Home / Learn / Leak Where the Chimney Meets the Roof
Staining on the wall or ceiling beside a chimney — or a damp patch on the brick in the attic — is nearly always failed flashing, not failed bricks. The metal that waterproofs that joint has a shorter life than the roof and a much shorter life than the chimney. Rebuilding it properly, step flashing and counter‑flashing both, is $1,265. Sealant is not a repair, and we won’t sell you one.
Every other part of a shingle roof is one material lying on top of another, shedding water downhill. A chimney interrupts that completely. It is a masonry column coming up through the field of the roof, and water running down the slope arrives at it from above with nowhere to go but sideways.
Worse, the two materials don’t move together. Brick and mortar expand and contract at one rate; wood framing and shingles at another. The joint between them is working against itself every day of the year, and around here it does that through a hundred‑degree summer swing and thirty or more freeze‑thaw cycles a winter. Nothing rigid survives that joint. Which is why the answer is never one sealed surface — it is two layers of metal that are allowed to slide past each other.
And because it is the hardest detail on the roof, it is the one most often done badly. A chimney leak is far more often an installation shortcut from fifteen years ago than it is wear.
Almost every bad chimney detail is a missing one of these two. Knowing which is which is how you read a quote.
Individual L‑shaped pieces of metal, one per shingle course, each lapped over the one below like a staircase. One leg lies on the roof under the shingle; the other stands up against the brick.
Pieces, not a strip. A single long piece of metal up the side of a chimney cannot shed water between courses, and it is the commonest shortcut we find.
A second layer, let into a groove cut in the mortar joint and folded down over the top of the step flashing. The groove is called a reglet. It is what stops water running down the brick face and in behind the first layer.
Cut in, not surface‑caulked to the brick. A bead of sealant on masonry is a two‑year repair at best.
On a wide chimney on a sloped roof, a small framed ridge behind it that splits water around both sides instead of letting it pond against the back wall. Code calls for one over 30 inches wide.
If snow and debris pile against the back of your chimney every winter, this is what’s missing — and it’s a separate, bigger job.
The two metal layers are the repair we price at $1,265. They work as a pair: the step flashing handles water on the roof, the counter‑flashing handles water on the wall, and the gap between them is deliberate, because that is what lets brick and roof move independently without tearing the seal. Caulk that gap shut and you have built the failure back in.
Repairs come off a flat‑rate book, so the number doesn’t depend on how long the job takes us or how urgent it sounded on the phone.
Shingles opened around the chimney, old metal out, new step flashing set course by course, a fresh reglet cut into the mortar, new counter‑flashing let in and the shingles woven back.
On a walkable roof. More on a steep or very steep one, because it’s slower and takes more gear. Waived if the visit turns into a roof.
Around four times a pipe boot, because it is four times the work: masonry cutting, metal bent to your courses, and twenty to thirty shingles lifted and relaid without breaking them.
Masonry repair — spalled brick, a failed crown, repointing — and a cricket if one is missing. Decking, if the sheathing beside the chimney has already gone soft. All photographed and priced before anybody starts.
One honest caveat, and it matters here: if the bricks and mortar themselves have gone, flashing won’t fix your leak. Water can travel straight through soft mortar joints and a cracked crown and come out inside with the metal perfectly intact. If that is what we find, we will tell you that you need a mason before you need us, and we will not take $1,265 to install flashing that won’t stop the water.
Every price we charge is on one page: see our full price card →
A chimney leak is worse than a pipe leak for one structural reason: the water runs down the inside of a wall rather than dripping onto the top of a ceiling.
The plywood right against the chimney stays wet and delaminates. It’s the piece hardest to replace, because it runs under the courses you’d rather not disturb.
Rafters and the headers framing the chimney opening are right there. Rot in a header is a carpentry job and the roof has to come apart to reach it.
Water tracks down the chimney chase into the wall cavity. Wet insulation, stained plaster, and the one place in a house where mould goes unnoticed longest.
Saturated brick spalls when it freezes — the face pops off in flakes. That turns a flashing job into a masonry job, which costs several times more.
None of this is fast and none of it is a scare tactic. It is just the order things fail in once that joint is open. The flashing is the cheap end of it.
This matters more on a chimney than anywhere else. Doing the flashing properly means lifting the shingles around the chimney — and old, brittle shingles break when you lift them. On a roof with a few years left, that’s a repair we can make hold. On a twenty‑year‑old roof, we’d be charging you $1,265 to disturb shingles that are about to be torn off anyway, and the new flashing would be thrown away with them. If that’s what we find, we will say so, show you the photographs, and give you a written replacement number at the same visit. The visit fee comes off if you do replace. You are free to do nothing with the number.
The reverse is just as true. If the roof is sound, the flashing is the whole problem and the flashing is the whole fix. One bad detail at one chimney is not a reason to replace a roof, and anybody who looks at a stain beside your chimney and quotes you a full replacement without getting on the roof is selling, not diagnosing. Our signs you need a new roof guide lists what genuinely warrants one.
Note also what we include on a full replacement: new step and counter‑flashing, never re‑used. Re‑using old chimney flashing on a brand‑new roof is one of the quiet ways a cheap quote gets cheap — and it puts a fifteen‑year‑old leak back under a new roof. What’s in our price →
Crown, brick faces, mortar joints, and the cap. If water is coming through the chimney rather than around it, flashing is the wrong fix and you need a mason.
Is there step flashing at all, or one long strip? Is the counter‑flashing cut into the mortar or caulked to the face? Is a cricket missing? That’s the diagnosis.
Every slope, the chimney from all four sides, and the attic where we can get to it. You see the failure yourself rather than take our word for it.
The flashing number, anything else we found, and a written replacement number if the roof is near the end — at that visit, while the photos are fresh.
$1,265 for step flashing and counter-flashing together on a standard masonry chimney, plus the diagnostic visit from $299 on a walkable roof. The visit fee is waived if the work turns into a roof replacement. Masonry repair and a missing cricket are separate and get priced after we’ve looked. Every price we charge is on our pricing page.
We won’t, because it doesn’t hold. Brick and roof framing expand at different rates, so a rigid seal across that joint tears itself open within a couple of seasons — and then water runs in behind a black smear nobody can see. Two layers of metal that slide past each other is the detail that works. If your chimney has already been caulked twice, that’s your answer.
That’s the first thing we check, and it’s why we don’t quote this over the phone. Water travels through soft mortar and a cracked crown just as readily as around bad metal, and new flashing won’t stop it. If the masonry is the problem we’ll tell you to get a mason before you spend money with us.
Because it’s a different scale of work: a reglet cut into mortar, metal bent to match your shingle courses, and twenty to thirty shingles lifted and relaid without breaking them. A boot is one gasket at one hole.
Code calls for one behind a chimney wider than 30 inches on a sloped roof, and it genuinely helps — it splits water around the chimney instead of letting it pond against the back wall. It’s a framed addition, not part of the flashing price, and we’ll tell you if yours should have one.
Often the cheapest permanent answer, and worth asking about — taking it down below the roof line and sheathing over the hole removes the leak and the detail that caused it. That’s a masonry and carpentry job rather than a roofing one, best done at the same time as a replacement. We’ll raise it if it fits your situation.
We’ll get on the roof, read the existing flashing detail, check the masonry, and tell you what it is and what it costs before we do anything. If it’s a repair, we’ll tell you it’s a repair.
Roofing per square, the repair book, the gutter minimum. Our price card →
A stain under a vent pipe, and why it’s the cheaper one. Pipe boot leaks →
Step flashing, counter‑flashing, cricket, reglet — one labelled diagram. Roof anatomy →
The signs that actually warrant a replacement. Signs you need a new roof →
Rather talk to someone? Contact us — we answer our own phone.
We photograph every slope, read the flashing detail, check the masonry, and give you the price before we do anything. If the roof is near the end, we’ll say so.
