Black streaks on the roof? Here's the Bearsden Fix
How to tell if it's black roof streaks
Four tells we look for on every Bearsden survey before quoting.
- Dark vertical streaks running from ridge to eaves, worst on north- or east-facing pitches
- Streaks that look worse after rain and appear to 'dry lighter' — that's the algae rehydrating
- Neighbouring houses on the same row showing similar staining
- A slightly rough or matte texture on tiles that used to look smooth
Why it happens on Bearsden properties
Uncleaned gutters spill water back onto tile edges, keeping the underside of ridge courses damp and accelerating streak formation from the top down.
The black streaks running down concrete or clay tiles are almost always a cyanobacteria called Gloeocapsa magma, feeding on the limestone filler in the tiles themselves.
In Bearsden specifically, bearsden's elevation and tree cover make it the moss-heaviest postcode on our entire round — north-facing slate routinely needs full soft-wash plus biocide — which is the single biggest reason this issue is more stubborn here than in a drier inland town.
Our Bearsden fix — step by step
- 1Roof survey
Ground and drone-level inspection to confirm tile type, pitch, condition and any slipped or cracked tiles that need addressing first.
- 2Manual moss removal
Where moss is present alongside the algae, we soft-scrape by hand before wetting the tiles — never with a pressure washer.
- 3Biocide soft-wash
A low-pressure application of a professional-grade sodium hypochlorite/benzalkonium biocide blend, dwelled and rinsed at low pressure.
- 4Gutter clear-down
Every roof clean includes a gutter clear — algae debris will otherwise wash straight into blocked runs.
- 512-month cover
A residual biocide film keeps regrowth at bay for a season; annual top-ups are optional and cheaper than a full re-clean.
One day for a typical 3-bed semi, two days for large detached or steep-pitched properties.
Bearsden quote to job completed is usually under two weeks.
£320–£620
£ per typical 3-bed roof
Every Bearsden quote is fixed-price in writing — no on-the-day surprises.
Bearsden-specific considerations
Large detached sandstone and inter-war villas dominate, with prestige modern detached around Kilmardinny. Slate roofs, mature trees and big gardens — moss is the headline issue here.
Bearsden's elevation and tree cover make it the moss-heaviest postcode on our entire round — north-facing slate routinely needs full soft-wash plus biocide.
A short run from our base. We schedule G61 jobs in clusters and frequently combine roof, render and gutters in one half-day visit. Nearest motorway is the M898, with routes via A809 and A810.
What NOT to do
Common mistakes we see on Bearsden properties before we're called in.
- Do not jet-wash the tiles — it strips the mineral coating and the streaks return worse within 12 months.
- Do not use household bleach — the concentration is wrong and it will scorch adjoining render and planting.
- Do not paint over the streaks — coatings peel within a season on damp Scottish roofs.
Chemistry & materials we use
- Sodium hypochlorite at controlled concentration for algae kill
- Benzalkonium chloride residual for 6–12 month regrowth cover
- Neutralising surfactant so run-off is safe for driveways and planting
- Never high-pressure water — pressure cracks the tile surface and voids most roof warranties
Black Roof Streaks — questions from Bearsden customers
Is your roof cleaning insured for my property?+
Yes — £5m public liability, and East Dunbartonshire Council addresses are on file weekly. Certificate sent before the job starts.
Can you treat one pitch only?+
Yes. On many Bearsden semis the streaks are only on the north or gable-facing side, and treating one pitch alone is significantly cheaper.
Do black streaks damage the roof?+
Long-term, yes — the algae etches the mineral coating on concrete tiles, which then absorb more water. In Bearsden that matters, because bearsden's elevation and tree cover make it the moss-heaviest postcode on our entire round — north-facing slate routinely needs full soft-wash plus biocide. Cleaned early, tiles are restored without replacement.
Will the streaks come back?+
The 12-month biocide layer prevents regrowth in that window. After that a light top-up spray every 12–18 months keeps Bearsden roofs clear — much cheaper than a full re-clean.
Talk to the East Dunbartonshire team
Fixed-price quote for black roof streaks on your Bearsden property. Fully insured, East Dunbartonshire Council-covered, 12-month guarantee on the work.
Related pages for Bearsden
Jump to a specific service, a nearby town, a postcode mini-hub, or an audience-specific package — all fully local to East Dunbartonshire.