pressure washer

I used it once on my roof. The problem is that the amount of cleaning of any surface with a pressure washer depends on how far away from the surface the nozzle is. It's very difficult to keep that distance constant therefore there will be areas that are more clean than others. Since you don't want to damage the roof you must keep the nozzle a good 12 inches from the roof.
It does work but probably not as well as Soft Scrub and a brush; but a lot less work.