Does roof cleaning damage tiles? Jet washing, scraping and treatments compared

The worry is real

Search any homeowners' forum and you'll find the same stories. "Water got into loft and down the chimney and leaked into house," wrote one Mumsnet user after a roof clean. Another warned: "Don't let cowboys powerwash your roof - this usually leads to dampness and damaged tiles." A DIYnot user who wanted to do the job himself asked whether a wire brush was okay or "likely to damage the surface of the tiles". The answer he got was "yes, it will", so he switched to a nylon scraper and a stiff, non-wire brush.

The good news is that the damage comes from particular methods, and you can ask about those before anyone goes up.

The methods compared

Why jet washing does the damage

High-pressure water strips more than moss. Marley warns that it can damage tiles, "particularly older or more delicate ones", and can "flood the roof and outlets with unwanted water, chemicals, and debris". From the ground, it says, "the upward movement of the spray can also lift and damage the tiles". In Marley's homeowner guide, Kevin Taylor adds that "the high-pressure water jets can crack or damage the roof tiles".

That's how water ends up in a loft after a clean. Tiles overlap so that rain running down the roof sheds off them. A jet aimed up the slope drives water the wrong way, under the laps, where the roof isn't built to keep it out.

Hertfordshire Trading Standards has warned specifically about doorstep "roof renovation" that combines pressure-cleaning with painting, saying experts advise it "is likely to cause damage to the tiles".

What about treatments?

A moss treatment kills what's left after the moss comes off and slows regrowth. It isn't a substitute for removal, and it isn't harmless. Marley warns that chemical washes "can be harmful to plants and animals" and that gutters and outlets should be protected. Historic England's research found that the longer-term effectiveness of common biocides "has been observed to be extremely limited".

Used properly, a treatment does its job without any pressure or foot traffic at all. That means a product approved for use in Great Britain, applied exactly as the label says, at low pressure, away from plants, ponds and drains.

Questions to ask any roof cleaner

• How will you take the moss off: by hand, or with a pressure washer?
• Will you stand on the tiles, or work from roof ladders?
• What treatment do you use, is it approved for use in Great Britain, and how will you keep it off my plants and pond?
• How will you protect and clear the gutters and downpipes afterwards?
• Will I get photos of every slope, before and after?
• Are you insured, and can I see the certificate?

If someone can't answer these clearly, or is pressing you to decide on the doorstep, read our guide on roof cleaning cold callers first.

If you think a clean has damaged your roof

• Look in the loft on a wet day for drips, damp timbers or wet insulation, especially below the slopes that were cleaned.
• From the ground, look for tiles that have slipped, cracked or lifted at the edges.
• Check the gutters and downpipes aren't blocked with moss, grit and debris washed off the roof.
• Photograph everything, and contact the company that did the work in writing.
• Get an independent roofer to inspect it and put what they find in writing.

How we clean a roof without damaging it

We take moss off by hand with scrapers and brushes, from roof ladders laid over the slopes, so we're not standing on the tiles. No pressure washers. Where it suits the roof, we follow up with an approved treatment at low pressure, keeping it off plants and ponds. Then we clear the gutters of everything that's fallen in and send you photos of every slope, before and after.

Written by Hawkes Roofing, roofers based in St Albans who remove roof moss by hand across Hertfordshire, Buckinghamshire and north-west London. Last reviewed 26 October 2026.