Crawlspace floor liner
Reinforced sheet material is laid across the soil with overlapped, sealed seams so ground moisture cannot evaporate into the space.
Ground moisture control · Greater Burlington
Vapor barrier installation: damp basements and crawlspaces
A vapor barrier matters because bare soil and porous masonry release moisture into the air continuously. A vapor barrier stops that path, but it is a moisture control, not a waterproofing system, and installing one over standing water simply hides the problem.
No phone call needed.
What this service includes
A vapor barrier is sheet material sealed across a crawlspace floor, up piers and walls, or applied as a wall liner in a basement, to stop ground moisture evaporating into the space. It reduces humidity, musty odour and condensation on cold surfaces. It does not stop bulk water: standing water, active seepage or a failed drain must be corrected first, or the liner traps water underneath and the space stays wet.
Common reasons homeowners call
Problems this service can fix
A dirt-floor crawlspace with damp soil
Persistently high basement or crawlspace humidity
Musty odour rising into the living space
Condensation on ductwork, pipes or cold walls
Rusting fasteners, hardware or appliance bases
Cupping wood floors above a crawlspace
An older liner that is torn, loose or no longer sealed
Repairs and systems
Repairs and systems
Pier and wall detailing
The liner is carried up piers and foundation walls and terminated so the seal is continuous rather than stopping at the dirt.
Basement wall liner
A drainage or vapor liner directs wall moisture behind the finished surface instead of into the room.
Bulk water correction first
Standing water, seepage and drainage faults are addressed before any liner goes down, so water is not sealed underneath.
Sealed and serviceable access
Access points, vents and penetrations are detailed so the space stays sealed and can still be inspected.
Dehumidification
Where sealing alone will not hold the target humidity, a drained dehumidifier is sized for the space.
Matching the option to the condition
Vapor barrier steps in the right order
A liner over a wet space traps water. The order matters as much as the material.
| Step | Purpose | What to confirm first |
|---|---|---|
| Correct bulk water first | A liner does not stop liquid water | That drainage is handled |
| Crawlspace floor liner | Limits ground moisture | Seams and edges sealed |
| Pier and wall detailing | Completes the barrier | Terminations |
| Serviceable access | Lets you inspect the space | A sealed but reachable hatch |
| Dehumidification | Controls remaining humidity | Whether it is needed |
- 01
Whether the floor is soil, gravel or concrete
- 02
Any standing water or evidence of past flooding
- 03
Current humidity and where condensation appears
- 04
Foundation wall material and condition
- 05
Insulation, ducts and utilities in the space
- 06
Structural condition of joists, beams and posts
Your estimate
What is included in the plan
Water first, liner second
A liner over active water traps it, and drainage, sump and grading corrections belong before the sheet goes down.
Thickness and reinforcement
Thin sheeting tears the first time anyone enters, and ask what material and thickness is included, and whether it is rated to be walked on.
Seams and terminations
An unsealed liner is a partial one, and the value is in overlapped, sealed seams and a proper termination at walls and piers.
It is not radon mitigation
Sealing can change airflow in the lowest level, and a vapor barrier is not a radon system, and testing is still the only way to know your level.
Already have an estimate?
Compare the complete vapor barrier installation scope.
Sources and Vermont specifics
What the Vermont energy code says about a crawlspace liner
Vermont's 2020 Residential Building Energy Standards describe the details a proper ground cover has to meet in an unvented crawlspace. Exposed earth must be covered with a continuous Class I vapor retarder. All joints must overlap by 6 inches and be sealed or taped. The edges must extend at least 6 inches up the stem wall and be attached to it. Where the walls are insulated instead of the floor above, the crawlspace must not be vented to the outside, and the insulation must be permanently fastened, run from the floor to finished grade, and continue at least 24 inches beyond that.
Those figures turn a vague promise into something you can check. A proposal should say what class of material, how the seams are sealed, how far up the wall the liner runs and how it is fastened. For basement walls, the same code calls for insulation from the top of the wall down to 10 feet below grade or to the floor, whichever is less. Compare bids on those specifics, not on the word encapsulation.
Sources: Vermont 2020 Residential Building Energy Standards, R402.2.9 and R402.2.11 (Efficiency Vermont summary). Checked September 26, 2026.
Common questions
Vapor Barrier Installation FAQs
Is a vapor barrier the same as encapsulation?
No. A vapor barrier is the sheet that stops ground moisture. Encapsulation is the complete system: drainage, a sealed and detailed liner, air sealing, insulation changes and usually dehumidification. A liner alone is one component of that.
Can a vapor barrier be installed over a wet crawlspace floor?
It should not be. Sealing over standing water or active seepage traps the water beneath the sheet and the space stays damp. Drainage and any sump work come first.
Does a vapor barrier help with radon?
Sealing work can change how the lowest level of a home ventilates, in either direction. It is not a radon mitigation system, and Vermont health guidance recommends testing because radon cannot be seen or smelled. Test after the work regardless.