What Is Counter-Flashing?
Counter-flashing (or cap flashing) is the visible upper metal on a chimney or masonry wall. Base and step flashing turn water off the roof, but their top edges would let water in behind them; counter-flashing solves this by embedding into a reglet — a groove cut into a mortar joint — or lapping down from behind cladding, hanging over the lower flashing like a metal awning. The two layers stay unfastened to each other so the chimney and roof frame can move independently without tearing the seal. It fails when the reglet sealant dries and cracks, mortar deteriorates, or an installer surface-mounts the metal with a caulk bead instead of cutting a reglet. Homeowners spot loose, rattling, or fallen strips of metal at the chimney, or leaks that appear only in wind-driven rain. Repair means grinding a clean reglet, bending new metal into it, wedging it, and sealing with polyurethane — masonry work as much as roofing work.
Important Distinction
Note: Counter-flashing covers the top of base/step flashing; it is the second layer of a two-part system, not an alternative to it. Caulking the top of step flashing directly to brick is a substitute that fails.
Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
How Counter-Flashing Relates to Other Topics
Counter-flashing exists to cover the top edge of step flashing: step flashing moves water off the roof plane, and counter-flashing cut into the masonry keeps water from getting behind it - a bead of caulk substitutes for neither.
Efflorescence appearing below the counter-flashing line means water is entering the masonry above it - the flashing can be perfectly sound while the chimney crown or brick lets water in behind the whole assembly.
Questions about Counter-Flashing?
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