Vapor Barrier vs. Full Encapsulation
When a plastic ground cover is enough and when you need the full sealed system.
The difference
A vapor barrier is a sheet of polyethylene laid over the dirt floor, often 6 mil, with the vents left open. Encapsulation seals the whole space: a thick barrier on the floor and walls, taped seams, sealed vents and rim joists, and a dehumidifier or conditioned air to control humidity.
When a vapor barrier is enough
In dry climates, or under homes with no moisture complaints, a quality ground cover can be all you need. HomeGuide prices barrier material at $0.30 to $0.70 per sq ft and an installed barrier at about $2 to $4 per sq ft; Angi puts a vapor-barrier job at $1,000 to $3,000.
When to encapsulate
In humid climates (most of the Southeast, Mid-Atlantic and Gulf Coast), open vents bring in summer air that condenses on cool framing. Sealing the space and drying it mechanically is the approach recommended by most building scientists for those regions.
Code note
Once vents are sealed, the 2021 International Residential Code (section R408.3) expects the space to be conditioned or dehumidified and the ground covered. Check your local code office, since adoption varies by state.
Sources
Sources: HomeGuide, Crawl Space Encapsulation Cost (Jan 14, 2026); Angi, Crawl Space Repair Cost (Oct 8, 2026); 2021 International Residential Code, Chapter 4. Retrieved Oct 11–13, 2026.
Prices are published US ranges from the sources listed on each page; anything we calculated ourselves is labeled as an estimate. Get at least three written, itemized local quotes. Run the estimator to build your own range.