What is the minimum overlap for joints in the polyethylene film moisture barrier applied over the exterior of a below-grade foundation wall?

The minimum overlap for joints in the polyethylene film moisture barrier applied over the exterior of a below-grade foundation wall is typically set at 6 inches. This standard is established to ensure a reliable seal that prevents moisture from penetrating through the joints of the barrier. An overlap of this magnitude allows for sufficient material coverage, which effectively minimizes the risk of water intrusion.

Properly overlapping joints is crucial in below-grade applications because foundations are susceptible to water damage and moisture-related issues. The 6-inch overlap strikes a balance between providing a strong barrier and being practical for installation. If the overlap were to be smaller than the recommended amount, it could compromise the effectiveness of the moisture barrier, allowing water to seep through more easily. Additionally, a greater overlap may not be necessary and could lead to unnecessary material use or complications during installation.