What is counter flashing? The metal that covers the joint
Counter flashing is the cover that keeps water from running behind the lower flashing. When it fails, the leak looks like a roof problem.
Counter flashing is the upper layer of metal that covers the top edge of the lower flashing. It is fixed to the wall, chimney or curb, not to the roof. Its job is simple: stop water from running down the wall and behind the piece underneath.
Where counter flashing sits
You find it wherever a roof meets something vertical. The lower piece, called base flashing, laps under the shingles and runs up the wall. The counter flashing hangs over the top of it like a cap.
The two pieces are not joined. That is deliberate. The house and the roof move a little with heat and weather, and a loose overlap lets them move without tearing the seal.
Counter flashing and cap flashing
People use the two names for the same thing, and often they are. Some roofers say counter flashing when it is a separate strip let into masonry, and cap flashing for the whole upper layer. If a quote uses either word, ask which piece they mean and ask to be shown it. We cover the chimney version in cap flashing.
How counter flashing fails
It sits high on the wall, so it takes sun, wind and rain with nothing to shelter it. The usual problems are slow ones.
- Rust along the edge, especially in steel pieces.
- Mortar that has crumbled and let the metal pull loose.
- A gap between the metal and the wall where water runs in.
- Sealant smeared across the top in place of a proper cover.
A sealant smear is the sign to take seriously. It often means the counter flashing has already failed once and been patched over.
What a leak from it looks like
A stain that appears after wind-driven rain, and not after gentle rain, often points at a gap high on the wall. The water enters above the roof surface, runs behind the base flashing and shows up inside as a ceiling stain near the wall. It can look like a bad shingle when the shingles are fine.
What to check from the ground
Use binoculars from the yard. Look along the top edge of the metal where it meets the wall. Rust streaks, a dark gap or a thick bead of tar all deserve a photo.
Inside, check the ceiling and the attic framing along the same wall with a flashlight, staying on the joists.
Why we do not show the repair
Resetting counter flashing means cutting into mortar or siding and working at the roof edge beside a wall. That is high, awkward work, and we do not publish the steps. Take your photos, note the stained room and ask a roofer which layer needs replacing. For the bigger picture, see what is roof flashing.
Frequently asked questions
What is counter flashing?
It is the upper piece of metal fixed to a wall or chimney that covers the top edge of the lower flashing and keeps water from running behind it.
Is counter flashing the same as cap flashing?
Often yes. Roofers use the names loosely, so ask which piece is meant and ask to be shown it.
Why is counter flashing not attached to base flashing?
The loose overlap lets the roof and wall move with heat and weather without tearing a seal.
Can sealant replace counter flashing?
No. Sealant dries and splits. A smear of it on the top edge usually means the metal cover failed and was patched.
How do I check counter flashing safely?
Use binoculars from the yard to look along the top edge, and check the attic framing near the wall from the joists. Do not go on the roof.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- NRCA. National Roofing Contractors Association
- US OSHA. 1926.501 — Duty to have fall protection (OSHA)