Whole roof cleanings come with a three-year guarantee that your shingles will remain algae-free, but you can generally expect it to stay clean and beautiful for at least four years before the algae becomes noticeable again. Every situation is a little bit different, and itu2019s not unusual for a roof to stay clean for five years or more after a professional non-pressure cleaning. This guarantee is transferable in the event that you sell your home.nnPartial roof cleanings are not recommended and DO NOT come with a guarantee. Itu2019s important to understand that roof algae is not visible to the naked eye in its early stages, so while you may not see it in some areas, itu2019s most likely already there and beginning to develop. The growth of algae is slowed in areas that receive maximum sunlight, but eventually it will become visible! Thatu2019s why itu2019s so important to treat the entire roof surface.