All glossary terms
Materials
Step Flashing
Definition: Step flashing is small, L-shaped pieces of metal installed where a roof slope meets a vertical wall (like a chimney or dormer). Each piece overlaps the next, creating a watertight seal.
Step flashing is the most-overlooked source of roof leaks in residential construction. Anywhere a sloped roof meets a vertical wall — chimneys, dormers, second-story walls above first-story roofs — water needs a path off the roof. Step flashing provides it.
How it works: small L-shaped pieces (typically 4×5 inches) interleave with each course of shingles as they run up the wall. One leg sits on the roof, one leg runs up the wall behind the siding. Each piece overlaps the next, so water cascades from one to the next down to the gutter without ever touching the wall sheathing.
Common failure modes:
- Continuous flashing instead of step pieces (a long L-strip looks faster to install but leaks within 2-5 years)
- Step pieces installed but not interleaved with shingles (water sneaks underneath)
- Failure to replace step flashing during re-roof (old flashing damaged by previous tear-off rarely seals properly)
- Sealant-only "repairs" instead of replacement (caulk fails in 1-3 years)
For estimating: step flashing is rarely a separate line item — it's bundled into the install of the roof itself. But on quotes for jobs with chimneys, dormers, or wall-roof intersections, mention "all step flashing replaced" explicitly. Customers ask whether old flashing will be reused, and the honest answer is "no, never" on a quality install.