The short answer
A roof does not need cleaning to a timetable. Look at them every year, clean when moss or algae is building up rather than waiting for damage, and expect shaded, north-facing or tree-covered slopes to need work sooner than open, sunny ones. A gap of a few years between cleans is usual on a sheltered roof, but a damp site may call for a look more often.
Why a single answer does not exist
Ask three roofers how often to clean a roof and you may hear three different numbers, and all of them could be right for the roofs they had in mind. Moss and algae are plants. They grow where there is water, shelter and something to grip, and how fast they take hold depends on the site more than on the calendar.
A roof that gets sun from mid-morning, sits clear of trees and has sound, smooth tiles can go years without a visible problem. Another roof on the same street, shaded by a neighbour's conifer and facing north, can be green within a single wet winter. Treating both on the same cycle either wastes money on the first or lets the second suffer.
The sensible approach is to let the roof tell you. Cleaning is a response to growth, set against a regular look, not a service to be bought on a schedule.
A rough guide by type of roof
Think in bands, not dates. The table sets out where different situations tend to land, and each is a prompt to look, not a promise.
| Situation | What to expect |
|---|---|
| Open, sunny, smooth tiles | Growth builds slowly; a clean is often needed only every few years |
| North-facing or lightly shaded slope | Algae and moss return sooner; plan a check each year |
| Under or beside trees | Leaves and shade speed growth; gutters want emptying every autumn |
| Older, rougher concrete or worn clay | Surface holds water; growth is quicker to return |
| Flat or low-pitched roofs | Water lingers; look after every wet season |
Our page on moss on the north side explains why one slope is so often worse than the other.
Signs it is time
Do not wait for a leak. By the time water is coming through, moss has usually been pushing at tile edges and blocking channels for a long while. The earlier signs are easy to spot from the garden or the road, ideally with binoculars.
Green or black patches that spread from one season to the next are the most obvious. Raised cushions of moss along tile edges, especially in the lower courses, hold water against the tile and lift it at the lap. Granules in the gutter point to a surface starting to break down. Moss growing into the valleys can choke the channel and send water over the side, and a pile of debris at the downpipe shoe is a hint that more is coming off the roof than should be.
Indoors, a brown mark on a ceiling after heavy rain, or a stain on the wall of a bedroom under the eaves, is the signal to get the whole roof looked at, not just cleaned. If you have a shed or outbuilding, see moss on a shed roof, where felt behaves quite differently.
Why cleaning too often can be as bad as too rarely
Every clean, however gentle, takes a little from the roof. Scraping loosens the tile face, jets drive water into the laps, and each time a roofer steps onto the roof there is a chance of a cracked tile. A roof cleaned every year to look spotless will wear sooner than one cleaned when growth demands it.
The opposite mistake is leaving moss to go unchecked for a decade. Thick moss soaks up water, stays wet through dry spells and pushes tiles apart as it swells. When it is eventually removed, the damage underneath is revealed, and the job turns from a clean into a repair. That is where a modest annual look pays for itself. MyBuilder's roof cleaning guide, updated on 21 August 2026, puts typical cleaning at £400 to £750 for a tile roof, so a clean at the right moment costs far less than patching a roof left too long.
What a clean should include
A clean that is only about looks misses the point of getting someone on the roof. A visit is a chance to catch the small faults that cause the big leaks: a slipped tile, a lifted ridge, crumbling pointing, a split lead flashing. Our page on the roof check during cleaning lists what we look at each time.
The method matters as well. A soft wash and careful hand removal are kinder to the covering, and can be repeated without damage, whereas repeated hard blasting cannot. You can compare the approaches in our guide to moss removal methods.
Setting your own routine
Pick one time of year, perhaps early autumn after the summer growth and before the leaves fall, and walk round the house with a pair of binoculars. Check every slope, the gutters, the valleys and the ridge. Take a photograph each year from the same spot and compare. Changes you cannot see week to week jump out year to year.
If growth is building, book a survey. Phone 01793 626096, or pass photos over on WhatsApp, and you will hear whether the roof wants cleaning now, can safely wait, or needs something different. Our service page on roof cleaning and moss removal covers the options. If we carry out any work, our workmanship is guaranteed for a decade in a written document.
One more habit helps: after any storm, take two minutes to look for tiles that have shifted. A cleaner roof is easier to read, and the sooner a slipped tile is found, the smaller the repair.