How much should each strip of underlayment for shingles overlap the previous strip at all end joints?

The correct amount of overlap for each strip of underlayment for shingles at end joints is 6 inches. This overlap is critical as it helps to ensure that water does not penetrate through the seams, providing a continuous barrier against moisture. A 6-inch overlap strikes a balance between sufficient coverage to prevent leaks and practicality in installation, making it a standard specification within the roofing industry.

This overlap is particularly effective because it minimizes the chances of water infiltration, especially in wind-driven rain scenarios. When installed properly, this overlapping technique will enhance the durability and longevity of the roof assembly by providing an additional layer of protection.

Other overlap requirements that might be considered, such as 4 inches or larger overlaps like 8 inches or 10 inches, may not be standard. While thicker overlaps can increase waterproofing, they can also complicate the installation process and may not conform to industry best practices, which recommend the 6 inches as optimal for balancing protection and ease of installation. Thus, proper adherence to these specifications is fundamental for effective roofing practices.