What is the green stuff growing on roof shingles?

The green stuff growing on roof shingles is typically algae, moss, or lichen. Algae thrive in damp, shaded areas and can create unsightly streaks, while moss and lichen can cause damage by retaining moisture against the shingles. This growth is often more prevalent in humid environments or on roofs that do not receive much sunlight. Regular maintenance and cleaning can help prevent and manage these issues.