Crawl space dehumidifiers and moisture control

Where is the water coming from?

• Rain. Downspouts that dump next to the foundation, clogged gutters and yards that slope toward the house.
• Groundwater. Poorly drained soils in parts of Nash and Edgecombe counties can hold a high water table for months in winter and spring.
• Humid air. Summer air entering through open vents, and air leaking down from the house.
• Leaks. Supply lines, drain pipes, a water heater relief line or a clogged HVAC condensate drain.

Crawl space dehumidifiers

Once a crawl space is closed, a dehumidifier is the most common way to meet the moisture-control requirement in Section R409.5 of the North Carolina Residential Code. A Town of Cary guide to closed crawl spaces summarizes that section as calling for a unit rated at least 15 pints per day with condensate drained to the outside. Units built for crawl spaces are compact, run on a humidistat and drain continuously. A portable unit sitting on the floor is easy to forget and can overflow onto the liner.

The NC Office of State Fire Marshal says the dehumidifier method doesn't require an H-3 heating license. The permit to close the crawl space is still required, and any new circuit follows the electrical rules.

Drains and sump pumps

If water comes in after storms, the fix is usually outside first: longer downspout extensions, cleaned gutters and soil regraded so it falls away from the house. When that isn't enough, an interior drain along the low side of the crawl space can carry water to a sump basin, where a pump sends it out and away from the foundation.

Signs the moisture control isn't working

• The musty smell comes back in July and August
• The dehumidifier runs nonstop but readings stay high
• Water collects on the liner near the unit, drain or sump
• The sump pump runs often in dry weather, or not at all in wet weather

What affects the price?

• Whether the crawl space is already closed
• Dehumidifier capacity and where it drains
• Length of interior drain and the number of sump pumps
• Electrical work for new equipment

Pricing comes from the crawl space company after someone has been under the house, measured it and seen what's there. We don't give prices, and a figure offered over the phone before that visit is a guess, not a quote.

Where we connect you with help

• Rocky Mount
• Nashville
• Tarboro
• Sharpsburg

Related services

• Crawl space encapsulation
• Vapor barrier replacement
• Crawl space repair and cleanup
• Sagging floor support

More background: Rocky Mount crawl space guide.