The answer to 'why is my asphalt shingles algae growth' is that algae growth on asphalt shingles is a common problem caused by a combination of moisture, shade, and nutrient-rich environments. Algae thrive in damp conditions and can discolor your roof, leading to an unsightly appearance.
Algae growth is often more prevalent on the north-facing side of the roof, where there is less direct sunlight. The algae feed on organic matter, such as dirt, pollen, and other debris that accumulates on the shingles. Over time, this can lead to premature aging and deterioration of the shingles.