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This might not be the most upscale job posting for roof cleaning pictures but thought I'd add it for a little tip on metal roofs. These were four trailers that the US Department of Agriculture occupies here in Tallahassee. As you can see they are in rough shape and they are getting new siding and roll on rubber membrane roofs. The contractor had us remove all the algae before the new roof, panels and awnings were put up. (had to scrub these suckers with deck brushes to pursuade the dead algae to come off)

 Here is the tip: Metel roofs + soft wash roof mix = bust your azz  (Even at a 3/12 pitch, these things were slicker than ice!)