Asphalt does not hold up to direct UV exposure. Shingles use small colored stone chips called granules to protect the asphalt from environmental elements and to provide an esthetically pleasing look. Over time these roof granules wear off. When this happens the asphalt surfacing starts to break down causing a downward turn in the shingle’s life. This is the reason why it is not recommended to pressure clean a shingle roof. Pressure dislodges the granules from their asphalt embedment. We have found improper ventilation to be a major cause of premature granule loss. It is also important to keep overhanging trees trimmed so they don’t brush off granules. Here is an example of shingle granule loss and the starting of shingle breakdown. This is a sign that roof replacement is near.