How Often Should You Clean Your Roof?

Advice to clean a roof every so many years sounds tidy, but a roof is not a boiler. Two houses on the same road, built together, can be in very different states ten years on. One faces the sun and has no trees; the other has a north slope shaded by a neighbour's conifers. A single interval would be too long for one and wasteful for the other.

The better rule is to watch the roof and respond to what you see. Growth is a slow process, so you are not racing anything. A thin green tint is a prompt to plan, not an emergency. Thick moss lifting tiles or filling valleys is the point at which waiting costs money, because water is being held against the roof and into the joints.

Early growth is mostly a matter of looks, while heavy growth is a matter of durability, and the survey shows which stage a roof is at. If you are unsure, send photos and we will tell you whether it can wait. Our page on how long a roof biocide treatment lasts covers the other side of the question.

Growth follows damp and shade. A north-facing slope dries slowly, so it is usually the first to green. Roofs under overhanging branches stay wet from drips as well as rain, and fallen leaves pile up in valleys and behind chimneys, keeping everything damp long after the weather has cleared.

Sheltered gardens, close terraces and houses beside water or a wood behave the same way. On the other hand, an exposed roof on a hill, with sun on all sides and wind drying it, can stay clean for a long time.

Trimming trees helps more than most owners expect. Letting light and air reach the slope slows growth and makes any later treatment last longer. If the trees belong to a neighbour, a polite request often works. Gutters count as well: a blocked one keeps the lowest tiles wet, and a clear run of guttering is part of keeping the roof clean.

Tile type changes how quickly growth takes hold. Concrete tiles have a rougher, more absorbent face, so they hold moisture and spores and often show growth sooner. Clay tiles are denser and can stay cleaner, but old clay peg tiles with weathered faces collect moss in the pores. Natural slate is smooth and sheds water well, though growth still settles in the overlaps and on shaded slopes.

Age matters in all cases. A new roof starts clean, and surface coating wears and weathers with time, so older tiles are rougher and hold more. That is a reason to start treating early rather than late.

Roofs with a mix of coverings behave differently on each part. A porch with a flat felt roof, a garage in concrete tiles and a main house in clay can all sit under one tree and still need cleaning at different times, so judge each roof on its own.

Method also differs by covering. Hard jetting wears the face off a tile or slate, so we choose gentler methods, and our page on moss on concrete roof tiles explains why that matters for concrete. Where the roof is clay, the same logic applies to older, softer peg tiles. A rougher face is also a faster-growing face, so protecting the surface protects the interval between cleans.

Look twice a year, in spring and autumn, from the garden and from an upstairs window if you can. Choose a dry day with good light. Check the north slope, the lowest rows of tiles, the valleys and the area around the chimney, and run your eye along the ridge line for gaps or tiles that sit out of line. Compare with last year's photo, which is why taking one is worth the minute.

Things to note are a green or black wash, raised cushions of moss, tiles with dark edges, and moss or granules in the gutter. Do not climb up to look. A phone with a zoom lens, or binoculars, does the job safely.

If growth is spreading, book a survey. You get pictures of the roof as it is, a plain explanation of what is on it and one written total. Nationally, Checkatrade's April 2026 table lists typical UK roof cleaning at £8.50 to £14 per m², so when comparing offers, look at what is covered for VAT and scaffold. Our roof cleaning and moss removal page explains the service in full. A single picture of the slope that bothers you most is enough to start the conversation, and it also shows us the type of tile.