Homeowners often ask whether they really need a full encapsulation, or whether a vapor barrier is enough. Both terms get used interchangeably online, but they describe very different scopes of work and very different price points.
Vapor barrier
A vapor barrier is a layer of polyethylene (typically 6–12 mil) laid across the dirt floor of the crawl space, with seams overlapped and tape-sealed. It slows ground moisture from rising into the joists. It does not seal vents, walls, or piers.
Full encapsulation
Encapsulation is a closed system: 12–20 mil reinforced liner across the floor and up the walls, mechanical fasteners and termite inspection gaps at the top, foundation vents sealed, access door gasketed, and a dedicated dehumidifier set to maintain RH below 55%. The crawl becomes a clean, dry, semi-conditioned space.
Which one fits the situation
- Vapor barrier: a relatively dry crawl, sound framing, and a goal of slowing ground moisture — for example, a newer home with good drainage already in place.
- Encapsulation: visible condensation on ducts, fungal staining on joists, persistent humidity issues upstairs, or a history of standing water.
What we usually recommend in WNC
For most homes in the Asheville area we lean toward encapsulation, because the climate is unusually humid for an inland mountain region and code-vented crawl spaces do not cope well with it. If a vapor barrier solves the problem, that is the recommendation we make.