10-11 years.I dont want to,& cant afford to replace it rite now.Ive heard of the zinc strips,but Ill be needing someone else to put those on. I'm 6' 3" think I should keep my weight off the roof,as its a good pitch & I dont want to damage it.I was hoping I could just spray something from the ground to kill it,but I guess zinc or copper attached would do that anyway.Then wash it off after,I guess.