When homeowners are given the option to choose the color of their new roof they usually tend to go with dark colors. Why? Darker colored roofs look better.
I chose a dark colored roof on the new house I had built a few years ago. But, had I known the potential savings in energy costs then, I might have chosen differently.
The principle is basic, the same as humans living in the tropics wearing white clothing to keep cool. They know that white clothing reflects the sunlight and heat from being absorbed into their bodies.
Reflecting sunlight from the surface of anything reduces heat transfer into the substructure.
Many studies have been done on this subject from independent labs to governmental agencies. All conclude that even in northern climates, energy saving can be realized from lighter colored roofing materials. Of course, the more south you go the bigger potential to save energy on cooling costs.
How Cool Roofs Work
Dark-colored roofing materials absorb sunlight, making them hot and heating the structures and air below. A white or special “cool color” roof absorb less sunlight, staying cooler in the sun and transmitting less heat into the home or building. This reduces the need for cooling energy if the building is air conditioned, or lowers the inside air temperature when air conditioning is not used.
The “coolness” of a roof is determined by two factors and their total reflects the effects on temperature:
• Solar reflectance — the amount of sunlight that is reflected
• Thermal emittance — the efficiency of the material used in emitting or releasing thermal radiation
Both properties are measured on a scale of 0 to 1 — the higher the values, the cooler the roof.
How much savings?
It is estimated that a cool roof can save 7 to 15 percent of cooling costs. Savings of this nature may not sound like a lot, but if you are spending hundreds of dollars a month to keep you home cool it equates to something like this $2400 yearly @ 15% = $360.
In addition it is also known that lighter colored roofs tend to last longer. Consistent absorption of high heat accelerates the deterioration roofing materials.