Insulating a basement wall
user-7275733
| Posted in Energy, Heating & Insulation on
We would like to finish our 2008 built basement in south east Michigan. There is no exterior insulation on the poured concrete walls.
The concrete walls have a stamped brick pattern on the inside and we were wondering if it is ok to use closed cell XPS/EPS panels, or is it necessary to use closed cell spray foam to prevent any air gaps between the wall (with the brick texture) and the insulation.
Our goal is to prevent any mold.
Also, is there any difference between the blue DOW and the pink Owens Corning insulation panels?
Replies
Closed-cell spray foam is so dense that it is difficult to trim. That’s why installers of closed-cell spray foam never fill a framing cavity completely. In a 2×4 wall, the installer will usually stop at a maximum depth of about 3 inches instead of 3.5 inches, leaving the typical bumpy surface of cured foam. This type of installation doesn’t need to be trimmed.
Investigate using InSoFast panels. The picture shows installed panels being covered with drywall
I used XPS panels in my basement, gluing the panels together with PL 300 foam board and keeping them up off the floor and with a good sized gap in the corners where i was able to spray great Stuff XPS to fill the gaps. Seams and fastener heads were taped.Then i built a 2x wall and added mineral wool insulation. I selected this approach because we could work in an area while using the rest of the basement, otherwise it would have been faster to have built the 2x wall and then spray foamed the entire cavity with closed cell foam, ending up with nearly the same R values.
One advantage of the closed cell spray foam is that it makes it easier to insulate the rim joist/top of concrete section. It was a lot of tedious work to cut the foam board attach to the rim and seal around the foam board/ top of cement, but with patience it can be done well.
The floor also has XPS 1" done in a similar way, but with ply on top. While i don't have any tests done to confirm the technique, the basement is the warmest part of the house! That's not bad for -25 deg. C / -13 deg. F winter!
There's nothing wrong with using XPS (the pink and blue are the same in terms of performance) over your brick textured surface. The key is to get a good seal from piece to piece, and all along the floor and where the foam ties in at the top of the concrete. You want to create a barrier separating the cold, potentially wet concrete from the warm, potentially moisture laden indoor air. Spray foam would work and be easy, but there's no problem with rigid foam if you want to go that route.
- Justin
Fine Homebuilding