Method #1 is a visual inspection of the gutters. Where black streaks are present, excessive lost granules accumulate in the bottom of the gutter. In some cases, the entire bottom is covered! Now, inspect the gutters where no problems are apparent. There are very few granules to be found here. Seeing is believing. Why? Protective granules are being loosened by stains. Permanent damage can result to any roof in less than 7 years! Most importantly, shingle manufacturers consider these stains a condition of the environment, and not a defect of the shingle. Therefore, the warranty does not cover this type of damage. The homeowner is on their own. Unless you just enjoy buying a new roof on occasion, you’ll need a roof cleaner to keep your roof clean.