When it comes to keeping building exteriors and outdoor structures clean, the recommendation often rests with the custodial professionals and/or building service contractors in charge.
However, most cleaning professionals don?t know the U.S. Environmental Protection Agency (EPA) has issued strict laws on how exterior cleaning is carried out, and they can ring up a pretty hefty bill if the proper precautions are not taken.
Pressure washing remains one of the best ways for cleaning professionals to maintain building exteriors and other outdoor structures.

I didn't find the right solution from the Internet.

References http://www.cmmonline.com/articles/23...from-epa-fines

whiteboard animation examples