Do I need a vapor barrier over rigid foam in a basement?
If you already have rigid foam against the concrete, you generally should not install an additional polyethylene vapor barrier over your framing. Conflicting advice leaves homeowners guessing whether a 6 mm poly layer is required before drywall, making it difficult to finish basement walls with confidence.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Consulting building codes and inspector opinionsDid this help you?
- 2Relying on the rigid foam to act as its own vapor barrier without adding polyethylene sheetingDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I've seen very mixed reviews, do I need a 6 mm poly vapour barrier on top of my studs/batts before drywall? Or do I not need it since I have the XPS?”source ↗
“With that amount of rigid Foam against the concrete you should not put up a vapour barrier.”source ↗
Where this came up
People with this problem also raised
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