Crawl space vapor barrier replacement
The plastic on the dirt under your house does more work than it looks like. When it's torn or missing, moisture from the soil moves straight into the space.
A crawl space vapor barrier, or ground cover, is the sheet of polyethylene laid over the dirt floor under the house. In Lexington, where the ground stays damp much of the year, a continuous, well-lapped cover is the cheapest single step toward a drier crawl space. Replacement makes sense when the old sheet is torn, bunched up, too thin, or covers only part of the floor.
What does a good ground cover look like?
- It covers all of the exposed soil, wall to wall, with no gaps around piers
- Seams overlap generously and are taped, not just laid side by side
- It runs a short way up the foundation walls and around the piers
- It's heavy enough that someone can crawl across it without tearing it
Signs yours has failed
- The plastic is shredded where people have crawled to reach plumbing or ducts
- It's been pushed into piles, leaving bare dirt showing
- There's water sitting on top of it after a rain
- The sheet is thin and brittle from age
- An inspection report calls it missing or inadequate
Why the soil matters here
A lot of central Kentucky sits on soils that weathered from limestone. The Maury series, for example, has a silty top layer over limestone residuum, and its official type location is a few miles north of downtown Lexington. Soils like that hold moisture and release it into the crawl space air. The vapor barrier is what stops that moisture from reaching your floor framing and insulation.
Vented or sealed: does it matter?
A ground cover helps in either case. The model residential code that Kentucky follows even lets a vented crawl space use far less vent area when the ground is covered with an approved vapor retarder. In a sealed crawl space the cover becomes part of a continuous liner that is sealed to the walls, and the space needs air control too. See crawl space encapsulation for that version.
What affects the cost?
- Crawl space size and clearance
- Thickness and type of material
- Whether the walls and piers are covered or just the floor
- Removal and disposal of the old plastic and any debris
- Any standing water that has to be dealt with first
The crawl space contractor you're connected with prices the job after measuring. We don't quote prices.
Common questions
Can I put new plastic right over the old?
Sometimes, if the old sheet is clean and dry, but most contractors pull out torn or dirty plastic so the new cover lies flat and seals properly.
Is a ground cover enough on its own?
If the crawl space stays dry and you have no humidity or smell problems, it may be. If ducts sweat or the house smells musty, a full encapsulation usually works better.
How long does a ground cover last?
That depends on the material and how often people crawl on it. Heavier covers hold up better to plumbers, HVAC technicians and pest inspectors moving around.
Towns this covers
Related services
For the Kentucky code, karst and radon background, see the Lexington crawl space guide.
Damp smell, cold floors or a sag you can feel underfoot?
One call puts you in touch with a crawl space contractor who works in Lexington and the surrounding Bluegrass counties.