Concrete over above-grade rubble foundation
I was visiting a home the other day, primarily in search of no/low cost energy improvement opportunities, when the customer asked about insulating his rubble foundation. I recommended ccSPF of course with a poly lining on the floor and up the sides of the walls to create an air and water tight assembly.
Upon leaving, I noticed that the exterior of the above-grade foundation seemed to be covered by what appears to be concrete. I couldn’t quite tell as most of his foundation was covered by snow. From the interior however this rubble foundation runs right to the sill, and I couldn’t see any evidence of a poured material.
Has anyone else seen something like this? Is it a common practice? I didn’t think so, but I could be wrong. It makes me wonder then if its still worth adding spray foam to the interior, since the majority of the leakage would have been from the above grade. Thoughts?
Thank you
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Mike,
Yes, I've seen examples of old rubble foundations that have been retrofit with parging or stucco. I've also seen examples of using one-sided forms to pour a thin layer of concrete against an existing rubble wall.
I'd like to remind you, however, that there are at least two reasons to consider installing spray foam. One reason is the one you mentioned: reducing air infiltration.
The second reason is to reduce heat flow by adding R-value to the wall assembly. Even if the foundation wall has a low level of air leakage -- and your comments don't really prove that the air leakage rate is actually low -- the wall could still benefit from improved insulation.
Martin,
Thanks for the response. I agree, without having had a blower door and IR camera I couldn't get a good sense for the air leakage. The snow backed up on the foundation likely made it appear as if it wasn't too drafty, although the cob webs throughout the crawlspace indicated otherwise.
I also agree that, aside from air leakage, adding R-value to the wall assembly would also be beneficial. Thanks