• Keir Hughes

How To Clean Your Roof

Below we discuss how your roof is cleaned. It is not only dangerous to climb a roof without experience or equipment to do so but the removal of moss, lichen and algae requires specialist tools and soft wash application systems. It is more cost effective to hire a professional every few years.

We will cover all aspects of roof cleaning in this post. What are moss, lichen and algae and where do they come from. The methods of removal, chemicals that are used and the benefits of hiring a professional to treat your roof.

What is moss, lichen and algae?


Mosses are small flowerless plants that typically form dense green clumps or mats, often in damp or shady locations. Unlike most plants, moss does not form roots and can grow on paved surfaces and areas where there is no soil. Moss forms from spores that are carried by wind currents and moving water. In most cases moss spores can not form in areas where healthy plants are already growing. Moss growing in your lawn or garden is often a sign of underlying problems in your soil that are weakening your plants and allowing moss to crowd them out. Moss that is removed often regrows unless the growing conditions in the area are improved.


A lichen, or lichenized fungus, is actually two organisms functioning as a single, stable unit. Lichens comprise a fungus living in a symbiotic relationship with an alga or cyanobacterium (or both in some instances). There are about 17,000 species of lichen worldwide. Lichens occur from sea level to high alpine elevations, in many environmental conditions, and can grow on almost any surface. Lichens are abundant growing on bark, leaves, mosses, on other lichens, and hanging from branches "living on thin air" (epiphytes) in rain forests and in temperate woodland. They grow on rock, walls, gravestones, roofs, exposed soil surfaces, and in the soil as part of a biological soil crust. Different kinds of lichens have adapted to survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, and toxic slag heaps. They can even live inside solid rock, growing between the grains.


Algae are a diverse group of aquatic organisms that have the ability to conduct photosynthesis. Certain algae are familiar to most people; for instance, seaweeds (such as kelp or phytoplankton), pond scum or the algal blooms in lakes. However, there exists a vast and varied world of algae that are not only helpful to us, but are critical to our existence. The algae growth on roofs are microorganisms which thrive in moist conditions. They spread by releasing spores into the air. Those spores usually require a moist surface to open. If the moist surface they land on is your roof, that's where they bloom.

Chemicals that are commonly used

Sodium hypochlorite

Is bleach but at an industrial strength. This way it can be mixed to the required dilution rate for each specific task. While bleach or sodium hypochlorite can be hazardous, when used properly, it can make the world at large a much healthier place. Here is a short list of some of the common residential and industrial uses for sodium hypochlorite:

Bleaching (both in homes and in hospitals, businesses and other public places)

  • Disinfection

  • Deodorising

  • Stain Removal

  • Water Treatment (for the public)

Bleach will neutralise and kill algae off your roof and remove the black streaking. However, this comes with risks. Bleach is corrosive and dangerous to plants and pets. It must be diluted before applied and plants must be rinsed down. Also, your home needs a proper place to drain chemicals.


A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism.

What Benz say about their roof cleaning biocide (bio Cleanz)

  • The powerful active ingredient is a similar purity to that used to disinfect hospitals

  • Can be used in conjunction with power washing as a post-treatment, or as a stand alone softwash solution

  • Fully biodegradable

  • Does not bio-accumulate

  • Ph neutral, so safe for materials and gentle on people

  • Controls algae, lichen, fungi, moss and mould

  • Safe for children and pets once treated surface is completely dry (use max 50:1 dilution to treat any surface children and animals may walk or play on)

  • Non-bleaching (contain no bleach or acids)

  • Not affected by hard or mineralised water

  • Harmless to all known building materials

  • Can be used as a pre-painting primer to kill algae and mould spores

  • Helps control wet and dry rot on wooden buildings, sheds, fences and decking

  • Soaks deep into porous surfaces – killing the micro-organisms responsible for unsightly discolouring, and potential structural damage – because of its low surface tension, which makes it an excellent "wetting agent".

  • Up to 8x stronger than biocides sold to the general public

In short, sodium hypochlorite will give you instant results but they won't last as long. Whereas with biocide, the results will start to become evident after 4-6 weeks but will continue to work over the coming months. This can leave your roof clean for up to 5 years, depending on many environmental factors.

Roof treated with biocide before and then after 12 months after treatment.

Methods of removal

Depending on what is growing on you roof, depends on the method used. For heavily moss covered roofs, a roof scrape would be used. The 'scrape' isn't as aggressive as it sounds! A laser cut tool (specific to the profile of your roof tiles) is attached to an extendable pole, which is then used to remove any moss from the surface.

The roof is then brushed off and rinsed down, gutters cleared, leaving the roof ready for an application of any chemicals (if required by the customer).

For a roof with just algae and lichen, we would not carry out the 'scraping' stage.

The chemicals are the applied at a low pressure by a extendable pole with either a spray nozzle or brush head.

Sodium hypochlorite is then rinsed off but biocide is left to soak in.

J.K. Aidan Cleaning Services roof treatments

When it comes to roof cleaning, J.K. Aidan are fully equipped to tackle most jobs. Our extendable pole system and scaffold tower means we can take care of your roof without stepping foot on it. Initially we would scrape off the moss, removing it as we go. Then a biocide will be applied to kill off any biological growth; fungus, moss, red and green algae, bacteria, lichen, pollen, mould and any other forms of embedded growth without the use of high pressure. Whether it's just a moss removal or a full roof clean and treatment we will; vacuum the gutters, clean the external of the gutters, clean the fascias and soffits. Based in Colchester, we cover most of Essex and Suffolk.

Roof before and after a roof scrape

I hope this answers a few questions you may have about roof cleaning and treatment. Get in touch if you have any questions or leave a comment below.

Don't forget to check out my other posts for more information on exterior cleaning.



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