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I live outside of Pittsburgh, PA.  I haven't been cleaning roofs that long, I have done about 20 total.  I am trying to bust into this market because it sorely needs it.  However, roof cleaning is big in FL and other parts of the country because people acknowledge that it is something that needs done.  Here it is not case.  It isn't until one neighbor sees another that they realize how good it can be.  My question is on tile roofs.  I haven't done one before.  The city of Pittsburgh has HUGE houses that are 90% slate or the half barrel tiles.  They all look like crap too, some have been pressure washed (very few) but for the most part they are all black.  So black that it seems like that is the color they are manufactured.  After all the coal and steel industry here I am wondering if they can even be cleaned.  Most of the houses end up looking so dark and drab.  I am trying to figure out what mix I should use for these houses.  I would assume that it is mainly dirt but with some algae mixed in.  I was thinking heavy TSP in the apple cider mix.  Other than that I have no clue.  Does anyone have a little guidance on things to try?  I should also mention that the roofs are almost all vertical in parts so it should be either really potent or sticky as hell.  Most of the houses that I am looking at are in the 5000 to 8000 square foot range. They are so big, steep, disgusting that I might have to price myself out of the opportunity.  Half of the ones would need a lift to boot. The picture of a real small house around here that best shows what I am up against. Even though its small in size there is a lot of roof sq. footage.  Imagine some of them that are huge. Thank you for any advice you could give.