You can see those ugly black streaks on roofs almost everywhere. Algae is a problem in most of the country, especially in hot, humid climates, and once it takes hold, it’s hard to get rid of, so prevention is the goal. For decades the industry has offered algae-resistant shingles. Early versions used zinc to prevent algae growth, but copper proved a more effective and longer-lasting solution to the problem.
Copper granules in shingles prevent algae growth, but the amount of copper is crucial; if there isn’t enough copper, even a so-called “algae resistant” roof might fail to prevent algae growth after the better part of a decade. The ugly streaking is an aesthetic nightmare and, if cleaned improperly, it can lead to structural problems as well.