Weather is a Factor in Algae Growth on ShinglesĬoastal, warm and humid climates tend to create the friendliest environments for algae growth, although the use of cheaper shingles has made algae growth a problem in almost every part of the United States. These algae use the crushed limestone filler as a main food source. To save money, most shingle manufacturers have switched to shingles containing asphalt but mostly made up of fillers such as fiberglass and crushed limestone, which encourages the growth of algae. Why does roof algae seem to be more common today that it was 20 years ago? Traditionally, asphalt shingles got their name from being made up of mainly asphalt-an oil based product-and felt material. This is also true for townhomes, condos and apartment complexes.

Because these spores are airborne, they can quickly spread from rooftop to rooftop in a neighborhood. They can be carried by wind, animals and even on your clothing. This is what makes those unattractive black streaks on your roof!Īlthough algae can be found on all types of roofing, it tends to be most common on asphalt shingles.Īlgae spores are airborne. Why does this algae appear to be black? Gloeocapsa has the ability to form a protective darkly pigmented outer coating that shields the algae from damaging UV rays.

By the time this algae is noticed by the homeowner, it has usually been on the roof at least two or more months. This algae growth usually begins as small spots and then eventually becomes visible streaks. The most common type is known as gloeocapsa magma-also known as blue green algae. Although these dark spots and ugly black streaks on your roof may look like dirt, mildew, soot or mold, what they really are is algae.

Terrible dark spore