Chimney Flashing: Repair or Replace?

Chimney flashing can be repaired when the metal is sound and only the seal has failed: dried-out caulk, a loose counter flashing edge, or an eroded mortar joint that the counter flashing sits in. It needs to be replaced when the metal itself is the problem: rusted through, bent or lifted so it no longer laps correctly, undersized for the chimney, or installed wrong in the first place (a single surface-mounted strip sealed with caulk instead of proper step and counter flashing). A repair is the right call when you are buying more years out of good metal. A replacement is the right call when a repair would be re-caulking a system that was never going to shed water.

In the Seattle area this decision matters more than in drier climates, because flashing here is wet for most of the year. Sea-Tac's NOAA 1991-2020 normals show about 29.65 inches of rain from October through March, roughly 73 percent of the annual 40.34 inches, and about 150 to 156 days a year with measurable precipitation. A marginal flashing job that would hold up for years in a dry climate gets found out in one Puget Sound winter.

What chimney flashing is, and why it fails

Flashing is the metal that closes the joint between the chimney and the roof. It is built in layers so that water always runs over a lap, never into one:

• Step flashing is a series of L-shaped pieces woven in with each course of shingles along the sides of the chimney.
• Counter flashing (also called cap flashing) is set into a cut groove or mortar joint in the masonry and bends down over the top of the step flashing.
• A back pan or cricket sits on the uphill side of a wider chimney to split water around it instead of letting it pile up against the brick.
• An apron covers the downhill side.

Flashing fails in a few predictable ways. The sealant at the counter flashing edge dries and cracks. The mortar joint the counter flashing is set into erodes, which is a masonry problem as much as a metal problem; BIA Technical Note 7B notes that improperly filled mortar joints lead to leaky walls. Galvanized metal rusts, starting at nail heads and bends. Roofers replacing shingles sometimes reuse old step flashing or skip the counter flashing and caulk the step flashing to the brick instead. And on older masonry, the chimney and the house settle at slightly different rates, which pulls the laps apart.

How to tell if chimney flashing is leaking

You can get a strong read from inside the house, and that is where we want you to look. Do not go on the roof.

• A stain on the ceiling or wall beside the chimney, not in the firebox, is the classic flashing symptom. Water is running down the outside of the chimney, not the inside.
• Wet framing or insulation in the attic at the point where the chimney passes through the roof deck.
• Stains that grow during long, steady rain rather than appearing instantly in a downpour. Flashing leaks are usually slow seepage.
• Rust streaks on the roof or siding below the chimney, which mean the metal is corroding.
• Visible lifted metal or gaps you can see from the ground or a window.

A leak in the firebox itself is more likely a cap or crown problem. If you are not sure which it is, a chimney inspection settles it, and our chimney leak repair page walks through all six entry points.

When flashing repair is the right answer

A chimney flashing repair keeps the existing metal and fixes the seal. It makes sense when:

• The step and counter flashing are both present, correctly layered, and not rusted.
• The counter flashing has pulled slightly out of its joint and can be re-bedded and re-sealed.
• The mortar joint holding the counter flashing has eroded and needs to be repointed so the metal has something solid to sit in.
• The sealant has failed at the edges but the metal underneath is dry and intact.
• A cricket is missing on a wide chimney and can be added without disturbing the rest.

Done right, a repair is not just a bead of caulk. It means cleaning the joint, repointing where the mortar has gone, re-setting the counter flashing, and sealing with a product rated for masonry and metal in wet conditions. Caulk on its own is a temporary patch, and in this climate it rarely lasts a full wet season.

When flashing should be replaced

A chimney flashing replacement removes the old metal and installs a new step, counter, apron, and back pan system. We recommend it when:

• The metal is rusted, pinholed, or brittle. Sealing rusted flashing buys months, not years.
• There is no counter flashing, just step flashing caulked to the brick. This is a common shortcut on re-roofs and it fails because caulk cannot bridge a moving joint.
• The flashing is a single surface strip or a roll-on membrane glued to the masonry.
• The laps are wrong: counter flashing tucked under the step flashing, step flashing on top of the shingles, or pieces too short to overlap.
• The roof is being replaced anyway. New shingles with old flashing is a false economy, and it is the best moment to do the job properly.
• Water has already damaged the roof deck around the chimney, which has to be opened up regardless.

A replacement should also be the answer when you have already paid for two or three repairs on the same flashing. At that point the repairs cost more than the replacement would have, and the attic framing has been wet the whole time.

The freeze-thaw factor

The reason flashing repairs need to be thorough here, not cosmetic, is the winter pattern. Sea-Tac's normal lows for December through February sit between 37 and 38 F. The region sees roughly 60 days a year that touch 32 F but only about 4 that stay frozen all day, so water that gets behind the counter flashing freezes at night and thaws by noon, repeatedly. The Brick Industry Association's Technical Note 18 describes what that does to saturated masonry: the ice expands, and repeated cycles cause cracking and spalling. On a chimney, that is the mortar joint your counter flashing depends on. A small gap in November is a loose counter flashing by spring.

Who repairs chimney flashing: a roofer or a chimney company?

Both can, and the honest answer is that flashing sits on the line between the trades. A roofer works the shingle side and will usually replace step flashing as part of a re-roof. The counter flashing is cut or bedded into the masonry, and the condition of the brick, mortar, crown, and cap above it decides whether the flashing job actually stops the leak. That is chimney work. We handle both sides of the joint, and when the roof itself needs work beyond the flashing, we will tell you so you can bring in a roofer rather than have us sell you something we should not.

If you have a roofer's quote for flashing, we will give you a free second-opinion quote. We price match and take 10 to 25 percent off, and we include the masonry check that a roofing quote usually does not.

What we do on a flashing call

We inspect the flashing, the mortar joints it is set into, the crown, the cap, and the attic side of the chimney where we can get to it. We tell you whether the metal is worth keeping. If it is, we repair it properly; if it is not, we quote a replacement and explain why. The quote is free and in writing. Same-day service is often available across Seattle, Tacoma, Everett, and the road-accessible Puget Sound, including Gig Harbor across the Tacoma Narrows Bridge.

If you're not happy, we're not done. We come back and make it right at no charge.

What to do next

• Look at the ceiling and walls next to the chimney and in the attic, if you can safely reach it, for staining or damp insulation. Note whether the leak appears in a downpour or after a long soak.
• Stay off the roof. A wet Seattle roof is not worth the look.
• Call 206-453-2045 or request a free quote online. Tell us what you are seeing and when.
• If you are planning a re-roof this year, schedule the flashing inspection first so the new roof and the chimney are handled together.

Related

• Water Stains on the Ceiling Near Your Chimney: 6 Causes
• Why Is My Chimney Leaking When It Rains?
• Chimney Flashing Repair service