Does algae hurt roof shingles?

Algae does hurt roof shingles, though the damage is gradual and less immediately destructive than moss. The most common algae, Gloeocapsa magma, causes black streaks and discoloration. While manufacturers and some sources say algae is primarily cosmetic, it does cause harm over time. Algae forms a dark coating that absorbs more heat from sunlight, increasing shingle surface temperature, which accelerates aging of asphalt and loss of volatile oils that keep shingles flexible. Algae also retains moisture against the shingle surface, keeping shingles damp longer after rain, which promotes granule loss and can lead to premature deterioration of the asphalt mat. Over many years, heavy algae growth can cause granules to loosen and wash away faster, reducing UV protection and shortening lifespan, though not as severely as moss which physically lifts shingles. Additionally, algae feeds on limestone filler in shingles, gradually breaking down that component. While a roof with algae streaks will still shed water, its curb appeal is reduced and its long-term durability is compromised compared to a clean roof. Moss is far more damaging than algae, but algae should still be cleaned using shingle-safe methods like oxygen bleach or commercial cleaners like Spray and Forget, and prevention with zinc or copper strips is recommended to avoid long-term damage.