Reducing heat loss and moisture in a stone basement
I’m more concerned with moisture than I am with heat loss. I have a full basement in my 140-year-old house. The floor is crumbling concrete; the walls are limestone up to grade and brick above that. I’ve gone around the sills, doors, and windows with spray foam and taken care of much of the air infiltration. I still need to deal with getting gutters to drain farther from the foundation and I could stand to do some grading around the house. The yard is pretty much flat but it wouldn’t be too much trouble to drain gutters to nearby hills. The soil is coarse sand.
What’s the problem? The basement is dry all winter but starts to get so humid this time of year that I can’t stand to be down there for more than a few minutes; there’s serious mold growth – I can feel it when I breath. The more humid it feels, the more damp patches there generally are on the floor – but they’re never very wet and are not near the walls. My first impression is that the water table is rising and seeping through the old slab; or could it be condensation? I can also tell which parts of the walls have routinely been damp because of spalling limestone and brick – it’s not all over the wall, but in isolated patches here and there. Only once in five years has water visibly come in through the walls and this was due to a blocked up gutter and soil erosion near the foundation.
What’s the solution? I’m pretty comfortable dealing with the floor (EPS, poly, and a new slab on top?), but I’m worried about any of my options for the walls because I’m not sure if any of the interior insulation/wall systems I might use would trap moisture and increase the spalling. This makes me think that my first line of defense for the walls should be on the exterior. I’m prepared to dig down a foot or two (in most places) if some sort of water shedding system would be ideal (poly and XPS pitched away and buried?) and I realize that I should get the downspouts farther away from the foundation. But I would really like a solution that allows me to fully insulate and air-seal the whole space and still be confident that I’m not compromising the durability of my foundation.
What would you do?
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