Crawl space encapsulation
Encapsulation turns a damp, vented crawl space into a closed space that's kept dry on purpose. Here's what goes into it.
Many older houses around Sumter were built with open vents in the foundation wall, on the theory that moving air would carry moisture out. In a summer as humid as Sumter's, the outdoor air pulled through those vents is often the main thing making the space wet. Encapsulation shuts out the outside air and the ground, then dries what's left.
What does the code require?
South Carolina enforces the 2021 International Residential Code, which lets a crawl space go without foundation vents if it follows section R408.3. The bare ground has to be covered by a continuous vapor retarder, with seams overlapped at least 6 inches and sealed or taped, and the edges run at least 6 inches up the foundation wall and attached. The space also needs one of these ways of handling the air:
- An exhaust fan running continuously at 1 cfm for each 50 square feet of floor
- Conditioned supply air at that same rate, with a return path to the house
- A dehumidifier rated to remove 70 pints of water a day for every 1,000 square feet
Ask the contractor whether the job needs a permit from the Sumter City-County Building Inspection Department or, for a Manning address, from the Clarendon County side.
How does a typical job go?
- Inspection. Wood moisture readings, a look at ducts, pipes and insulation, and a check for standing water, rot and termite damage.
- Prep. Hauling out debris and wet insulation, fixing leaks, and repairing rotted wood or drainage problems before anything gets covered.
- Sealing. Closing the vents and filling gaps at the rim joist and foundation.
- Lining. Laying a heavy liner over the ground and up the walls, taping seams and fastening edges.
- Drying. Installing a dehumidifier or another code-approved option, often with wall insulation.
Can it lower energy use?
It can. Building America research for the U.S. Department of Energy found that unvented, conditioned crawl spaces reduced heating and cooling energy use by 15 to 18 percent and cut humidity by more than 20 percent in the homes studied. How much you see depends on your house, your ducts and the quality of the sealing.
What changes the price?
- Square footage and how much room there is to crawl and work
- Liner thickness, and whether it covers the walls and piers
- Tearing out old insulation, trash or a failed plastic sheet
- Drains, a sump pump or a dehumidifier
- Framing repairs uncovered during prep
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 encapsulate a crawl space that took on water in a big storm?
Only after the water problem is solved. Gutters, grading, a drain or a sump usually come first, because a liner over standing water just hides the problem.
Will a sealed crawl space still pass a CL-100 inspection?
A dry, sealed crawl space usually gives lower moisture readings, but the pest inspector still needs to get in and see the wood. Ask the installer how access will be kept open.
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.