Some people here in the Tampa Florida area, consider a dirty shingle roof to be just a cosmetic problem. Oh sure, they do realize there is a plant growing on their roof. And some of them know that plant can spread to their driveway, house, and even to the neighbors house. But they are under the mistaken impression that a filthy dirty roof is nothing more then a reason for their property managers or homeowners associations to “pick on them”.
This video clearly shows the damage that can be caused to a shingle roof if it is not cleaned.