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,