Why Algae Forms on Roofs
If you’ve noticed dark streaks or green patches on your shingles, that’s algae growth, a common issue in humid climates and shaded areas. Moisture, organic debris, and limited sun exposure create the perfect environment. Over time, these colonies spread, making your roof look dirty, streaked, and prematurely aged.
The Main Cause - Gloeocapsa magma (Cyanobacteria)
- Prevalence: The primary cause of black streaks and stains on roofs across Canada.
- Habitat & Growth: Thrives in warm, moist conditions, especially on northern roof slopes with limited sunlight.
- Feeding Mechanism: Grows particularly well on asphalt shingles because it feeds on the calcium carbonate present in limestone, a mineral filler commonly used in shingle materials.
- Appearance: While cyanobacteria are naturally blue-green, on roofs they develop a dark protective sheath to shield from UV rays, creating the characteristic black streaks.
Other Roof Growths
Although Gloeocapsa magma is the most widespread, other organisms may also affect roofs in Ontario:
- Moss: A true plant with leaves and stems. Moss thrives in damp, shaded areas, retains water, and can lead to structural damage and roof deterioration.
- Lichen: A complex organism made up of algae and fungus. Lichens appear as persistent spots, adhere strongly to shingles, and are difficult to remove.
- These growths are less common than Gloeocapsa magma, but they still pose risks to roof integrity and often require specialized cleaning methods.