The answer to how to clean asphalt shingles is to use a soft-bristle brush and mild detergent solution. Start by gently scrubbing the shingles to remove any dirt, mold, or mildew buildup. Rinse the shingles thoroughly with a garden hose to wash away the cleaning solution. This should be done every 1-2 years, or as needed, to maintain the appearance and longevity of your asphalt shingle roof.
It's important to avoid using harsh chemicals or power washers, as these can damage the shingles and cause premature wear. If you have significant staining or moss growth, it's best to consult a professional roofer for a more thorough cleaning and treatment.