Map courtesy of BECP Resource Center
Energy Efficiency Overhead
Climate Zones 1 through 3
So you live in a warm climate, where the summer's sun and heat are oppressive. Air conditioning is unavoidable and expensive, as your energy usage climbs with the temperatures. Here it's all about reflectance.
- A COOL ROOF VIDEO QUICKIE -
Cool the roof! The idea is to lower the amount of heat passing into your house by lowering your roof's surface temperature. If you need a new roof, you'll find many types of "cool" products. They're mostly white, but there are colors - even in darker hues - to choose from, depending on the products. And yes, it is possible to use a field-applied coating to cool an existing roof, as well. Two important factors determine the efficiency of a cool roof:
- Solar reflectance (R), or the ability to reflect sunlight (between 0 and 1.0% efficiency).
- Thermal emittance (E), or the ability to release heat that has been absorbed (between 0 and 1.0% efficiency).
The coolness of a roofing product is established using the Solar Reflectance Index (SRI). The SRI assigns a coolness rating of 0 to a black roof on a sunny afternoon. Its R value (solar reflectance) is given as .05, and its E value (thermal emittance) is 0.90. The SRI of a white roof on that same afternoon is 100. Its R is .80, and its E is .90. The higher the SRI, the cooler the roof's surface.
Aging is also a factor in the coolness rating. Exposure to the elements, stress, thermal expansion and biological growth all affect a roof's SRI over time. A new roof typically reaches steady R and E values after about 3 years, after which the roofing material is measured again for any changes in coolness.
Check our "GO DEEPER" column (above right) to find out how much $$$ you could save if you cooled your roof, then find the products that can do it in the "Cool Roofs Ratings List." You'll have some real facts at your fingertips when you start to talk with roofing contractors.