Lichen does not have roots like most other plants and it can grow without soil. In moist or damp climates lichen flourishes, growing on roofs and walkways and garden walls. Some people feel its lovely silver shading adds colour and charm. Admired for its tenacious ability to survive, lichen grows on roofs worldwide. However, if allowed to grow, it may turn black and become visually unattractive. Even though it does not harm the roofing material, homeowners may want to eliminate its presence.
Inspect the roof shingles visually. Lichen will build up on the north side of buildings and in areas shaded most of the day.
Clean the roof annually. Sweep off dirt, branches and debris and then wash down the roof surface with a garden hose with a pressure nozzle. Cleaning removes materials that trap water on the surface of the roof shingles and delays the drying process. Start at the peak of the roof and work down so as to not drive water under the shingles. To correctly wash a roof you will need to stand at the top of the roof and point the hose downward. Potentially dangerous, roof cleaning should proceed with safety uppermost in mind. Do not attempt to clean steep pitched roofs without adequate safety gear.
Mix 1 cup of biodegradable liquid dishwashing soap and 1 cup powdered oxygen bleach in 5 gallons of water and apply to lichen prone areas with a push broom brush or hand scrubbing brush. Scrub gently. Rinse with clear water. Commercial chemical preparations, though costly, have proven effective. Follow manufacturer's label directions carefully. Purchase lichen and roof stain removal chemical products at building supply and home and garden stores.
Enlist the services of a professional roofing contractor to remove excessive lichen build-up on the roof. Roofers have the equipment and experience required to do the job safely.
Install zinc strips after cleaning the roof. Zinc will prevent lichen from accumulating. Zinc strips (1/2 inch wide and 2 to 3 inches long), available for purchase from hardware stores and home and garden centres. Attach by nailing along the ridge line of the roof. Strips should be nailed horizontally along the peak of the roof, spacing them about 6 to 8 inches apart. Follow manufactures instructions.
Spray patches of lichen with vinegar until thoroughly saturated. An application of vinegar kills lichen. The odour intense odour will quickly disappear as the vinegar dries and evaporates. To remove the lichen, scrub with a firm brush with soapy water. Use an organic liquid soap. A roof scrapping tool (a long handled tool with a flat scrapping blade) can also aid in lichen removal.
Apply shingle oil with an airless sprayer. After the shingles are clean and dry, spray with shingle oil to preserve the wood and discourage the growth of fungi, mould, lichen and algae.
Zinc strips are considered to be effective for up to one year for most brands.
Lichen accumulation on roofs is really a minor problem that will not hurt the roof. Most professional roofers advise that it is possible to do more damage to the roof by trying to remove lichen, than the lichen will ever do to harm the roof. Always use a stable ladder and safety harness when climbing on the roof.