TPO or Thermoplastic Polyolfin is  a single ply reflective roofing made for commercial applications. There is also a PVC roofing but we do not see that very often in this Middle Tennessee area.   Its energy efficient nature makes it great to help commercial buildings be more green.  The white nature reflects the warming uv rays helping everything from the AC units to the roof system itself work better.  When the roof collects dirt and turns green from mold and mildew it looses it energy efficient nature.  Because this is a thin one ply material it takes special care when cleaning.  We never use any pressure to clean this delicate roof and have found the best way to clean is to use a soap mix that kills mold and mildew while cleaning the dirt.  The second step is to agitate with sponges and low pressure rinse to keep any damages from happening to the roof membrane or the structure below it.  Trust TLC Pressure Washing to take care of this or any type of commercial roofing system.  GAF has a great blog post all about the commercial roofing membrane HERE.  This is not the type of roof to not know how to clean as damage can be very expensive to fix, only trust someone with the training and knowledge to get the job done right without damage to the roof or building.