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Fiberglass BIB Vapor Barrier

mritterjr | Posted in General Questions on


I’m in CZ4 and just had the walls of our new addition insulated yesterday.  They did the BIB system with blown in fiberglass.  It left me wondering if there should be any vapor barrier as the mesh netting certainly doesn’t qualify.  Is paint on drywall sufficient enough in this application, or should there be something added?  Wall assembly is pretty basic, starting from the outside:

Hardie – WRB – 7/16 plywood sheathing – 2×4 framing – blown in fiberglass – BIB netting – drywall.



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  1. Expert Member


    What did you use as your air-barrier?

    1. mritterjr | | #2

      there are actually 2 layers. The first layer is a cheap housewrap my contractor used (everbilt or equivalent). Outboard of that is the nice hardie fabric wrap. The rest has been air sealed with a combination of caulk, expanding foam, and siga tapes, mostly from the inside but a little outside as well (where the sheating meets foundation, etc.)

      1. Expert Member
        MALCOLM TAYLOR | | #3


        Perfect. So if you are only worried about vapour diffusion, and you are in CZ4, (not 4 marine), you don't need an interior vapour-retarder.

        1. mritterjr | | #4

          Good deal - thanks for the info!

          1. Expert Member
            MALCOLM TAYLOR | | #5


            I should have added: With two coats of latex paint on drywall, you end up with a class 3 vapour-retarder anyway.

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