The short answer
Sometimes. Cleaning is worth the money when moss or algae is keeping tiles wet, filling gutters or hiding faults, because it slows wear and gives a roofer a clear view of the covering. Where the growth is only a thin tint on sound tiles, it is a matter of looks. Either way, the method matters more than the decision to clean.
When a clean earns its keep
Cleaning pays for itself when the growth is causing a measurable problem. Thick moss that holds water against the tiles, lifts their edges or slides into the guttering is the clearest case. Removing it reduces the load of water on the roof, takes away a source of blockages and lets the tiles dry between showers.
It also helps when you need to see what is underneath. Cracked or slipped tiles, flaking surfaces and failing ridge mortar are hard to spot under a green carpet. Once the growth is dealt with, the covering can be inspected closely, and any repair that turns up is found before it becomes a leak.
Selling a house is another reason. A tidy roof lifts first impressions from the road, and a buyer's surveyor is likely to look harder at a mossy one. A clean with a photographed survey gives you a record of the condition either way.
Finally, there is safety. Algae makes a slope slippery for whoever has to climb up to reach a chimney, an aerial or a gutter. Our answer on whether moss damages a roof shows how growth turns from cosmetic to costly.
When it is mainly about appearance
A thin green or grey tint on a well-drained slope, with clear gutters and sound tiles, does little harm. The tile still sheds water and the structure is unaffected. Cleaning in that case is a choice about how the house looks, and it is a perfectly reasonable one as long as you know that is what you are paying for.
It is worth being cautious about promises that cleaning will add years to a roof. It may slow wear where growth was holding water, but it cannot bring back a tile face that has already worn off, and it will not rescue a covering that is failing. How long a covering lasts depends on the covering itself, and published lifespans are typical ranges, not promises, so a clean cannot be sold on years gained.
Equally, a spotless roof is not proof of good health. Underlay can age and flashings can fail beneath perfectly clean tiles. If you are paying for a clean, ask for the roof to be checked at the same time, so you get information as well as appearance.
If the question is purely cosmetic, there is no hurry. Take pictures each spring and autumn, and decide when the look bothers you or the growth changes character.
Method matters more than the decision
A bad clean can cost more than no clean. A clean goes wrong most easily with a jet. Marley does not recommend jet washing tiles, since the force wears the face away. A rougher tile stays wetter, and growth takes hold again sooner. Scraping and hard brushing cause similar harm.
The kinder route is a biocide treatment: a gentle brush or spray, then a wait. The growth withers and rain carries it off across several weeks, so the result is gradual. Trade-only biocides are not for homeowners, according to the Health and Safety Executive, so a roofer using approved products is part of what you are buying.
Look at what each quote proposes: the method, how the roof will be reached, whether the gutters are cleared and whether the debris is taken away. Our guide to roof cleaning methods compared will help you read a quote with confidence.
The best value is a gentle method on a roof that needs it, with the gutters cleared and any faults found while the roof is accessible.
How to decide for your own roof
Start with evidence. Photograph each slope from the ground in spring and autumn. Run an eye along the gutters for moss and grit, and check the loft for damp after a wet spell. If you see thick moss, blocked gutters or water marks, cleaning is worth having. If you see a light tint and nothing else, you can wait.
If you are on the fence, ask for a survey. We examine the whole roof, photograph what we find, explain it in plain words and say whether cleaning would help or not. If it would not, that is what you are told. If it would, the survey also shows what else wants attention, such as a cracked tile, so you can plan the work in one go.
Trees and shade change the answer. A roof under branches will green up quickly after a clean, so a trim or a gutter guard may be a better investment than repeating treatments. The answer on moss returning goes through what to expect.
Price depends on the roof and its access, and is set once the survey is done. The roof cleaning and moss removal page lists the work we do.
