I am retrofitting a 1920’s era, balloon framed, south-half, east west semi in Toronto and am hoping somebody can weigh in on my approach. All my work is from the interior.

On the outside of the stud cavity there is plank sheathing ~1/2″ x 8″ with gaps and kraft paper. The west face is brick clad, and the south and east have aluminum siding with a minimal foam backing and shingles behind. I suspect, but am not certain, there is also brick behind that. I know builders can skimp on side and rear, but the same style neighboring houses are brick on all sides.

My plan is to install R14 Roxul in the cavity followed by MemBrain ‘Smart’ vapour retarder and latex painted GWB. The thought is that this will resist changing seasonal temperatures and vapour drives, and during the summer allow the wall to breath and dry to the interior. Based on Martin’s response about Latex paint perms in an early 2010 post, it seems like the paint and MemBrain will change fairly in tandem and therefor might be redundant.

My concern is that the brick will act as a reservoir and the asphalt and siding are not particularly breathable and I risk trapping moisture during times when the MemBrain is tightest. I will also have a gap in this system in the bathroom which we’ve decided not to touch currently and in the kitchen where it is currently insulated but without barrier. Those would be fixed in the next few years.

I am going to do the work myself, and am not interested in the spray foam.

Any thoughts are much appreciated.