| First off, there are two primary kinds of organic tile - clay and concrete. The clay forms are made by baking clay once it has been placed into a mold. The amount of time and intensity of heat (up to 18+ hours and 2000 degrees F) achieved during firing determines the density of the tile produced, which can then be glazed or textured. A so called black core is caused when the tile is not heated for a long enough period during firing, resulting in a fully tempered surface that conceals a black carbon filled interior. This deficiency can compromise the ability of the tile to resist salt water intrusion, moisture, and affect the overall strength of the material. Concrete tiles are produced by mixing water, sand, color pigment, and Portland cement in a number of different proportions. The mixture is projected into molds with the use of high pressure and is then cut and transferred to a curing chamber where the tiles harden. The shapes and colors of concrete tile are altered by varying the shape of molds, which can be extremely expensive for the manufacturer to fabricate, so the options tend to be limited by commercial pressure (the larger markets, like California for instance, tend to have more selection in terms of shapes) or by changing the color of pigment additives. Color selection can vary from region to region due to taste: earth tones in the west, white and pink in Florida, and blue or gray in the Northeast…
Metal Tiles are a versatile material that can take many shapes. They are press formed while being manufactured, which means the steel, generally coated with aluminum or zinc, can be forged into the likeness of asphalt, slate, or wood shingle. The tiles themselves can then be painted one of any number of colors and coated with crushed stone for aesthetic purposes.
The climate surrounding a structure must be taken into account before covering a roof with any particular tile. Life in a cold area that experiences severe winters can lead to damage for clay tiles – broken eave tiles and possible excessive weathering in product of a lower grade (the choice quality ranking for these materials is Grade 1, meaning it has passed the standard test to judge greatest resistance to severe frost action and least water absorption, or ASTM – C-1167). Metal tiles tend to fare better as metal sheds snow making them less prone to ice dam formation. Ice dams are created when snow melts over the heated section of a home or business, which then runs down and freezes at the cold eaves, building in time to a mass that, with repeated cycles of freeze and thaw, can force its way between roof covering, creating leaks at the eaves. Metal also has an excellent strength to weight ratio, which helps with the forces associated with wind loads.
A strong storm with subsequent strong winds can test the integrity of a tile roof system. Metal tiles do have the advantage of strength, but also benefit from an ingenious installation method that ties each of the panels together. They are attached via what the NRCA calls a flat seam, which is when one panel edge is folded back onto itself and the other under, so that the two can then be hooked together. The metal tiles, however, are only well seated so long as what they are connected to – usually batten strips installed over a continuous roof deck – can be relied upon while under stress. If the roof deck is not constructed to withstand high wind loads, then the roof may fail regardless of the material selected to cover it. Clay tiles have to be installed properly, or else high winds may cause catastrophic failure. The tiles can be affixed to the underlayment by several different methods.
Otherwise known as felt paper, the underlayment is an asphalt saturated, non-perforated organic sheet that serves two key functions: to provide temporary protection from the weather and represent a secondary weatherproofing layer beneath the metal or clay tiles. New self-adhesive “hybrid” underlayments are being used on metal roofs and can include a self-healing property that provides a seal in the locations where fasteners have penetrated the felt during installation of the finished roofing system.
Often nailed or screwed to battens atop the underlayment using lugs, the tiles can also be attached with foam adhesive, or mudded (using a mortar mix). The latter is the most prone to failure in high wind events and according to FEMA, mortar-set is not recommended in lieu of mechanical options (screw, etc…), as the tiles themselves may become airborne projectiles and cause damage to surrounding property… One alternative, however, is to install a mechanically fastened interlocking clay system, which tends to stand up quite well to wind due to a lower profile and enhanced design.
Another consideration to take into account is the threat of fire in the vicinity of your home or business. In terms of metal and organic tiles, their fire ratings tend to be quite good since they are composed of materials that do not burn easily, if at all. As a result, these materials are recommended for use in areas that are prone to wildfires, and may qualify the property owner for a discount on their fire insurance (make sure to inquire with you insurance agent). | 
