How much should the side lap be at all end joints for single underlayment installation?

In single underlayment installation, maintaining a proper side lap at all end joints is crucial for ensuring a watertight seal and preventing leaks. A side lap of 4 inches is recommended because it provides adequate coverage and a buffer against water infiltration. This overlap helps direct water away from seams and enhances the overall durability of the roofing system.

Using a 4-inch lap strikes a balance between creating a robust barrier while also not being excessively wasteful of materials. Proper installation practices dictate that laps are uniform and consistent throughout the roofing project to maintain integrity and performance.