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Condensation at tape joints

user-7182223 | Posted in General Questions on

I have a relatively new home in VA, zone 4 that has a few 2nd floor walls that are adjacent to an attic space. the 2 by 4 walls were insulated with R13 fiberglass and 2 inch foam board (between the studs and attic, green stuff from lowes). Joints were taped with 3m vapor barrier tape. 

I’ve noticed in Nov. , early Dec. (When the house humidity is still in the mid 40s and it drops into the 20s at night) I get a small amount of condensation behind the tape. Haven’t noticed any mold or issues directly behind the foam board.

My thought are to use a couple inches of closed cell spray foam at all the joints to prevent this in the future.

Curious of thoughts or other options from the experts?

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  1. Expert Member
    Zephyr7 | | #1

    You probably have some air getting to the backside of the tape through the gap between foam panels. We call those "three dimensional airflow pathways [or networks]". In your case, it's probably not a big deal and should be a very small amount of condensation. If you're concerned, inject some canned foam into the gaps between foam panels. You don't really need closed cell spray foam here, canned foam works fine.


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