What's growing on your roof?

There are two types of algae that typically grow on your roof, "black algae" and "moss" which is greenish colored in nature. Algae and moss do have some similarities but are also very different and require different procedures to remove or prevent.

Black algae is often mistaken as mold or mildew because of the black discoloration and streaks it leaves throughout the roof. Coastal and humid climates foster a better environment for algae to grow. Algae discoloration typically begins as small spots on your roof then quickly transform into a streak on the roof. Algae spores are carried by the wind or animals and can quickly spread from one rooftop to another. But don’t panic, there is no scientific evidence that algae is damaging to your asphalt shingles. However, aesthetically it is very unappealing.

Moss is greenish in color and flourishes in moist and damp environments. Moss usually grows on the north side of your home because it receives less sunlight and stays damp longer than south facing roof planes. Another culprit for moss is overhanging tree branches that provide additional shade and drop debris on the roof. Debris that falls on the roof can hold moisture and act as a food source for moss. Moss can also be carried by the wind or animals and easily spread throughout the neighborhood. Unfortunately moss can be detrimental to asphalt shingle performance. Moss can cause the leading edges of shingles to lift or curl. Lifting or curling shingles can increase the risk of shingle blow-offs during high winds.

Don't worry, algae and moss can be removed from your roof with the right approach. A word of advice; never use a pressure washer to remove mold or algae from asphalt shingles. Doing so will cause granule loss and premature failure of the roof system.

The good news, several asphalt shingle manufacturers make algae resistant shingles. The most prominent asphalt shingle manufacturers have a 10-year duration where the shingles are warranted against algae growth.