Crawlspace moisture in coastal Georgia: why it happens, what works

Why crawlspaces stay wet here

• Humid outside air. The old idea was that vents "air out" a crawlspace. In the humid Southeast it often works in reverse: muggy summer air flows in, hits cooler surfaces under the house, and condenses — the crawlspace gets wetter, not drier.
• A high coastal water table and flat lots — ground moisture rises as vapor off bare soil year-round.
• Site drainage — short gutters, clogged downspouts, and grading that slopes toward the house all send roof water under it.
• Plumbing that drips quietly for months where nobody sees it.

The upstairs symptoms people miss

• A musty smell that's strongest when the AC kicks on (air from below gets pulled up through floor penetrations).
• Hardwood floors cupping — edges rising — from moisture underneath.
• Doors sticking and trim gapping seasonally more than they should.
• Indoor humidity that stays high no matter what the thermostat does.
• Insulation sagging or falling below the floor — soaked insulation doesn't hold itself up.

What actually works (in order)

The fix sequence matters — sealing a crawlspace before you fix bulk water just traps the problem:

• First, bulk water: extend downspouts, clear gutters, correct grading, fix plumbing leaks. Cheap, unglamorous, and it's half the battle.
• Ground vapor barrier: heavy plastic over the soil stops the constant vapor rise. Even a basic, well-lapped barrier changes the math.
• In this climate, sealing and conditioning usually beats venting: a sealed (encapsulated) crawlspace with a dehumidifier holds a dry number year-round instead of following the weather.
• Then remediate what grew: joists and subfloor with growth need proper treatment — after the space is dry, or it returns.
• Keep score with a $15 hygrometer. Under about 60% relative humidity is the commonly cited target to keep mold from getting comfortable.

When it's a remediation job, not a maintenance job

Visible fuzzy growth across joists, insulation coming down wet, standing water after rain, or a musty smell upstairs that's getting stronger — at that point the crawlspace needs assessment, drying, and treatment, not just a roll of plastic. It's one of the most common calls we take in the Coastal Empire, in historic homes and newer builds alike.