For example: if you need a roof vent and the metal vent is designed to last 30 years or the life of the roof. Our workmanship is guaranteed on that roof vent for 30 years. If you want your moss treated but not removed. I cannot guarantee that because 1. it is not the right thing to do. You should have your roof moss removed first, and in the event that you need a new roof and your roof is too far gone to brush or wash, then you should get a new roof and keep it treated. Dead moss comes back to life a lot faster then it will take new moss to grow.