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Flashing Failures Explained
Almost every flat roof leak traces back to a transition, not the open roof. Here’s what actually goes wrong at parapet walls, chimneys, and skylights.
Parapet Walls & Termination Bars
Where the roofing membrane runs up a parapet wall, a metal termination bar holds it against the wall, usually sealed with caulking. Caulking dries out and cracks over time — and when it does, water doesn’t just sit on top, it gets funneled directly behind the bar and into the wall assembly. A cap on top of the parapet fails the same way where the cap meets the wall.
Counter-Flashing at Chimneys and Walls
Proper counter-flashing sits in a groove cut into the wall or chimney masonry, so water physically can’t get behind it. When that groove seal fails — or someone’s caulked over the flashing instead of resealing the groove itself — water runs down behind the flashing rather than over it, and it can travel a surprising distance before showing up as a stain.
Skylight Curbs
The skylight itself sits on a curb, with flashing tying that curb into the surrounding membrane. Leak reports about a specific skylight are almost always about that flashing detail, not the glass or the unit itself.
Frequently Asked Questions
Why doesn’t caulk alone fix a flashing leak?
Caulk isn’t designed as a standalone waterproofing layer — it dries out and cracks within a season or two. A real flashing repair reseals the actual transition, not just the visible gap.