Roof Cleaning 101: Removing Black Streaks and Algae Safely

What those black streaks really are

The dark stains running down many Northeast roofs are caused by Gloeocapsa magma, a hardy algae that feeds on the limestone filler in asphalt shingles. Left untreated, it spreads, traps heat, and shortens the life of your roof.

It thrives in our humid summers and shaded, north-facing slopes — which is why neighboring homes often show streaks on the same side.

Why you should never pressure wash a roof

High pressure strips the protective granules off shingles and can void your manufacturer’s warranty. The correct method is soft washing: a low-pressure application of a specialized cleaning solution that kills the algae at the root and rinses clean.

HydroTitans soft washes every roof by hand, protects your landscaping, and leaves shingles looking restored without the damage. A treated roof typically stays streak-free for years.