Roof Care / Moss Removal

Roof moss removal and roof cleaning in London

Moss holds water against your tiles, adds weight to the roof and blocks the drainage. We take it off with the method your covering can actually survive, and treat what is left so it does not come straight back.

Get a moss removal survey

Moss on a roof is a structural problem, not a cosmetic one

Moss is a sponge bolted to the outside of your roof, and everything it does badly follows from that. It holds rainwater against the tile instead of letting it run off, so the covering stays wet for days after the weather has cleared. In a London winter that trapped water freezes, expands inside the pores of the tile, and takes the surface apart a fraction at a time. The tile does not crack in one go. It erodes.

It also weighs something. Saturated moss beds on a large roof add a load nobody designed for, spread unevenly across slopes and concentrated in the valleys, and on an old roof with tired battens and corroded nails that is not a trivial addition. Thick beds sitting along the laps also lift the tail of the tile above, breaking the seal that the overlap depends on, which is how wind-driven rain gets underneath a covering that looks intact from the street.

Then there is the drainage. Moss sheds constantly, and everything it sheds goes into the valleys, the gutters and the hoppers. A blocked valley holds water on the roof rather than moving it off, and a blocked gutter sends it down the wall instead. Most of the genuine damage moss causes is not on the tiles at all: it is the damp wall, the rotten fascia and the saturated wall plate that follow from the blockages.

None of which means every green roof needs cleaning tomorrow. A thin algal film on a sound tile is cosmetic and can wait. The judgement is about what the growth is doing rather than how it looks.

Because the drainage is where the real harm shows up, a moss job and a gutter and valley clearance belong on the same visit, and we treat them as one piece of work rather than two quotes.

Where the growth has already been sitting long enough to have done damage underneath it, what follows is pitched roof repair and re-roofing rather than a clean, and we would rather tell you that at survey than after taking your money for a wash.

Benefits

How we take moss off a roof

The method follows the tile

Slate, clay and concrete each survive a different treatment. What the roof is made of, and how weathered it is, decides the method rather than what is quickest.

Killed at the root, not scraped

Scraping takes off what you can see and leaves the root system in the pores of the tile, which is why a scraped roof greens up again within a season.

Drainage cleared the same visit

Taking moss off a roof puts a great deal of it into the gutters and valleys. Clearing them afterwards is part of the job, not an extra line on the quote.

Roofers doing the work

A cracked tile or a perished flashing found under a moss bed gets reported and priced, not covered back over with the next pass of the lance.

What we offer

Four ways to get moss off, and what each one suits

There is no universal method. Each of these is right on some roofs and destructive on others, so what follows says both what it suits and what it must never go near.

Manual removal

Hand scraping with tools matched to the tile profile, working down the slope. SUITS: thick beds on almost any covering, and the only sensible first step where the growth is deep. NEVER: as the whole job on its own, because it takes off what is visible and leaves the root system in the tile, so the roof greens up again within a season unless it is treated afterwards.

Soft washing

Low pressure water carrying a specialist agent that kills the growth rather than blasting it off. SUITS: natural slate, old clay, weathered or fragile tile, and anything in a conservation area. This is the right method for most of the Victorian and Edwardian stock in South and West London. NEVER: expect it to be instant, because it works over the following weeks as the dead growth weathers off.

Pressure washing

Higher pressure water to lift ingrained soiling and carbon pollution that a soft wash will not shift. SUITS: sound modern interlocking concrete tile, used selectively and at a controlled distance. NEVER: natural slate, old clay, any tile that is already eroding, and never aimed up the slope, because that drives water under the laps and into the roof space.

Biocide treatment

A pH-neutral solution applied once the roof is clean, which soaks in and neutralises the spores left in the surface. SUITS: every covering, and it is the step that turns a clean into something that lasts. NEVER: applied to a wet roof or in the rain, and never a substitute for taking the thick beds off first.

When you would want one

Is the moss doing harm, or only looking bad?

These are the signs worth acting on, and the ones that can wait until it suits you. The distinction matters, because cleaning a roof is not free and doing it too often is its own kind of wear.

Act on: thick beds along the laps

Moss deep enough to sit proud of the tile and lift the edge of the course above it. That breaks the overlap the roof relies on, and once wind-driven rain can get under a tile the covering has stopped doing its job whatever it looks like from the road.

Act on: growth in the valleys

A valley is the one part of a pitched roof that cannot clear itself. Anything growing in one is also holding whatever the slopes shed, and a valley that holds water rather than moving it is a leak that has not happened yet.

Act on: clumps in the gutters and hoppers

If moss is arriving in the gutter it is already detaching from the roof in quantity. That is both a drainage problem now and a sign the beds above are thick enough to be shedding, which is usually the point at which the roof is worth doing.

Act on: a slope that stays wet

One elevation still dark hours after the rest has dried is holding water somewhere. On a north-facing slope under trees that is often moss, and a covering that never fully dries is a covering that is ageing faster than the one opposite it.

Can wait: a thin green film

Algae on a sound tile is a stain rather than a growth. It has no depth, holds almost no water and does nothing structural. It will keep coming back too, so cleaning it is a decision about how the house looks rather than about the roof.

Can wait: lichen crusting on slate

The flat grey and yellow crusts on old slate are slow growing and largely superficial, and taking them off aggressively does more harm than leaving them. Worth watching rather than attacking, and frequently better left entirely on a listed or conservation roof.

Scope

What else happens at the same visit

Every gutter, hopper and downpipe cleared of what the clean has dislodged, and tested with water before we leave
Valleys cleared to the lining and checked, since that is where the shed moss collects first
Loose, slipped or cracked tiles found under the growth reported with photographs, and priced separately rather than quietly ignored
Ridge and hip bedding checked, because that is the mortar most likely to be at the end of its life on an old roof
Flashings and abutments looked at while there is access, as moss beds frequently hide a failed mortar fillet
Ground, planting and drains protected before work starts, and the site washed down afterwards

The warning

What a bad pressure wash actually does

This is the part of the job that goes wrong, and it goes wrong the same way every time: someone arrives with a lance and a fixed price and treats every roof as the same roof. The damage is not always visible on the day, which is why it keeps happening.

Old natural slate

Worst case

Weathered slate delaminates in thin layers, and high pressure finds every one of them. It lifts the laminations, drives water between them, and on a roof with corroded nails the vibration alone is enough to break slates free. What you get is a clean roof shedding slates for the next two winters, and the cause is invisible on the day the invoice is paid.

Concrete tile

Slow damage

A concrete tile is protected by a thin factory-applied surface layer, and pressure takes it off. Underneath is porous aggregate, which then absorbs water, weathers rough and gives moss a far better surface to grip than it had before the clean. The roof looks best on the day it is washed and greens up faster than it ever did afterwards.

Any tile, aimed the wrong way

Water ingress

A pitched roof is watertight because each course overlaps the one below, which works against water falling downwards. Pressure directed up the slope goes under the laps by design, and from there into the felt, the battens and the insulation. This is how a cleaning job produces a leak in a roof that was not leaking.

Ridges, hips and mortar

Collateral

Bedding mortar on ridges and hips is often the oldest thing on the roof and the first thing pressure removes. A ridge tile that has lost its bedding is a genuine hazard, not a maintenance item, and it is a common outcome of a fast clean on an old roof.

How to tell it was done badly

Afterwards

Grit and surface fragments washed out onto the ground rather than moss alone. Tile colour noticeably lighter and more uniform than before. Mortar debris at the base of the downpipe. Slates or ridge tiles out of line. Any of those means material came off the roof that was meant to stay on it.

Why moss comes back, and what actually extends the interval

Moss returns because London roofs are a good place to grow. Spores are airborne and constant, the tile surface holds enough moisture and dust to root in, and nothing about cleaning a roof changes the conditions that made it attractive in the first place. Anyone selling a permanent solution is selling something that does not exist. What is genuinely on offer is a longer interval.

Four things move that interval, and only one of them is the clean itself. The first is whether the root system was killed or merely scraped off, which is what the biocide step is for and why a scrape-only job is the shortest-lived of all. The second is how much light and air the roof gets: a south-facing slope in the open dries within hours and stays clear for years, while a north-facing slope under mature trees can be visibly green again in a couple of seasons however well it was done.

The third is the surface itself. A sound glazed or smooth tile gives moss very little to grip, while an eroded concrete tile is effectively a growing medium, which is why a roof that has been pressure washed badly regrows faster than it did before. The fourth is the drainage, because a valley or gutter that stays full keeps the surrounding tiles wet and reseeds the slope above it every time it rains.

So the honest answer to how long it will last is that it depends on your roof rather than on our method, and we would rather tell you at survey that yours is a three year roof than quote five and be wrong. Overhanging branches cut back and the gutters cleared annually will do more for the interval than any product we could apply.

The interval is also the argument for putting the roof onto a planned roof care schedule, where the gutters get cleared each year and the growth gets treated before it is thick enough to need taking off by hand.

Cleaning, your guarantee and your insurer

Two questions come up often enough to answer here. The first is whether cleaning affects a workmanship guarantee on the roof. Our own 10-year workmanship guarantee covers the work we carried out, and having the roof cleaned does not affect it. What can affect any roof guarantee, ours or another contractor's, is damage caused by somebody else working on the covering, so if your roof is under a guarantee it is worth telling whoever holds it before a cleaning contractor goes up. A badly done clean that breaks tiles is damage caused by a third party, and that is a conversation nobody wants to have retrospectively.

The second is insurance. Home insurance generally covers sudden and accidental damage rather than deterioration, and moss growth is deterioration by any reading. A roof that has failed because water sat in a blocked valley for three winters is a maintenance failure, not a storm claim, and an insurer that sends someone to look is entitled to say so. That is the practical reason to keep the drainage clear rather than an argument about any specific policy, and we cannot tell you what your own wording says.

Where it does become relevant is evidence. If work is carried out and photographs of the roof before and after exist, the condition of the covering on that date is documented. That is useful for a later claim, for a buyer's surveyor, and for a freeholder or managing agent who wants to show that maintenance was actually done rather than merely invoiced.

What our own guarantee covers, how long it runs and what happens if you sell the house is set out on the guarantee page.

How it works

How the work runs

Free survey

We establish the covering, its condition and how much of the growth is structural rather than cosmetic. A roof with slipped or cracked tiles gets those addressed first, because washing a roof with holes in it just puts water inside.

Method, photographs and an itemised price

You get the recommended method with the reason for it, photographs of what we found, and a price split into cleaning, treatment, access and anything else the survey turned up.

Protection and access

Ground, planting, drains and any glazing are covered, and access is set up. Most domestic roofs here are worked from a tower or from ladders with roof ladders rather than full scaffold.

Removal

Thick beds come off by hand first, then the covering is soft washed or, on suitable concrete tile only, pressure washed at a controlled distance. Work goes down the slope so nothing is driven under a lap.

Drainage cleared and site washed down

Gutters, hoppers, valleys and downpipes are cleared of everything the work has dislodged and tested with water, and the ground is washed off before we leave.

Biocide, once the roof is dry

Applied to a dry roof in suitable weather, which sometimes means coming back rather than finishing the same day. It then works over the following weeks rather than instantly.

Why choose us

Why customers choose K & M Roofing

HYDRONYLON Approved Contractor, a certification most London roofers do not hold.

One team for the whole job, from survey to sign-off.

Rated 5.0 on Google from 60+ reviews.

Qualified roofers doing the cleaning, so a cracked tile or perished flashing uncovered during the work gets reported and put right instead of hidden.

Transparent pricing with no hidden costs, and a 10-year workmanship guarantee.

What our 10-year workmanship guarantee covers, how it differs from a manufacturer product guarantee, and what falls outside it.

Where we work

Where moss gives us the most work

Growth is worse on some London stock than others, and it is usually the trees and the tile that decide it rather than the postcode.

Roofing in Acton: The dense tree cover around Acton Park, and the postwar estate concrete tile whose eroded surface gives moss something to grip.
Roofing in Croydon: Valleys and chimney abutments on the Shirley and Addiscombe stock, where moss and silt build up until the valley holds water rather than moving it.
Roofing in Wimbledon: Deep valleys on the large roofs facing the wooded Common, and the interwar concrete tile down towards Raynes Park.

Knowledge

Frequently asked questions

It does real damage, though indirectly and slowly, for the reasons set out at the top of this page: trapped water eroding the tile surface, thick beds breaking the overlap, and shed clumps blocking the drainage. The short version is that moss will not put a hole in a sound covering this year. It shortens the life of the roof and causes the blockages that do the expensive damage, and those show up as damp walls and rotten roofline rather than as a hole.

For most London roofs the answer is every five to ten years, but the interval depends far more on your roof than on any general figure. A south-facing slope in the open can go well beyond ten years; a north-facing slope under mature trees can need attention in three. The better question is how to lengthen the interval rather than how often to repeat the job, and the answer to that is a biocide treatment after cleaning, the gutters cleared annually and overhanging branches cut back.

On the wrong roof it certainly will, and the damage is frequently invisible on the day the invoice is paid. The section above sets out what it does to slate, to concrete tile, to bedding mortar and to a roof it is aimed up rather than down. Pressure washing has a legitimate use on sound modern interlocking concrete tile at a controlled distance and almost nowhere else. If somebody quotes to pressure wash a Victorian slate roof, get another quote.

Typically three to five years on a London roof, and where in that range depends on shade, tree cover and aspect rather than on the product. It also works gradually rather than instantly: it neutralises the spores in the surface and the dead growth weathers off over the following weeks, so a roof still looking patchy a fortnight afterwards is normal rather than a failed job.

Usually not. Most domestic moss removal in London is done from a tower or from ladders with roof ladders where needed, which keeps the cost down considerably. Full scaffold becomes worthwhile on very steep roofs, on tall buildings, where several elevations need working at once, or where the cleaning is happening alongside repairs that need proper access anyway. We tell you which at survey and price the access as its own line rather than burying it.

It is priced by roof area, covering, how thick the growth is, pitch and access, because a steep slate roof reached from scaffold is a different job to a low concrete roof reached from a tower. What moves it most is how much has to come off by hand before anything else can start, and whether you want the biocide treatment that decides how long the result lasts. There are no reliable published UK rates for roof cleaning that we would stand behind, so we do not quote a per square metre figure sight unseen and would be wary of anyone who does over the phone. A binding price from K & M Roofing Solutions follows a free survey.

The removal is the easy part and the roof is the dangerous part. Roof work causes serious falls every year and a mossy roof is a slippery one, so a domestic ladder against a gutter is a bad way to find that out. Beyond the safety of it, scraping alone leaves the root system in the tile so the growth returns within a season, brittle old slate breaks under the weight of somebody who does not know where to stand, and the debris still has to come out of the gutters afterwards. Treating a low garage roof you can reach safely from the ground is reasonable. A two-storey slate roof is not.

Yes, and with particular care. Slate is thin, brittle and hung on nails that grow fragile with age, so walking a slate roof carelessly causes far more damage than the moss ever would. We work from proper roof access, clean by soft wash rather than pressure, leave lichen crusts alone where taking them off would do more harm, and re-fix any slates that turn out to be loose while we are up there. On a listed or conservation-area roof we would rather do less and tell you why.

Our own 10-year workmanship guarantee covers the work we carried out and is not affected by the roof being cleaned. Damage caused by a third party working on the covering is the thing that can affect any guarantee, so tell whoever holds yours before a cleaning contractor goes up. The section above covers the insurance side.

Yes, and it is not an optional extra. Taking moss off a roof puts a great deal of it into the gutters, hoppers and valleys, so a cleaning job that leaves the drainage full has created a worse problem than the one it solved. Every gutter, hopper and downpipe is cleared of what the work dislodged and tested with water before we leave, and the valleys are cleared to the lining and checked while there is access to them.

Free on-site estimate

Let us talk about your roof

Tell us what is going on and we will arrange a free survey. No pressure, no hard sell, just honest advice and a clear price.

Request a free survey office@kmroofingsolutions.uk

Mateusz07544 188268