Removing moss from a roof is only half the job. The reason moss comes back so quickly after a basic clean is that pressure washing or scraping only removes the visible growth — the spores rooted in the tile surface are left behind, ready to regrow as soon as conditions are damp again. Preventing moss from returning means killing it at the root.
Why moss regrows so fast
Moss, algae and lichen spread through spores. A clean that only lifts the top growth leaves those spores in place, and our damp climate across Dorset, Somerset, Wiltshire and Hampshire gives them everything they need to return within months. That's why a roof that was "cleaned" with a pressure washer often looks green again the following winter.
The biocidal softwash that stops regrowth
The key to preventing regrowth is a biocidal softwash applied after the mechanical clearance. The biocidal solution kills algae, lichen and fungal spores at the root — not just the visible growth on the surface. Because the treatment works on the spores themselves, the roof stays cleaner for years rather than months.
At Clearstone, every roof clean includes this biocidal treatment as standard. It's the difference between a roof that looks clean for a few months and one that stays clean for 2–3 years before any significant regrowth.
Our guarantee and warranty
We back our treatment with a 2-year organic growth guarantee on all of our roof cleans. If organic growth or moss returns to any treated roof slope within the guarantee period, we return and retreat free of charge.
We also offer an extended 5-year organic growth warranty (subject to terms and conditions). To keep the 5-year warranty active, a discounted follow-up softwash treatment is required in Years 3 and 5. The treatment price is agreed at the time of your original roof clean and guaranteed not to increase — so you know your maintenance cost upfront. You can spread the cost with monthly payments, and any MEWP or cherry picker hire required for access is charged separately.
What you can do to help
A few things keep the roof cleaner for longer between treatments:
- Keep gutters and downpipes clear so water doesn't overflow onto the roof surface
- Trim back overhanging branches that shade the roof and keep it damp
- Address any persistent damp patches or leaks promptly
Watch the short answer
In this short video, we explain how we prevent moss from coming back after a roof clean.
Related questions
Get your free roof cleaning quote or call us on 01747 413013.
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