Where a roof slope runs alongside a vertical wall — a dormer cheek, a chimney side, the wall above an attached garage — water has to be steered down the roof without slipping behind the siding. Step flashing roof details solve this with a deceptively simple system: individual L-shaped metal pieces, one woven in with every shingle course, each overlapping the one below like scales. Done right, it outlasts the shingles. Done wrong — or replaced with a single bent strip of “continuous flashing” — it quietly rots wall sheathing for years before anyone notices. Here’s the full detail: sizes, sequence, kickouts, and the failure patterns to check on your own roof.
Part of our Roofing guide — explore the full guide →
Why Individual Pieces Beat One Long Strip
A roof-wall intersection concentrates water: the roof plane sheds its own rain plus everything draining off the wall above. A single continuous L-strip laid along the joint has two fatal flaws. First, shingles can only be sealed on top of it, so capillary water and wind-driven rain travel sideways under the shingle edges with nothing to stop them. Second, thermal movement over a 12-foot run opens fastener holes and seams.
Step flashing fixes both by working with the shingle lap logic: each shingle course gets its own flashing piece, lapped over the piece below by at least 2 inches (3 is better). Any water that gets onto a flashing piece is delivered on top of the shingle below it, back into the drainage plane. There’s no continuous seam to fail and no path that runs uphill. This is the same shingle-lap principle that governs the whole roof — if you’re new to it, our how to shingle a roof guide covers the coursing logic step flashing plugs into.
Piece Sizing and Materials
- Standard piece: 5 × 7 inches bent at 90° — a 5-inch width split into a 2- to 2.5-inch roof leg and 2.5- to 3-inch wall leg, 7 inches long to guarantee 2+ inches of headlap with 5⅝-inch shingle exposure. Codes commonly require pieces at least 4 inches on each leg; 5 × 7 and 4 × 4 × 8 are the ubiquitous pre-bent sizes.
- Length rule: piece length must exceed shingle exposure by at least 2 inches. Metric shingles with 5⅝-inch exposure want 8-inch pieces; standard 5-inch exposure works with 7-inch.
- Materials: pre-bent galvanized steel (26-28 gauge) is the budget standard at $0.30-$0.60/piece; aluminum ($0.40-$0.80) is easiest to cut and bend but must not touch treated lumber or masonry mortar; copper ($3-$6/piece) for slate, cedar, and chimneys where it will outlive everything. Match metal to fasteners — galvanized with galvanized, copper with copper — to avoid galvanic corrosion.
The Weave Sequence
Step flashing installs as you shingle, one piece per course:
- Prep the wall. Housewrap or WRB on the wall should lap OVER the top of the flashing wall legs when the wall is finished — water on the wall must land on the flashing, not behind it. On existing walls, siding comes off to at least 6 inches above the roof plane.
- Underlayment first. Roof felt or synthetic turns up the wall 3-5 inches behind where the flashing will sit. In ice-dam country, run self-adhered membrane up the wall at this joint.
- First piece at the eave. Set the starter course shingle, then place the first step flashing on top of it, tight into the corner, roof leg over the shingle. Fasten with two nails high on the ROOF leg only — never through the wall leg into the wall, and never low where shingle coverage won’t seal over the hole.
- Shingle over, flash over, repeat. The next shingle course covers that flashing’s roof leg; the next flashing piece sits on top of that shingle, lapping the previous piece by 2-3 inches. Shingle, flash, shingle, flash, up the entire run.
- Hold the shingle back. Keep shingle edges about ½ inch off the wall so debris and water don’t wick at the joint.
- Counter flash or lap the cladding. Siding laps down over the wall legs (leaving a 1½-2 inch gap above the roof surface); on brick or stone, a separate counter flashing cut into a mortar reglet covers the step legs. Step flashing alone against masonry is incomplete.
Kickout Flashing: The Piece Everyone Skips
At the bottom of the run, where the roof edge meets the wall and water leaves the roof, an ordinary step piece dumps its stream straight down the face of the wall — or behind the gutter and into the wall assembly. The kickout (diverter) flashing is a modified first piece with its lower edge bent outward at roughly 110°, flinging water away from the wall and into the gutter.
Missing kickouts are among the most expensive small defects in residential construction: the classic symptom is a vertical stain or spongy stucco/siding directly below a roof-wall corner, often hiding thousands of dollars of rotted sheathing. Pre-formed kickouts cost $5-$15. If your home has roof-wall intersections that end at a gutter, walk outside and check for them today.
Common Failures and Fixes
| Failure | What you see | Fix |
|---|---|---|
| Continuous strip instead of steps | Long L-metal, often caulked heavily | Rework with true step flashing at next reroof; caulk is a countdown timer, not a repair |
| No kickout | Stain/rot below the roof-wall corner | Retrofit kickout; repair wall |
| Face-nailed wall legs | Nail heads through siding-side metal | Pull, seal holes, refasten on roof leg |
| Reused old flashing at reroof | Pinholed, creased 25-year-old steps under new shingles | Always renew flashing with the roof — labor is already paid |
| Tar as flashing | Black mastic smeared along the joint | Temporary at best; rebuild the detail properly — roofing cement is for minor sealing, not primary waterproofing |
Special Cases
- Chimneys: step flashing runs up both sides, but the uphill face needs a cricket or back pan and the downhill face an apron; all of it gets counter-flashed into mortar joints.
- Metal roofs: standing-seam and screw-down panels use their own sidewall flashing extrusions with closure strips, not shingle-style steps — the concept (lap over panel, under wall cladding, kick out at the bottom) carries over. Details differ by profile; see our metal roofing guide.
- Stucco walls: the highest-risk cladding for this detail. Stucco must terminate above the roof on a weep screed with the WRB lapped over the flashing; stucco run tight to shingles traps water permanently.
- Low-slope tie-ins: below 4:12, extend membrane up the wall and lengthen laps; below 2:12 the whole joint becomes a membrane detail, not step flashing.
DIY Difficulty and Cost
Material is trivial — a bundle of 100 galvanized steps costs $30-$60, a kickout $10. The real cost is sequence: proper step flashing on an existing roof means removing and re-laying the shingle courses and the lower siding along the wall, which is why a 12-foot flashing repair quotes at $500-$1,500. A competent DIYer re-shingling their own roof can absolutely step-flash correctly; retrofitting flashing under an existing roof without disturbing it cannot be done right, no matter what the tube of sealant promises.
FAQ
How much should step flashing overlap?
Minimum 2 inches of headlap between successive pieces; 3 inches in high-wind or ice-dam regions. The wall leg should rise at least 4 inches above the roof plane (2 inches minimum roof leg per code, 4 inches typical).
Should step flashing be caulked to the wall?
No. The system works by gravity lapping, and the top of the wall leg must stay open behind the siding’s drainage plane. Sealant belongs only at counter-flashing reglets on masonry.
Can I see if my roof has proper step flashing?
From a ladder, look along the roof-wall joint: you should see the small horizontal edge of a separate flashing piece at every shingle course, disappearing under the siding, plus an outward-bent kickout at the bottom. One continuous line of metal or heavy tar means the detail is wrong.
Bottom Line
Step flashing is cheap, unglamorous, and the difference between a dry wall and a rotted one. One piece per course, 2-inch laps, nails high on the roof leg only, cladding over the top, kickout at the bottom. Insist on it in every reroof quote — and if your estimator says “we’ll just run some L-metal and seal it,” get another estimator.
