Metal Roofing comes in two different categories, Exposed Fastener and Hidden Fastener. Metal roofing can consist of a high percentage of recycled material and is 100% recyclable. It does not get as hot as asphalt, a common roofing material, and it reflects heat away from the building underneath in summertime. On a larger scale, its use reduces the heat island effect of cities when compared to asphalt. Coupled with its better insulating abilities, metal roofs can offer not only a 40% reduction in energy costs in the summer, but also up to a 15% reduction in the energy costs in the winter according to a 2008 Study by Oak Ridge National Laboratory. This finding is based on the use of a strapping system of four inches between the plywood and "cool-color" metal on top, which provides an air gap between the plywood roof and the metal. Cool-color metals are light, reflective colors, like white. The study went on to say that re-sealing and insulating air ducts in the attic will save even more money. Because of their longevity, most metal roofs are less expensive than asphalt shingles in the long run.
Exposed Fastener metal roofing normally consists of a 26 guage PBR panel or 29 or 26 guage AG panel that is mechanically attached through the roof panels with EPDM rubber washer #10 x 1.5" screws into an appropriate substrate. The point of maintenance becomes where these screws penetrate the roof panels leaving a reliance on the epdm washers to keep precipitation out. These roofs normally carry a 40 yr Paint finish only warranty with a 5 yr workmanship warranty.
Hidden Fastener metal roofing is normally either a 24 or 26 guage mechanical standing seam, snap lock standing seam, or flat seam panels that are attached with hidden #10 pan-head screws under the sheets in clips that secure the panels to the substrate without penetrating the exposed panel. The hidden fasteners are the key to being such a long lasting roof, by not relying on the epdm washer screws of the Exposed Fastener roofs. Hidden Fastener roofs tend to be almost double the price of most Exposed Fastener systems but will far outlast with much less maintenance. Hidden Fastener systems, if installed correctly, are a true "lifetime" roof.