Crawl space moisture control
Water gets under a house three ways: rain, groundwater and humid air. Effective moisture control handles each one, in that order.
A dehumidifier can't keep up with storm water flowing under the house, and a sump pump does little when the real problem is August air pouring through open vents. Pinning down the source first saves money and avoids paying for a fix that doesn't work.
Start with rain and surface water
Sumter averages close to 49 inches of precipitation a year, and the October 2015 flood dropped more than 20 inches on parts of the city in a few days. The cheapest moisture fixes are often outside:
- Gutters that are clear and big enough for heavy downpours
- Downspouts that discharge several feet out instead of at the foundation
- Soil that slopes away from the house
- Beds and mulch kept below the top of the foundation wall
Then deal with groundwater
The Mimms and Scapo soil series, both first described in Sumter County, are flood plain soils with a seasonal high water table within a foot of the surface from November to May. Where a house sits near that kind of ground, water can seep up into a low crawl space in the cooler months. Fixes include an interior drain along the footing that feeds a sump pump, an exterior perimeter drain, or regrading. The IRC also says that if groundwater can rise to within 6 inches of a crawl space floor, the floor has to be brought up to the outside grade unless an approved drainage system is installed.
Finally, dry the air
For a sealed crawl space, the IRC accepts a dehumidifier sized to remove 70 pints of water per day per 1,000 square feet of floor as one way to keep the air dry. Crawl space units are built to run in low, tight spaces and usually drain to a pump or outdoors.
How wet is too wet?
South Carolina's wood infestation regulation, 27-1085, treats wood moisture readings of 20% or more, or standing water in the crawl space or around the foundation, as excessive moisture. It says decay fungi become active at 28% and above. Those are the readings a CL-100 inspector writes down. The same regulation says a sump pump can't be installed without a drain or trench system leading to it.
What to ask about a sump or dehumidifier
- Where will the water discharge, and is it far enough from the foundation?
- How will I find out if the unit stops working?
- What maintenance does it need, and how often?
- Does it have its own circuit and a protected outlet?
We don't quote prices. No two crawl spaces are alike, so the company you're connected with prices the work after someone has gone under the house, measured it and found where the moisture or damage is coming from. A figure offered over the phone before that visit is a guess.
Where we connect you with help
Common questions
Can I put a regular household dehumidifier in my crawl space?
Household units aren't built for a dirt-floored, open crawl space and usually can't keep up. Crawl space models are made for the job, and they work best once the space is sealed.
Should I just close my foundation vents in summer?
Closing vents without covering the ground and drying the air can trap moisture and make things worse. Talk to a crawl space company about sealing the space properly.
Related services
More background: Sumter crawl space guide.
Musty air, sweating ducts or a floor that sinks near the bathroom?
Call and we'll connect you with a crawl space company that works in Sumter County.