The Vapor Barrier Is the Floor of the Encapsulation System

Crawl Space Vapor Barriers: how it works and when it's the right call.

Installation starts with clearing debris from the crawl space floor and identifying any active water source that needs to be addressed with drainage before the barrier goes down. The vapor barrier, typically a reinforced material well beyond the thickness of basic construction plastic, is then laid across the floor and run up the walls, with each sheet overlapped and sealed at the seams to close any gaps. Termination bars or mechanical fasteners secure the barrier to the walls so it stays in place. Sealing the crawl space vents happens as part of the same project, since an open vent lets in the same humid air the barrier is meant to keep out, just from a different direction. Once the floor, walls, and vents are sealed, a dehumidifier sized to the space handles whatever humidity remains, which is what makes it a complete crawl space encapsulation rather than a sheet of plastic. Skipping the vent sealing or the dehumidifier and stopping at the vapor barrier alone tends to produce condensation on the framing above the barrier instead of on the dirt below it, which moves the moisture problem rather than solving it.