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Community and Q&A

Air sealing in marine 4.

olandsns | Posted in Energy Efficiency and Durability on

I am building a small carriage suite and admittedly haven’t gotten too deep into this as I’ve really been focused on satisfying the building department.

our local inspectors here in coastal BC expect to see an interior air barrier, typically 6mm poly. I understand this is still acceptable in colder climates, but are we really that cold in marine 4?
where we will have a heat pump with some summer cooling do we risk moisture issues? Building will have an HRV. 

Am I better off to use the sealed drywall strategy? Will I, as an owner builder, be able to achieve the less than 3 ach I’m required to doing this? 

if you can point me to some resources I’d be happy to dig in. Thanks. 

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  1. Expert Member


    Problems with interior poly air-barriers occur primarily when they are used in warm climates with prolonged periods of air-conditioning where that (cold) side vapour-barrier allows the build-up of moisture over time. We simply aren't seeing that in houses here. Coupled with assemblies designed to dry to the outside, and the required rain-screen on walls, interior poly doesn't cause problems in coastal BC.

    If you do have some misgivings about using it, I'd suggest a variable-perm membrane instead - although you should run that by your inspector first. A plain reading of that code requirement makes no provision for anything over 1 perm to be used.

    Poly has a couple of advantages over air-tight drywall. The first is the code wants the interior poly primarily as a vapour-barrier (although in most construction here it serves as an air-barrier too), so you would have to coat the wall with a vapour-barrier paint for the gypsum to serve that function. Poly is also part of the accepted construction practices in BC, meaning it, and all the associated details, are familiar to all the trades - and being exposed it lends itself to inspection for its integrity, and for further air-sealing.

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