Moss on your roof: should you remove it?

Does moss damage a roof?

Usually not, unless there is a lot of it. The National Federation of Roofing Contractors (NFRC), a roofing trade association, says moss on roof tiles is rarely a problem and only needs removing if it is blocking gutters, outlets or other drainage points. Marley, a roof tile manufacturer, says low to moderate moss or lichen is a natural part of the ageing process on many pitched roofs and, in normal circumstances, does not harm the tiles or slates.

The harm comes from quantity. The NFRC's guidance note on moss, GN58, says its main effect is that it holds water: rain drains off the roof more slowly and stays in contact with the tiles for much longer. A thin green film does little. Thick cushions filling the tile laps or packed into a valley are a different matter.

Why your roof grows moss

GN58 says the rough surface of a tile filters dirt out of rainwater, dead leaves lodge on it and spores blow onto it. Moss does best near trees and in shady, damp conditions. North-facing slopes stay damp for longer and may grow more, while steep roofs shed water faster than shallow ones and are less likely to grow it. Some concrete tiles with a sanded or granule face are the first to attract moss, and that rough face is common on the concrete interlocking tiles of post-war estates.

Yorkshire weather helps it along. The Met Office's climate summary for North East England, which takes in North, West and South Yorkshire, describes the Pennines as frequently cool and wet. On the higher ground, 45 to 50 days with 1 mm of rain or more is the norm between December and February, against about 30 in the drier areas nearer the coast.

When does roof moss need dealing with?

Roof moss needs dealing with when it affects drainage: when it blocks gutters and valleys, or grows so thick that water sits on the roof instead of running off. GN58 says severe growth that affects drainage should be carefully removed. Signs it has reached that point:

• Gutters that overflow in heavy rain, with green clumps in them or on the path below. Our gutter cleaning guide covers what blocked gutters do to fascias and walls.
• Moss packed into valleys or around outlets, so water backs up where it should drain fastest.
• Thick cushions across whole slopes. Marley says a heavy build-up keeps the roof wetter for longer. Wienerberger, a roof tile manufacturer, says tiles covered in moss stay damp, which makes clay tiles more prone to delamination, where the clay surface separates from the body of the tile.
• Heavy growth on slate or stone slate. Bradford Council's conservation guidance says excess moss holds water and can speed up the deterioration of both.

It is probably cosmetic if the growth is thin, the gutters run freely and nothing is getting in. A green north slope under a tree is no reason on its own to spend money.

Moss often gets the blame for lifted or slipped tiles, but a tile that has moved needs a roof repair whatever is growing on it. If you have a damp patch or a drip indoors, find the source first. Our guides on how to find a roof leak and damp patches on the ceiling explain how.

What is the safest way to get moss off a roof?

The safest way is to scrape it off by hand, done by someone trained and equipped to work at height, with as little walking on the roof as possible. GN58 describes hand scraping from properly supported crawling boards or ladders, avoiding foot traffic on the roof as much as possible.

Marley says homeowners should not go onto the roof to remove moss themselves because of the risks, and Wienerberger warns that walking on tiles can leave hairline cracks that go unnoticed even when nothing breaks. Please stay off your roof. Things you can do from the ground:

• Sweep up clumps that land on the path or patio before they make it slippery.
• Watch the gutters in a downpour and note where they overflow.
• Take zoomed-in photos of the roof so a roofer can judge it before visiting.
• Have overhanging branches cut back, if the tree is yours, so less shade and fewer leaves reach the roof.

Asbestos cement. Many older garages and outbuildings have asbestos cement roofs. GN58 says never to scrape or brush what may be an asbestos cement covering. HSE's guidance for workers says asbestos cement roofs are always fragile and cannot bear weight, and it treats cleaning them as asbestos work, with the debris bagged as asbestos waste. If you are not sure what your garage roof is made of, leave it alone and ask.

Why is pressure washing a roof a bad idea?

Pressure washing can drive water into the roof space and damage the surface of the tiles. GN58 says moss should not be removed by pressure washing because it can force water into the roof space, particularly when sprayed upward from the ground. Marley says most roofing professionals do not recommend it, and that it can damage tiles, especially older ones, and flood the roof and its outlets with water and debris.

Marley also says a high-powered jet wash can damage the surface of a slate or tile and considerably reduce its expected life, and Wienerberger says jet washers can strip the colour from concrete tiles. Trading Standards in Nottinghamshire in 2015 and Hertfordshire in 2020 both warned that pressure-cleaning roofs can damage the tiles.

Do moss killers and biocide treatments work?

They can, if the product is approved for the job and used as the label says, but the dead moss still has to come off the roof and out of the gutters. GN58 says a chemical wash can be used on a roof with care, because the solution can harm plants and animals, and that care is needed to keep it out of watercourses.

HSE says the control of moss is regulated under the plant protection products rules, and that products for removing lichen or mould from surfaces such as masonry and tiles come under separate rules. Spraying a pitched roof is still work at height, so leave it to whoever is taking the moss off. Dead moss loosens and washes into the gutters over the following weeks, so plan to clear them afterwards.

Copper strips. GN58 describes copper strips fitted across the top of the roof once the moss has been removed. They release copper ions that act as a natural biocide, and rain carries them down the slope to prevent regrowth. Fitting them is a job for a roofer.

What about lichen and moss on stone slate and older roofs?

Some lichen and moss is normal on stone slate and old slate roofs, but heavy growth can speed up decay and some rare mosses on stone roofs may be protected, so check before anyone cleans one. On the stone slate roofs of the Pennine towns and the Dales, lichen is part of the look.

Historic England's advice on stone slate roofing says excess moss can retain moisture and accelerate delamination. It also says some rare mosses that live on stone roofs may be protected, giving Grimmia ovalis as an example, and that owners should check with the local nature conservation organisation before cleaning. It adds that all British bats and their roosts are protected.

Never let anyone tar or coat a slate or stone slate roof. Bradford's guidance says a coating can seal the roof void, and the lack of ventilation can cause problems such as fungal attack and infestation of the roof timbers.

Moss once had a job on these roofs. It was driven into the joints of stone slates to keep the weather out, a practice known as mossing, and Derbyshire County Council's guidance notes that the accounts of Shibden Hall near Halifax record a payment for it. For work on a stone roof, see our stone slate and heritage roofing page.

Should you accept a doorstep offer to clean and coat your roof?

No. Turn down unsolicited offers to clean and coat your roof. The NFRC says it has had an unprecedented number of calls from people approached about moss removal, usually followed by the tiles being painted, and it does not recognise moss removal or roof painting as a true roofing discipline. The warnings add up:

• The NFRC urges extreme caution with any claims made for roof coatings unless the product carries credible UK third-party accreditation.
• GN58 warns that painting a roof after cleaning may invalidate the tile manufacturer's guarantees.
• Nottinghamshire Trading Standards warned in 2015 about cold callers claiming their roof coating gave thermal insulation and implying that a government grant was available. It said painting the tiles gives no benefit to a home's thermal efficiency and that no government grants are available for roof coating.

If you have already agreed to work at the door, you can usually cancel. Citizens Advice says a service costing £42 or more agreed away from the trader's premises has a 14-day cooling-off period, and under the Consumer Contracts Regulations 2013 that period can be extended by up to 12 months if the trader never gave you the cancellation information. If you asked for the work to start within those 14 days, you pay for the work done before you cancel. The Citizens Advice consumer helpline is 0808 223 1133.

Which? advises never signing anything on the spot or handing over money upfront, and the NFRC advises getting at least three quotes for any work, using conventional roofing methods. Roofline's inspections are free, our quotes are free and itemised, and if your moss can be left alone, we will say so. Send photos on WhatsApp to 07413 797731 or book a free inspection.

This guide is general information about roofing in England and is not a substitute for advice about your own roof. Standards and regulations are updated from time to time; check the current edition before relying on a specific requirement. Written by Roofline, roofers across Yorkshire. Last reviewed September 2026.