The sun, wind and humidity can all be tough on your asphalt shingles. One of the most common questions homeowners asks is: if the dark streaks on their light colored shingles means that they need a new roof. The answer is not necessarily!
Light colored asphalt shingles can develop discoloration (black streaks) from blue green algae, spread by airborne spores, that grows during the humid summer months. In most cases the algae is not harmful to the shingles and is only cosmetic. As always, it is best to check the warranty information and manufacturer’s suggestions as to how to clean the shingles to remove the algae.
One of the most common suggestions made by manufacturer’s are to make a 50/50 solution of bleach and water to spray gently (pressure washers are not recommended!) on the shingles on an overcast day. Allow the solution to soak in and then follow with a fresh water rinse. This should remove most of the algae with out damaging the shingles.
Most new shingles have an algae-resistant warranty of 10 years.