Q: What are the black streaks on my roof? A: Usually visible on North-facing light-colored roofs ranging from five years old, discoloration or streaking is sometimes mistaken as dirt, moss, or granule loss. It is actually caused by algae growth that propagates in areas of the roof that receive less direct sunlight, and thereby retain a higher level of moisture. Although most noticeable on light shingle colors, the algae affects all asphalt shingle roofs, including darker colors. The discoloration caused by the algae is in no way indicative of a shingle defect. This is an aesthetic concern and will not harm the shingle or shorten the life of the roof. The algae discoloration is difficult to remove from roofing surfaces, but may be lightened using various solutions available at most lumberyards. Notes: Cleaning the shingles is a temporary solution as it will eventually grow back due to higher humidity levels in areas of limited exposure to direct sunlight. The cleaning process will have to be repeated every few years. Care must be taken when cleaning the algae as to not remove excessive amounts of granules that are attached to the surface of the shingles.