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

The minimum overlap for joints in the polyethylene film moisture barrier applied over a below-grade foundation wall is 6 inches. This requirement helps ensure the integrity of the moisture barrier by preventing water infiltration that can lead to issues such as mold growth, structural deterioration, or damage to the foundation.

When the polyethylene film is installed with a 6-inch overlap at the seams, it creates a stronger, more reliable barrier against moisture. The increased overlap provides a larger area for adhesion when using sealants or tapes, which is particularly important in below-grade applications where the risk of water pressure is higher.

Moreover, while sealing joints with adhesive may reduce the need for overlap in some applications, it is typically recommended to maintain a minimum overlap to accommodate any potential movement, settling, or changes in moisture conditions that might compromise the seal. The 6-inch overlap approach is therefore widely considered a best practice in construction to ensure the effectiveness and longevity of the moisture barrier.