Insulating stone basement walls with rigid foam
If I install rigid foam insulation on my rough ashlur stone foundation it, obviously, will not fit flush against the foundation as it would on poured concrete of concrete block foundations. Will the voids cause problems or serious reductions in the insulation value?
I planned on sealing the edges; we don’t have much of a water problem in my area due to excellent sandy soil, so I don’t think I will be creating a moisture problem. I would use an appropriate adhesive to secure the foam directly to the walls and at some point perhaps use the same technique for green/blue board drywall. This is a laundry room so I don’t want it to look bad but, it’s not quite the same importance as if it were a Family room.
Does this make any sense as a possible method of reducing heat losses? Can anyone foresee problems with what I am suggesting?
Replies
The voids won't cause problems (other than for attachment) and won't reduce insulating value, so long as the sheets are sealed reasonably tightly at top, bottom and edges. And even with a less than perfect installation the improvement in comfort would be substantial.
Moisture problems are a possibility in general, but probably not in your situation.
Insulating stone basement walls with rigid foam
Thanks for the feedback.
You don't mention the type of foam you plan to use. I'd go with EPS or XPS, but avoid poly-iso. You want this assembly to be able to dry to the interior, because basement walls can't effectively dry to the exterior.
Also, I'd argue that you will have a bit of a problem with loss of performance due to convective loops (when trapped pockets of air heat up and rise, then cool off and fall, creating loops). Will it make all that much of a difference in a well sealed wall, in a basement, in a laundry room? probably not. And the benefits will outweigh the drawbacks.
I think the ridgid foam will work ok, but spray foam would be ideal here. When you finish the wall, consider paperless drywall rather than green/blue board.
Closed cell spray foam
I think that closed cell spray foam would be ideal for you job. Make sure it's closed not open cell.