Crawl spaces: the Carolina problem child

The vented crawl space was designed on the theory that outdoor air would dry things out under the house. In the Southeast the outdoor air in July is the moisture. Vents let in humid air, it condenses on cool ducts and joists, and you get the musty smell, the cupped floors, and eventually the mold report.

Signs your crawl space is losing the fight

Musty smell that gets stronger in summer.
Hardwood floors cupping upstairs in humid months.
Sweating ducts or standing condensation on the vapor barrier.
Insulation batts sagging or falling from the subfloor.

Encapsulation, honestly priced

Full encapsulation means sealing the vents, laying a heavy liner up the walls, insulating the foundation walls instead of the subfloor, and controlling moisture with a dehumidifier or a supply vent. Done right it is transformative for the smell, the floors, and the energy bill. It is also several thousand dollars, and quality varies wildly between crews. Get the moisture reading and the drainage story before anyone quotes you a liner.

The middle ground nobody sells

If encapsulation is out of budget, a ground vapor barrier lapped and taped, band joists sealed, and fallen batts rehung gets you a surprising share of the benefit for a few hundred dollars in materials. It is not glamorous, which is why nobody advertises it.