During the 1970s, 80s and 90s hundreds of thousands of structures were erected and the roofing material of choice was tile. Over the years, many problems have developed with regard to the installation procedures which were employed during those years. To begin with, tile manufacturers generally specified a felt underlayment, which consisted of 1 layer of 30# felt.Additionally, flashing details required one flashing to be placed around any penetration. It was also recommended that only the 2 courses of tile around the perimeter, not every tile, be nailed, because it was assumed that the weight of the tile would hold it in place.At the ridge and hip peak levels no weatherblock was required. Tile roofing, like everything else, has evolved over the years. For example, it is now imperative that 2 layers of 40#tile felt underlayment, not 1 layer of 30# felt, is necessary.The flashing details, instead of 1 flashing around a penetration, now requires 2 flashings, a base and a secondary flashing. It is now required by most manufacturers that every tile be nailed, not just those at the perimeter.Weatherblock, consisting of either mortar, or a manufactured component is now required to be installed at hip and ridge peak areas. The above steps should be considered imperative. A tile roof, properly installed, with adherence to manufacturers specs., and building codes will truly last the length of life of the structure upon which it is installed