If you've noticed green streaks creeping across your roof tiles, dark patches on the north-facing side, or moss building up in the tile channels, you're not alone. Across Dorset, Somerset, Wiltshire and Hampshire, our damp climate makes roofs a perfect home for moss, algae and lichen.
Left unchecked, that growth traps moisture against the tile surface. In winter, that moisture freezes and thaws, gradually lifting and cracking tiles — and shortening the life of your roof. The good news is that it can be removed safely, without the high-pressure washing that causes more harm than good.
Why pressure washing a roof is a bad idea
It's tempting to think a powerful pressure washer will blast moss away in seconds. It will — but it will also:
- Strip the protective granular coating from concrete tiles
- Force water under tiles and into the felt membrane beneath
- Dislodge ridge tiles and pointing
- Spread moss spores across your driveway and gutters, where they'll regrow
Pressure washing a roof is the fastest route to an expensive re-roof. The right approach is far gentler.
The low-pressure, biocidal method we use
At Clearstone, we clean roofs using a controlled low-pressure wash — hot or cold, depending on the tile type and the level of growth — followed by a gentle biocidal softwash treatment.
- Manual moss clearance. We carefully remove the heavy moss build-up by hand and with soft tools, working from scaffolding or roof crawling ladders to minimise foot pressure on fragile clay or concrete tiles.
- Low-pressure rinse. A controlled wash lifts the remaining algae and staining without forcing water where it shouldn't go.
- Biocidal softwash. A biocidal solution is applied to kill algae, lichen and fungal spores at the root — not just the visible growth on the surface. This is what keeps the roof cleaner for far longer.
Because the treatment kills growth at the root, the roof stays cleaner for years rather than months. Our roof cleaning is backed by a 2-year organic growth guarantee, with an optional extended 5-year warranty that requires discounted follow-up softwash treatments in Years 3 and 5 to stay active.
Which roofs can be cleaned safely?
Most concrete interlocking tiles, clay tiles and slate roofs can be cleaned safely with the low-pressure method. Older or more fragile roofs — particularly very old clay peg tiles — need extra care, and sometimes a biocidal-only treatment (no mechanical clearance) is the safer choice.
If you're unsure, the best first step is a free roof inspection. We'll assess the tile type, the level of growth, and whether cleaning is safe — and we'll tell you honestly if it isn't.
How long does a clean roof last?
With the biocidal softwash applied, most roofs stay visibly cleaner for 2–3 years before any significant regrowth. The 5-year warranty option extends that protection further, with the cost of follow-up treatments agreed up front and guaranteed not to increase.
Get a free roof cleaning quote
If your roof is showing signs of moss, algae or lichen, don't wait for the winter frost to do the damage. We cover homes and businesses across Dorset, Somerset, Wiltshire and Hampshire from our Shaftesbury headquarters.
Get your free roof cleaning quote or call us on 01747 413013.
Need this done for your property?
Get a free, no-obligation quote from the Clearstone team across Dorset, Somerset, Wiltshire & Hampshire.