I'm considering replacing the old fiberglass insulation in my century-old home's basement with rigid foam board and sealing the edges with Great Stuff to air seal it. However, I'm worried about potentially trapping moisture in the basement, especially since it's an older home. Would this be a concern just because I'm using foam, or only if I were to fully spray the foam in all the cavities? I live in the Midwest where winters can get really cold. I should also mention that some parts of the basement ceiling are finished, making certain areas of the rim joists inaccessible for insulation. If I can only insulate about 50% of the rim joists, is it even worth doing?
2 Answers
Be cautious with rigid foam board since it can be flammable. You might want to think about covering it with drywall for safety or consider other insulation options. Just a heads up!
Polyiso boards are good; they’re thermoset and won't melt like others, but they might not perform as well as cheaper options. Just something to consider!
How old is your home exactly? The type of exterior sheathing and siding around the rim joist is also important. Knowing what your rim joist sits on and the foundation wall material can change the best insulation strategy.
My house is 99 years old with regular vinyl siding. The rim joist seems to be on particle board with a cement foundation wall.
I was thinking about using rockwool over it too for added protection and better R-value, but there are still lots of spots I can't reach.