Can a roof be cleaned with a pressure washer?
Great concept VERY bad idea! Not only will it cause mega damage but it also does not work. Highly pressurized water will temporarily remove the visible stains, but does not kill all the algae spores. So you can expect the algae to come roaring back, usually within months. And if that is not bad enough, the toll it takes on the roof can be extremely costly. It will remove granules from shingled roofs GREATLYdiminishing the omni important reflective properties which severely shorten the life of the shingle. High pressure will flip up and separate shingle seals, tear and break off edges and basically push water into places its not supposed to be. Water leaks are a major concern. Often these leaks go undetected for weeks or months, causing even more damage to the wooden decking, trusses and rafters in the attic areas. High pressure will also cause color-fading on tile roofs. Pressuring washing is condemned by A.R.M.A. and all the major shingle manufactures and may void your roofs warranty.
