Today I did a partial job that only needed one corner of the house done. The roof was only 5 years old, but already had green stage 3 algae! The customer had just removed a tree from his yard that covered part of his roof. This coverage from the tree allowed the algae to grow very fast on the shingles. Algae loves shade and moisture. Make sure all tree branches are at least 3 to 4 feet off the roof. Hopefully this will allow sunlight to the shingles. This home owner was very smart to call us and protect their 5 year old roof and to have the tree removed that was causing the problem.