Wine Cellar Question #71

Hey there,

I’m aware that if one uses spray foam (e.g., closed cell) insulation that a separate vapor barrier isn’t needed. My question is, would there be a downside (aside from cost/labor) to installing a 6mm vapor barrier in addition to the spray foam? And if you did install one, I’m assuming it would go immediately outside the insulation?

Thanks in advance,

Jeremy

Bump

Jeremy
A quick google turned up some in depth articles about places where a double vapor barrier works, but my take away (and understanding of building codes) is that in almost all applications it’s not a good idea. I don’t see a reason to try, and the downside can be condensation and the resultant issues inside your wall assembly.

https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-092-doubling-down—how-come-double-vapor-barriers

Thanks, Andrew. I was thinking the same. My only reason for considering it was that, if the spray foam doesn’t completely cover the studs (I’m building out a room with concrete walls) then there would be gaps where the vapor barrier existed.

Yeah, studs are a complicating factor… we call that “thermal bridging” in construction, which can cause issues even with vapor barriers etc. I’m inclined to think that in this case it won’t matter.

If you wanted to really go down a rabbit hole, you could- use metal studs, or use standard studs in an “advanced framing” framing pattern. I’m not under the impression that either of these would be needed in building a cellar, but it might be fun to play around with it if the idea strikes you as interesting.

Ok…What about placing the studs 24” on center vs. standard 16”? They aren’t load bearing, and it would allow for more efficient insulation.

Yeah, that would work fine.