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Community and Q&A

Gaps Between Stud Wall and Foam Board

aberrant | Posted in General Questions on

In the middle of finishing my basement in MA. I’m at the point where I’m insulating. I have a 10″ poured concrete foundation. I used R7.5 rigid foam board directly against the concrete and taped the seams as my continuous insulation layer/vapor barrier. I built my 2×4 walls directly in front of the foam board however due to the walls not being plumb/level there are gaps between the stud wall and the foam board. In some cases these gaps are up to 2″. I’m using Roxul R15 in the 2×4 stud walls.

I opted to push the Roxul up against the foam board instead of flushing it with the front of the studs which effectively in some cases will create an air gap between the Roxul and the drywall. From all the reading I’ve done it seems that it would be better to have that air gap between the drywall and the cavity insulation than between the cavity insulation and the foam board.

Did I do this the right way? Will that up to 2″ air gap between the Roxul and drywall create issues? Do I need to use a vapor barrier before I drywall? Should I have left the air gap between the foam board and the Roxul?

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  1. Expert Member


    You are fine. You don't need an interior vapour-barrier, and the gap behind the drywall is not a problem.

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