Ask three roofers how to get moss off a roof and you may hear three different answers. Each can be right for the roof they have in mind. The real question is which method suits the covering above your head: a concrete tile, a clay pantile, a Welsh slate or a Cotswold stone slate. They are different materials, with different weak points, and a method that is routine on one can ruin another.
This guide compares the four methods professionals use: hand scraping, soft washing, biocide treatment on its own and pressure washing. It judges each on what it does to the roof, not on speed or price alone. If you are weighing up doing the work yourself, our answer on removing roof moss yourself is about homeowner safety, which is a separate matter. For the full service, start at roof cleaning and moss removal.
What moss does to a roof, and why the method matters
Moss is a living mat. Its stems and root-like threads grip the surface of a tile or slate, and the mat holds water against the covering long after rain has stopped. On a rough concrete tile it can bind into the surface texture. On a slate it settles into the laps, the strips where one slate overlaps the next. On a Cotswold stone slate it roots into the weathered face and the gaps between slates.
Removal therefore has two jobs. The first is to take the growth off. The second is to leave the covering as sound as it was before. A method that does the first and harms the second has swapped one problem for another, which is why the choice of method deserves more thought than the choice of day.
Three questions that decide the method
Before settling on how to clean, we establish the material, its age and its state. A tile with a worn surface skin is different from one with an intact skin. A slate with rusted nail fixings behaves differently when walked on than one fixed with copper. Stone slates hung on oak pegs cannot be treated as if they were nailed. The answers narrow the field before price enters the conversation.
Whether the moss needs removing at all
Sometimes the best method is none. Light growth on a sound roof can wait, and our answer on whether moss should be removed sets out when action is worth taking. Where it does need to come off, the sections below compare what is on offer.
Hand scraping and brushing
Scraping is the oldest method. Working across the slope, the roofer uses a plastic or wooden scraper and a stiff brush, lifting the moss away in sheets and brushing the surface behind it. There is no water pressure and no chemical, and the force applied is the force of a hand.
Where it suits
Scraping is the method of choice on fragile coverings. Old clay tiles, thin slate and stone slates all tolerate it far better than they tolerate a jet of water. The Cotswold District Council guidance on stone slate roofing, from 2000, records that annual scraping can double the life of a stone roof, which tells you the method has a long record on exactly this material. On a stone roof the work is done carefully, because the slates sit on pegs and can be loosened or cracked by the wrong pressure from a boot or a tool.
Where it falls short
Scraping takes the visible growth, but it leaves spores and fine residue in the surface, so regrowth can start again from what remains. It is also slow on a large roof, and it needs the roofer to be on the slope, which brings the question of how the roof will be reached. The MyBuilder cost guide, updated 21 August 2026, puts manual scraping at £5 to £10 per m², the lowest of the three rates it lists, reflecting simple tools and a lot of labour. Our guide to roof cleaning and moss removal costs sets the three rates side by side.
Soft washing
Soft washing uses low-pressure water to rinse the roof, usually together with a cleaning solution applied to the surface. The intention is to loosen and kill the growth with chemistry rather than force. The moss is then rinsed off or left to die back and wash away in rain.
Why it is gentler on the surface
The surface of the covering is not blasted. A concrete tile keeps the thin coloured layer on its face; a clay tile keeps its fired surface; the laps are not flooded. That is why soft washing is a common choice for tiled roofs, where the aim is a result without wear. The MyBuilder guide gives soft washing at £15 to £20 per m², the highest of the three rates, because the job involves mixing, applying and managing the solution as well as washing.
What it still needs
Soft washing is not a free pass. The solution runs off the roof, so planting, ponds and drains below need to be protected or rinsed, and it needs dry conditions for the treatment to do its work. It also depends on the roofer's judgement: too much water directed up a slope, even at low pressure, can find its way under the laps. Our full explanation of soft washing and biocide treatments covers how the treatment works and what results to expect.
On slate and stone
Soft washing can be used on slate with care, since the surface is dense and the solution does not need force. On stone slates it is used more cautiously, if at all. A porous stone can hold moisture and carry the solution further into the face, and conservation advice usually favours the gentlest route available.
Biocide treatment on its own
A biocide is a chemical that kills the living growth. Applied by itself, without washing or scraping first, it is sprayed onto the roof and left. Over the following weeks the moss browns, loosens and comes away in wind and rain. No one steps on the covering beyond the spraying itself, and no water pressure is used.
Why it appeals
It is the least physical of the methods, which suits a roof that is fragile or hard to walk on. The cost is lower than a full wash, because the job is shorter, and there is little disturbance. On stone slates and old clay it is sometimes the least invasive way of dealing with growth that is thick but not heavy enough to cause harm.
What it does not do
It does not remove the dead growth quickly. The roof can look worse before it looks better, with brown patches left in place, and some of the debris ends up in the gutters, which then need clearing. Its effect also depends on weather, because rain too soon after spraying can reduce what the roof takes up. For that reason a biocide alone is better thought of as treatment than as cleaning.
Treatment kills the moss. Cleaning removes it. A roof that needs both should have the treatment come second, so that it reaches the surface and not the mat above it.
Run-off is the main safety consideration. Our answer on whether roof moss killers are safe for plants and pets deals with precautions and product labels, which are a separate subject from this comparison.
Pressure washing
A pressure washer fires water at high pressure through a narrow nozzle. On a roof it blasts the moss out of the surface and strips the covering clean in a fraction of the time that hand work takes. It is quick, and it makes a roof look new, which is why it remains popular.
The risks to the covering
The same force acts on the roof itself. High pressure can wear the surface layer from concrete tiles, drive water sideways under the laps and into the underlay, and crack thin or weak slates. MyBuilder warns that delicate tiles can be harmed by pressure washing, and gives it £10 to £15 per m², a rate between scraping and soft washing. A tile that has lost its surface layer holds moss more readily the next time, so the damage can make the original problem worse.
Stone and old coverings
On stone slates the risk is higher still. The slates are laid with generous laps and held by oak pegs, and a hard jet can knock pegs askew, split a slate along its bedding or leave the face scoured. Many older coverings in the Stroud valleys are not suited to this method at all, and we would not use it on them. Our guide to why pressure washing can damage your roof explains the mechanisms in detail.
When it might be appropriate
On a sound, modern concrete tile roof, a pressure wash used with care and at moderate settings can be a reasonable choice. The key words are sound and modern. If the roofer cannot say what the covering is and what condition it is in, a pressure washer should not be the first tool in hand.
Matching method to material: tile, slate and stone
Putting the methods against the coverings gives a rough guide to what is appropriate. Treat it as a starting point for the survey, not a rule, because the condition of a roof can overrule the material.
| Covering | Usually suitable | Take care or avoid |
|---|---|---|
| Concrete tiles | Soft washing, scraping, biocide | Pressure washing, which can wear the surface layer |
| Clay tiles and pantiles | Scraping, soft washing | Pressure washing on older or worn tiles |
| Natural slate | Scraping, soft washing with care, biocide | Pressure washing, which can crack or lift slate |
| Cotswold stone slate | Hand scraping, light treatment | Pressure washing, any heavy wash |
The survey before the method
We look at your roof first, with photographs, and then choose. The survey checks the covering, how well it is holding, how steep the slope is and what stands below the eaves. Only then is a method written onto the quote. If the roof needs a mix, such as hand scraping on the worst areas followed by a light treatment, the quote names both.
Protected buildings
Listed and conservation-area roofs call for the gentlest available method. Check with Stroud District Council's planning team whether your building is listed or covered by special controls, because cleaning is not always a matter of preference. Our guide to cleaning listed roofs explains when to speak to the conservation officer.
How to choose, and what to ask a roofer
You do not need to be an expert to judge whether a roofer is proposing the right method. A few plain questions are enough, and the answers will tell you a good deal.
Questions worth asking
Ask which method will be used and why it suits your roof's covering. Ask what is done to protect the laps and the underlay. Ask where the removed moss goes, and how the gutters will be cleared. If a treatment is applied, ask what it is and how long before you should expect to see a result. A roofer who has looked carefully at the roof will answer without hesitation; one who proposes the same method for every roof may not have.
Red flags
Be wary of a quote that names no method at all, one that promises a roof that looks brand new in an afternoon, and any suggestion of aggressive washing on stone or old slate. The lowest price is not necessarily the lowest cost if the surface is damaged. A claim that nothing will grow back is also unrealistic; treatment slows regrowth, and our answer on how quickly moss grows back explains what to expect.
What you get from us
Our survey produces photographs of the roof and a written quote that names the method and the reason for it. Debris leaves with us, and the work carries our 10-year workmanship guarantee in writing. If the roof turns out to need repair rather than cleaning, the quote says that instead, and the repair is priced as its own item.