Know Your Roof · Flashing & Roof Edge
Counter Flashing: The Second Layer That Keeps Flashing Dry
Quick answer
Counter flashing is a second piece of flashing installed over the top edge of the base flashing, usually set into a wall or the mortar of a chimney. It blocks water from sneaking behind the base flashing, and it lets the roof and wall move a little without breaking the seal.
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Base flashing and counter flashing work as a pair
The base flashing lies on the roof. The counter flashing hangs from the wall and laps down over it. The two overlap without being fastened together, so they can flex as temperatures change.
Where you'll see it
Chimneys, set into the mortar joints. Brick or stucco walls that meet a roof. Parapet walls on flat roofs. Skylight and curb details.
How it goes in
In masonry, a slot called a reglet is cut into the mortar. The counter flashing is set into the slot and sealed. On a wall with siding, the siding itself can do the covering.
Common problems
Sealant that's cracked or pulled away. Mortar breaking down. Rusted or loose metal. Or no counter flashing at all, with sealant used instead.
What does counter flashing repair cost?
Counter flashing is typically reset or replaced along with the base flashing. Flashing repair around a wall, chimney, or valley typically runs $400 to $900. A minor repair that includes flashing, a vent boot, or one or two shingles runs $400 to $750. The final number depends on how much flashing is damaged and how hard it is to reach, and every job starts with a free roof inspection.
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