Crawl space encapsulation
Encapsulation turns a vented, damp crawl space into a sealed one that stays drier through Upstate summers. Here's what the job involves.
An encapsulated crawl space, called an unvented crawl space in the building code, is cut off from humid outdoor air and from the moisture rising out of the soil. Vents and gaps are sealed, the dirt and usually the walls are covered with a heavy liner, and something is added to keep the humidity under control. Without that last piece, a sealed crawl space can simply trap moisture.
What does the code ask for?
South Carolina uses the 2021 International Residential Code with state modifications. Section R408.3 covers unvented crawl spaces. It requires a continuous vapor retarder over exposed earth, with seams overlapped at least 6 inches and sealed or taped, and the edges carried at least 6 inches up the stem wall and sealed to it. It also requires one of several air options: continuous exhaust, a conditioned air supply, using the space as a plenum in existing houses, or dehumidification sized at 70 pints a day per 1,000 square feet. Many companies install liners thicker than the minimum, but the code is the floor, not the target.
How does a typical job go?
- Inspection. Looking for water, rot, termite or beetle damage, plumbing leaks and the state of existing insulation.
- Water first. Gutters, grading, or an interior drain and sump if the crawl space takes on water. Red clay that holds water under a liner is still a problem.
- Cleanout. Pulling old plastic, fallen batts and construction debris.
- Sealing. Closing foundation vents and gaps around pipes, wires and the access door.
- Liner. Laying the ground cover with taped seams and fastening it up the walls and around piers.
- Air control. Usually a dehumidifier, sometimes a supply-air connection to the HVAC system.
Permits and licensing
Whether electrical, mechanical or building permits apply depends on what's being installed and where you live: the City of Spartanburg, Spartanburg County or another town. South Carolina's Residential Builders Commission requires a residential builder license for jobs over $5,000. Ask who holds the license and who pulls any permits.
What drives the price?
- Crawl space size, height and how hard it is to get around in
- Liner thickness and whether walls and piers are covered
- Debris and old insulation removal
- Drainage work needed first
- Which humidity control method is used
Pricing is set by the crawl space company after someone has been under the house, measured it and seen what's wrong. We don't quote prices, and a figure given over the phone before an inspection is a guess at best.
Where we connect you with help
Common questions
Is a sealed crawl space allowed under the SC code?
Yes. South Carolina uses the 2021 IRC with state modifications, and Section R408.3 covers unvented crawl spaces, including the ground liner and the approved ways to handle the air.
Should drainage be fixed before encapsulating?
Yes. If rain gets into the crawl space, gutters, grading or a drain and sump should be handled first or as part of the same project.
Related services
- Crawl space dehumidifiers
- Wood rot and moisture damage
- Sagging floor support
- Crawl space drainage and sump pumps
More background: Spartanburg crawl space guide.
Musty smell, sweating ducts or a floor that's started to dip?
Call the number above and a local crawl space company will help you figure out what's happening under the house.