Heat leaking through basement into garage
I’m trying to understand if it is expected to have some thermal transfer from the basement into the garage along walls that are shared with living spaces.
I’ve included three images. The first photo is pre-drywall. I added a red arrow where the heat is leaking out. Below the door is basement where the rim joists are insulated with closed-cell spray foam.
The second photo is post-drywall. I attempted to seal the the gap between the bottom of the drywall and garage slab with canned spray foam.
The final image is a thermal image that shows some heat leaking out of the bottom of the wall.
Is there something that is causing this? The basement walls (concrete) are currently uninsulated.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Did you spray the closed cell foam in the rim joists down to the top of the concrete foundation? If not, air could be getting through that gap.
This is what it looks like on the inside. Is it air that's leaking? Or just heat through thermal transfer?
Looks to me like heat is leaking by conduction, not air leakage. I'm guessing that you have at least 6" of foam in the band joist area, somewhere north of R30. You can see a little bit of thermal bridging at the solid wood joist ends and subfloor in the IR photo. But the warmest area looks like the slab itself It is probably being warmed by heat conducted through the foundation walls and into the slab. Concrete has very high heat conductivity and even if there is a mechanical seam between the wall and the garage slab, you're still going to have many times the heat loss there as you have in the band joists.
This is just one reason that foundation walls should be insulated. You're getting the same heat loss (or more) everywhere the foundation walls are exposed above grade and only a bit less where they are in soil contact.
In reply #1, mgensler asks about the spray foam installation. My recommendation is always as he suggests: Run the spray foam continuously down from the band joist area, across the sill plate, and down onto the foundation for a few inches. If there is interior rigid insulation on the walls, run the foam down a few inches onto that (SPF after the wall foam is installed). This achieves several goals: It helps to air seal the sill and band that are otherwise difficult to seal. It also helps to protect the sill plate from interior moisture condensation that can soak the sill and rot the joists. And it reduces the heat leakage that you are seeing in your thermal image.
Thanks. That makes sense.
When finishing the basement, my plan was to install 2 or 2.5 inch thick polyiso foam board on the walls, then frame. I would skip batt insulation entirely.
If I was to add more closed cell spray foam down across the sill plate and onto the rigid foam a few inches, would you frame first, then add the spray foam? Also, how high up the wall would you run the rigid foam? Right up to the bottom edge of the sill plate (don't cover it)?