We all know that wearing white or “cooler” colors during sunny summer days can help keep us cool because light colors reflect the sun’s rays rather than absorbing them like dark colors. Scientists today are applying this phenomenon to new technologies in building and construction, using white and light-colored roofing materials to create “cool roofs” made of plastic for both commercial and residential buildings.
Similar to clothing, cool roofs help keep interior temperatures lower. According to the Environmental Protection Agency (EPA), 90 percent of roofs in the U.S. are made of dark materials that absorb heat and drive up the cost of cooling homes and commercial buildings in warm climates. Dark roofing such as asphalt can reach temperatures as high as 150º-190º F, leading to higher utility bills, increased energy use and accelerated deterioration of the roof.
The alternative “cool roof,” made of plastic materials such as white vinyl, has both a higher solar reflectance and emittance, so it can reflect infrared and ultraviolet rays from the sun and then efficiently cool itself by releasing heat absorbed from the sun. A white vinyl roof can reflect 80 percent or more of the sun’s rays and emit at least 70 percent of the absorbed solar radiation. This reduces the amount of heat transfer to the building interior, reducing the need for air conditioning.
U.S. Energy Secretary Steven Chu, a Nobel Prize winner in physics, is promoting lighter colors for roofs to encourage energy savings. Plastic coatings can be applied to an existing roof to deflect nearly 85 percent of the heat, thereby reducing the surface temperature by as much as 50 degrees and allowing homeowners to maximize energy efficiency and the life of their roof.
Consumers can calculate cost savings from the use of cool roofs using several online tools, including the Cool Roof Calculator developed by the US Department of Energy (DOE).