A carpet of lichens on the roof can be very annoying. They completely wipe out the aesthetics of the roof leaving an ugly and unpleasant image of an ancient building probably constructed during World War 1. I bet you would not love to leave in such a house especially in this era of class consciousness.

Removing lichen from the roof entails; Firstly cleaning roof tiles using a stiff brash, chemicals or a pressure washer. Secondly metal roofs can be washed by a sodium hypochlorite solution. Thirdly Asphalt roof shingle is cleaned by power washing or sweeping and roof chemical treatment. Finally a cedar roof is washed by a soft cleaner like sodium per carbonate.

Roof Tiles

Roof tiles are appealing until when they are affected by lichens. They can be cleaned using a stiff brash, chemicals or a pressure washer. Scrapping off lichen by use of a stiff brush is a simple way of cleaning roof tiles. This method is quick and easy to use. Alternatively a person can decide to use chemical solutions which include moss killers, fungicides and anti moss treatment.

Pressure washer is a fast and efficient way of cleaning when done by a professional. However it is not advisable due to the long term effect on the tiles. A high pressure of water is shot out on tiles to push away dirt and lichen. The important aspect of this method is that a stream washes places where a person cannot clean with cleaning tools.

Roof tiles can also be scrapped and cleaned then a chemical solution applied by spraying to kill plants (Roofing Superstore). Physically removing any extra moss and applying the required chemicals on the tiles without water is also a good way of cleaning tiles. Lichen will dry up and later blown away with wind.

Metal roofs

Metal roofs are made up of different types of metals. You should consider the type of the metal roof and check with the manufactures before using any chemicals to clean. The manufacturers can advise you depending on the type of metal roof.  Some metals react with different types of chemicals which may cause a long term effect on the metal roof.

 Types of metal roofs include copper, aluminum, and zinc, steel and tin. Some of these metals may react with the solution that is used for cleaning lichen on the metal roof. There are three cleaning processes that one may consider which include scrubbing, power wash and Wet and forget.

Procedure of Removing Lichen on Metal Roofs by Wet & Forget

Cleaning lichen by wet and forget process is applied yearly to prevent growth. The cleaning process is as follows;

  1. A hose end sprayer is attached to the garden hose and joined to the jet tip.
  2. It is turned on and soaked to the affected area.
  3. The process is repeated after 4 to 5 hours before it dries up.
  4. It is then left to allow the wet and forget to wipe out lichen.
  5. The process is repeated annually.

Procedure of Removing Lichen on Metal roofs by sodium hypochlorite

  1. Wash the roof with 2% sodium hypochlorite solution.
  2. The bleach is applied with a soft bristle broom and left for 3-5 minutes.
  3.  It is rinsed off with water.
  4. A detergent is added to improve wetting.

A higher than recommended concentration of sodium hypochlorite solution is detrimental to long term performance. (Information Bulletin 3).

When a metals roof is made of zinc metal, zinc strips can be used to prevent lichen from growing on the roof.  When rain rolls on the zinc strip any particles are carried down the roof.  This metal is poisonous to lichen and moss thus it makes it wither, die and fall off. It keeps off lichen for five years or more (Rotban Ultra Cleaning).

Lichen also avoids galvanized steel, copper and zinc since these metals work as a natural biocide.

Asphalt roof shingles

Cleaning of Asphalt roof shingle should not be a onetime process but it should be done regularly. It will prevent accumulation of, leaves, debris and dust from accumulating on the roof and leading to growth of lichen. Cleaning should also be done with care to avoid damaging shingles and reducing the roofs life span.


Cleaning process is as follows;

  1. Prepare a cleaning solution by mixing 4.4 liters of hot water, 1 cup of chlorine bleach, 1 cup of chlorine detergent and 0.25 cup of trisodium phosphate.
  2. Use a sprayer pump to spray the asphalt tiles with the solution.
  3. Wait for the stains to fade within 10 to 15 minutes.
  4. Scrub the affected section gently with a mop.
  5. Use a sprayer washer to rinse down the roof.
  6. Wash the gutters to avoid corrosion caused by the cleaning solution.
  7. After several months the rain will wash the solution leaving the roof sparkly clean.

Plants should be watered before cleaning to prevent foliage from bleach. Protective clothing and a strong ladder should be used (Advanced Window Systems, LLC).

Removing lichen cannot prevent future growth. If roof cleaning is not done with care a person may damage shingles thus reducing the life span of the roof. When the roof surface holds moisture, lichens and moss speed wearing out of the roof shingles surface. (InspectAPedia).

 Preferably soft wash cleaning process can also be used. First inspect the roof and identify the areas damaged by lichen.  A specially mixed detergent is then sprayed on the roof. The detergent kills all algae, mold and lichens feeding on shingles. After cleaning the detergent is rinsed using a soft washing machine (Roof Cleaning& Power Washing Services.)

Cedar Roofs

Cedar roofs are long lasting and can last for at least 10 years or more. It is also strong and can withstand strong wind. When cedar roofs are infested by lichen, its life span automatically reduces. Cleaning of the cedar roof, maintenance and preventing growth of lichen can increase its life span.

Gentle cedar roof cleaning process;

  1. Removing the sources of remains accumulation, lichen, and moss and mold growth.
  2. Removing over hanging branches and trees that are on the roof can minimize growth of lichen on cedar roofs.
  3. Wash-down the roof with a soft cleaner.
  4. Soak the roof in sodium per carbonate as the active ingredient. Oxygen or chlorine bleach solutions rapidly kill external molds and algae.
  5. As the fungus is removed the wood changes color from a dirty gray to buff tan.
  6. Over time the ultraviolet emission in sunlight will partly damage wood surfaces.
  7. The bleach solution will then take away some weathered wood fibers from the surface. It is the best method to use but it takes effect after 6 months.

Cleaning cedar roof soft wash process is a better option. Apply specially formulated solution in the Cedar roof to kill the fungus.

Growth of lichen is widespread in areas of periodically dump cool weather conditions. Roofs that experience a lot of sunlight have less lichen compared to those with less sunlight on the roof.  Organic matter like leaves, twigs or debris on the roof speed up growth of lichen on the roof. More lichen grows on surfaces that are moist and shaded.

Cleaning can be tiresome especially when there is no remedy to prevent future growth of lichen. Prevention can be done by keeping the surfaces roof surfaces dry by use of “external water repellant.” Always trim branches hanging on the roof and keep the roof clean.

Based on the above information it is clear that lichen can be removed on different types of roofs using different processes. All the processes mentioned have limitations. Some chemicals that are used to remove lichen may affect the roof thus the manufacturers’ advice if of essence. The chemical solution should be in the prescribed ration to prevent corroding of the roof. 

When using a pressure washer one is advised to involve an expert to avoid damaging the roof. Cleaning should be done continuously to prevent growth of lichen on the roof. Preventive measures should be taken by removing leaves, twigs or debris on the roof.

Accumulation of the leaves and dirt on the roof holds moisture which accelerates growth of lichen. If you are a victim, all is not lost.  The roof can still recover its beauty if you consider the methods mentioned above.

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