What is the purpose of counter flashing on a roof?

Counter flashing is an essential component in roofing systems, specifically designed to prevent leaks at locations where roof penetrations occur, such as chimneys, walls, and skylights. It serves as a protective barrier that overlaps the flashing installed on vertical surfaces, directing water away from critical areas and ensuring that any moisture that may infiltrate the joints or seams is channeled back to the exterior of the building.

This aspect of waterproofing is crucial as it not only enhances the building's overall durability but also prolongs the life of both the roofing materials and the structural elements beneath. By properly installing counter flashing, the likelihood of water intrusion is significantly reduced, addressing one of the most common causes of roofing-related issues.

While thermal insulation, aesthetic appeal, and mechanical attachment are important considerations in roofing, they do not directly relate to the primary function of counter flashing, which is centered on leak prevention.