Do asphalt shingles last less time in coastal BC?

The region is a natural experiment in shingle life. Sidney's compact, windy townsite gets more sun and less moss than anywhere else in Greater Victoria, and 25-year-old laminate roofs there are common. Fifteen kilometres away in the Highlands or on a north-facing Broadmead slope under retained Douglas fir, the same product is often finished at 15 because the moss never dries out. The shingle is the same; the microclimate is not.

Salt and wind add a second axis on the water. Cordova Bay bluffs, Dallas Road in James Bay and the south side of Colwood take storms straight off the strait, and wind-lifted tabs and stripped granules on the exposed slopes age those roofs from the top down while the leeward slopes look new. Any lifespan you read for 'coastal BC' is really a range whose ends are a few streets apart.

Asphalt shingles age three ways: the bitumen binder oxidises and stiffens, the granules that shield it from UV wash off, and physical forces (wind, moss, foot traffic) lift and crack the tabs. In cold-prairie climates the first two dominate, driven by sun and freeze-thaw. In Greater Victoria the third dominates. Winters are mild and damp rather than cold, shade is deep and long under mature trees, and moss establishes on the granules, wicks water under the tabs and levers them up.

Rain volume is almost beside the point, which is why 'rainy climate' advice from Vancouver or Seattle overstates the problem for Victoria. The city sits in the Olympic Mountains rain shadow with December at about 109 mm and July at 14 mm; it is the length of the damp season, roughly October to April, and the shade that matter.

Most of the difference is local and controllable.

• Sun: south and west slopes in the open outlast north slopes in shade
• Trees: keep branches back; needle drop and shade are the biggest single factor
• Moss control: zinc or copper strips near the ridge and treatment every 12–18 months where needed
• Ventilation: a balanced soffit-and-ridge path keeps the deck dry and the shingles cooler in summer
• Shingle grade: laminate with algae-resistant granules over 3-tab
• Installation: correct nailing, ice-and-water in valleys and at eaves, new flashing rather than re-used
• Slope: steeper roofs shed water and debris faster than low slopes

Take the manufacturer's figure as a ceiling and work down. A laminate roof in full sun, on a simple gable, with an attic that breathes and no moss can reach the top of our 20–30 year range. Subtract for each shaded slope, each mature conifer overhanging the roof, each valley that collects needles and any history of moss left untreated. If the roof is past 15 years and shows curling, bare patches or moss lifting the tabs on more than one slope, it appears consistent with the last third of its life, and an inspection will tell you more than any table.

For a longer-lived option on a shaded lot, the metal comparison pages set out the numbers; on a sunny lot, a well-installed laminate remains the value choice.