I highly recommend treating the roof twice a year, after it has been cleaned. More treatments if you are in high mossy areas with trees and lots of shade. It is OK to have your roof cleaned and treated any time of year, but the months that are best for doing maintenance or treatment only (after we have cleaned your roof) is March through Early July and September October. We do not guarantee any amount time for the treatment to last, because we do not know what nature does and every situation is different. We guarantee our work, so if we say that we will apply 12 gallons of treatment, then we will apply 12 gallons of treatment. If you ask me how long the stuff is going to last, I will say I don’t know. It is the customers responsibility to keep an eye on the roof checking for any signs of green so that we may stay on top of it and keep it treated, keep it dead or off.
I have tested pretty much all moss killers and inhibitors on the market and have found that they all work about the same and last for about the same amount of time. I can guarantee our work, but I cannot guarantee what nature does.
I appreciate you as a customer bu if you need a roof cleaning company that can guarantee a certain amount of time for the moss not to return, we are not your guys. There are companies that do that but they are the start ups, because they don’t understand the process yet. Northwest moss is no joke, it will return if not properly dealt with.