Lenzie Black Roof Streaks: Cause, Fix and Cost
How to tell if it's black roof streaks
Four tells we look for on every Lenzie 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 Lenzie properties
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.
West-of-Scotland roofs sit wet for long stretches — north-facing pitches, tiles shaded by trees, and gable ends that catch driven rain all give the algae the moisture it needs.
In Lenzie specifically, mature tree cover and high garden boundaries mean shaded north walls — slate roof moss and gutter leaf-fall are the headline issues in lenzie — which is the single biggest reason this issue is more stubborn here than in a drier inland town.
Our Lenzie 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.
Lenzie quote to job completed is usually under two weeks.
£320–£620
£ per typical 3-bed roof
Every Lenzie quote is fixed-price in writing — no on-the-day surprises.
Lenzie-specific considerations
One of the most distinctive sandstone-villa villages in central Scotland — large detached Victorian and Edwardian homes dominate, with modern detached infill around Boghall.
Mature tree cover and high garden boundaries mean shaded north walls — slate roof moss and gutter leaf-fall are the headline issues in Lenzie.
Train-line corridor north from Glasgow — Lenzie work is typically combined with Bishopbriggs and Kirkintilloch into a single morning route. Nearest motorway is the M80, with routes via A806 and A803.
What NOT to do
Common mistakes we see on Lenzie 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 Lenzie customers
Do black streaks damage the roof?+
Long-term, yes — the algae etches the mineral coating on concrete tiles, which then absorb more water. In Lenzie that matters, because mature tree cover and high garden boundaries mean shaded north walls — slate roof moss and gutter leaf-fall are the headline issues in lenzie. 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 Lenzie roofs clear — much cheaper than a full re-clean.
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 Lenzie semis the streaks are only on the north or gable-facing side, and treating one pitch alone is significantly cheaper.
Book a Lenzie roof survey
Fixed-price quote for black roof streaks on your Lenzie property. Fully insured, East Dunbartonshire Council-covered, 12-month guarantee on the work.
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