The answer to 'how to clean asphalt shingles' is to use a soft-bristle brush and a mild detergent solution. Gently scrub the shingles to remove any dirt, mildew, or moss buildup, then rinse thoroughly with a garden hose. Avoid using high-pressure washers, as they can damage the shingles.
It's recommended to clean your asphalt shingles every 1-2 years, or as needed, to maintain their appearance and extend the life of your roof. If you have significant damage or staining, it's best to call a professional roofing contractor for a more thorough cleaning and inspection.