On an asphalt shingle roof, the shingles get all the attention, but the metal does most of the hard work. Every place where water changes direction, or where the roof meets a wall, a chimney or a skylight, is protected by a piece of bent metal called flashing. On houses across Whitby, from the newer streets of Brooklin and Taunton North to the older homes near Downtown Whitby and Port Whitby, flashing is where most leaks begin and where most repairs end.
- Where Metal Flashing Sits on a Shingle Roof
- How Flashing Is Installed So It Lasts
- Keeping Flashing Working Through Whitby Winters
Where Metal Flashing Sits on a Shingle Roof
A typical two-storey house in Williamsburg or Pringle Creek has more flashing than most owners realise. Drip edge runs along the eaves and the rake edges so water falls into the eavestrough instead of curling back under the first course of shingles. Valley flashing lines the trough where two roof slopes meet, and because a valley collects water from both sides, it carries more water than any other part of the roof during a heavy rain or a spring melt. Step flashing is a run of small L-shaped pieces woven into each course of shingles where the roof butts against a wall, a dormer cheek or the side of a chimney. Counter flashing is set into the mortar or wall above and laps down over the step flashing. Pipe boots seal plumbing stacks, and every skylight has its own flashing kit around the frame.
Most of this metal is pre-finished aluminum or galvanized steel, chosen because it can be bent on site and holds paint well. Copper turns up on some older or higher-end homes. What matters more than the metal is how it laps: each piece has to shed water onto the piece below it, never into a seam.
How Flashing Is Installed So It Lasts
Flashing works with the underlayment beneath it. In valleys and around openings, a self-adhered ice and water shield membrane goes down first, so that if ice backs up under the shingles in February, the water meets a sealed layer rather than bare wood. The metal then goes over it, followed by the shingles. Around a skylight, the head piece sits under the shingles above, the sill piece sits over the shingles below, and step flashing climbs both sides. Get that order wrong and the skylight will leak no matter how good the unit is.
The most common shortcut is caulk. A bead of sealant around a chimney or skylight looks tidy on the day it goes on, but it dries and cracks after a few freeze-thaw seasons and lets water run behind it. For readers wondering what correct detailing looks like at the most leak-prone spot on many roofs, this walk-through on how roof valley flashing is detailed around skylights in Whitby covers the flashing types, the usual failures and when a repair turns into a replacement. If you are comparing it with other approaches, the notes on what a regular roof inspection should check are a useful companion.
Local contractors see the same pattern. C.D. Roofing & Construction Ltd., a family-run roofer based in Whitby since 1994, notes on its own skylight repair page that flashing is the culprit more often than the skylight unit itself, and that a skylight installed with caulk instead of proper step flashing and counterflashing will leak eventually. The fix it describes is the textbook one: lift the shingles around the opening, re-seat or replace the flashing so it is woven into the shingle courses, and re-shingle.
Keeping Flashing Working Through Whitby Winters
Whitby sits on the north shore of Lake Ontario, and the swing between thaw days and hard frosts is what wears flashing out. Water gets into a small gap, freezes, expands and pushes the gap wider. A few habits catch problems early:
Check from the ground in spring and fall. Binoculars will show lifted valley metal, a pipe boot with a split collar, or a thick smear of caulk around a chimney that usually means an earlier repair was a patch.
Look in the attic after a heavy rain or a quick thaw. Dark stains on the rafters below a valley, a chimney or a skylight point straight to the joint that is failing. Damp insulation does the same.
Keep eavestroughs clear. When they overflow, ice builds at the eaves and pushes meltwater back under the drip edge and the first courses of shingles.
Plan flashing with the shingles. Flashing usually outlasts one set of shingles but not two, so a re-roof is the right time to replace step, counter and valley metal together rather than reusing old pieces. Good attic airflow helps here too: a cold, well-vented roof deck melts less snow from below, which means less ice at the edges, as covered in this note on why ventilation extends shingle roof life.
If you are heading to a Whitby roofer from Lynde Shores Conservation Area on the waterfront, the route below runs north to the Brooklin office.
C.D. Roofing & Construction Ltd.
8 Mildenhall Pl, Whitby, ON L1M 0C9
(905) 430-7911
Flashing is a small amount of metal doing a large job. Laid in the right order, over the right membrane, and replaced with the shingles, it keeps a Whitby shingle roof dry through every thaw.