Dry-stone stacked foundation, water and radon
Gosh, do I need help w this one. It’s a 1820s house in Columbia County NY with a largely stone foundation and backed against a small mountain. The “root cellar” with mechanicals and a dirt floor is under the living room, the rest is crawl space with dirt floor or slab. The 10×14′ cellar has heavy springtime water ingress where the dry stacked stone meets bedrock. The previous homeowner reported ~12″ of standing water during a tropical storm Irene and the sump losing power. The exterior water ingress can only be managed so much by gutters/french drains, given grade against mountain. There’s no appetite for the cost of a full excavation to “footings” – if that’s even possible w this type of foundation. It’s literally dry stone stacked w/o mortar! There’s also a 3 month reading of radon at 4.0. So… I’m thinking a layer of washed gravel in the cellar is necessary to allow the water to flow to the sump. Then a radon-rated vapor barrier on ground/walls, taping best able around multiple mechanicals and piers (it’ll be a beast) – and adhered to where there actually is mortar, directly under the sill plate. Questions: 1) do you think an interior french drain to the sump is necessary? 2) spray foam insulation on walls necessary? had a few subs recommend, but worry about freezing/drying 3) would you pursue a radon system drawing under the vapor barrier or an HRV w radostat? I don’t want to unnecessarily over-engineer this… Oh, and there’s mice galor! So thinking of caulking sill/rim joists and filling w rock insulation btwn. Heard they hate that stuff. Many thanks in advance for any advice and/or validation.
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