Black streaks on the roof? Here's the Houston Fix
Black streaks on the roof is one of the most common calls we get from Houston homeowners, and it peaks in year-round. Houston sits 13 miles from Glasgow in Renfrewshire, with the valley holding damp far longer than the map suggests. This page walks through why it happens on PA6 properties, how we fix it, and roughly what it costs.
How to tell if it's black roof streaks
Four tells we look for on every Houston 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 Houston properties
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.
Once a colony establishes, spores travel airborne to neighbouring properties — which is why streaks tend to appear in clusters along a street rather than one house at a time.
In Houston specifically, shielded by the gryffe valley — gutter debris from mature trees and slate moss on shaded sides are the headline maintenance issues — which is the single biggest reason this issue is more stubborn here than in a drier inland town.
Our Houston 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.
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
One day for a typical 3-bed semi, two days for large detached or steep-pitched properties.
Houston quote to job completed is usually under two weeks.
£320–£620
£ per typical 3-bed roof
Every Houston quote is fixed-price in writing — no on-the-day surprises.
Houston-specific considerations
Conservation-area cottage terraces in the old village, premium modern detached through Crosslee and Barochan, and rural-fringe stone cottages towards Bridge of Weir.
Shielded by the Gryffe Valley — gutter debris from mature trees and slate moss on shaded sides are the headline maintenance issues.
Off the A761 — Houston jobs combine well with Bridge of Weir, Kilbarchan and Bishopton stops on a single tight route. Nearest motorway is the M8, with routes via A761 and A737.
What NOT to do
Common mistakes we see on Houston 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.
Black Roof Streaks — questions from Houston customers
Is your roof cleaning insured for my property?+
Yes — £5m public liability, and Renfrewshire Council addresses are on file weekly. Certificate sent before the job starts.
Can you treat one pitch only?+
Yes. On many Houston 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 Houston that matters, because shielded by the gryffe valley — gutter debris from mature trees and slate moss on shaded sides are the headline maintenance issues. 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 Houston roofs clear — much cheaper than a full re-clean.
Get black roof streaks sorted this month
Fixed-price quote for black roof streaks on your Houston property. Fully insured, Renfrewshire Council-covered, 12-month guarantee on the work.
Related pages for Houston
Jump to a specific service, a nearby town, a postcode mini-hub, or an audience-specific package — all fully local to Renfrewshire.