Roofing Glossary

Counter Flashing

Counter flashing is the outer layer of a two-part flashing system used at chimneys and masonry walls. While base (step) flashing comes up from the roof surface, counter flashing comes down from above — embedded into the masonry mortar joints — overlapping the base flashing to shed water over it.

The two layers work like shingles: the upper layer always overlaps the lower, so water is shed outward at every point. Proper counter flashing is cut into the mortar joints of the chimney — not just surface-mounted with caulk — so it cannot peel away.

Surface-mounted counter flashing held on with caulk alone is a common shortcut. It works until the caulk fails, which it always eventually does, and then water runs straight behind the base flashing.

Why It Matters

Chimney leaks are notoriously misdiagnosed. If a chimney has been re-caulked repeatedly and still leaks, the counter flashing was probably never properly embedded — the fix is real metalwork, not more sealant.

Questions about your own roof? Request a free estimate or call Nucci Brothers Roofing at (301) 458-1003.