Under-floor mold
How Crawl Space Mold Gets Into Your Floor Framing in Jennings Lodge
Most crawl space mold isn't from a flood. In warm months, foundation vents pull in muggy outside air, and when it hits the cooler underside of the house, it condenses right onto the framing. The joists, the subfloor sheathing, and the sill plates and rim joists along the foundation stay wet long enough for growth to coat them in white, gray and dark patches.
Bare soil adds a second moisture source. A crawl space with no vapor barrier, or a torn one, lets ground moisture evaporate straight into the air under the floor, and standing water after storms keeps it there. Fiberglass batts between the joists soak it up, sag and fall, and uninsulated ductwork sweats and drips onto everything below.
Here's the part homeowners in Jennings Lodge don't expect: the stack effect pulls crawl space air up into the living area as warm air leaves through the attic. That's why a stale smell in first-floor bedrooms so often leads back to the crawl.