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How to achieve an air barrier

ross_n | Posted in Green Building Techniques on

I am building an oceanfront cabin in the Canadian Gulf Islands. I am not concerned about a vapor barrier but want to know the best way to achieve an air barrier. Interior cladding will be T&G pine (not drywall). Exterior siding will be cedar board & batten.

It has been suggested that I use a polyethylene “vapor barrier” on the inside of exterior walls under the T&G. I am reluctant to do this, as I am concerned about penetrations affecting the integrity of this air barrier. I am also concerned about possible moisture problems resulting from a polyethylene vapor barrier.

It has also been suggested that I use taped Tyvek (or a similar product) on the outside of the sheathing to create an air barrier. Again, I am concerned about numerous penetrations of this barrier (nail holes for siding etc.). Also, I have a preference for two layers of building paper (vs Tyvek) for the exterior drainage plane (the building will have a rain screen).

A third opinion is to sheath the building with ½” plywood and tape all seams to achieve an air barrier. Exterior of this would be the double layer of building paper, rain screen, then siding.

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  1. GBA Editor
    Martin Holladay | | #1

    The last option you listed -- taping the plywood sheathing with high-quality tape -- is the best of your listed options, and is the option most commonly used. (You could also use Zip System sheathing and Zip System tape.) For more information on these issues, see these two articles:

    Return to the Backyard Tape Test

    Airtight Wall and Roof Sheathing

    Remember: You'll need a plan to extend your air barrier over your ceiling, and you'll need a plan at all transition areas to make sure that the air barrier is continuous.

    You didn't mention what type of insulation you plan to install between your studs. If you are thinking of using an air-permeable insulation like fiberglass or mineral wool, you also need an interior air barrier. (Otherwise, a small flaw in your exterior air barrier will pull lots of air through the cracks between the boards on your wall.) The standard solution is to install drywall and tape the drywall. Then install your T&G boards on the interior side of the taped drywall. Ideally, your electrician will install airtight electrical boxes as well.

  2. Dana1 | | #2

    The interior t& g needs to be air tight too, unless you are insulating the cavities with inherently air-tight foam. Otherwise air transported moisture WILL convect into the cavities and become adsorbed into the exterior sheathing over the winter.

    You might get away with it if the exterior sheathing is asphalted fiberboard instead of plywood, but it would be far better to use a layer of thin gyprock or thin plywood detailed as an interior air barrier between the t & g pine and the rest.

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