Vapor Barrier and Vents

Vapor Barrier

Vapor barriers are intended to prevent moisture vapor from entering the crawlspace area. The vapor barrier is usually comprised of sheets of 6 millimeter or thicker polyethylene (plastic). The sheets are laid in rows over the soil. The edges of the sheets are overlapped (minimum 24") and taped or sealed to form a continuous barrier that will trap the rising moisture. The vapor barrier is commonly placed only over the soil area. However, it is becoming more common to continue the vapor barrier up the foundation wall and secure with tape or glue.

Crawlspace Vents Crawlspace vents were originally designed to prevent moisture vapor from accumulating in the crawlspace by providing openings for the moisture to pass to the exterior. The general requirement is one square foot of vent opening for 150 square feet of under-floor area. Many crawlspaces in new construction today are part of conditioned air and do not require venting.