It’s risky. An unvented crawl space (insulated foundation walls) is really a tiny basement. If water gets into the unvented crawl space, it’s essentially in part of your interior conditioned space. Because there is no air or moisture barrier between the crawl space and your home, and there is usually active air exchange between the crawl space and the interior, the flood water contaminants and mold will pollute your home interior. The same is true with basements, but basements are big enough to go into and clean up. You can’t easily do that in a two-foot crawl space.

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