Exterior cleaning of siding and roofs should only be done using the Soft Washing techniques, high pressure will damage these surfaces. Mold & algae are living organisims, a high pressure washer will "scrape" off the top layer but leave behind the roots. It will return shortly.
A soft Wash will kill and remove the contaminants and the siding will stay clean for 18+ months while a roof wash will be good for 2+ years.
Visit JC Power Wash, Soft Wash & Roof Cleaning LLC to learn more