Roof cleaning in Toronto should never involve a pressure washer. The black streaks and moss on shaded shingles are living organisms, and the right way to remove them is to kill them at the root with a low-pressure soft wash, not to blast them and the shingle granules off together. That is the only way we clean roofs.
Why Do Toronto Roofs Grow Moss and Black Streaks?
Toronto’s mature tree canopy is beautiful, and it keeps north-facing roof slopes in shade most of the day. Add humid lake summers and you have the perfect home for Gloeocapsa magma, the algae behind black streaks, along with green moss and grey lichen. The algae feed on the limestone filler in asphalt shingles and spread from roof to roof on the wind. Moss holds moisture against the shingles and can lift their edges.
Rosedale, Forest Hill, Hoggs Hollow and Unionville see the worst of it, but any roof under big trees is at risk. Left alone, moss and lichen shorten shingle life and can push water under the tabs.
What Is Roof Soft Washing?
Soft washing uses chemistry instead of force. Our SoftWash low-pressure line applies a measured mix of diluted sodium hypochlorite and a surfactant that helps it cling to the shingles. The mix dwells long enough to kill algae, moss and lichen, and then the roof is gently rinsed where appropriate. Water pressure stays about the same as a garden hose.
Why Pressure Washing a Roof Is a Mistake
Asphalt shingles are covered in ceramic-coated granules that protect the asphalt from UV. A pressure washer strips those granules away, which ages the roof by years in an afternoon. It can also drive water under shingle tabs and into the roof deck. Many shingle manufacturers specifically warn against pressure washing and recommend low-pressure cleaning with diluted sodium hypochlorite instead.
Types of Roof Growth We Treat
| Growth | What it looks like | Treatment |
|---|---|---|
| Gloeocapsa magma (algae) | Black or dark grey streaks running down the slope | Soft wash, lightens same day |
| Moss | Green, cushiony clumps along edges and shaded areas | Soft wash, releases over next rains |
| Lichen | Flat grey-green crusty patches | Soft wash, may need follow-up |
When Should You Book Roof Cleaning?
- Black streaks are visible from the street
- Moss is building along the lower edges or north slope
- You are listing the home and want photos to show a clean roof
- Gutters keep clogging with granules and organic debris
- You want to extend the life of a roof in good structural shape
We work in calm, dry, mild weather, usually spring through fall. Winter roof problems are ice dams, which our ice dam removal service handles with a steam rig.
How Much Does Roof Cleaning Cost in Toronto?
Pricing
Typical roof soft washing runs $450-$850 and takes 2-4 hours. A bungalow or small roof is usually $450-$550, a two-storey home $550-$750 and large or heavily mossed roofs $750-$850. Large estate roofs and steep pitches are quoted individually. Pair it with a house wash for a better combined rate.
What to Expect on Roof Cleaning Day
- Arrival and check. The crew confirms the slopes to treat, checks gutters and looks for loose or damaged shingles from the ground and ladder.
- Garden protection. Beds and shrubs below the eaves are soaked with clean water. Downspouts are directed away from sensitive plants where possible.
- Application. The soft wash mix is applied from the eaves upward at low pressure. Crews stay off the roof surface whenever the slope can be reached from a ladder.
- Dwell. The solution works for several minutes. Black streaks start to lighten almost immediately.
- Gutter and plant rinse. Gutters and downspouts are flushed and plants are rinsed a second time.
- Photos and explanation. You get ladder photos and a clear explanation of what will happen with any remaining moss over the next few rains.
Common Roof Problems We Solve
Black streaks on the north slope
Gloeocapsa magma loves the slope that gets the least sun. Soft washing clears the streaks the same day in most cases.
Moss along the eaves
Moss collects where water lingers at the bottom edge. It dies on contact and loosens over the following rains, with no scraping.
Lichen around vents and chimneys
Lichen is the toughest growth to clear and may need a second application. It slowly releases once dead.
Granules in the gutters
Some granule loss is normal with age, but heavy loss after pressure washing or scraping is a warning sign. Soft washing adds no granule loss of its own.
Keeping Moss and Algae Away
Trimming branches to let in light, clearing gutters each fall and booking a soft wash before growth gets thick all extend the time between cleanings. Zinc or copper strips near the ridge can slow regrowth on some roofs, and we can advise whether they suit yours.
Roof Cleaning Across the GTA
Power Pressure Washing Toronto soft washes roofs throughout Toronto Central, in shaded estates in North York, on wooded Oak Ridges Moraine lots in Richmond Hill, in Unionville and Markham Village, and across the rest of the GTA. For siding, stucco and heritage masonry, see our soft washing service. Our blog post on soft washing a Toronto roof goes deeper on the method.
