Flashing Fails More Often Than Shingles
If you asked most homeowners which part of their roof is most likely to leak, they would say the shingles. It is a reasonable guess, but it is wrong. The most common source of residential roof leaks in Calgary is not a shingle failure — it is a flashing failure. Flashing is the metal (usually aluminum or galvanized steel) installed at every transition point on the roof: where the roof meets a chimney, where it meets a wall, where vents and pipes penetrate the surface, where two slopes meet in a valley, and at the drip edge along the eaves.
Each of these transition points is a joint between dissimilar materials that expand and contract at different rates as temperature changes. In Calgary, where a single winter can deliver 30 or more significant temperature swings, those joints are stressed repeatedly over six months. The sealant dries and cracks. The metal shifts and lifts. The bond between flashing and the adjacent surface weakens incrementally. By spring, the damage is done — it is just not always visible from the ground.
Chimney Flashing — The Most Complex and Most Vulnerable
Chimney flashing is typically the most failure-prone assembly on any residential roof because it involves the most components and the most material interfaces. A properly flashed chimney uses step flashing along each side (overlapping metal pieces woven into the shingle courses), counter flashing embedded in the mortar joints of the chimney masonry, a back pan on the downhill side, and a cricket or saddle on the uphill side to divert water around the chimney.
Every one of those components can fail independently, and Chinook cycling accelerates the process. Step flashing can loosen as shingles shift. Counter flashing can pull out of mortar joints as the masonry expands and contracts. The back pan can develop sealant failure. And the cricket, if one was installed, can develop its own flashing problems at the junction with both the chimney and the roof surface.
Check your chimney flashing in spring by looking for visible gaps, rust, lifted edges, cracked sealant, and mortar deterioration at the counter flashing line. From inside the attic, check the area around the chimney penetration for water stains, damp wood, or active moisture. Chimney leaks are notorious for causing damage that is out of sight until it becomes severe.
Vent Pipe Flashing — Simple But Easily Overlooked
Every plumbing vent, exhaust pipe, and other penetration through the roof has a boot or collar that creates a seal around the pipe. These are typically made of rubber, neoprene, or a metal-rubber combination. The rubber degrades over time from UV exposure and temperature cycling, becoming brittle and cracking.
A cracked vent boot is an open hole in your roof. It is also one of the simplest and cheapest repairs in all of roofing — a new boot costs $15 to $30 in materials and takes a professional about 20 minutes to install. Ignoring it costs whatever the water damage to your decking, insulation, and ceiling eventually adds up to.
Check vent boots in spring by looking for visible cracks, gaps between the collar and the pipe, or boots that appear distorted or flattened. From the attic, check below each penetration for any signs of moisture.
Valley Flashing — High Volume, High Stakes
Valleys collect water from two converging roof slopes, so they carry the highest water volume of any point on the roof. Valley flashing needs to be intact, properly positioned, and clear of debris to handle that volume without allowing water underneath.
After a Calgary winter, check valleys for debris accumulation that could redirect water flow. Look for flashing that appears bent, displaced, or corroded. If the valleys on your roof use a closed-cut or woven shingle method rather than exposed metal flashing, check for shingle wear in the valley line where water flow is heaviest — this area wears faster than the surrounding surface.
Drip Edge and Eave Flashing
Drip edge is the metal strip along the eaves and rakes (the sloped edges) of the roof. It directs water away from the fascia and into the gutters.When drip edge fails, water runs behind the gutter and down the fascia — the primary cause of soffit and fascia rot.
In spring, check the drip edge for any sections that have pulled away from the deck, are visibly rusted, or appear bent or displaced by ice. On the eave side, the drip edge should direct water into the gutter trough, not behind it. On the rakes, it should prevent water from running along the underside of the deck and dripping off the edge in an uncontrolled manner.
Roof-to-Wall Step Flashing
Anywhere the roof meets a vertical wall — at dormers, at second-storey wall steps, at additions — step flashing is installed in overlapping pieces woven into the shingle courses. Each piece directs water outward onto the shingle below rather than allowing it to run down the wall surface and into the wall cavity.
Step flashing can be displaced by ice, loosened by wind, or undermined by debris accumulation against the wall. In spring, check these transitions for gaps, lifted pieces, and any signs of water staining on the wall below the transition line. Step flashing failures can direct water into the wall cavity, causing damage that remains hidden inside the wall for months before it shows symptoms on the interior surface.
What Professional Flashing Repair Involves
Minor flashing repair — resealing a joint, re-bedding a counter flashing piece, replacing a vent boot — is straightforward maintenance that prevents far more expensive damage. Most professional repairs take one to three hours and cost accordingly.
Major flashing work — replacing chimney flashing, re-doing valley flashing, or addressing widespread step flashing failure — involves removing the surrounding shingles, installing new flashing properly, and re-shingling the area. This is not a DIY project. Flashing work done incorrectly is worse than no repair at all because improperly placed sealant and metal can redirect water deeper into the assembly rather than away from it.
Spring Is the Diagnostic Window
Flashing damage accumulates during winter and reveals itself in spring. The narrow window between snowmelt and spring storms is when these failures are most visible and most accessible for repair. Waiting until a rainstorm finds the gap means waiting until water is inside your roof structure — and at that point, the repair has become a repair plus a cleanup plus possibly a mould remediation.
Angel’s Roofing treats flashing inspection as a core part of every spring assessment — checking every chimney, vent, valley, wall transition, and drip edge. Their crew checks every chimney, every vent, every valley, every wall transition, and every drip edge — because they know that flashing failures cause more leaks than shingle failures in this climate. If your flashing needs attention this spring, their team fixes it right the first time so you head into storm season with every joint sealed and every edge tight.
Flashing Materials — What Works Best in Calgary
Not all flashing materials perform equally in Calgary’s climate. Galvanized steel is the most common and is adequate for most applications, but it corrodes over time, especially at cut edges where the galvanized coating is compromised. Aluminum flashing resists corrosion better but is softer and can be dented or deformed by ice.
Copper flashing is the premium option — it is highly corrosion-resistant, extremely durable, and develops a patina that many homeowners find attractive. The cost is significantly higher, but on high-value homes or in applications where flashing replacement is particularly difficult (such as steep chimneys), the longevity of copper can justify the investment.
Regardless of material, the quality of installation and sealant matters more than the metal itself. Properly installed galvanized flashing with quality sealant will outperform poorly installed copper every time. When evaluating a roofing contractor, ask specifically about their flashing techniques and materials — this is where the difference between good and excellent workmanship shows up most clearly.
Sealant Selection and Lifespan
The sealant used on flashing joints is the weak link in the assembly. Most polyurethane and silicone-based roofing sealants have a functional life of five to ten years in Calgary’s climate. After that, they begin to dry, crack, and lose adhesion. Re-sealing flashing joints every five to seven years is a maintenance task that dramatically extends the life of the flashing assembly and prevents the leaks that develop when old sealant fails.
Ask your roofer about the sealant products they use and their expected lifespan in Calgary’s conditions. A contractor who uses premium sealant and recommends a re-sealing schedule is thinking about long-term performance, not just the immediate project.
About Angel’s Roofing — Flashing Experts Who Find Leaks Before They Find You
Flashing failures are the number one source of roof leaks in Calgary, and they are almost impossible for homeowners to spot from the ground. Angel’s Roofing conducts detailed flashing inspections at every transition point — chimneys, vents, walls, valleys, and edges — to catch failures before water finds its way inside. Our team repairs and replaces flashing using proven methods built for Calgary’s punishing temperature swings. Stop leaks at the source — visit www.angelsroofing.ca to book your inspection.
