How do I seal a crawl space, with a below-grade basement with an existing slab?
I do a load of work retrofitting “new” green building practices into 80-100 year old homes. Sealed crawl spaces is a particular retrofit specialty, but even after installing a half dozen or so we still run into our head scratchers. See, here in the clay filled piedmont of North Carolina, no one builds basements on a flat lot. The drainage problems are too many. Of course, builders didn’t figure that out until mid-century, so there are plenty of historic homes stuck with below-grade basements.
I want to seal them. Here’s how I want to do it:
These basements are designed to let moisture in and get it out via sump pump, so moisture management is key. Sealing it without dealing with the water will trap water and create a pool under the vinyl. Adding to the problem, these old basement slabs have no vapor barrier underneath, so short of pouring another slab I have to waterproof from above. We have been using a roll on waterproofer on the floor, similar to what you’d use on exterior waterproofing. It doesn’t give me total confidence, so on the next project, I want to seal the ENTIRE room with our 6m reinforced vinyl. That includes the walls and floors. I’ll through scrap carpet on the floor, just to protect the seal. For water, I’ll cut out a channel around the edge of the slab (under the vinyl) to direct water to the sump pump, and the pump is engineered to take water from below and above the vinyl barrier.
Covered with our bright white poly, the basement room will look like a looney bin (I say this lovingly); it’s the perfect place for the client’s 3 year old to serve a few time-outs.
Question: For a retrofit, does the vinyl floor and wall seem like a good idea?
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