"Tile roofs last forever"... Have you ever heard someone say this? Although the roof tiles last a very long time, the roof system does not last forever.
Tile roofs can vary in life drastically from one another. The varying life depends mostly on a few factors such as the type of underlayment, the quality of the installation of tiles and the use of proper flashings. The tiles themselves can last a very long time, but the underlayment is what can cause the need for roof work.
Underlayment comes in many varying forms. These vary in the way they are installed: self-adhesive and mechanically fastened, and the what they are made of: asphalt-saturated felt, rubberized asphalt and synthetic materials. Some of these products can be installed with two layers instead of one in order to increase the life of the roof. There are positives and negatives to all of the types and the proper installation of the products can often have more of a factor than the material used.
There are many details that a licensed roofing contractor will need to consider when installing the underlayment. There are installation details at the flashings, any roof penetrations, roof valleys, ridges and along headwalls that are all important to increasing the longevity of the roof.
Based on experience, most of the roofs in the valley will end up lasting 15-25 years before they begin to have significant problems.