Three kinds of chimney, one weak point
On Airdrie roofs, “chimney” can mean three quite different things, and each one leaks in its own way. What they share is the joint where they pass through the roof — a joint that has to shed rain, snowmelt and wind-driven water while the roof and the chimney move at different rates through every freeze and thaw.
Masonry chimneys
Brick and block chimneys are found mostly on older homes in Old Town Airdrie. They need two layers of flashing: step flashing woven into the shingles, and counter-flashing set into the mortar joints and folded down over it. As mortar ages and the brick moves with the seasons, the counter-flashing loosens and water gets behind it.
Framed chimney chases
Many homes built across Airdrie’s subdivisions since the 2000s have a framed chimney chase: a wood-framed box, clad in siding or stone, that encloses a metal fireplace flue. Where it meets the roof, it needs the same step and counter-flashing as a brick chimney. On top, it has a metal chase cap. Cheaper caps rust, sag and hold water, and that water finds its way down the inside of the chase — which looks exactly like a flashing leak from inside the house.
Metal flues and vents
Furnace and water-heater flues, and other metal vents, pass through the roof with a flashing boot and a storm collar. Boots crack, storm collars loosen, and hail dents and deforms both.
How chimney flashing fails in Airdrie
Freeze-thaw. Airdrie’s winters, broken by chinook thaws, cycle between freezing and melting over and over. Water that gets into a mortar joint or behind a loose piece of flashing freezes, expands and pries it open a little further each time.
Caulk instead of flashing. One of the most common findings on newer homes: a bead of caulk doing the job flashing should do. Caulk hardens and cracks within a season or two in this climate.
Missing or undersized crickets. On wider chimneys, water and snow pile up on the uphill side unless a cricket splits the flow. Without one, that’s where the leak starts.
Short or missing step flashing. Each course of shingles along the side of a chimney needs its own piece of step flashing. Missing pieces, or pieces cut too short, let water run under the shingles.
Wind-driven rain. Rain driven sideways by northwest wind finds gaps on the windward side of a chimney that ordinary rain never reaches. Leaks that only appear in storms from one direction often start here.
Hail. Hail dents flashing, cracks flue boots and chips mortar and chase caps.
How we repair chimney flashing
- Find the real source. We inspect from the attic and the roof, and check the chimney cap or chase cap as well as the flashing, because a leaking cap can look like a flashing leak.
- Remove the old flashing and the shingles around the chimney.
- Repair the deck and framing if the leak has been going on long enough to cause rot.
- Install membrane around the base of the chimney as a second line of defence.
- Install new step flashing, one piece per shingle course, woven into the shingles.
- Install counter-flashing. On masonry, it’s set into cut mortar joints; on framed chases, it’s integrated behind the siding or stone.
- Add a cricket on the uphill side of wider chimneys where it’s missing.
- Replace the shingles and seal them in place.
For metal flues, we replace the flashing boot, reset the storm collar and seal it properly.
What you can check yourself
You don’t need to climb onto the roof to spot most chimney problems. From inside and from the ground, look for:
- Stains on the ceiling or wall beside the fireplace, especially after rain or on a mild day after snow
- Damp or darkened framing around the chimney when you look into the attic with a flashlight
- Water or rust inside the fireplace or on the damper
- Rust streaks down a framed chase below the cap, or a cap that looks dished or sagging
- Flashing that looks lifted or bent when you view the chimney from the street with binoculars
- Crumbling mortar, missing bricks or a cracked crown on an older masonry chimney
On newer homes, also look at where the chase meets the roof on its uphill side. If siding or stone runs down onto the shingles without visible metal flashing, water may be relying on caulk alone.
Chimney flashing during a roof replacement
If your roof is due for replacement, the chimney flashing should be replaced with it — never reused. Old flashing that’s bent back and re-nailed rarely seals properly around new shingles. A replacement is also the right time to add a missing cricket or remove a chimney you no longer use. See roof replacement in Airdrie.
When the chimney itself needs work
Sometimes the flashing isn’t the problem — the chimney is. Crumbling mortar, a cracked crown on top, or spalling brick lets water into the chimney itself, and no amount of flashing will stop it. We’ll tell you when that’s the case so you can have a mason address the masonry.
What chimney flashing repair costs
| Repair | Typical job | Notes |
|---|---|---|
| Full reflash around a brick chimney | $400–$700 | Step, counter and apron flashing. |
| Metal flue or chase flashing | $300–$500 | Storm collar, boot or chase top seal. |
| New cricket + rotted deck repair | $1,500–$3,000 | After a long-term leak. |
Get an exact quote for your roof
Most Airdrie chimney jobs are one of the first two rows; a cricket or rot repair only comes into it when a leak has gone on for a while. For how chimney work compares with other repairs, see the roof repair cost guide.
Across Airdrie
We re-flash masonry chimneys on older homes in Old Town, framed chimney chases on two-storeys in Cooper’s Crossing, King’s Heights, Hillcrest and Reunion, and metal flues across the city. For other leak sources, see roof leak repair; for urgent leaks, see emergency roof repair.