When I began remodeling my master bathroom last month, I found the exterior wall ripe for some serious improvement. It had a number of problems, and I was excited to find them.
It was worse than I imagined in some ways. The photo at right shows the wall partially opened up.
Yes, there was insulation behind the bathtub, but as usual, there was no interior sheathing on that section. Here’s a list of the problems I found:
Image #3 (below) shows the approach I took. I couldn’t do anything from the outside because of the brick veneer, so my first objective was to eliminate the air leakage pathways in the sheathing. I chose to use the cut-and-cobble method and put extruded polystyrene (XPS) foam board in the back of each cavity. I sealed the pieces of rigid foam into place with one-part spray foam and a professional foam gun. I had to tack most of them into place to hold them there while the foam cured.
The reason I chose XPS instead of polyisocyanurate is its better drying capability. A half inch of XPS has a vapor permeance of about 2 perms, making it a Class 3 vapor retarder. Polyiso, with its foil facing, has a permeance less than 0.2, making it a Class 1 vapor retarder.
On top of the XPS, I installed unfaced fiberglass batts. I chose unfaced batts because the kraft paper facing is unnecessary in an above-grade wall in our location (IECC Climate Zone 3). The paper facing also makes it harder to install the batts well.
I installed the batts with minimal compression and so they completely filled the cavities. Yes, because of the 1/2″ of XPS in the cavity, they’re all compressed a little bit in depth. Because they’re friction fit against the studs,…