Vapor Barrier and Vents

Vapor Barrier

Vapor barriers are intended to prevent the moisture vapor entering crawlspaces area.  The vapor barrier is usually comprised of sheets of 6 millimeter polyethylene (plastic).  The sheets are laid in rows over the soil.  The edges of the sheets are overlapped and tapped to form a continuous barrier that will trap the rising moisture.  In most locations, the vapor barrier is placed only over the soil and secured with weights.  In some regions, the vapor barrier is continuous over the foundation wall and secured to the sill plate.

Crawlspace Vents Crawlspace vents prevent moisture vapor from accumulating in the crawlspace by providing opening for the moisture to pass to the exterior.  Vents are required on new homes.  The general requirement is one square foot of vent opening for 150 square feet of under-floor area.