Chickens and cows have long roosted and roasted under corrugated tin roofing. As an inexpensive and long-lasting material, metal covers agricultural out buildings, factory and industrial sheds, and makeshift housing. But plunking a big expanse of tin or other sheet metal over support walls isn't likely to yield energy savings, or much comfort for that matter. Metal has a high conductivity -- it holds a lot of heat -- and if it's dull and angled without taking advantage of reflectivity, heat will simply settle in and the space beneath will become like an oven.
Many scout groups and science classes experiment with reflectivity. Holding a mirror at an angle where it reflects the sun downward onto a flammable surface, such as a patch of dry grass, can start a fire if you wait long enough. That's how powerful the sun's reflective energy is. Holding a magnifying glass over dry grass on a sunny day magnifies the rays and can also start a blaze from the heat energy.
Modern, energy-efficient metal roofing acts as a giant mirror of sorts by reflecting the heat and energy up into the air. A white or light-colored metal surface reflects best under testing, at about 67 percent reflectivity, and even some newly developed "cool colors" send the rays away [source: Florida Solar Energy Center]. And while asphalt tiles don't have the power of a magnifying glass, they do intensify the heat from the sun by holding it long after the sun itself has called it a day. Dark shingles, with a lower reflectivity of about 22 percent, tend to release the heat into the structure's surrounding air below and make it warmer [source: Florida Solar Energy Center].
Of course, not many people would want a giant mirrored surface on the top of their lovely home, but most do want the energy savings or a break from the white noise hum of constant air conditioning, and that's more than achievable with today's metal roofing. With fitted whole-panel to single shingle-like designs, metal roof systems have come a long way from the backyard coop. Whether formed from the most popular steel and aluminum or the most expensive copper and stainless steel, metal roofs fit all housing and commercial architectural types.
But at what cost? Next we'll look at the green and "how much green?" aspects.