Does using T & G wood plank instead of drywall affect where we put the vapor & air barrier?

Sue Colbourne
Updated: Aug. 26, 2020

We want to use fir T and G for our interior walls instead of drywall (new build with plywood exterior sheathing and Tyvek - which will eventually have cedar shingles). What's the best thing to use for air and vapour barriers and where should we put them in the wall assembly so they work best? 

Responses (3)

Sue Colbourne 4 years ago
Mike Reynolds 4 years ago

6 mil poly barriers are actually not as a big a problem with ceilings, the vapor drive isn't quite as problematic as with walls. In the Edelweiss Demo House we used vapour barrier paint on the walls but we used poly on the ceiling. As for your building inspector, that could go either way, so if you want to try vapour barrier paint (or vapour retarder primer) check with an inspector ahead of time. As for the toxicity, We used Benjamin Moore vapor barrier paint which was low VOC but not Zero VOC unfortunatetly. 

The honest answer is that from a scientific point of view, painted wood will actually act as a vapour barrier, meaning vapour will move through it so slowly that it would qualify as a vapour barrier, but it is highly unlikely youll find a building inspector to accept that for new home construction. And I say that with the caveat that you should not even consider that if you don't have a proper air barrier in some other form. Be sure to read this page about the difference between Air Barriers and Vapour Barriers as they are often combined in one product but perform completely different tasks.