maintenance matters Cool By: Jessica Clark At The Top Improve your building’s sustainability and bottom line with a cool roof. D Do you ever wonder if your roof could be more than just a roof? Do you wish it could reduce energy costs and increase the life of the roofing system and air conditioning (AC) unit? Do you ever wonder if the roofing mate-rial you choose can have an effect on the occupant comfort in the living spaces below — or even help combat global warming? Cool roofs can do all this and more, even while maintaining the color, texture and aesthetic value of traditional roofing materials. With options in virtually every roofing material and slope, in new construction and remodel projects across the map, cool roofs may be the perfect next project for your facility. How Do I Know What’s Cool? You can identify cool roofs by understand-ing two simple radiative properties of roofs as they relate to solar radiation and heat. When sunlight hits your roof, it can either be absorbed or reflected. In order to realize the benefits mentioned above, your roof should reflect as much sunlight as possible and absorb as little as possible. Solar reflectance is the percentage of solar radiation that your roof reflects on contact. This is crucial because whatever sunlight is not reflected is absorbed and degrades Some municipalities offer rebates for installing cool roofs because they help decrease your building’s draw on the power supply. into heat. Solar reflectance can be measured and is reported as a value between 0 and 1. Thermal emittance, a measurement of the ability of your roof to reradiate any absorbed heat, is also measured on a scale of 0 to 1. Solar reflectance and thermal emittance are sometimes combined into one calcula-tion called the solar reflectance index (SRI). Code bodies and voluntary green build-ing programs sometimes use SRI because the single value is indicative of both the roof’s solar reflectance and thermal emit-tance properties. SRI is measured on a scale of 0 to 100, though particularly poor and good roofs can rate below 0 or above 100, respectively. It is important to note that roofing materi-als may have a low solar reflectance and high thermal emittance or vice versa. A cool roof will have both a high solar 38 CM/Cleaning & Maintenance Management ® • May 2011
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