How do I create a complete air barrier using a vapour retarding primer?

Mihai Wilson May 3, 2018, 10:15 p.m.

After reading about vapour retarding primers on ecohome I am sold on using this technique to air-seal my 50's house after doing renovation work. The missing part is how do I deal with recessed lighting and electrical boxes that penetrate the walls and ceiling. Any tips on this? 

Responses (1)

Ecohome May 4, 2018, 9:14 a.m.

Glad you checked in First Mihai, because the short answer is that you can’t - the vapour retarder primer won’t do anything for air leakage. What it can be used for is to stop moisture diffusion, which means preventing the moisture in the indoor air from being absorbed into the drywall and permeating into the wall assembly.

If you saw the building science video about it where we used it at the Edelweiss House, we had an entirely separate air barrier in that wall assembly, a peel and stick membrane on the exterior sheathing (seen below). 

The confusion over managing air and vapour movement comes from the fact that usually one product (6-mil polyethylene) is  used as both the vapour barrier AND air barrier, but air leakage and vapour diffusion are actually two entirely different things.  (Read more about that here)

I’m not sure how extensive your renovation will be or what stage you’re at, but if you’re stripping the walls to the studs you can either go with an exterior air barrier (in which case the vapour retarder primer is an option since you've dealt with air leakage), or an interior air/ vapour barrier like the standard 6-mil poly. 

Feel free to give some details of what stage you are at and how extensive your renos will be and we can hopefully problem solve a bit with you if you’re not too deep into it yet.