BuildMeter guide · Structures & Carpentry
Roof Step Flashing Planning Guide
Estimate step-flashing pieces from shingle courses and understand the required relationship between shingles, underlayment, wall drainage plane, counterflashing and kick-out flashing.
Direct answer
What to know first
A sloped roof-to-wall intersection generally needs one step-flashing piece at each shingle course, layered so each piece drains over the course below. A kick-out at the lower end and correct integration with the wall water-resistive barrier are essential parts of the detail.
Open Roof Step Flashing CalculatorOne step-flashing piece follows each shingle course
For an asphalt-shingle roof meeting a sidewall, the initial material count is the sloped wall length divided by shingle exposure. Round upward and add the kick-out, starter and spare pieces required by the detail. The piece count is only one part of the water-management system.
| Component | Role | Separate quantity? |
|---|---|---|
| Step flashing | Interwoven with successive shingle courses | Yes, usually one per course |
| Kick-out flashing | Directs concentrated runoff away from the wall | Yes |
| Counterflashing | Covers the vertical leg in masonry or other details | Often separate |
| Membrane/WRB transition | Connects roof and wall water-control layers | Measure separately |
Worked example
Two roof-wall runs are each 18 ft long. With a 5.625 in. shingle exposure, each run crosses about 39 courses. The two walls need 78 field pieces. Add two kick-out or starter pieces per run for 82 pieces, then 10% waste for 91 pieces. One 100-piece box covers the planned order.
Layering is more important than sealant
Step flashing should be interwoven with shingles so every upper piece sheds onto the lower piece. The upturned leg must connect behind or into the wall drainage plane. At the lower end, the kick-out should direct water away from the wall and into the gutter or clear of the cladding.
Common mistakes
- Using one long continuous flashing instead of step pieces where the roof system requires them.
- Leaving the wall water-resistive barrier behind the vertical flashing leg.
- Omitting the kick-out at the bottom of the run.
- Relying on face-applied sealant as the primary water-control strategy.
- Failing to account for counterflashing at masonry walls.
Sources and professional limits
- U.S. DOE Building Science Education — step flashing at roof-wall intersections
- U.S. DOE — kick-out and step flashing
- Building Science Corporation — common flashing details
Roof and wall details, corrosion resistance, piece size and fastening must follow the selected materials and project requirements.