Make your shingles last longer
Black streaks on the north- and west-facing and shaded areas of your asphalt-shingled roof can really wreck the appearance of your home. The streaks look like mold, but they’re actually algae colonies that form in your shingles and feed on moisture and the limestone filler agents in the shingles.
Using shingles that have been treated with algicide keeps the growth at bay for about 10 years (thus the 10-year algae warranty). But once the algicide wears off, your roof hosts an all-you-can-eat buffet for the neighborhood algae spores. As the algae eat away at the limestone, they dig into the asphalt and dislodge the light-reflecting granules. That’s the beginning of the end of your roof. So it pays to clean your shingles as soon as you spot algae growth.