Chimney flashing repair in Gatineau is the single most-requested fix Cossette Roofing handles outside of full re-roofs — and for good reason. In Quebec’s freeze-thaw climate, the seal where your chimney meets your roof is the first thing to fail, and it’s the source of roughly 80% of the leaks our crews trace inside Outaouais and Ottawa homes. If your ceiling has a brown stain near the fireplace, your attic insulation feels damp after a thaw, or you can see daylight around your chimney from inside the attic, your flashing is almost certainly the culprit.
This guide explains what chimney flashing is, why it fails so quickly in Gatineau winters, the warning signs every homeowner should watch for, and how a proper repair is done by an RBQ-licensed roofer.
What Is Chimney Flashing and Why Does It Matter?
Chimney flashing is the system of metal pieces that seals the gap between your chimney and your roof deck. It is not a single piece of metal — it is a layered assembly designed to shed water away from one of the most vulnerable joints on any roof.
A complete flashing system has four parts:
- Step flashing — L-shaped metal pieces tucked under each course of shingles along the chimney sides
- Counter flashing (or cap flashing) — metal embedded into the chimney mortar joints, bent down over the step flashing
- Apron flashing — a wider piece at the front (downhill side) of the chimney that diverts water around the base
- Cricket or saddle — a small peaked structure on the back (uphill side) of any chimney wider than 30 inches, required by Quebec building code to divert snow and ice
When all four pieces work together, water hits the chimney, runs down the sides, and is channeled away from the roof deck. When even one piece fails, water enters the attic, soaks the insulation, rots the roof deck, and eventually shows up as a stain on your ceiling — usually months after the actual leak began.
Why Chimney Flashing Fails So Fast in Gatineau and the Outaouais
The Outaouais region puts more stress on chimney flashing than almost any other roof component. Three forces work against it year-round:
1. Freeze-Thaw Cycling
Gatineau averages over 70 freeze-thaw cycles per winter. Each cycle expands and contracts the metal flashing, the shingles around it, and the brick mortar of the chimney itself. Sealants that look fine in October crack and pull away by March. Cossette’s emergency dispatches spike every February for exactly this reason — water finds the new gap the moment a thaw arrives.
2. Ice Dam Pressure
When ice dams form along the eaves and around chimneys, melted water backs up under the shingles. A properly installed step-and-counter flashing system handles a few inches of standing water. A nail-and-caulk shortcut — common on builder-grade installations from the 1990s and early 2000s — fails the first time water sits against it for more than a few hours.
3. Mortar Erosion
Counter flashing is set into a groove cut into the chimney’s mortar joints, then sealed. Forty Quebec winters later, the mortar erodes, the seal pulls free, and water runs straight behind the flashing into the attic. This is the most common failure mode on chimneys in older Hull and Aylmer homes — the metal still looks fine from the ground, but the seal at the brick is gone.
Warning Signs Your Chimney Flashing Needs Repair
Most chimney flashing leaks are detected too late. By the time water shows on the ceiling, the roof deck and insulation have usually been wet for weeks. Watch for these earlier warning signs:
- Brown or yellow stains on the ceiling near the fireplace, even small ones
- White chalky residue (efflorescence) on the chimney brick inside or outside the home
- Damp, compressed, or musty-smelling attic insulation around the chimney chase
- Visible rust streaks on the flashing metal or on the shingles below the chimney
- Cracked, curled, or missing caulk along the top edge of the flashing
- Daylight visible from inside the attic where the chimney passes through the roof
- Loose bricks or crumbling mortar on the chimney itself — a chimney problem becomes a roof problem fast
Any one of these signs is enough to book a roof inspection. Two or more, and you almost certainly have an active leak that hasn’t reached the living space yet — at which point Cossette’s roof repair services can address the flashing before the damage spreads to the deck or insulation.
How a Proper Chimney Flashing Repair Is Done
There is a right way and a fast way to repair chimney flashing. The fast way is a tube of roofing tar smeared over the existing seal — it works for one season, sometimes two, and then the leak comes back worse. The right way takes a full day and looks like this:
Step 1 — Inspection and Diagnosis
A certified roofer inspects the chimney from the roof, the attic, and the interior. The goal is to determine whether the flashing alone has failed, or whether the chimney mortar, the surrounding shingles, the roof deck, or the attic ventilation also need work. Cossette includes this inspection in every free estimate across Gatineau, Hull, Aylmer, and Ottawa.
Step 2 — Removal of Old Flashing and Shingles
The shingles immediately surrounding the chimney are carefully lifted, and all old step, counter, and apron flashing is removed. Any rotted roof deck is cut out and replaced with new plywood. This step is non-negotiable — installing new flashing over rotten deck sheathing is the single most common reason a repair fails within two years.
Step 3 — Installation of New Step and Apron Flashing
New step flashing is installed piece by piece, woven into each course of shingles as they go back on. A new apron is installed at the front of the chimney, and on chimneys wider than 30 inches a cricket is built on the uphill side to divert water and snow. All metal is pre-painted galvanized steel or aluminum, sized to match Quebec roofing standards.
Step 4 — Cutting In and Sealing the Counter Flashing
A fresh groove is cut into the chimney’s mortar joints with a masonry blade. New counter flashing is bent to shape, inserted into the groove, and sealed with a high-grade polyurethane mortar sealant rated for Quebec’s freeze-thaw range. This is the step most repair crews skip — and the step that determines whether the repair lasts 20 years or two.
Step 5 — Final Seal and Cleanup
All exposed seams are sealed, the surrounding shingles are replaced or renewed, and the work area is cleaned. Cossette provides a workmanship warranty on every flashing repair, with manufacturer warranties on the materials used.
How Much Does Chimney Flashing Repair Cost in Gatineau?
Pricing varies with the size of the chimney, the condition of the surrounding shingles, the condition of the chimney mortar, and whether a cricket is required. As a general guide for the Gatineau and Ottawa market:
- Minor reseal of existing flashing in good condition — lower end of the spectrum, when the metal itself is still sound
- Full step and counter flashing replacement on a standard residential chimney — mid-range, the most common scope of work
- Full replacement plus cricket installation, deck repair, or chimney mortar repointing — higher end, often combined with surrounding shingle replacement
Cossette Roofing provides a free, written, no-obligation estimate for every chimney flashing project in Gatineau, Hull, Aylmer, Ottawa, and the wider Outaouais region. Pricing is itemized so you can see exactly what is being repaired and why.
How to Make Sure You Hire a Licensed Roofer
Chimney flashing work falls under Quebec’s regulated roofing trade, which means the contractor must hold a valid RBQ licence (subclass 7.0 — Insulation, waterproofing, roofing and siding). Before signing any quote, ask for the contractor’s RBQ licence number and verify the licence in the RBQ Licence Holders’ Repertory. An unlicensed contractor leaves you with no licence security, no recourse, and often no insurance — and on a flashing repair, the consequences of a failed seal land squarely on the homeowner.
Cossette Roofing holds RBQ Licence 5697-7788-01, full liability insurance, and BBB accreditation since 2020. The licence number appears on every estimate, contract, and invoice — exactly as Quebec law requires.
When to Repair the Flashing vs. Replace the Whole Roof
If the rest of the roof is in good condition and the leak is isolated to the chimney, a flashing repair is the right call — a properly executed flashing repair lasts 20 to 30 years on a Quebec home. If the surrounding shingles are curling, granule loss is heavy, the deck is soft in multiple spots, or the roof is more than 20 years old, replacing the flashing in isolation is a short-term fix on a roof that is already failing. In those cases Cossette recommends a full replacement so that the new flashing is integrated into a new roof system from day one.
A certified roofer should always tell you both options after the inspection, with honest reasoning for each. If anyone gives you a quote without going on the roof and into the attic, get a second opinion.
Get Your Chimney Flashing Inspected by a Certified Cossette Roofer
Cossette Roofing has been repairing chimney flashing across Gatineau, Hull, Aylmer, Ottawa, and the entire Outaouais region since 2005. Every roofer on the team is annually trained in shingle, metal, and elastomeric membrane systems. The company holds RBQ License 5697-7788-01, full liability insurance, and BBB accreditation since 2020.
If you suspect a leak around your chimney — or you simply want a professional to inspect the flashing before winter — request a free, no-obligation estimate. A certified Cossette roofer will visit your property, inspect the flashing from the roof and the attic, and give you a written quote with no hidden fees. For active emergencies — water actively coming through the ceiling, storm damage, or ice dam failure — Cossette’s 24/7 emergency roofing service dispatches a crew 24 hours a day, 7 days a week, 365 days a year.
Call 819-777-7177 or request a free quote at our website.
Cossette Roofing — RBQ License 5697-7788-01 — 18 Rue Buteau, Gatineau, QC J8Z 1X4 — Serving Gatineau, Hull, Aylmer, Ottawa, Kanata, Orléans, Embrun, Clarence-Rockland, Cornwall and the entire Outaouais region.