What is the recommended top lap distance for single underlayment at all horizontal joints?

The recommended top lap distance for single underlayment at all horizontal joints is 2 inches. This measurement is crucial because it ensures that the underlayment provides adequate coverage and protection against water infiltration. When two sheets of underlayment are overlapped by this distance, it helps direct water down the surface, preventing it from seeping through the joint.

A lap distance of 2 inches strikes a balance between effective waterproofing and practicality during installation. If the overlap were too small, there could be a higher risk of leaks, while an excessive overlap might lead to unnecessary material waste and increase the overall weight on the roof structure.

In roofing practices, adherence to these guidelines is essential for maintaining the integrity of the roofing system and ensuring long-lasting performance, ultimately safeguarding the building from potential moisture issues.