The answer to 'why is my metal roof algae growth' is that metal roofs can be prone to algae, moss, and mildew buildup due to their dark color and ability to retain moisture. This growth can occur in damp, shaded areas and can cause discoloration, staining, and even damage to the roof over time.
Some common causes of metal roof algae include poor ventilation, lack of sunlight, and high humidity in the local climate. Symptoms may include green, black, or brown stains on the roof surface, as well as a slimy or fuzzy texture. To address this issue, you'll need to clean the roof regularly and consider preventative measures like installing a roof coating or improving ventilation.