Removal of Lichens From a Roof

Defining Lichen

• Lichen is not a single organism, but rather two different organisms living in mutually beneficial symbiosis. The main structural organism of a lichen is a fungus. The fungus' rhizomes act to attach and support the bulk of the lichen. The other living creature that makes up a lichen is an algae. Algae are single-celled photosynthesizing organisms that live among the rhizomes of the fungus. The algae produce the food necessary to support both itself and the fungus.

Lichen on Roofs

• Roofs are a common environment to find lichens growing, as they provide a favorable atmosphere. Roofs are generally designed to shed water, so they are a low-moisture growing surface. Most roofs have at least some area with good exposure to direct sunlight throughout the course of the day, maximizing the lichen's opportunities for photosynthesis. Different types of lichen prefer different temperatures and amounts of light, so the shading and temperature in your location will affect the appearance of the lichen on your roof.

Treatment

• No matter what the appearance of the lichen on your roof happens to be, the treatment will remain the same. It is difficult to remove lichen completely, as spores are frequently left behind. Lichen attaches firmly, so physical removal is not a good option, as it may harm the finish of the roof. Contract with a roofer to remove the lichen from your roof, as they have access to specialized chemicals that are more efficacious at lichen eradication. Fungicides may be used, but they are not ideal, as they can also harm your roof's finish. The safest solution is to treat your roof with a solution of two percent bleach and water.

Prevention

• Periodic treatment with a bleach water solution will kill spores before they have an opportunity to become a serious issue. Some roofing materials are commercially available that have been developed to be resistant to lichen. Another low-maintenance method of preventing lichen growth is to install a copper or zinc strip near the apex of the roof, underneath the shingles. The strip should have its surface exposed along the length of the roof. This way, when rainwater flows over the strip and off the roof, copper or zinc residue will be carried with it. This residue will eliminate new lichen growth.