Why this usually happens
Airborne algae spores land on your roof and feed on the limestone filler in asphalt shingles.
Shade, dampness, and humidity let it spread into the streaks you see.
It spreads roof to roof, so once it is in a neighbourhood it tends to show up everywhere.
Why you should not ignore it
The algae eats away at the protective granules on your shingles, shortening your roof's lifespan, and can lead to moss if ignored. Many homeowners replace roofs that could have been cleaned — and the staining drags down your whole home's curb appeal.
Roof streaking is common throughout Durham Region because shade, tree cover, humidity, lake-effect moisture, and changing seasons all leave shingles damp for long stretches. The stains are especially noticeable from the curb on lighter shingles and on roof slopes that face north or sit below mature trees. The right response is careful treatment, not aggressive blasting, because the roof surface is a protective system that should be cleaned without stripping granules.
What to do next
- Do not pressure wash a roof — high pressure strips granules and voids many shingle warranties.
- Avoid harsh chemicals or stiff brushing.
- The correct method is soft washing — low pressure with a treatment that kills the algae at the root so it does not just grow straight back.
A safe exterior cleaning approach
Our roof soft washing safely removes algae streaks, moss, and staining without damaging your shingles — using low pressure and the right cleaning solution. Serving homes across Durham Region.
Related DSS services and local pages
Frequently asked questions
Will the streaks come back?
Soft washing kills the algae at the root, so it stays clear far longer than a surface rinse; periodic maintenance keeps it gone.
Is roof soft washing safe for shingles?
Yes — it uses low pressure, unlike pressure washing, which damages shingles.
Does algae really shorten roof life?
Yes — it degrades the granules that protect your shingles.