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Pressure Washers Cause Damage During Moss Removal

When getting rid of moss and other debris that might have gathered on your roof you might be recommended to use a pressure washer. Initially this might seem like an easy and effective method that requires minimal effort, however roofing professionals are now warning against it.

Bob Richardson, Head of Technical and Training at the NFRC, is one of those who would not recommend pressure washers for homeowners: “High pressures can damage tiles or reduce their overall service life”.

So, whilst people may be seeking to protect their roof coverings by eradicating moss and other vegetation they could actually be causing more damage than good.

Why do people use pressure washers for moss removal?

Often, homeowners will opt for pressure washers at the first sign of moss on their roof. Moss, if allowed to get out of hand, can cause multiple issues.

Firstly, if there is excessive moss in valleys and other water channels then the flow of water will be affected. This can lead to rainwater pooling, which puts pressure on the roof below and can lead to a leak.

If moss falls into gutters then they can become blocked and cease to function effectively. If the gutters have rubber seals, moss will cause these to perish, leading to a leak from the gutter joints.

A further, less known, issue that moss can cause concerns water seeping into tiles and slates. Moss will absorb water and, over time, this will soak into tiles and find its way between layers of slates. During cold weather the water will then freeze, expand and create cracks in the roof covering. This simply encourages further water ingress and can encourage leaks and dampness.

Because of the multitude of problems that can be caused by moss, people often want to deal with the problem as quickly as possible. Pressure washers can be appealing in this respect, so those who are unaware of the risks attached will often use this method to rid their roof of moss.

How do Pressure Washers Cause Damage?

Many roof tiles have a protective coat over them. This layer is there to guard against adverse weather conditions like wind, rain and hail that can cause damage and lead to repairs.

As the name would suggest, pressure washers spray water at a high pressure. When this jet comes into contact with the roof covering it removes the protective layer. As a result, the tiles are far more susceptible to damage from the weather. So, whilst you may think you are doing your roof some good by ridding it of the potential problems caused by moss you could actually be doing more damage than you realise.

What Methods Can I Use to Get Rid of Moss?

Manual Brushing

Our recommended method of moss removal is to do it by hand with wire scrapers and brushes. This is a thorough but labour intensive option, but it will work wonders on any moss or lichen that has formed on your roof.

Having said that, this can be a dangerous undertaking for homeowners without proper training or qualifications to work at height. You will find that many roofing companies (like us, for instance) offer moss removal as part of their package of services. By leaving it to professionals you don’t have to risk your own safety and can know that experienced roofers who understand the importance of moss removal are getting between the cracks!

Preventative Action

We also recommend that homeowners be proactive in all aspects of their roofs’ maintenance, including moss removal. In all walks of life it’s better to prevent an issue before it’s manifested rather than wait for a problem to occur and then react to it! For moss, an anti-fungicidal sealant can be applied to the roof covering. This inhibits the growth of moss, meaning you won’t have to worry about moss removal.

Alternatively, having regular inspections of your roof’s condition can make sure that everything is still as it should be and your roof is doing its job effectively. This isn’t just a good idea for making sure moss isn’t doing any damage, but any other issues like loose or cracked tiles, missing mortar or poorly functioning flashings.

This isn’t just important for keeping leaks and water ingress from affecting your home, but also for insulation and to protect the value of your home.


So there are lots of options open to homeowners to deal with moss, lichen and vegetation found on their roof. Whilst pressure washing can seem like the most straightforward and effective method to tackle this, and prevent damage to the roof covering in the process, it is never a method that we would recommend. Enlisting the help of a roofing company for moss removal places minimal risk on homeowners who aren’t used to working from height and ensures a thorough job is done. Additionally, taking proactive measures to prevent the occurrence of moss in the first place means you’ll protect your roof for longer by stopping any issues before they even arise!

Get in touch with our team to find out more about our moss removal service.

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