When is the best time to clean your roof? For roof cleaning in Harrisburg, the best time to do it is fall and early spring. For roof cleaning, the only acceptable form of cleaning is soft washing. In Harrisburg, most houses have shingled roof's which can be damaged by pressure washing. Fall is geat becasue it allows us to spray an algicide onto the roof and get the maximum amount of dwell time. This is becasue the tempture is much lower which means that the solution doesnt ev