Plenty of tiled roofs go green. Moss builds along the overlaps, lichen spreads across the faces, and the north slope darkens first. The temptation is to treat every tiled roof the same way, but clay and concrete are different materials with different weak points. Clay is fired earth: hard, colour-fast through the body, and brittle at the edges. Concrete is cast, with a coloured surface layer that does a lot of the visual work. A method that suits one can spoil the other. This guide explains how each type is cleaned, why overlapping and interlocking tiles change what is safe, how to tell when cleaning is the right answer and when the roof needs attention first, and what the typical UK costs look like. Our main roof cleaning and moss removal service covers the wider picture; this guide stays with tiles.
Clay or concrete: how to tell which you have
The method depends on the material, so the first step is identifying it. Clay tiles usually show variation. Colours run from orange to deep red to brown across a single slope, edges are slightly irregular, and old tiles often have a slight curve or camber. Plain clay tiles are small and flat, laid in many overlapping courses, and each one is held on the batten by a pair of small nibs along its top edge. Clay pantiles have a deep S-shaped profile and interlock along the sides.
Concrete tiles are more uniform. Faces are even, edges are crisp, and the colour sits on the surface rather than running through. Where a corner has chipped, you can see grey cement underneath. They tend to be larger than clay plain tiles, and most are interlocking, with a groove along one edge that locks into the next tile. Some imitate plain clay, and those can fool a casual look from the pavement.
The two weather differently. Clay stays much the same colour for a very long time; concrete tends to fade, and HomeBuilding magazine (2020) says concrete tiles typically fade in colour and so will need replacing in 20 to 30 years, while other sources give longer lives. We set out the typical lifespans on our page about clay or concrete tiles.
If you are not sure, a close photograph of a tile edge, or a loose piece in the garden, is enough for us to tell. On the survey we also check the tile type matches the rest of the roof, since repairs over the years sometimes mix them.
Cleaning clay tiles
Clay is the more forgiving surface, but only up to a point. The fired face resists a good deal, and gentle cleaning suits it well. What it dislikes is impact and sideways force. Clay plain tiles are thin and held by small nibs. A boot in the wrong place cracks a tile or snaps a nib, and a cracked tile will leak long before the owner notices.
For that reason the work is done from boards or a roof ladder, not directly on the tiles. Moss is lifted off by hand, working from the ridge downward and bagging it for removal. Lichen and the green film are then treated with a biocide, a solution that kills the growth at the root, applied at low pressure and left to work. The rinse follows, directed downhill.
The overlap is the tricky part on plain tiles. Water forced upwards at that point goes under the tile and onto the battens and underlay, so the direction of the rinse matters. On pantiles, moss collects in the troughs and along the side laps, and it can be lifted out by hand before anything is applied. If the moss has packed the channel, water has been spilling over the side of the pantile rather than following the trough, which can mark the wall below.
Older clay is more porous, and a surface that has weathered over many years can look patchy once the growth has gone. That is not damage. It is the tile showing its age, and it usually evens out as the treatment settles. If the clay is softer or starting to spall, where the face flakes away in frost, we tell you before cleaning, since gentle is the only option.
Cleaning concrete tiles
Concrete tiles need a slightly different mindset. The body is cement and sand, and the colour is typically in a surface layer. Hard scrubbing or high pressure can wear that layer away, leaving a paler, rougher face that holds moisture and regrows moss sooner. A roof that was bright for a month after a pressure wash can look worse, and grow greener, a year later.
So the same principle applies as on slate and clay: moss off by hand first, then a low-pressure biocide treatment, then a controlled rinse. Concrete is generally more tolerant of the walking than thin clay plain tiles, but a cracked interlocking tile still leaks, and the weight of a person is enough to do it if the tile is not supported by its battens. Boards are used here too.
One difference is moisture. Concrete is more absorbent than fired clay, and a roof that has held moss for years may have taken up water in the surface. The tile can look darker after cleaning and take a few dry days to settle. We mention this because owners sometimes read a damp, dark finish as a bad job, when it is just the tile drying out.
Concrete roofs are also where we most often see the question of coatings. Some companies offer a coloured sealant sprayed on after cleaning. We assess those on their merits on our page about roof coatings, and the main caution is that a coating over unrecoverable tiles hides the problem and adds a maintenance cycle of its own. Cleaning should be judged on its own, first.
Why pressure washing is a poor fit for tiles
Tiled roofs are where pressure washing is most commonly sold, and it is where we see the most avoidable harm. MyBuilder's roof cleaning cost guide (2026) cautions that a pressure lance risks harming delicate tiles, and it gives the typical UK price as £10 to £15 per m², against £15 to £20 per m² for soft washing. The cheaper method is not the cheaper outcome.
On clay, a hard jet can crack thin edges and chip the nibs, and it can shift worn tiles from their bed. On concrete, it strips the coloured layer. On both, it drives water into the laps and onto the underlay. Older roofs may have no underlay at all, in which case the water goes into the loft, and the staining shows on the ceiling a few days later.
Pressure also does little about the cause. The spores that start moss are blown in on the wind and settle in the pitted surface the jet has created. A roughened tile gives them a better foothold than a smooth one did. Many owners find the roof green again within a season or two, and take it as proof that cleaning does not last, when the method was part of the cause.
The alternative takes longer but leaves the surface in better shape. Hand removal and a low-pressure treatment protect the tile, let the biocide do the work, and leave the surface smooth enough to shed water. We go through the reasoning on our page about pressure washing a roof, and how long the work takes on our short answer about roof cleaning time.
What to check before and after the clean
A cleaning visit is an opportunity to look at the tiles properly, and it is worth using. Before any cleaning, we look for cracked, slipped or missing tiles, because water should not be sent over a gap. We look at the ridge and hip tiles, where mortar has often cracked. BS 5534:2014 no longer relies on mortar by itself to hold ridge and hip tiles, so a loose mortared ridge goes on our list. We look at the verge, where a cement fillet may have cracked, and at lead flashings at the chimney.
Tiles themselves can show frost damage, with faces that flake away. Our answer on frost damaged tiles explains the cause. A flaking tile cleaned hard will lose more of its face, so these are noted and handled gently or replaced.
The gutters come next. Whatever moss comes off a tiled roof ends up in or near them, and a gutter that is already part-blocked can overflow during the rinse. We clear the outlets before and after, and our page on moss blocking gutters explains why that matters for the walls beneath.
Afterwards we review the result from the pavement and again from the boards. We look for tiles that shifted, any that were broken in the clearing, and any area where the growth was thicker than expected and needs a second pass. If something does need repair, you see it with your own photographs, and the repair is priced separately from the clean.
Cost, regrowth and when cleaning is the wrong answer
Typical UK ranges reported by MyBuilder's roof cleaning cost guide (2026) put tiled roof cleaning at about £400 to £750, with cleaning in general starting from about £300. A pitched roof overall runs £450 to £850, and slate sits higher at £500 to £1,000. The fixed price arrives after the survey and reflects the roof size, the tile type, the access and the method.
Regrowth depends on the site more than the method. A north slope below trees, or a roof near damp ground, will grow moss quickest. A treated roof is not protected for ever, and we tell you honestly what to expect rather than promise a clean that lasts. Trimming back overhanging branches and keeping gutters clear are the cheapest ways to slow it.
Cleaning is the wrong answer when the covering is simply worn out. Where tiles are crumbling, if the underlay has perished, or if slipped tiles are appearing on every slope, the money goes further as a repair or a re-cover. The decision is laid out in our answer on cleaning against replacing. Re-covering a roof is also regulated: Building Regulations approval is not normally needed below 25 per cent of the building envelope and 50 per cent of the roof, and a new covering 15 per cent heavier or more brings approval and a structural check whatever the area.
Where cleaning is right, we recommend it and price it, and we ask you to look at a few tiles near the gutter first so you can judge whether the surface is sound enough to take it. Where it is not, we tell you what we would do instead.