Most Calgary roof leaks start at flashing around chimneys, valleys, and walls. See how proper flashing installation stops water at these common leak points.
Most roof leaks in Calgary do not start in the middle of a roof plane. They start at the edges - around a chimney, along a valley where two roof sections meet, or where a roof meets a wall. These transition points are covered by flashing, a set of metal or synthetic components that direct water away from the seams in a roofing system. Flashing rarely gets much attention during a roof replacement quote, but it is often the single biggest factor in whether the finished roofing system stays watertight for its full expected lifespan.
This guide covers the main types of flashing used on Calgary homes, why they matter more in Alberta's climate than in milder regions, and what to check for during a roof inspection or before signing off on a roof replacement.
Asphalt shingles and metal roofing panels are designed to shed water when installed on a continuous, unbroken slope. Every place that breaks that continuity - a chimney, a skylight, a vent pipe, a dormer wall, a valley where two roof planes meet - creates a seam where water can work its way underneath the roofing material if it is not properly redirected. Flashing is the metal or synthetic component installed at these seams to keep water moving across the surface and off the roof rather than pooling or seeping through.
Flashing is typically installed in layers, woven into the asphalt shingles or metal roofing courses as the roofing contractor works up the roof, rather than applied as a single strip after the fact. This layering, sometimes called step flashing at wall intersections, is what allows water to flow over each piece in sequence instead of finding a gap to exploit.
Chimney flashing typically has two parts: base flashing that sits against the roof deck and steps up the sides of the chimney, and counter-flashing that is embedded into the chimney's mortar joints and folds down over the base flashing. This two-piece design allows for slight movement between the roof structure and the masonry chimney without opening a gap for water. Chimney flashing failure is one of the most common sources of interior leaks reported to a roofing contractor, particularly on older Calgary homes where the original flashing has corroded or the mortar has cracked.
Valleys, where two roof slopes meet at an angle, concentrate a large volume of water and snowmelt into a narrow channel. Open metal valley flashing, or a woven asphalt shingle valley reinforced with an ice and water shield membrane underneath, needs to handle that concentrated flow without allowing water to back up under the shingles on either side. Valleys are a common point of ice dam formation in Calgary winters, which makes proper flashing and underlayment here especially important.
Where a roof meets a vertical wall, such as at a dormer or where a lower roof section meets a second-storey wall, step flashing and continuous counter-flashing work together to shed water away from the wall assembly. Poorly installed wall flashing is a common cause of hidden water damage inside walls, since a small leak here can travel some distance before it becomes visible as a stain on an interior ceiling or wall.
Every plumbing stack, exhaust vent, and roof-mounted mechanical unit needs its own flashing boot or collar. These are usually made of rubber, lead, or a combination of metal and synthetic materials, and the rubber components in particular have a shorter service life than the surrounding asphalt shingles. A roof inspection that focuses only on the shingles themselves, without checking the condition of vent boots, can miss one of the more common sources of a slow, hard-to-trace leak.
Calgary's freeze-thaw cycles put more stress on flashing than a climate with more stable winter temperatures. Metal flashing expands and contracts with temperature swings that can range widely within a single day during a Chinook, and repeated movement over the years can work fasteners loose or open small gaps at seams that were originally sealed tight.
A few climate-specific factors worth understanding:
Flashing is manufactured from several different metals, and the choice affects both cost and longevity. Aluminum flashing is lightweight, resists corrosion well, and is a common pairing with aluminum gutters and asphalt shingles on standard residential projects. Galvanized steel flashing is more rigid and often used on commercial roofing and metal roofing installations, though it can eventually rust if the protective coating is scratched or worn through during installation.
Copper flashing is the most expensive option but also the most durable, often outlasting the asphalt shingles or metal roofing panels installed around it. It is most commonly seen on chimney flashing for higher-end homes, where its distinctive weathered patina is treated as a visual feature rather than a flaw. Mixing incompatible metals, such as installing aluminum flashing directly against copper, can cause galvanic corrosion over time, which is why an experienced roofing contractor pays attention to which metals are already present on a home before selecting replacement flashing.
A thorough roof inspection should include a specific look at flashing condition, not just the general state of the asphalt shingles or metal roofing. Homeowners can look for a few visible warning signs themselves between professional inspections:
Any of these signs is worth raising with a roofing contractor promptly, since flashing repairs are typically far less expensive than the interior repair work that follows an undetected leak.
Damaged flashing is easy to overlook during an insurance adjuster's visit after a hailstorm, since adjusters often focus primarily on the condition of the asphalt shingles themselves. A homeowner who has photos of chimney, valley, or vent flashing from before a storm has a much stronger basis for including flashing repair or replacement in a storm damage claim, rather than discovering months later that water has worked its way into the attic through a seam the adjuster never inspected closely.
A roofing contractor documenting storm damage for an insurance claim should note flashing condition explicitly in their report, separate from general shingle damage, since insurers sometimes require this level of detail before approving flashing replacement as part of the claim.
One of the most common shortcuts on a low-cost re-roofing job is reusing old flashing instead of installing new material. Old flashing may look intact from the ground but can be thin, corroded, or no longer properly sealed at its seams. A roofing contractor performing a full roof replacement should install new flashing at every chimney, valley, wall intersection, and vent penetration as standard practice, not as an optional upgrade.
Asking specifically about flashing scope before signing a roofing contract is one of the more useful questions a homeowner can ask, since it is an area where corner-cutting is common but not always obvious from a written estimate alone.
Homeowners planning a broader exterior renovation - new asphalt shingles alongside James Hardie siding or vinyl siding - should also confirm how flashing at wall intersections will be handled where the two trades meet. Siding installers and roofing contractors sometimes assume the other trade is responsible for a given seam, and a gap in that handoff is a common, preventable source of leaks around windows, dormers, and second-storey wall transitions. Naming one contractor as responsible for the full flashing scope, roof to wall, removes that ambiguity before work begins.
Flashing rarely gets the attention that shingle brand or color does, but it does more to determine whether a roof stays watertight through Calgary's freeze-thaw cycles, hailstorms, and wind-driven rain than almost any other single component. A roof replacement that gets the flashing details right, using appropriate metals and proper layering at every seam, is worth paying slightly more for over one that treats it as an afterthought and leaves these details for the homeowner to discover the hard way, years later, during the next spring thaw.
Contact Raico Roofing for a free quote.