Insulation on Mortared Stone Foundation

I saw something that I had never seen yesterday. Someone insulated the exterior foundation walls with sprayed-on cellulose. Then to make it even more interesting, it is a stone foundation.
The insulation is at least 19 years old, as the current owners have been lived here that long and did not do the insulation.
The house was built in 1890. It has settled quite a bit. The floors are quite uneven with slopes going in different directions in different areas of the house. There are only a few minor cracks in the house walls and ceilings, which the owner says were there when they moved in. I’m guessing that previous owners did quite a bit of pretty good cosmetic repairs to cracks that have not reopened. The exterior foundation has been parged, also more than 19 years ago. The parging is in excellent condition. So, it looks like the foundation is relatively stabile.
My question is about the insulation. Stone foundations are not exactly water resistant. The cellulose was in good condition. Typically, cellulose insulation is mold resistant and though, some of the insulation was slightly damp, there was no evidence of mold or other related deterioration.

Have any of you seen this done and do you know of problems thay might arise or be typical of insulating a foundation in this manner?

When cellulose soaks up moisture in enclosed areas, it can take a long time to dry out. Moisture dramatically cuts R-value and may lead to the formation of mold and mildew.

It’s treated to resist mold and fire but not proof. long term IMO wrong material for the job

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Was the area conditioned? If not IMO that’s a problem.

Even though there was no evidence of mold or any organic growth present at the time of inspection, I would think that it won’t be long before there is, especially in any area with a high moisture content or wet insulation on the walls. I can only imagine what the back side of that insulation looks like.

You guys make good points and I was expecting the insulation to be soaking wet, but amazingly, it was barely damp. The area is not conditioned at all. The area was not particularly humid. I could see the back side of the insulation in a few places and it looked pretty good. Gotta say that I was surprised it looked as good as it did. I told the owners that if someone had asked me about doing this, I would have said “No” and I still think it is not an advisable thing to do.

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One the potential risks… you can’t see when the actual stone foundation cracks or fails in the future.

Note that closed cell spray foam (SPF) is water shedding… to a point. Eventually the closed cell structure breaks down just enough that water enters. The stuff gets heavy and dries out insanely slowly. It’s like a sponge you can’t squeeze.

Termites might be an issue? They like cellulose, especially if in contact with the ground. I would at least hope there is an about a 6" inspection window up along the rim joist.

Cool find, 1st for me.

Not an acceptable food source

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Thanks Mark! (I would still want the inspection window me thinks :wink:)

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