Roof Algae & Black Streak Removal in Cobham
Those dark vertical streaks on north-facing roofs aren't dirt — they're a cyanobacteria called gloeocapsa magma. We treat it with a tile-safe biocide that kills the colony and lets rainfall lift the residue away naturally over 2–4 weeks.
What's included
- Targets gloeocapsa magma and green algae
- No-rinse biocide system — gentle on tiles
- Visible results in 2–4 weeks of weathering
- Optional ridge-mounted zinc strips for long-term prevention
Our process
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Step 1
Identification
We confirm whether the discolouration is algae, lichen or staining from overhanging foliage.
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Step 2
Biocide application
A low-pressure biocide is sprayed across all affected pitches.
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Step 3
Natural weathering
Rainfall washes the dead colony away over 2–4 weeks.
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Step 4
Optional zinc strips
Discreet zinc strips at the ridge release ions that inhibit future algae growth.
Frequently asked questions
What are the black streaks on my roof?
Gloeocapsa magma — an airborne algae that feeds on the limestone filler in modern asphalt and concrete tiles. It thrives on north-facing pitches with limited UV.
Will the streaks come back?
Eventually, yes — typically after 4–6 years. Zinc or copper strips at the ridge significantly slow recolonisation.