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A guide to roof moss removal

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  • Post published:August 21, 2019
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  • Post last modified:August 22, 2019

Only a few decades ago, roof moss was more of a countryside issue in the UK. Today, it’s one of the biggest problems affecting urban buildings. Property owners are seeking companies to carry out roof moss removal every day. As a result roof cleaning companies increase their workforce to cope with the ever-rising demand.

What could have changed to make roof moss so prevalent?

The increase in roof moss has a lot to do with the cleaner air in towns. In the years before the ’80s, many industries were releasing all sorts of chemicals and toxic gases into the atmosphere. The pollution resulted in acid rain which destroyed moss and other biological growths, preventing them from becoming pronounced. With the lower number of factories today, the rain falling on roofs is not as acidic as it used to be some years ago. While reduced pollution is a good thing, it has resulted in better conditions for roof moss growth.

Having been in the roof cleaning business for a number of years, we have the first-hand experience in dealing with roof moss. We have, over the years, gained knowledge on how its growth occurs, the possible damages it can cause, and the different ways to control it. We compiled all that and came up with this guide.

The information here is meant to help you identify when you need to take action regarding moss removal, and how to go about it. Also, answers to questions people have been asking us and which you may also be having, first, how moss grows on a roof.

It all begins with moss spores landing on your roof. If conditions are right, the spores grow in to become visible green streaks on the roof. Unchecked, the growth continues and produces a carpet-like structure that covers parts of your roof.

Can Moss Cause Damage to a Roof?

Yes, it can, especially if in large amounts and long-standing. However, the kind of damage or its extent depends on the type of roofing material you’ve used on your building. Some roofs are more vulnerable, while others are resistant to moss damage and not affected even by excessive growths.

Which roof materials are prone to damage and which ones are not?

Clay tiles can delaminate as a result of moisture caused by moss growing on its surface. The risk increases in the winter when freezing occurs and causes expansion. To minimize the possibility of such occurrences, clay tile roofs are often built steep to allow for total drainage of rainwater. Regularly removing moss from these roofs can also help to keep them dry all the time and prevent damage.

Cement tiles are easily damaged by moss compounded if the tile is if weak or dusty. Cleaning a cement surface to remove moss and other biological growths is essential; prolongs the lifespan of the cement tile.

The brickwork of chimneys and the cement cap are also at risk of damage by moss. Moisture can get in there and cause loss of structural integrity when it freezes during the low winter temperatures.

The guttering and downpipes installed on your building can block as a result of moss washing down from the roof. In large amounts, the debris can cause gutters to bend or even break as a result of the added weight. Drain pipes, in addition to blocking, can burst when trapped water freezes and expands.

Ways to Remove Moss from Your Roof

There are two ways;

  1. Scraping and brushing the moss off and then applying chemical at low pressure

( softwashing )

  1. Power washing

Both methods are effective. However, carrying them out requires that you be on the roof which not only presents a safety risk but can also result in slight damages to the tiles. The work is, therefore, better left to a professional who can do it safely and in a thorough way.

It’s almost always inevitable that you will carry out minor repairs after a roof cleaning activity. There will be tiles that break or chip at the ends and other slight damages that require cementing and other remedial works. You will also need to clean the guttering and unblock the downpipes.

Power washing is necessary if you want your roof re-coloured after the moss is removed. Also, if you want to apply a sealant to enhance protection. An advantage of power washing is that it removes other contaminants as well, resulting in a cleaner roof that can hold the sealant better.

After How Long Will Moss Reappear After Removal?

It depends on the method of used. Cleaning without the application of any biocide will see moss return within a period of 6 to 12 months, while chemicals can prevent regrowth for several years.

Of course, the rate of regrowth will depend on many factors such as;

  • Whether you’ve used an effective biocide to kill off moss spores after cleaning the roof
  • The competence of the professionals you’ve hired to clean your roof and apply the biocide
  • Whether the roof receives enough direct sunlight or if it’s shaded by trees and other


  • The climate; wet weathers promote the growth of moss
  • The neighbouring rooftops. If infested by moss, spores are likely to migrate to your roof and cause new growths soon after cleaning
  • If you later employ control measures to prevent recurrence such routine cleaning

Using Chemicals to Eliminate Moss

Chemicals are necessary when removing moss from your building. Without chemical treatment, live spores remain on the roof. It only takes the spores a few months to grow into visible moss. Within no time, you’re faced with the same problem, requiring you to repeat the roof cleaning process. It can be costly for you given that biological growths are a never-ending problem in the UK.

A chemical will penetrate the areas you cannot reach when removing moss such as the overlapping joints or the cracks in the structure. These are the spots where spores will hide and cause regrowth soon after you’ve cleaned the roof. Using a biocide, therefore, assures you of thorough moss removal.

The application of chemicals is not a permanent solution, though. You will still need to repeat the process every few years to prevent new growths. An advantage of using a biocide is that future biological growth will not come from the roof itself but from migrating spores, a process that can take time.

What Equipment is Needed to Applying the Chemicals?

Chemical application is better done using a sprayer. Just like in other chemical spraying activities, it’s essential that you wear protective gear such as hand gloves and a mask. Again, it’s advisable for this activity to be carried out by a skilled person. The heights involved require adequate experience to avoid safety issues. A professional will also know the hidden areas that require attention, the right chemical concentration to use and many other requirements.

During the whole process, ensure the following:

That nearby lawns and gardens are covered, windows and doors are closed and downpipes disconnected.

Spray on a calm day. Wind causes the chemical to blow about and affect the nearby vegetation and animals.

Apply when the weather is dry and rain not likely to fall. Rainwater can wash away the chemical and reduce its effectiveness. The contaminated rainwater would also cause a risk to the animal and plant life around.

Cloudy days are better; the chemical won’t evaporate too fast, and you’re assured of adequate time for it to work and eliminate the spores.

Which Chemicals are Suitable and for How Long Will they Last on Your Roof?

Moss removal requires chemicals with a high concentration. Such chemicals are more effective when it comes to destroying the moss together with its spores, ensuring a longer time before regrowth occurs.

The staying power of moss removal chemicals is low. According to the EU regulations that were enacted some years ago, biocides and other chemicals should become inactive as soon as they dry up. While this may reduce a chemical’s long-term effectiveness, it makes it safer to use.

A biocide whose effects are long-lasting would present a risk to plant and animal life. You can imagine what would happen every time it rained and the chemical washed down the roof. It would make the area around your house unsafe especially for children who are likely to play around the areas contaminated by the chemical.

Is Chemical Re-application Necessary?

It is. After the initial moss removal, re-applying a biocide helps to control future growths and you never have to repeat the physical roof cleaning. Chemical application is a simpler activity, cheaper, and less time-consuming than removing moss growth. You only need a few hours to spray a biocide, while scraping a roof of moss can take as long as a whole day. Sometimes, the person applying the chemical can do so from the ground using a long pole. As a result, there’s minimal damage to the roof, which relieves you of the costs to repair chipped tiles.

After How Long Will You Need to Re-apply a Chemical?

It can be after 2 or even 3 years. It depends on the biocide you applied and the predisposing factors such as shade or the condition of nearby roofs. With the right chemicals and environmental conditions, it can be quite sometime before you need to spray your roof with a chemical again.

Many people who have had success checking moss growth are those who employ a maintenance plan. After a specific period, their roofs are cleaned, repaired and sprayed with a moss killing chemical. The maintenance plan also involves checking guttering and drainpipes for blockage or breakage and unblocking or replacing them.

Ways to Reduce the Growth of Moss

Moss is better controlled than removed. It’s cheaper, plus you won’t need to perform cleaning activities often which protects your roof from damage. To control moss, it’s essential that you understand what accelerates its growth. As we have seen, some conditions promote biological growths on surfaces, and avoiding them can significantly reduce the rate at which moss covers your roof.

What steps can you take? Ensure the following;

  • Avoid damp conditions

Moss grows well in moist conditions. That’s why the north-facing side of a roof often has moss and the south-facing one little or no growth. Other conditions that make moisture to remain on a roof for longer include overhanging branches of trees. It can also be bushes or live fences that have overgrown to block sunlight.

Make sure you’ve pruned such trees and hedges. In cases where moss is already there, it’s necessary to remove that, too. The sponge-like nature of this biological material soaks in rainwater and makes the roof to remain wet for long, increasing the rate of growth.

  • Clean the roof of debris

Leaves and other materials may get blown onto your roof. Left to accumulate, the debris covers the roof and leads to retention of moisture. Over time, the damp conditions result in moss finding favourable condition to grow.

Check the roof for deposited materials from time to time. Remove it yourself if the roof is not too high or if you have the required equipment. You may hire a roofer if the process to remove the materials proves too challenging.

  • Consider removing TV aerials and other receivers

TV aerial or receiving dishes attract birds which perch there for hours and cover the roof with excrement. This, together with the little shade caused by the arterial and dish, lead to moist conditions and increased moss growth.

With today’s technology, you may not need a roof aerial to receive TV in your house, so you have no reason to let it cause moss to grow on your roof. You could opt for internet TV and keep organic growths away.

Painting, Applying a Coat our Sealant to Protect a Roof From Moss Damage

Roof coating is a popular way to protect roofing materials from the dangers of environmental elements. Usually applied to the side that’s exposed, paint also makes a building’s roof to look aesthetically pleasing. It works by discouraging the growth of moss as most biological materials don’t find smooth surfaces conducive.

The downsides of applying a coating or sealant is the cost to carry out correctly. Besides that, not everyone likes the idea of a coloured roof. However, the sealant need not be coloured. There are clear ones for those who dislike altering the original look of their roofs.

You will need to apply a biocide from time to time, even after you’ve painted your roof. That’s because the sealant doesn’t kill off spores. It only slows down the rate of growth and some moss will eventually cover the roof after several years. Some roofing materials hold a coating or sealant better than others, a good example being concrete. If your roof is clay tiles, you may not benefit much from painting it.

Questions Many People Ask About Moss Removal

With the problem of moss affecting so many property owners across the country, there are numerous questions clients have asked us. They include the following.

Can I Spray My Roof With a Biocide Without Cleaning the Moss First?

While doing so would lower the costs involved, it wouldn’t provide you with the best of results. The dead moss would remain on the roof, washing down into the guttering, drainpipes and other areas around the building. The result is decayed organic matter that presents another danger of blocking drain ways. The best procedure would be to scrape the moss first, remove it from the roof and dispose of it safely.

Gutter Guards and Downpipe Filters; Are They Useful?

As we saw earlier on, moss growing on the roof can get dislodged and find its way into the gutters and rainwater pipes. It leads to clogging and finally blockages. Gutter guards are meant to prevent moss materials from clogging while filters are fitted to keep moss from entering downpipes and causing them to block. However, these are not effective when it comes to preventing moss damage.


Gutter guards and filters only work to block leaves and other bigger debris. Fine materials such as moss will pass through easily and clog gutters and rainwater drainpipes. The guards and filters will, therefore, only work when there’s no moss on the roof. The only practical way to protect guttering and downpipes is to scrape moss from the roof.

Is Copper Effective at Killing off Moss?

There are various copper roofing products on the market that are meant to prevent or even kill off the moss. But do they work? The simple answer is yes they do. However, they have their drawbacks and cannot be relied on to control or eliminate moss.

The copper material to control moss growth is usually placed on the ridge of a roof. When rainwater falls on the material, a sulphate is produced which then flows down the roof and halts the growth of more moss. There are many downsides to this moss control method. They include;

  • It doesn’t kill off moss, only preventing growth. That means existing moss as remains on the roof unless action is taken to remove it
  • Gives better results only when used on flat-tiled roofs
  • The cost of copper is too high which makes the method unnecessarily expensive
  • You cannot control the flow of the sulphate which results in unsightly streaks of moss growth where its effect was not felt
  • Copper can cause corrosion to aluminium and galvanised parts of a roof such as screws and gutters
  • Its action does not extend beyond three metres from the ridge. You cannot, therefore, use it on a large roof

To Sum Up

Roof moss is a common problem in the UK. Because you cannot entirely prevent the problem from occurring, the best approach would be to employ control measures. The method you choose to check moss growth will depend on many factors. Cost is one of them. Some ways to control moss such as copper ridges are way too expensive and may not be worth the expenses. The level of effectiveness is another. Not all methods to prevent moss growth will work, and you have to make a wise choice.

Cleaning the roof and applying a biocide offers the best way to eliminate growths and ensure the problem doesn’t recur too soon. It’s simple to perform and won’t cost you a lot. While you can opt for a DIY approach with the method, it’s highly advisable that you hire a professional. You will not only achieve better results but will also make the process safer.

Enrolling for a roof cleaning and maintenance plan ensures no excessive moss ever grows. Apart from keeping your roof safe, routine cleaning means a visually pleasing building that looks as good as new for years. Keeping your roof moss-free also protects your guttering and drain pipes from damage and saves you the cost of repairs. Overall, the method you choose to maintain your roof matters a lot.

If you require more information please call us on 08000933267 advice is free.

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