WARNING! Your Roofing should never be cleaned with the use of power washer!
Roofing manufacturers warn against this themselves.
See what North America's largest roofing manufacturer GAF have to say about how to remove black algae here
They have given specific instructions on the proper way to clean a roof
"DO NOT PRESSURE WASH YOUR ROOF"
Read directly from a number of the leading manufacturers here on our website. You may be very shocked, if you have been thinking about letting a contractor pressure wash your roof! We follow the exact guidelines in regards to roof cleaning so you need not worry about voiding your warranty or shortening the life span of your roof by doing anything detrimental to you roofing. That is our service guarantee and why should choose us to clean your roof!