Cap Flashing - Metal Cover Flashing for Water Shedding
A cap flashing is a metal cover flashing that sheds water over the top edge of another flashing, wall, or roof penetration detail.
What It Is
Cap flashing is the upper protective piece in a flashing assembly. It overlaps the material below it so rainwater is directed out and away instead of being allowed to enter behind siding, masonry, roofing, or trim.
In residential construction, cap flashing is used wherever an exposed top edge needs a weatherproof cover. It is especially important around windows, doors, parapets, and transitions where gravity-driven water can otherwise work behind the finish layer.
Where It Is Used
Cap flashing is used above window and door heads, on top of masonry walls, at parapets, around roof-to-wall intersections, and as part of chimney and counterflashing systems. The exact shape depends on the assembly, but the purpose is always to cover and drain the upper edge.
How to Identify One
A cap flashing is usually a bent metal piece with a horizontal top and a downward leg that throws water clear of the surface below. You will often see a small drip edge at the bottom. Rust, open laps, sealant failure, or missing pieces are signs the detail is no longer reliable.
Replacement
Replacement requires matching the profile and integrating the new flashing correctly with the surrounding siding, masonry, or roofing. Surface caulk alone is not a substitute for properly lapped cap flashing because the detail depends on gravity, overlap, and drainage.
Frequently Asked Questions
Cap Flashing — FAQ
- What does cap flashing do?
- Cap flashing covers the top edge of a wall, opening, or flashing assembly so water is forced to shed outward. It prevents rain from getting behind siding, trim, stucco, masonry, or roofing details.
- Is cap flashing the same as counterflashing?
- Not always. Counterflashing is a specific flashing layer that covers base flashing, while cap flashing is a broader term for a top cover that sheds water. Some details use one piece that functions as both.
- Can missing cap flashing cause leaks?
- Yes. If the top edge of an assembly is exposed, water can run behind the finish surface and soak the wall or roof structure. Leaks often show up well below the actual failure point.
- Can cap flashing be repaired with caulk?
- Caulk can temporarily seal a small gap, but it does not replace missing overlap or failed metal flashing. A durable repair usually means installing new flashing with the correct shape and lap.
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