The short answer
It is safe when the method suits the tile. Gentle hand tools, careful footing and a treatment applied to its label leave the surface intact. Powerful jet washing is the risk, and Marley does not recommend it for tiles or slate. Clay, concrete and old peg tiles each need their own care, and a survey reads the covering before choosing a tool.
Tiles do not wear out from being cleaned. They wear out from being cleaned badly, and the difference is mostly down to the tool in the roofer's hand.
Where tile damage comes from
A roof tile has a surface that was made to shed water for decades. Clay tiles have a fired skin, and concrete tiles have a coloured face layer. Anything that wears through that skin lets water in and shortens the life of the tile.
Why do hard washes worry roofers?
Marley's guidance is blunt: powerful jet washing is not recommended, as it can strip a tile's face and noticeably shorten how long the covering lasts. A hard jet can also drive water up under the overlapping tiles and into the underlay, the membrane lying under the battens, and it throws moss and grit around the garden. The surface looks bright on the day and rougher a year later, which is when moss finds it easier to take hold again.
The footprint matters too. Tiles crack when a boot lands in the wrong place, particularly on a cold morning or on a brittle old tile. Feet are placed on the support points, and boards or a roof ladder spread the load across the slope.
The answer on pressure washing a roof explains why you should avoid high pressure on tiles.
Clay, concrete and old peg tiles
Different tiles need different treatment, and a roofer should read the covering before choosing how to clean it.
Are concrete tiles more or less delicate than clay?
Neither is delicate, but each fails differently, and a roofer should know which one is overhead. Concrete tiles carry a face coat that can be abraded, which is how colour is lost over the years. Our page on faded concrete roof tiles shows what that looks like. Clay tiles are tougher on the surface but can be brittle underfoot. Old hand-made peg tiles, the small tiles hung from timber pegs, need the lightest touch of all, as the BRE 60-year figure for clay tiles is described as clearly not a reliable guide for them.
Somerset has its own tile heritage too. Bridgwater's yards turned out plain tiles, ridge tiles and pantiles, with the Double Roman profile following, so many older roofs here carry clay that deserves care. We read the tile before choosing the tool, and photograph anything already cracked, chipped or lifting before it is touched.
Listed homes and conservation-area homes keep their covering as it is: cleaning is not a change of material, but any replacement is a different question, put to Somerset Council's planning team.
A tile-safe method, step by step
Cleaning to protect the tile follows a simple sequence, and none of it needs force.
What is the order of work?
First the roof is checked for loose or broken tiles, which are secured or noted before anyone walks near them. Then the bulk of the moss is lifted by hand, with a brush or a plastic scraper, and bagged. The surface is then treated with a biocide, a product made to kill moss, algae and lichen, applied within its authorisation, as article 17(5) of the retained Biocidal Products Regulation requires. Low-pressure rinsing, where it is used, only carries away the loosened residue.
The treatment then does its work over the following weeks. Moss turns brown and releases, and rain clears most of it. That slow finish is one reason the surface is not blasted: the product does what force would otherwise do.
Gutters are cleared at the end so that nothing is left behind. Our guide to soft wash roof cleaning covers the approach, and the roof cleaning and moss removal hub has the rest.
Signs a roof should not be cleaned yet
Sometimes the kindest thing for a tile roof is a repair first. Cleaning is a surface job, and it does nothing for a structure that is failing underneath.
When should cleaning wait?
Warning signs include tiles that rock when pressed, several cracked or flaking tiles in a row, a slope that sags, or daylight visible from the loft. Brushing a roof in that state can make faults worse, and a clean laid over a weak covering is money spent on the wrong job. Likewise, tiles with a flaking, powdery face have lost their protective layer; a clean cannot restore it, and a coating or replacement may be the better route.
In those cases you hear it from us straight, with the evidence in the photographs, and we suggest a sensible order: repair first and clean after, or skip the clean and plan a re-roof when the covering is nearly spent.
If you are unsure which camp your roof falls into, send a photo. The survey that follows leads to a single written total for work that suits the tiles you actually have.
Tile cleaning, answered
Can a clean void a tile maker's warranty?
Check the manufacturer's documents for your tile, since terms differ. Marley does not recommend powerful jet washing, as it can scar the face of a tile and shorten its life, so a jet is the method to avoid. Keep your paperwork, and ask us to note the method used on your survey.
Will moss treatment stain my tiles?
A treatment applied to its label should not mark the tile, but a dead mat of moss can leave dark streaks until rain washes it away. That is a normal part of the process. If you notice staining that does not clear after a few weeks of rain, tell us and we will look at it.
The full picture: Roof cleaning and moss removal in Taunton ยท More short answers