Short Answer
Step flashing is installed where a roof meets a vertical wall or similar surface.
Detailed Explanation
Step flashing consists of small, L-shaped pieces of metal installed in a stair-step pattern where a sloped roof meets a vertical wall (like a chimney, a dormer, or a second-story wall). Each piece of step flashing is bent to cover the roof-to-wall joint, with one leg on the roof plane (under the shingle) and one leg up the vertical wall. Each piece overlaps the one below it, creating a shingled pattern that directs water down and away from the joint. Step flashing is one of the most critical — and most commonly improperly installed — flashing details on a roof. If it's missing, damaged, or improperly lapped, water can enter at the roof-to-wall transition.
Why It Matters
Step flashing is the primary water-management detail at roof-to-wall transitions. Its proper installation is essential for preventing leaks at chimneys, dormers, and wall intersections.