Interior air barrier over batts
So I am getting near completing my flash and batt attic project. It is 3″ (r21 turned out 3″-4″) Gaco OnePass Low GWP, R30 Rockwool, 1-3″ polyiso furring strips on framing to increase depth.
There are areas behind knee walls and above the collar ties that will not have drywall directly on them (see photos). I am told batts should have a 6 sided air barrier. This will need to be a flexible product in my case at there is limited access to these spaces.
I am considering using Membrain or Tyvek.
Is there any benefit of one vs the other from a moisture standpoint? The foam is 1.7 perm @ 1″.
It is about $180 in materials for either product. Is an interior secondary air barrier worth it in this application?
(Sorry, all the photos need a 90deg clockwise rotation, not sure what happened)
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I would follow the recommendations here (and code of course).
IMO a second air barrier is beneficial, even more so with cold sheathing.
Hi Matt,
Your insulation strategy needs to be able to dry inward, because water vapor could possibly condenses on the inside surface of the closed-cell foam. I also think a secondary air barrier could be beneficial. Both of the products you are considering will allow for inward drying. So, for $180, why not go for it? Just pay attention to the details--tape the seams, maybe tape over the fasteners. To be effective, air barriers need to be continuous.
Thanks for the input.
How tear resistant is Membrain? The spaces I would be putting this are a bit convoluted, so it would be nice if it was not fragile. How's it compare to 6-mil poly?