Cleaning interval
How often should a house roof be cleaned?
The short answer
There is no fixed interval. How often a house roof needs cleaning depends on how quickly growth returns, and that depends on shade, nearby trees, the pitch and the type of covering. A look from the ground once a year tells you more than a calendar does. Clean when moss is building up along the tile edges or reaching the gutters, and leave a thin even film of algae alone until it spreads.
A roof is cleaned when its condition calls for it, not on a timetable. Here is how to judge when that moment has come for your house.
Why the answer is a condition, not a date
People like a number of years, and a number would be easy to give. It would also be wrong for many roofs. Growth follows the conditions around the house: how much sun reaches each slope, how long the surface stays damp after rain, what stands overhead dropping leaves and seed, and how rough the covering is. Neighbours with matching houses may need a clean years apart.
The useful question is what your roof looks like now. Moss that has started to form a cushion along the tile edges is the sign to act on. A light green haze on one slope is far less urgent. Once you have decided it is time, our guide to the best time of year to clean a roof helps with the season, and is moss bad for a roof explains what waiting costs.
A yearly look from the lawn or the pavement
The simplest routine is also the most reliable. Once a year, pick a dry day, step back from the building and study each slope in turn. Binoculars help, and so does a phone camera zoomed in, because you can compare this year's picture with last year's. You are looking for three things: cushions of moss along the lower edge of each course of tiles, dark staining that has spread since the last look, and green growth in the gutters or at the foot of the downpipes.
Never climb up to check. A ladder against a wet gutter or a boot on a mossy tile is how a routine look becomes a hospital visit. If something from the ground looks wrong, such as a slipped tile or a sagging ridge line, that is a repair question rather than a cleaning one, and photographs taken during a roof survey settle it.
Shade, trees and the north slope set the pace
The side turned away from the sun stays damp longest, so growth starts there and comes back there first. A roof tucked under tall trees is another fast case: the canopy keeps the light off, drips onto the tiles after rain and feeds the roof with a steady fall of leaf litter that holds moisture against the surface.
An open, sunny, south-facing roof on a breezy plot may stay clean far longer than the one next door. Rougher coverings, such as older concrete tiles, give growth more to grip than smoother ones. Near the sea the weather is often damp and blustery, but we would not give a seaside roof a shorter interval by default. Judge each slope by what is on it. Where moss has formed on a shaded side only, treating that side early can be enough, and the survey will say so.
Cleaning too often has a cost of its own
It is tempting to book a clean every year just to be safe. Each aggressive clean takes a little of the surface from a tile, and a roof that has been blasted repeatedly can end up rougher and quicker to re-grow. Gentle treatment is a different matter, but even that is not needed when there is nothing worth removing.
The sensible pattern is to inspect often and clean rarely. Treat the early signs on the shaded slope, and plan a fuller clean when growth is thick enough to hold water against the tiles or to drop into the gutters. If you cannot tell where your own roof sits, our survey photographs show the growth up close and we say whether it can wait. For the mechanics of a fuller job, see how moss is removed from a roof.
Fitting a clean in with other roof work
A clean is often easiest to time around other jobs. If the gutters are being replaced or the fascias painted, access is already in place, and the roof edge can be cleared at the same visit. If a leak is being traced, clean first where the growth hides the tiles, so the cause can actually be seen.
Before a house sale, a clean can show the roof's real condition to a buyer's surveyor, which sometimes helps and sometimes uncovers a repair that was already needed. After storms, check for lifted tiles before you worry about moss. If you want a view of the overall job and the choices behind it, our main roof cleaning and moss removal page sets out how the work is done, and a written total price arrives once the roof has been seen.
Different coverings keep different rhythms
The roof covering changes the answer. Natural slate has a hard, dense face that gives growth little to hold, so a slate roof can stay clean for a long stretch unless trees hang over it. Clay tiles are porous and can hold moisture, and concrete tiles, especially older ones with a rough finish, give moss plenty to grip. A flat roof drains slowly, so algae and moss can settle in the damp spots between its falls.
None of this tells you a number of years, and nobody who has not seen your roof can. What it does tell you is where to look first. Check a concrete tile roof with shaded slopes more often than a sunny slate one. Take notes on the lowest courses and the valleys, because that is where water lingers. If you are weighing the money, whether roof cleaning is worth it sets out the case for acting early and the case for leaving well alone.
Related questions
Timing questions
Should a roof be cleaned after every winter?
Not by default. Winter leaves a roof damp for longer, so spring is a good moment to look, but cleaning is only worth booking if the look shows moss building up. A roof with a light film and open sun can go another season without any work.
Does a new roof need cleaning in its early years?
Rarely. New coverings start clean, and growth takes time to take hold. A yearly look from the ground is still sensible, mainly to catch leaf build-up in the gutters and valleys before it holds water against the tiles.