The "Authority" I mention, is that of the roofing manufacturers themselves.
Of course, this would be true everywhere. I just named my { Chuck Bergman Roof Cleaning and Pressure Washing } county in Florida and nearest towns, for my advertising purposes.
If you have a 35 year warranty on your roof, do you think the roofing manufacturer will honor it, if you have it pressure cleaned, say 8 years after installation, or whenever, to remove that black ugly algae?
Probably not.
Why?
Because they say specifically not to pressure wash.
So, if you do it anyway, that is their way out of losing money on your warranty claim!
Plus, the reason they say not to use a pressure washer, is because it causes premature roof damage.