White roofs work because of the physics of sunlight. Dark roofs absorb and hold more than 80% of solar energy, while white ones can reflect 75% of it away. That makes a white-roofed building cooler and cheaper to air-condition.
In 1998, when reflective roofing was just beginning to pick up steam, a group of pioneers set up the Cool Roof Rating Council (CRRC) to standardize the testing and labeling of cool roof products. In the process, they discovered that Cool Roofs have a number of benefits:
"The most obvious advantage of this feature is lower energy use and, therefore, reduced utility bills," the CCRC website states. "Cool roofs, however, offer several additional benefits including an increased life of the roof, thanks to decreased thermal stress on materials, reduced HVAC system size, thanks to the smaller peak cooling loads, increased comfort for building occupants, diminished peak demand effects on the power grid, [and] reduced urban heat island effect, which in turn helps minimize the formation of greenhouse gases and smog."
Energy Star, another promoter of cool roofing, says white or reflective roofing can lower roof surface temperature by up to 100 degrees F, and reduce peak cooling demand by 10% to 15%.
Surprisingly, a cool roof does not pose a large additional cost if it's installed as part the construction or renovation process. Some cool roof options, in fact, add no additional cost. Many roofing manufacturers, such as Carlisle, Henry, GAF, and others, offer cool white roofing products at a price that's identical to the darker colored materials.