Yes you can use a pressure washer on a roof if you have the right set up and the proper tip / PSI -. The first step is to rinse the roof with your chemical and you can follow that with a light pressure wash. ( a wide fan tip is needed and more gallons for minute ) When you spray with the wand you need to be able to put your hand in front of the tip showing that it wont cut your hand. Always wash down the roof and never never wash if the roof is to old. This method has been proven to work by the guy who trained me for over 25 years in the roofing business. Everyone has there opinion about roof cleaning methods and I respect that but there is no need to put down one method. My trainer has installed roofs and cleaned them for 25 years like I said and has inspected all of them. * If done properly it is safe and very effective way of removing all moss, algae, lichen and dirt from the shingle.
