Most roofers know that the unattractive black streaks that sometimes appear on asphalt shingles aren’t fungus or soot, but algae. Algae growth, which also occurs on wood shingles and concrete tiles, is found in all but the driest climates. Fortunately, algae do not eat asphalt. “If you can live with the black streaks, it won’t hurt the shingles,” says Husnu Kalkanoglu, director of technology at CertainTeed’s roofing division. Although no one has yet studied whether algae growth shortens shingle life, that hasn’t stopped experts from speculating. “If anything, algae might extend the life of the shingles by providing the asphalt with some protection from UV light,” says Kent Blanchard, assistant VP of manufacturing at Tamko, a shingle manufacturer. But Ingo Joedicke,
