Why does my chimney flashing leak after every storm?

What a storm-only chimney leak is telling you

If your chimney leaks after every storm but stays dry in light rain, you've got a flashing problem. That's the near-certain answer.

Flashing is the metal and sealant that bridges the gap where the chimney passes through the roof. When it's sound, water slides right past. When it fails, wind-driven rain gets behind it and rides straight into your attic.

The reason it only shows in storms is simple. Gentle rain falls straight down and drains off. Storm rain comes in at an angle and gets pushed up under any loose edge.

So the leak isn't random. It's a specific gap that only opens up when the wind and water hit it just right.

The good news: flashing repairs are usually well under a thousand dollars if you catch them early. The bad news: people ignore these for years, and that's when the framing rots.

The usual suspects, ranked

In the field, chimney flashing failures fall into a short list. Let me walk you through them in the order I actually find them.

Number one is counterflashing that's pulled out of the mortar joint. That's the metal cap tucked into a groove in the brick. Mortar shrinks over 15 to 25 years, the metal loosens, and storm wind lifts the edge.

Right behind that is old roofing tar cracking open. Somebody 'fixed' the leak years ago with a bucket of black cement. It dries, alligators, and splits, and now it funnels water instead of blocking it.

Then there's step flashing on the sides of the chimney. If a piece is missing or someone ran it as one long strip instead of interwoven L-pieces, driven rain slips under it.

Wide chimneys have their own issue. Anything past about 30 inches wide needs a cricket, a little peaked diverter on the uphill side. No cricket means water piles up behind the chimney until it finds a seam.

The outliers are cracked chimney crowns and rusted chase covers. Those aren't roof flashing at all, but they read like a flashing leak from inside, so a good diagnosis checks them too.

What the pro will do

There is no do-it-yourself path we recommend for this repair. The safe and lasting fix comes from a licensed pro who can diagnose the true cause and complete the work correctly.

Booking a qualified tech protects your safety, your warranty, and your home. Call a licensed professional to handle it end to end.

What this costs in 2026

Costs swing based on what actually failed, so here's the honest range.

A simple counterflashing re-seat and reseal, where the existing metal is fine but the seal or mortar let go, runs about $250–$1200. That's the low end and the most common storm-leak fix.

A full reflash, meaning new step flashing and new counterflashing woven back into the shingles and remortared, is typically 500 to 1,500 dollars depending on chimney size and roof pitch.

Adding a cricket to a wide chimney adds carpentry, so budget 500 to 1,200 dollars on top of the flashing work.

Replacing a rusted chase cover on a factory-built chimney runs $250–$1200 for the fabricated part and install, more if it's stainless.

If you've waited long enough to rot the decking, add 500 to 1,500 dollars for tearing out and replacing the wet plywood. That's the expensive lesson of ignoring a small leak.

Can this wait?

Short answer: not long. This is a high-urgency symptom.

It's rarely a middle-of-the-night emergency unless water is actively pouring in or getting near electrical. But every storm that comes through while you wait pushes more water into the framing.

Roof decking is plywood or OSB. Soak it repeatedly and it delaminates and rots. Rafters follow. Mold sets up in the insulation.

The math is brutal. A 400 dollar flashing fix ignored for two winters can become a 2,500 dollar deck-and-frame repair.

If you're heading into freeze-thaw season, move faster. Trapped water freezes, expands, and cracks mortar and sealant wider with every cold night.

Get it inspected within a couple of weeks, sooner if the leak is heavy. This is the kind of thing that's cheap to fix and expensive to neglect.

Chimney type changes the whole picture

Before you or a contractor diagnose anything, figure out what kind of chimney you have. The failure points are different.

Masonry chimneys (real brick or stone) have a concrete crown on top and metal counterflashing tucked into the mortar joints. These fail at the mortar and the crown as they age past 20 years.

Factory-built chimneys, common in homes built from the 1980s on, are a framed box, often wrapped in siding or a fake brick panel, with a metal chase cover on top. These fail at the chase cover, which rusts, and at the base flashing.

If you've got a wood or siding-clad chimney box and see rust streaks running down the sides, that chase cover is your leak. No amount of flashing work fixes a rusted cover.

Older homes (pre-1970) sometimes have flashing that was never quite right to begin with, or has been tarred over so many times you can't tell what's under there. Those usually need a full reflash rather than a patch.

How we diagnose this at HomeSymptom

We build these pages around what actually shows up on service calls, not what ranks well.

The ranking of causes here reflects field frequency. Loose counterflashing and cracked tar are genuinely the top two things we find behind storm-only chimney leaks.

Cost ranges are 2026 US figures for typical single-family homes, pulled from common regional pricing. Steep roofs, tall chimneys, and premium metal push you toward the high end.

Fall risk and waterproofing make this pro work. Have a licensed roofer handle the diagnosis and repair.

When something falls outside roof flashing, like a cracked crown or a masonry problem, we say so and point you to the right trade. A leak diagnosed wrong just costs you twice.