What is the term for the overlap of roofing material that prevents water penetration?

The correct term for the overlap of roofing material that prevents water penetration is side lap. This overlap is crucial in roofing applications, as it allows each successive layer of roofing material to effectively shed water rather than let it seep through the joints. Properly executed side laps ensure that if water gets under the top layer, it can still drain off without penetrating through to the underlying structure. This technique is especially important in maintaining the integrity of a roof, preventing leaks and extending the lifespan of the roofing system.

In roofing terminology, head lap refers to the vertical overlap at the top edge of roofing courses, while margin generally refers to the edge or boundary of the roofing material. Exposure pertains to the amount of roofing material that is visible after installation, which does not directly relate to the overlap intended to prevent water penetration. Understanding these distinctions highlights the significance of side lap in effective roofing practices.