Since your roof is constantly exposed to the outside elements, it means your roof is going to degrade over time. The rate at which it degrades will depend on a number of factors. These include; the quality of the original materials used and the workmanship, the amount of abuse it has to take from the elements, how well the roof is maintained and the design of the roof. Most roofing contractors will quote around 20 years for a well-built and well-maintained roof, but that can never be guaranteed because of the above factors. Our advice is to always keep your roof well maintained and get regular inspections to make sure it lasts as long as possible.