In a perfect roofing world, every roof would have a small slope without any obstructions. But that’s not the case. Roofs have joints and structures like chimneys and ventilation. Flashing is what’s used to protect the roof around these areas. Its main job is to keep water from entering. Most flashing is a thin strip of material, generally metal. It’s placed in the valleys and around protrusions so water can be deflected and run off the roof. The roofing company typically decides the exact type of flashing. Appliances such as boots (around pipes) vents, chimney re-leading and step and valley metal are all features of flashing.