Under-floor mold
How Crawl Space Mold Gets Into Your Floor Framing in Minorca
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.
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. Batts between the joists absorb that dampness and droop, while cold supply ducts sweat and drip onto the insulation and the dirt.
Here's the part homeowners in Minorca don't expect: the stack effect pulls crawl space air up into the living area as warm air leaves through the attic. That upward airflow is why first-floor rooms in Minorca homes often smell musty when the crawl space is the real source.