Where Your Roof Meets Your Chimney: The Importance of Proper Flashing
Water damage is the most common — and most preventable — threat to a chimney system. Most homeowners know to watch for a damaged crown or missing cap, but there's another failure point that causes just as much trouble: the flashing.
At Haulin' Ash Chimney Services, flashing problems are among the top findings on our inspections. A bad flash job can send water into your attic, walls, and ceiling for years before anyone connects the leak to the chimney.
What Is Chimney Flashing?
Flashing is the weatherproof barrier where your chimney meets your roof. Because a chimney is a rigid masonry structure penetrating a flexible roofing surface, that joint is inherently vulnerable — the two materials expand and contract at different rates, shift with settling, and take the full brunt of wind-driven rain.
Properly installed flashing uses two layers: step flashing runs up the sides of the chimney in overlapping L-shaped pieces integrated with the roofing material, while counter flashing is embedded into the chimney masonry and laps down over the step flashing. Together they create a barrier that handles movement without opening gaps. When only one layer is used — a common shortcut — the system will eventually fail.
How Flashing Fails
Flashing degrades gradually. By the time water shows up inside, the damage has usually been building for a season or two.
The most common failure modes we see: sealant-only installations, where a roofer skips counter flashing and runs a bead of caulk around the chimney base — it looks fine initially, then cracks and pulls away within a few years with nothing underneath it. Flashing nailed to the masonry rather than embedded into a mortar joint, which won't stay watertight long. And mortar joint failure at the counter flashing, where the masonry around the embedded flashing cracks and separates over time.
Even properly installed flashing has a service life. Galvanized steel corrodes. Joints open up. These issues are easy to miss from the ground.
What the Water Does Next
When flashing fails, water doesn't always appear immediately or obviously. It may travel along rafters or wall framing before showing up as a stain somewhere seemingly unrelated to the chimney — saturating insulation, promoting mold, and rotting structural framing along the way.
What We Check
During an inspection, we examine all four sides of the flashing for lifting, gaps, corrosion, and improper installation. We check where the counter flashing meets the masonry and confirm the step flashing is properly integrated with the roof. Everything is documented with photos.
Repairs range from resealing minor gaps to full flashing replacement, depending on what's there and how far gone it is.
Your roof can be in perfect shape and still leak at the chimney if the flashing is compromised. It's a small detail with outsized consequences — and exactly the kind of thing a trained eye catches before your drywall does.
---
Haulin' Ash Chimney Services provides chimney inspections, repairs, and maintenance throughout the greater Seattle area. CSIA-certified, following NFPA 211 standards on every inspection.
