Step Flashing
Also called: wall flashing, sidewall flashing
Step Flashing is the series of individual L-shaped metal pieces woven into the shingle courses where a roof slope meets a vertical wall. Each piece laps the one below, forming a stepped waterproof joint, and it is a classic source of chronic leaks when it is done badly or reused.
What it means
Step flashing waterproofs the junction where a sloping roof runs into a vertical wall: alongside a dormer, against the side of a chimney, where a lower roof meets an upper storey.
It is made up of many small L-shaped pieces rather than one long one. Each piece has one leg up the wall and one leg on the roof, and each is installed with a shingle course so that it laps the piece below. The result is a stepped, overlapping series that carries water down the joint and out onto the roof surface.
Why it has to be stepped
Because of how water moves at a wall junction, and this is the part that gets designed out by people trying to simplify it.
Water runs down the wall face and arrives at the roof line. It also runs down the roof alongside the wall. Both flows have to be caught and directed out over the top surface of the shingles, not underneath them.
A single continuous strip cannot do that, because the shingle courses are laid in overlapping steps and a straight piece of metal cannot lap each one. Water finds its way behind it at the course joints. The stepped arrangement exists precisely so that each piece can sit on top of one course and under the next, maintaining the lap the whole way up.
Continuous flashing at a slope-to-wall junction is one of the more reliable ways to produce a leak that is very hard to trace.
Why it fails
Age and corrosion, in older installations, particularly where the metal was thin or poorly chosen for the environment.
Reuse, which is the common one. The flashing is woven into the roof, so tearing the roof off disturbs it. Removing it carefully, straightening it, and reinstalling it under new shingles is more work than replacing it, and metal that has been in place for decades is rarely in good enough condition to justify the effort. A new roof with old flashing at the walls will frequently leak at the walls.
Sealant used as a substitute is the third. Where the geometry has not been built properly, sealant is often applied to hold the line, and it works for a while. It is a maintenance item pretending to be a detail, and it fails.
Why it matters on claims
Because leaks near walls, chimneys, and dormers are extremely common, and their cause is frequently not the storm.
A homeowner with a chronic leak at a dormer that got worse after heavy rain is likely describing a flashing problem that predates the event. That runs into wear and tear and workmanship exclusions rather than storm cover.
Establishing whether a leak is new or long-standing is therefore one of the more useful early questions, and homeowners usually know the answer.
Common mistakes
Reusing old flashing on a new roof is the most common and the most predictable failure.
The second is sealing rather than reflashing.
The third is scoping a roof replacement without including wall flashing, then discovering during the job that it cannot responsibly be left.
On the call
Persistent leaks near a chimney, dormer, or where a roof meets a wall are usually flashing rather than shingles, and they often predate the storm. Capture whether the leak is new or long-standing, because a long-standing flashing leak points somewhere very different from storm damage.
This is how our agents handle it on storm appointment calls and day-to-day roofing answering service intake.
Questions people ask about step flashing
- Can step flashing be reused on a new roof?
- It is generally poor practice. The pieces are woven into the shingle courses and fastened, so removing the old roof disturbs them, and metal that has been in place for decades is often corroded or deformed. Reused flashing is a common cause of leaks in an otherwise new roof.
- Why not just run a continuous strip along the wall?
- Because a continuous piece cannot lap the individual shingle courses. Water running down the wall needs to be directed onto the top of each course in turn, and only a stepped arrangement of separate pieces does that. Continuous flashing at a slope-to-wall junction tends to leak.
- Is a flashing leak covered by insurance?
- It depends on cause, like everything else. Storm damage to flashing can be covered; a long-standing leak from flashing that was installed badly or has corroded with age runs into the wear and tear and workmanship exclusions.
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