Crawl space encapsulation
Encapsulating a crawl space means sealing it off from humid outdoor air and damp ground, then actively keeping it dry. Here's how it's done in the Rocky Mount area.
North Carolina's Residential Code doesn't use the word encapsulation. It calls the finished result a closed crawl space and sets out the rules in Section R409. The basic idea: shut the vents, cover the ground so soil moisture can't evaporate into the space, and use one of a short list of approved methods to control humidity from then on.
What does North Carolina's code require?
Under R409, the ground in a closed crawl space gets a vapor retarder of at least 6-mil polyethylene or an equivalent. The NC Office of State Fire Marshal has said that running that liner up the foundation walls is allowed but not required. The code also requires one of five moisture-control methods: a dehumidifier, supply air from the HVAC system, house air moved by a fan, an exhaust fan, or making the crawl space conditioned space. Many companies install a thicker, reinforced liner than the code minimum. Ask what thickness they're proposing and why.
How does a typical job go?
- Look first. The crew checks for standing water, rotten or wet wood, termite activity, leaking pipes and the shape the insulation is in.
- Deal with water. If rain runs under the house, gutters, grading or a drain and sump come first. Sealing a crawl space that still floods just traps the water.
- Clear it out. Old plastic, fallen insulation and construction debris come out.
- Close it up. Vents and gaps around pipes, wires and the access door get sealed.
- Line it. The liner goes down with overlapped, taped seams, and often up the walls and around piers.
- Control humidity. A dehumidifier is the most common choice, though some homes use one of the HVAC-based methods.
Permits and licenses for encapsulation
The Fire Marshal's office says a permit is required to convert a vented crawl space to a closed one regardless of cost. Its licensing interpretation adds that the supply-air and conditioned-space methods need an H-3 heating license, while the dehumidifier and exhaust-fan methods do not. In Rocky Mount, the city's Inspection Services Division issues the permit; elsewhere, the town or county does.
What drives the cost?
- Square footage, wall height and how much room there is to work
- Liner thickness and whether walls and piers get covered
- How much old insulation, plastic and debris has to be hauled out
- Drainage or wood repair needed before sealing
- The humidity-control method and equipment
Pricing comes from the crawl space company after someone has been under the house, measured it and seen what's there. We don't give prices, and a figure offered over the phone before that visit is a guess, not a quote.
Where we connect you with help
Common questions
Do I have to cover the walls when I encapsulate?
No. The NC Office of State Fire Marshal says pulling the ground vapor retarder up the walls is allowed but not required. Many companies recommend it anyway; ask why for your house.
Can a crawl space that floods be encapsulated?
Only after the water problem is handled. Grading, gutters or an interior drain and sump should be fixed first or included in the same job.
Related services
- Vapor barrier replacement
- Dehumidifiers and moisture control
- Crawl space repair and cleanup
- Sagging floor support
More background: Rocky Mount 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 your part of Nash or Edgecombe County.