I put a new roof on my house last year and installed radiant barrier under the shingles. I can feel the difference in my upstairs rooms. Check out the article below from Chris Curles and Associates of InfraRED Home Inspections of Atlanta.
There are several ways to keep your cool when electrical bills make you a little hot under the collar during warm weather months. A cool roof lowers electrical bills and keeps a home more comfortable by reducing the amount of heat that is transferred inside. Cool roofs are designed to maintain a lower roof temperature while the sun is shining.
There are a number of ways a cool roof can be created, including the installation of radiant barriers within the attic as well as radiant shingles on top of the roof.
Radiant heat travels in a line and heats anything solid within its path. When the sun heats a roof, it is the sun’s radiant energy that makes the roof hot. A large portion of this heat is conducted through roofing materials to the attic side of the roof. The hot roof material further radiates the heat energy onto the cooler attic surfaces, including the air ducts and the attic floor. This heat will continue to be conducted down through a home’s walls and ceilings into the rooms below.
A radiant barrier in the attic can reduce the amount of heat that is transferred from the underside of the roof to the other surfaces in the attic. Such a barrier is effective because of its ability to reflect back the radiant heat rather than allow its further transmission to areas below. Most barriers available today have a reflectiveness of 95 to 97 percent.
Radiant barriers are more effective in hot climates than in cool climates, especially when cooling air ducts located in the attic. Some studies show that radiant barriers can lower cooling costs between 5% – 10% when used in a warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system.
And the greater the temperature difference between the sides of the radiant barrier material, the greater the benefits of a radiant barrier can offer. In cool climates, it’s usually more cost effective to install more insulation than a radiant barrier.
Some of the most popular names in radiant barriers/solar foil include Attic Foil, eShield, Prodex, Green Energy Barrier, SolarGuard and Reflectix.
Reflective roof shingles can also greatly reduce the warming effects of the sun by reflecting heat upwards. Although white materials tend to be good solar reflectors, colored roofing materials can also be made to reflect more sunlight.
More than half of the sunlight reaching the earth is invisible to the human eye, and even though it is visually undetectable, this invisible sunlight still beats down on and heats our roofs. A colored surface that reflects much of the invisible sunlight is called a cool-dark color, or cool color. A cool-dark color reflects more sunlight than a similar-looking conventional dark color, but less than a light-colored surface. For example, a conventional dark colored surface might reflect 20% of incoming sunlight, a cool-dark colored surface, 40%; and a light-colored surface, 80%.
Currently, Landmark Solaris, Owens Corning, GAF, and 3M, among others all manufacture reflective roofing shingles in cool, dark colors. Both radiant barrier material and some reflective roofing shingles qualify for an energy tax credit of up to $500 under the Tax Relief, Unemployment Insurance Reauthorization and Job Creation Act of 2010.