When installing a single layer of underlayment, what is the minimum required lap for sheet installation?

In roofing practices, particularly when it comes to installing underlayment, the lap is crucial for ensuring proper water resistance and overall roof integrity. A minimum lap of 2 inches for sheet installations of underlayment is specified to provide adequate overlap between successive sheets. This overlap is essential because it helps prevent water infiltration that could occur if there are gaps between sheets.

With a 2-inch lap, there's a sufficient material overlap to allow for expansion, contraction, and the movement of building materials due to temperature variations. This also aids in directing water away from seams, which are vulnerable points where leaks could potentially occur. Proper lap measurements are part of best practices in roofing installations, contributing to the longevity and effectiveness of the roofing system.