Crawl space encapsulation
Encapsulation, which North Carolina's code calls a closed crawl space, keeps humid outdoor air and ground moisture out from under the house.
An encapsulated crawl space is sealed off from the outdoors. The vents are closed, the dirt floor is covered with a vapor retarder that's often carried up the walls and piers, and a method of moisture control keeps the air from turning stale and damp. In Goldsboro's humid summers, that usually makes the crawl space drier than leaving it vented.
What does the North Carolina code require?
Closed crawl spaces are covered by Section R409 of the North Carolina Residential Code. According to the Office of State Fire Marshal's interpretation, the ground vapor retarder has to be at least 6-mil polyethylene or equivalent and should cover essentially all the exposed earth. The retarder can be installed as a full interior liner on the walls. If it is, the top edge stops 3 inches below the top of the masonry wall, leaving a 3- to 4-inch termite inspection gap below the sill, and the liner goes at least 4 inches up interior piers.
Section R409.5 then lists the allowed moisture-control methods: a dehumidifier, supply air from the HVAC system, house air, an exhaust fan, or treating the crawl space as conditioned space.
Permits and the H-3 license
The Office of State Fire Marshal says converting a vented crawl space to a closed one requires a permit regardless of cost. Its licensing table says the supply-air and conditioned-space methods need an H-3 heating license, while the dehumidifier and exhaust fan methods don't. House air drawn through ducted HVAC counts as supply air. Ask which method a company is proposing and who holds the license.
How does a typical job go?
- Inspect for standing water, wood damage, pests, leaks and old insulation.
- Handle water first: gutters, grading, or an interior drain and sump if needed.
- Repair damaged framing and clear out debris.
- Seal the vents, the crawl space door and gaps around pipes and wires.
- Lay and seal the ground liner, overlapping and taping the seams, then line walls and piers if planned.
- Install the moisture-control method and confirm humidity is coming down.
What if the Neuse floods again?
Encapsulation manages everyday humidity and ground moisture. It is not flood protection. If river water gets in, wet insulation and liner usually need to come out and the space has to dry before it's sealed again.
What affects the price?
- Square footage and crawl space height
- Liner thickness and wall and pier coverage
- Repairs, cleanup and drainage needed first
- Which moisture-control method is chosen
Pricing comes from the crawl space company after someone has been under the house with a flashlight and a tape measure. We don't quote prices, and a figure offered over the phone before that visit is only a ballpark.
Where we connect you with help
Common questions
How thick does the liner have to be in North Carolina?
The NC Residential Code minimum for a closed crawl space ground vapor retarder is 6-mil polyethylene or equivalent. Thicker reinforced liners are a common upgrade.
Can the wall liner go all the way up to the wood?
No. The code says a wall liner stops 3 inches below the top of the masonry wall, leaving a 3- to 4-inch gap below the sill for termite inspection.
Related services
More background: Goldsboro crawl space guide.
Damp smell, sweating ducts or a floor that's started to dip?
Call and we'll put you in touch with a crawl space company that works in Wayne County.