I have been cleaning roofs for ten years and have come to the conclusion that some home owners think they know more about roof cleaning then I do or they dont want to take my advice. If a roof cleaner knows what he is doing then pressure washing is the safest and most effective way to clean a roof. It will remove less granuals then a brush and get the roof cleaner, but because people think that they know so much I wont even pressure wash on a roof. They heard that pressure washing is hard on a roof so that 30 seconds of knowledge is more valuable to them then my ten years experience in the field.
Also, customers dont want me to treat a roof in the rain because of fear that the treatment wont work as well. The truth is, right after a roof is clean its not that important to treat it. Its important to treat your roof once a year and the following years after you have had your roof cleaned is when we need to worry about the rain and the treatments. If you want to be the customer that tells me not to work in the rain, thats fine but you had better keep that roof treated annually if you really want to be a maintenance all star.