The answer to 'why is my soffit algae growth' is that algae growth on your home's soffit (the underside of the roof overhang) is a common problem caused by moisture, shade, and lack of airflow. Algae thrives in damp, dark environments and can discolor and deteriorate the soffit material over time.
Some common causes of soffit algae include poor ventilation in the attic, overhanging trees or shrubs blocking sunlight, and excessive moisture from leaks or poor drainage. Symptoms include green, black, or brown discoloration and a slimy or fuzzy texture on the soffit.