What is step flashing?

Step flashing is a series of L-shaped metal pieces, typically made of aluminum or galvanized steel, that run along the joint where a sloped roof meets a vertical surface like a wall, chimney, or dormer. Each L-shaped section is installed to overlap the shingle course directly below it, creating a stair-step pattern that guides water down the roof and away from the wall.

The horizontal leg of each piece sits on top of the shingles, while the vertical leg laps up against the wall. As roofers apply shingles above, each new course covers the horizontal portion of the flashing below it. This layering is critical because it creates a continuous water-shedding system that prevents rain from flowing behind the wall.

Improper installation is one of the leading causes of roof leaks in Greater Hartford homes. Common mistakes include not overlapping the pieces correctly, nailing through both the flashing and shingle in ways that trap water, or failing to match the flashing placement with the shingle layout. If the vertical leg is not seated properly against the wall or if mortar joints deteriorate around it, water can seep into the structure. Even small gaps or misalignment can allow moisture to migrate under the shingles and into the attic or walls, leading to rot and mold growth.

Proper installation requires careful alignment with each shingle course and secure fastening that does not compromise the water-shedding path. If you notice leaks near chimneys or walls that meet the roof, step flashing problems are often the culprit, and roof repair contractors should inspect and replace damaged sections.