Crawl space encapsulation and vapor barriers
Encapsulation turns a damp, vented crawl space into a closed one that stays drier year-round. Here's what it involves in Greenville, NC.
Encapsulation, which North Carolina's building code calls a closed crawl space, means shutting out the humid outdoor air and the moisture rising from the ground. The vents are sealed, the dirt floor is covered with a vapor retarder, and some method of humidity control is added so the space doesn't simply trap moisture.
What does the NC code require?
Section R409 of the North Carolina Residential Code covers closed crawl spaces. It calls for a ground vapor retarder of at least 6-mil polyethylene or an equivalent, and it allows that retarder to be run up and sealed to the walls as a full interior liner. The code also lists specific moisture-control methods, such as a dehumidifier, supply air from the HVAC system, or an exhaust fan. Thicker, reinforced liners are common upgrades, but the code minimum is the starting point.
What happens during an encapsulation job?
- Inspection. Checking for standing water, wet or damaged wood, pests, plumbing leaks and the condition of existing insulation.
- Fixing water first. Gutters, grading or a drain and sump if water gets in. Sealing a crawl space that floods doesn't solve the problem.
- Cleanup. Removing debris, old plastic and fallen insulation.
- Sealing vents and openings. Including gaps around pipes and wires.
- Installing the liner. On the ground with seams overlapped and taped, and often up the walls and piers.
- Humidity control. Usually a dehumidifier or a connection to the HVAC system, depending on the method chosen.
Permits and licenses
The NC Office of State Fire Marshal says a permit is required to convert a vented crawl space to a closed one, regardless of cost. If the plan uses supply air from the HVAC system or makes the crawl space conditioned space, the state's interpretation says the work requires an H-3 heating license. Ask the company which method it's proposing and who holds the license and pulls the permit.
Just replacing the vapor barrier?
If you want to keep the crawl space vented but the plastic on the ground is torn or missing, replacing the ground cover is a smaller job. It cuts down on moisture coming up from the soil but doesn't deal with humid air coming in through the vents.
What affects the price?
- Square footage and how tight the crawl space is
- Liner thickness and whether walls and piers are covered
- Old insulation or debris that has to come out
- Drainage work needed before sealing
- The humidity-control method and equipment
The crawl space company prices the job after getting under the house and measuring. We don't quote prices, and any number given over the phone before an inspection is only a rough starting point.
Where we connect you with help
Common questions
Is encapsulation the same as a vapor barrier?
No. A vapor barrier is just the plastic on the ground. Encapsulation, or closing the crawl space, also seals the vents and adds humidity control, as Section R409 of the NC Residential Code describes.
Should I fix water problems before encapsulating?
Yes. If water runs into the crawl space after rain, grading, gutters or a drain and sump should be handled first or as part of the same job.
Related services
- Crawl space dehumidifiers
- Damp and musty crawl spaces
- Sagging floor and joist support
- Crawl space drainage and sump pumps
More background: Greenville, NC crawl space guide.
Musty smell, damp insulation or a soft, bouncy floor?
Call now and a local crawl space company will help you figure out what's going on under the house.