Green algae and black streaking on conservatory roofs is a common problem in Cornwall. Learn why it happens, what not to do, and how professionals approach the cleaning.
A green, streaky or blackened conservatory roof is one of the most common property maintenance issues across Cornwall — and one of the most frequently mishandled. This guide explains why conservatory roofs deteriorate so quickly in our climate, what you should never do, and how professional cleaning restores them safely.
Why Conservatory Roofs Get So Dirty in Cornwall
Cornwall's maritime climate provides ideal conditions for biological growth:
- High humidity: Cornwall's damp air provides constant moisture for algae and lichen colonisation
- Mild temperatures: Year-round mild conditions prevent the frost that kills algae in colder regions
- Salt air: Coastal properties experience additional mineral deposition that discolours polycarbonate and glass panels
- Shaded aspects: Conservatories on north and east-facing aspects receive less direct sun, accelerating green algae growth
Most Cornwall conservatories develop visible green algae within 12–18 months of installation. Without treatment, lichen and black mould follow, causing permanent staining if left too long.
Types of Conservatory Roof — Different Cleaning Requirements
Understanding your roof type determines the correct cleaning method:
Polycarbonate panels: The most common type. Polycarbonate is lightweight and translucent but prone to surface scratching and UV degradation. It must be cleaned with low-pressure soft-wash methods — never high-pressure washing.
Glass panels: More durable than polycarbonate but still sensitive to high-pressure cleaning at close range. Glass conservatory roofs respond well to pure water cleaning with specialist cleaning solutions.
Solid tiled roofs: Require the same approach as standard roof tiles — biocide treatment and careful low-pressure rinsing. The gutters and UPVC frames need specialist attention.
What NOT to Do — Common Mistakes
Never use a pressure washer on polycarbonate panels. This is the single most damaging mistake homeowners make. High-pressure water: - Cracks and crazes the polycarbonate surface irreversibly - Blows water past rubber gaskets and seals, causing internal leaks - Destroys the UV-protective coating on the panel surface - Can void warranty on relatively new conservatories
Never use undiluted bleach. Neat bleach damages UPVC frames, rubber seals and surrounding garden planting. It also doesn't prevent regrowth — only specialist biocide treatments do.
Never walk on polycarbonate panels. They are not load-bearing and will crack under a person's weight.
How Professional Conservatory Roof Cleaning Works
Professional conservatory roof cleaning uses a soft-wash approach:
- Pre-treatment: A specialist biodegradable biocide is applied to the roof surface and allowed to dwell. This kills algae, lichen and mould at the root.
- Low-pressure rinsing: After the biocide dwell period, the roof is rinsed at low pressure using pure water. This removes the dead biological material without damaging panels or seals.
- Frame and gutter cleaning: UPVC frames, cills and gutters are cleaned as part of the service using UPVC-safe solutions.
- Post-treatment: A residual biocide treatment is applied to slow regrowth — typically extending the time before the next clean is needed.
How Often Should a Conservatory Roof Be Cleaned?
In Cornwall's climate, most conservatory roofs require professional cleaning every 12–24 months. Factors that influence frequency include:
- Proximity to trees (leaf debris and shade accelerates growth)
- Aspect (north and east-facing conservatories require more frequent cleaning)
- Proximity to the coast (salt air increases mineral deposition)
- Whether a biocide post-treatment was applied
Cost of Conservatory Roof Cleaning in Cornwall
Conservatory roof cleaning in Cornwall typically costs between £120 and £350, depending on the size of the conservatory and the level of biological growth. This includes cleaning of all roof panels, gutters and UPVC frames.
Severe lichen colonisation may require a two-stage treatment — an initial biocide application followed by a return visit for full removal.
Frequently Asked Questions
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