Preventative maintenance primary purposes are to detect and stop roof problems from occurring; and to increase the service life of your roof. At Aegis we highly recommend the roof to be inspected semi-annual, preferably late fall and early spring.
To pressure clean a roof takes a lot of experience and knowledge of the roof system being pressure cleaned. One has to make sure that the company they hire to pressure clean their roof is very knowledge of the roof system that is on the roof.
Hiring a company that dos not have the knowledge will reduce your roof life expectancy drastically as well as create leaks that you did no h have before.