Black streaks and stains, found on asphalt shingles, are eyesores waiting to make a home unsightly, invite plant matter and fungi to attach to shingles and cause damage if untreated. The black streaks are mold or fungi. They get survival strength through photosynthesis and a limestone filler found in shingle composition.

Shingles, made today, are mostly limestone and fiberglass. Algae thrive on the limestone it uses as a food source. It is a black alga found only on the north or east facing sides of a roof. The algae can form a coating that protects it from UV rays.

Little or no light areas produce a blue-green color. Another self-protecting factor enjoyed by the algae is areas of a roof where moisture is most prevalent. These areas are cool and shady. According to both the American Roof Manufacturers Association and the Canadian Asphalt Shingle Manufacturers Association, the algae is only an aesthetic issue.

However, roofs having algae on them attract other life forms capable of causing damage. An algae and fungus combination creates a new type called lichen. It is a photosynthetic fungus with roots that wrap around granules. The plant feeds on shingle filler. Once attached, lichen is hard to remove. Dried out lichen comes back to life when moisture or rain appears. Power washing and scrubbing cause more damage.

Moss is another organism that grows on roofs. It shortens the lifespan of a roof because retained moisture freezes in cold climates and causes damage to granules and shingles. Roof cleaning is not a Do-It-Yourself project. Without proper equipment and training, the result is sometimes disastrous. Professional roof cleaning removes streaks and discoloration for much less that roof replacement costs.