Roof Cleaning

The dark streaks on asphalt roofs are almost universally caused by Gloeocapsa Magma — an airborne cyanobacteria (algae) that feeds on the limestone filler in asphalt shingles. It starts as small spots and spreads in streaks that run down the roof slope with water flow. In early stages it's cosmetic, but long-term, algae retains moisture against shingles and accelerates the loss of protective granules.

Green growth (moss, lichen) is structurally more serious. Moss root systems can physically pry up shingles, and lichen bonds so tightly to the shingle surface that removal requires longer dwell times and higher-concentration treatment. Lichen left untreated for years causes visible pitting and surface damage.

High-pressure water blasts the mineral granules off asphalt shingles. Granules protect the asphalt layer from UV radiation and are the primary defense against accelerated weathering. A roof pressure-washed at 2,000+ PSI loses years of life in an afternoon. Any company that proposes pressure washing your shingles should be declined immediately.

The Asphalt Roofing Manufacturers Association (ARMA) recommends a diluted sodium hypochlorite solution applied at low pressure — this is the industry standard. The solution kills algae and moss on contact and washes off in the next rain without damaging granules.

For moss and lichen — yes, definitively. Heavy moss coverage causes mechanical damage to shingles and voids many manufacturer warranties. For algae alone, the primary benefit is cosmetic and preventative: the dark streaks age a home's appearance significantly and removing them before a home sale is one of the highest-ROI cleaning investments.

After cleaning, many pros recommend installing zinc or copper ridge strips. As rainwater runs over the metal, it releases ions that inhibit algae and moss regrowth for 3–5 years per set of strips.