Q: What is a cool roof?
The ideal “cool” roof is one whose surface is minimally heated by the sun, such as a bright white roof. However, there are varying levels of cool. "Cool” can refer to roofing products whose surfaces are cooler than that of comparable standard products. For example, the afternoon surface temperature of a specially designed “cool” red roof is higher than that of a bright white roof, but lower than that of a standard red roof. An example of a “hot” roof is one with a standard black surface, which grows very warm in the sun.
Q: What happens to sunlight reflected from a cool roof?
On a clear day about 80% of sunlight reflected from a horizontal roof will pass into space without warming the atmosphere or returning to Earth.
Q: What is a “cool color”?
About half of all sunlight arrives in the invisible “near-infrared” spectrum. Standard light-colored surfaces strongly reflect both visible and near-infrared sunlight, while standard dark colored surfaces reflect modestly in both spectra. Special dark and medium-colored surfaces that strongly reflect near-infrared sunlight are called “cool colors.” The solar reflectance of a cool dark color can exceed that of a standard dark color by about 0.4.
Q: Are green roofs cool? What about thermally massive, super-insulated, and/or ventilated roofs?
There are a variety of roofing assembly technologies that can reduce the flow of heat into a building, including but not limited to solar-reflective, thermally emissive surfaces; vegetative cover (green roofing); thermally massive construction; super-insulation; and ventilation. We reserve the term “cool roof” to refer to one that stays cool in the sun by virtue of high solar reflectance and (preferably) high thermal emittance.
Q: When should I install a cool roof?
We recommend selecting a cool product for new construction or when an old roof is scheduled to be retrofitted. It is rarely economical to replace a mechanically sound roof just to increase its solar reflectance.
Q: Can I paint my roof white or a cool color?
There are specialized white elastomeric coatings available for low-sloped products and cool color polymer coatings available for tiles that can be sprayed on existing roofs.
Q: What does a cool roof cost?
The price of a cool roof is typically comparable to that of a standard (hot) roof of the same type, because coloration is responsible for a very small portion of the total installed cost of any roofing product.
Q: What are the benefits of a cool roof?
Selecting a cool roof instead of a standard (hot) roof directly benefits the occupants of the building, and indirectly benefits the entire community. Installing a solar-reflective roof can also immediately slow global warming through a process called “global cooling.”