I am doing a bathroom remodel, poly plastic vapor “barrier” was on the the outside wall under Sheetrock and on a part of the ceiling, it was not in the bathtub tile surround drop down ceiling I tore out to get to a full height ceiling, but is there on either side of that portion of the ceiling. I tried to search local code but didn’t find what is required, it talks a lot about exterior walls, but I am led to believe just paint Class III is acceptable. This question is only for areas outside of the Wedi waterproofing in the shower tiled area, and I plan to use the wet area Sheetrock beyond. I saw videos saying don’t use poly, it would be worse than nothing and never on ceiling because the roof is vented. They also say never call it a barrier because it is not. I am in Zone 5 in Colorado, a very dry climate. I originally thought I’d just use some 6 mil to complete the missing areas, get some fancy tuck tape to repair breeches etc. I tried to look at what kind of vapor retarder is needed in code and saw information that said it has to be marked with some ASTM number, which I don’t think the regular type of poly at HD has. I will probably check with RBD to confirm since I pulled a permit, but what a confusing subject for a DIYer, and based on my research it is not straightforward even for some builders. Anyone can say what should be acceptable? Take out the poly, keep it and fix, walls and ceiling? replace with something else?

  • Is the poly located on the interior or the exterior side of the wall? Commented Apr 26 at 2:24
  • 1
    Interior of the outside wall.
    – Billyboy
    Commented Apr 26 at 11:30


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