Crawl space moisture is easy to ignore because most homeowners rarely go underneath their homes. But excess humidity, exposed soil, damaged vapor barriers, plumbing leaks, HVAC issues, and poor moisture control can create conditions where mold grows for years before anyone notices. In this guide, Mold Patrol co-owner Brian Murphy explains why crawl spaces become damp, what a vapor barrier actually does, why simply closing vents can sometimes make things worse, and what homeowners should check to keep the area dry. You’ll also learn when crawl space moisture may be connected to mold, indoor air quality, and conditions inside the home.