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Community and Q&A

Bonfiglioli wall/air vs. vapor barrier/paint?

Colleen65 | Posted in Green Building Techniques on

Hi –  Doing my first major project and know just enough to be dangerous, so please bear with me…  We have a 1962 ranch in Central VT, climate zone 6.  Winters usually dip below 0 degrees for several weeks, summers are often humid and can reach the 90s at times – I expect this will be more common in the future due to climate change.  Poorly insulated (R7?)with holes at the top and bottom of each stud bay to allow the wall assembly to “breathe”.  Several people told me that’s not done any longer and just increases the draftiness of the house.  Condensation on the walls on the bedroom end of the house (we lower the heat in those rooms in the daytime), some mold, can’t put furniture against the walls in those rooms.  Ventilation is an issue, so we’ve recently started running dehumidifiers in the bedrooms.  Exterior was painted 2 years ago, so husband and I decided it made no sense to ruin a $6000 paint job to add anything to the exterior.   Couldn’t get on anyone’s schedule for at least a year and not really in the budget anyway.   In June I decided to do it myself.  Original plan was to gut the walls, deal with any mold damage on the framing (thankfully there was none), replace R7 with R15, and re-sheetrock.  Then I discovered GBA and read about the Bonfiglioli wall…

Six months later, I have the following wall assembly: wood clapboard siding, tar paper (not sure how intact it is, but what I could see looked OK), plank sheathing, 2×4 studs furred out to 2×6(ish) with 1″ polyiso strips and 3/4″ plywood strips screwed into studs with 4″ decking screws (planned on 1″ plywood but local store said they only had 3/4″, so figured I’d smoosh the insulation 1/4″, knowing I might knock off a bit of R-value), 5 1/2″ mineral wool insulation, Certainteed Membrain, gypsum board.  The holes in the stud bays were filled with foam, interface between stud bays and sheathing were caulked.  Membrain was sealed with caulk and taped according to directions, but I did have spots where the drywall screws got twisted up in the Membrain, leaving holes.  Drywall seams were taped and mudded with 3 coats.  Here are my questions:

1) Does anyone see any fatal flaws with what I’ve done so far (a little late to ask, I suppose)?  Praying I don’t need to re-do anything…
2) The more I read, the more confused I’ve become about which part of the assembly counts as an air barrier and/or vapor retarder.  I thought the Membrain was supposed to be both, but not much of an air barrier with the holes in it.  But I’ve read some Q&A here that said holes don’t matter, that sheet rocking using tight seams and thorough mudding would count as an air barrier.  But do I want an air barrier on the interior if the whole assembly was designed to dry to the interior during the summer?
3) What kind of paint to use?  I think it needs to be permeable, but how many perms?  At one point I read that regular acrylic/latex isn’t permeable enough, then I read that latex paint IS good enough.  Mineral paint is quite expensive and not sure if it’s necessary.  I read that the joint compound and gypsum board will absorb paint differently, so needs a primer/sealer.  But I would think a primer/sealer wouldn’t be permeable enough.  Is there such a thing as a primer without the sealer?  Most brands of paint I can’t even find permeability ratings.  Would love some guidance here, ideally mention of a few brands that would work in this situation, especially if they’re easily obtainable.

Thank you for any advice or direction.  I have learned SO much from this website!

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  1. Expert Member


    1) It sounds to me like you have done a great job, and should have no worries.
    2) Your combination of the sealed Membrane (with the odd hole), and the drywall should provide a fairly effective air-barrier. The Membrane will function well as a variable-perm vapour retarder.
    3) Your walls have good drying in either direction. You don't have the same concerns with summertime drying as you would if you had a vapour-barrier on the interior (the Membrane being variable perm removes this concern). You can use regular latex paint on the interior.

    1. Colleen65 | | #2

      Thank you, Martin, I appreciate your reassurance. I've picked out the paint and can't wait to get the room finished! Then on to the next...

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