I've been of the mindset for many years that one should clean roof annually and every cpl years do the treatmemt process. I 've got a local guy that does bumper to bumper RV repair and he says that these treatments are like putting Johnson's floor wax on......in a couple weeks/months they are washed off. He recommends cleaning/washing once a year and taking a close look at the entire roof for cracks, etc. then repair as necessary. If roof is good one year then the next year, if anything pops up, it would be minimal.