Words from Steve Clarke, EcoStar Director of Research & Development. We are often asked about cool roofs. What are they? What is the benefit? The term “cool roof” was coined to describe roofs that minimize heat build-up when exposed to solar radiation. The primary drivers for developing this technology are:
- Reducing energy consumption by lowering the load on air conditioners
- Mitigating the urban “heat island” effect, wherein the heat absorbed by city buildings elevates the temperature in the surrounding area significantly above what it would be in the absence of those buildings.
Heat islands pose a health risk for those unable to escape the heat, and stress the electrical grid supplying power to all those air conditioners.
Let’s Get Technical
Solar radiation spans the ultraviolet, visible, and infrared spectra. Ultraviolet radiation is high energy, and degrades unprotected plastic, but only comprises about 5% of the total energy in solar radiation, so for cool roofing purposes we ignore it. Most of the energy (about 50%) that comes from the sun is in the visible spectrum. The remaining 45% of the solar radiation is in the infrared spectrum, and not visible to the naked eye. The infrared spectrum is the part of solar radiation where we can impact the temperature of the roof without affecting its color, and is therefore the most important when considering cool roofing.
Light in the visible spectrum affects what we perceive as color. The color we see corresponds to the light that is reflected from the surface, the rest being absorbed. So the color white is actually representative of all visible light being reflected. For black, all visible light is being absorbed. For green, say, only those wavelengths of light that we perceive as the color green are reflected, everything else is absorbed. Most of the energy that is absorbed ends up being re-radiated as heat, thus a black surface will get much hotter in the sun than a white one.
How Do You Reduce the Roof Temperature?
You could have a white roof, but our guess is that you prefer colors. That means we need to use pigments that absorb light in the visible spectrum so we can get colors, but reflect light in the infrared region to reduce the heat on the roof. Fortunately, in recent years pigment companies have developed materials based on metal oxides that are both reflective in the infrared region, and absorbing in the visible region. In addition, these materials have the advantage of being very colorfast, so they are well suited to use in long-term outdoor applications. By using these materials, it is possible to make all but the darkest colors meet the requirements for EPA’s EnergyStar program.
How Can EcoStar Help?
EcoStar offers a line of cool colors in all Empire products. EcoStar has three Energy Star® rated colors including Sea Salt, Drifting Dunes and Saratoga Sunset, which are available in multiple profiles including Traditional Slate, Niagara Slate, Shake and Shake Plus.