A crawl space vapor barrier is a heavy plastic sheeting laid directly over the exposed soil in a crawl space, blocking ground moisture from evaporating upward into the crawl space air, addressing one of the most significant and persistent sources of crawl space humidity.
This represents the most basic level of crawl space moisture control, often serving as a first step before more comprehensive measures like full encapsulation are considered.
Because bare soil constantly releases moisture into the air above it, even a simple vapor barrier can make a noticeable difference in a crawl space’s overall humidity levels.
What Does a Crawl Space Vapor Barrier Involve?
- Heavy-duty plastic sheeting, typically six mil or thicker
- Coverage of the entire exposed soil area
- Overlapped and taped seams between sheets
- Extension partially up the foundation walls in more thorough installations
Why Are Crawl Space Vapor Barriers Important?
Exposed soil in a crawl space continuously releases moisture into the air above it, and a simple vapor barrier interrupts this process at its source, often producing a noticeable reduction in crawl space humidity even without any additional measures like a dehumidifier or full encapsulation. This makes a vapor barrier one of the most cost-effective moisture control improvements available for a crawl space.
While a basic vapor barrier addresses ground moisture specifically, it doesn’t address humidity entering through vents or gaps in the foundation, which is why more comprehensive encapsulation, sealing the entire space rather than just the ground, offers more complete protection where moisture problems are more severe. This cost-effectiveness makes it a sensible starting point even for homeowners not yet ready for a full encapsulation project.
Crawl Space Vapor Barrier vs. Crawl Space Encapsulation
A vapor barrier alone addresses ground moisture specifically. Encapsulation is the more comprehensive approach, sealing the entire crawl space including walls and vents in addition to covering the ground, offering more complete moisture control overall.