The short answer
Expect roughly $2–$4 per sq ft installed for a crawl space vapor barrier (HomeGuide, January 2026). Material alone is a fraction of that, which is why the do-it-yourself price and the contractor price look so different. The liner helps because the soil under a house gives off water vapor all year, and in a Charlotte summer that vapor meets warm, humid air.
It is one part of the job, not the whole job. A liner with no plan for the moisture that still gets in, or laid over a space that floods after rain, usually disappoints.
What the code requires
North Carolina covers closed crawl spaces in its R409 code section. The ground liner is the first requirement: polyethylene at least 6-mil thick, or equivalent, covering all exposed earth.
Two details trip up cheap installs. The liner has to be sealed to the walls and to beam columns, at least 4 inches up the columns. Where it runs up the foundation wall, it has to stop 3 inches below the top of the masonry wall, leaving a gap for termite inspection. Those details matter more than the brand of plastic.
What it does and what it does not
A liner cuts the vapor coming out of the soil. HUD’s guidance notes that moisture in a crawl space brings mold, mildew and wood rot, and makes insulation less effective. Oak Ridge National Laboratory’s work on sealed crawl spaces carries a warning that fits here: without an effective vapor barrier, a sealed space can collect moisture, especially where the water table is high.
What a liner does not do:
- It does not remove water that runs in. That needs grading, gutters or an interior drain, which HomeGuide prices at $800–$3,000 installed
- It does not dry the air. A dehumidifier does; HomeGuide prices a dehumidifier at $1,000–$3,000 installed
- It does not repair damaged wood or framing.
Liner only, or the full package
| What the quote covers | What you get | Cost reference |
|---|---|---|
| Liner only | Ground covered, walls and vents unchanged | $1,200–$4,000 (HomeGuide) |
| Full encapsulation | Liner, sealed walls and vents, moisture control | $4,865-$14,595 (Angi, Charlotte) |
Quotes for these two are not comparable, so put them side by side only after you know what each includes. The encapsulation cost page explains why full quotes vary so widely.
When a liner alone makes sense
A liner by itself can be a reasonable step when the space is dry after heavy rain, the wood is sound, and the main problem is a damp smell or moisture rising from bare soil. If you see standing water, soft or stained joists, or condensation on ductwork, get the cause looked at before covering the ground.
What to ask before you sign
- What material, and what overlap at the seams?
- Is the liner sealed to the columns and walls, or just laid on the ground?
- Does the quote say what happens to the vents?
- Is drainage included, or is it a separate line?
- How would a failed seam or wet spot be noticed later?
- Are any structural findings listed and priced separately?
Where to go next
If you are deciding between leaving things vented and closing the space, read vented vs closed crawl spaces. If the floor feels soft, start with the sagging floors page.
Want a contractor to look at it? Call to schedule a crawl space inspection.