Most roof leaks in Whitby homes do not start in the middle of the shingles. They start where the roof meets something else: a skylight curb, a chimney, a wall, a plumbing stack or a valley. That joint is sealed by flashing, and when flashing fails, water follows it straight into the attic. This guide explains the main flashing types, how they fail in Durham Region's freeze-thaw winters, and when a repair turns into a replacement.
Understanding Basic Roof Flashing Types and Functions
Flashing is thin, bent metal (usually aluminum, galvanized steel or copper) that directs water away from a joint and back onto the roof surface. On a typical pitched roof in Brooklin, Williamsburg or Pringle Creek you will find several kinds working together:
Step flashing is a series of small L-shaped pieces woven in with each course of shingles where the roof runs up against a wall or the side of a chimney. Counter flashing (also called cap flashing) is set into the masonry or wall above it and laps down over the step flashing, so the two can move independently as the house expands and contracts. Valley flashing lines the trough where two roof planes meet, the spot that carries the most water in a spring melt. Pipe boots seal plumbing vents and exhaust stacks. Drip edge runs along the eaves and rakes so water drops into the eavestrough instead of wicking back under the shingles.
Skylights get their own flashing kit. A deck-mounted skylight sits on the roof deck with a factory flashing set around it, while a curb-mounted skylight sits on a raised wooden frame that is wrapped with step flashing and a head and sill piece. Either way, the flashing is only as good as the underlayment beneath it: an ice and water shield membrane around the opening is what stops wind-driven rain and ice backup from reaching the wood.
Identifying Common Flashing Issues and Repair Techniques
Whitby sits on the north shore of Lake Ontario, and homes from Port Whitby up to Taunton North go through repeated freeze-thaw cycles every winter. Each cycle opens small gaps a little wider. The problems we see most often are:
Sealant used in place of flashing. Roof cement or caulk around a skylight or chimney looks fine for a season or two, then dries, cracks and lets water in behind it. Sealant is a backup, never the main seal.
Missing or short counter flashing on chimneys. Older chimneys in Downtown Whitby and Port Whitby often have flashing that was face-nailed to the brick instead of cut into the mortar joint, so water runs behind it.
Rusted or lifted valley metal and pipe boots with split rubber collars, both common on roofs that are 15 years old or more.
Skylight leaks that are really condensation. Moisture dripping from the inside of a skylight in January is often warm, humid air meeting cold glass, not a flashing failure. A proper inspection separates the two before any money is spent.
The right repair depends on what failed. A lifted piece of step flashing can be re-seated and the shingles around it replaced. A cracked pipe boot is swapped for a new one. Where flashing was installed wrong in the first place, the only lasting fix is to strip the shingles around the joint, install new underlayment and flashing correctly, and re-shingle. For skylights and the flashing around them, homeowners across Durham Region book
skylight and flashing repairs by C.D. Roofing & Construction Ltd., a family-run Whitby roofing contractor working in the area since 1994.
Advanced Repairs: When to Replace and Professional Tips
Flashing usually outlives one set of shingles but not two. When the shingles are worn out, reusing old flashing under a new roof is a false saving, so a full roof replacement is the natural time to replace step, counter and valley flashing together. The same goes for skylights: if the skylight unit itself is near the end of its life, replacing the unit and its flashing kit at the same time avoids paying twice for labour on the same opening.
A few practical points for Whitby homeowners:
Look from the ground first. Binoculars from the driveway will show lifted metal, missing pieces and heavy caulk around a chimney or skylight. Avoid walking on the roof yourself, especially from November to April.
Check the attic after a heavy rain or a fast thaw. Stained rafters or damp insulation under a skylight, chimney or valley point straight to the failing joint.
Ask how the repair will be done. A good answer names the flashing type, the underlayment and how the new metal ties into the shingles, not just "we will seal it".
Ask about insurance and safety. Crews working on your roof should be covered by liability insurance and WSIB, and trained in Working at Heights.
C.D. Roofing & Construction Ltd. uses in-house crews rather than subcontractors, is a BP Platinum Installer, carries $5M in liability insurance and backs its work with a 10-year workmanship warranty. The team works across Whitby, Brooklin, Ashburn, Lynde Creek and Rolling Acres, and in Oshawa, Ajax, Pickering and the rest of Durham Region.
C.D. Roofing & Construction Ltd.
8 Mildenhall Pl, Whitby, ON L1M 0C9
(905) 430-7911
Monday to Friday, 8:00 AM to 8:00 PM
Flashing is a small part of a roof with an outsized effect on whether it leaks. Knowing the types, spotting the early signs and insisting on proper flashing rather than sealant will keep a Whitby roof dry through the next freeze-thaw season.
