Under-floor mold
How Crawl Space Mold Gets Into Your Floor Framing in Franklinton
Crawl space mold rarely starts with a single leak. It comes from humid outdoor air pouring through foundation vents in summer and meeting wood that's cooler than the dew point. Floor joists, subfloor sheathing, sill plates and rim joists stay damp for months, and the growth spreads across the wood grain in white, gray or black patches.
Exposed dirt makes it worse. 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.
What happens under the floor doesn't stay there, because the stack effect draws air from the crawl space up through gaps around pipes, wires and ducts into the rooms above. That's why a stale smell in first-floor bedrooms so often leads back to the crawl.