vapor to pass to the outside. In addition, assuming your interior vapor barrier is actually effective, and you pay careful attention to flashing and detailing your siding, there should be little vapor within the wall to feed the mold. The spores are already there, but if there is no moisture, it shouldn't be a problem.
I say carry on (although I would would have used thicker foam and strapping to hang the siding). The minimal R value of 1/2" foam is hardly worth the effort though I suppose it's better than nothing.