Chimney Flashing: The Small Detail That Keeps YourRoof Dry
If you’ve ever had a mysterious water stain appear on your ceiling near the fireplace,
chimney flashing is probably the culprit. It’s one of the most overlooked parts of a roofing
system, yet it’s responsible for sealing one of the most vulnerable spots on your entire
house: the joint where the chimney meets the roof.
What Is Chimney Flashing?
Flashing is thin, weatherproof material — usually metal — installed at the intersection of your
roof and chimney to prevent water from seeping into the gap between them. A roof is
designed to shed water efficiently across a continuous surface, but a chimney interrupts
that surface completely. Without flashing, rainwater and melting snow would run straight
down the chimney’s sides and into your attic or walls. Flashing works by creating a layered barrier that directs water up and over the joint rather than letting it pool or seep through.
The Three Parts of a Flashing System
Most chimney flashing systems are made up of three components working together:
1. Base (or apron) flashing This piece sits against the front of the chimney and lies flat
over the roof shingles below it, directing water away from the chimney’s downhill side.
2. Step flashing Installed along the sides of the chimney, step flashing consists of
individual L-shaped metal pieces layered with each row of shingles — like shingles
themselves, each piece overlaps the one below it so water is channeled downward and
outward.
3. Counter (or cap) flashing This is embedded into the chimney’s masonry (or mortar
joints) and folds down over the step and base flashing. It’s the final layer that keeps water
from getting behind the step flashing and into the wall.
Common Materials
Galvanized steel – affordable and durable, though it can rust over time if the coating wears down
Aluminum – lightweight and corrosion-resistant, but shouldn’t be used on masonry
chimneys since it reacts poorly with mortar
Copper – the gold standard; extremely long-lasting and develops an attractive patina,
though it comes at a premium price
Lead – historically common and still used in some regions for its flexibility, though less
common in new installs today
At Pinnacle Roofing we often use 24 gauge Kynar coated steel. The steel is very rigid and has to be custom bent with a special tool called a brake. On most of the projects we complete we either include this service as part of the job or bring the importance of adding a high quality flashing around the chimney as an upgrade to our clients. We have noticed a majority of our competitors simply leave the existing flashings and choose to do nothing.
Signs Your Flashing Is Failing
Flashing doesn’t last forever. Watch for:
Rust stains or streaking on the chimney or roof
Water stains on ceilings or walls near the chimney
Visible gaps, cracks, or lifted metal at the flashing joints
Deteriorated caulk or sealant around the counter flashing
Efflorescence (white, chalky residue) on interior brick, a sign of moisture intrusion
Most flashing failures happen not because the metal itself wears out, but because the
sealant or mortar around it deteriorates, or because the flashing was installed incorrectly in
the first place — a surprisingly common issue even with reputable roofing crews.
DIY or Call a Professional?
Minor recaulking or resealing around existing flashing is a manageable weekend project for
a handy homeowner. But a full flashing replacement — especially step flashing, which
requires removing and reinstalling shingles — is a job best left to a professional roofer or
mason. Working at a roof-chimney joint means dealing with both roofing and masonry
systems, and a mistake here can lead to expensive water damage down the line.
The Bottom Line
Chimney flashing is a small detail with an outsized impact on your home’s protection from
water damage. A well-installed, properly maintained flashing system can last decades, while
a poor one can cause leaks within a single rainy season. If your home has a chimney, it’s
worth having flashing inspected annually — ideally alongside a routine roof or chimney
inspection — so small issues get caught before they become expensive repairs.
Pinnacle Roofing has completed all types of chimney flashings and we custom bend our pieces on site so the chimney will have a clean custom piece of metal that will in most cases out perform the time you live in your home.