my house is an old house (app 70 yrs). It originally had cedar shakes on the roof. An asphalt shingle roof has been installed over the old cedar roof. The previous owners of the house told us that is what the insurance company recommended. After about 10 years, the roof has sags in it from not having any decking & proper support. I have heard that the insurance companies have decided this procedure was not the best. What suggestions do you have for reparing the roof?