INTRODUCTION Given the current economy and political landscape, it is more important than ever to keep up with market trends and evolving policies. For the building industry, remaining competitive means be – coming familiar with green standards and practices. Green build ing is a design and construction technique intended to efficiently use re – sources and minimize a building’s im – pact on the environment and on occupant health. Two main goals in green building are to re – duce operation costs and to reduce building footprint. A cool roof is an effective way to achieve these goals by reducing both energy consumption and a building’s impact on the environment. Figures 1 (above), 2 (right), and 3 (left) – Three examples of CRRC-rated roofing products (from left to right): a white, fieldapplied coating; a standing seam metal roof; and a barrel tile roof. Photos cour tesy of HydroStop, Custom-Bilt Metals, and MCA Superior Clay Roof Tile, respectively. 30 • I N T E R FA C E A U G U S T 2009 When used appropriately, a cool roof can reduce energy costs by maintaining a more constant internal temperature in warmer months, thereby reducing the need for air conditioning. Average energy savings can range from 10 – 30% of peak cooling demand, depending on the climate zone and building architecture.1 Hot, dry climates have the greatest potential for energy savings via cool roofs. Additionally, because a cool roof absorbs less solar energy in the form of heat, the roof itself experiences fewer temperature variations, reducing the thermal stress on the materials and extending their lifespans. From an environmental standpoint, a cool roof can also help conserve energy and reduce CO2 emissions, smog, and excess heat in urban areas. What Is a Cool Roof? Though many factors contribute to energy performance, a cool roof can be defined by the radiative surface properties of the roofing material: namely, solar reflectance and thermal emittance (Figure 4). When sunlight hits an opaque surface, a fraction of the energy is reflected, a fraction is absorbed and reemitted as infrared light, and the remainder is absorbed and transferred as heat to the building below. Solar reflectance refers to the fraction of reflected solar radiation, and thermal emittance refers to the fraction of solar radiation that is re-emitted as infrared light. A cool roof minimizes solar heat gain by first reflecting a portion of the incoming solar radiation and then reemitting a significant percentage of the remaining absorbed energy. Codes, standards, and programs that specify cool roofing requirements may also reference a calculated value called the Solar Reflectance Index (SRI). SRI allows actual measured solar reflectance and thermal emittance values to be combined into a single value. Cool roofs are available in a wide range of materials and colors and can be applied to virtually any building or roof slope. Contrary to popular belief, cool roofs are not just white but are available in all colors. Advances in technology have developed cool color pigments that efficiently reflect solar energy (light) in the Near Infrared (NIR) spectrum, whereas standard colors tend to absorb NIR energy. The NIR spectrum is invisible to the human eye, so two seemingly identical colors in the visible spectrum can perform differently in the NIR spectrum (Figure 5). Each building is unique in its combination of design, climate, and microclimate, allowing for no single “best fit.” However, with a large and growing product selection, it is now easier to integrate a cool roof into green building design for all manner of building types. Benefits of Cool Roofing In addition to energy savings and reduced energy costs, cool roofs provide a variety of indirect environmental and health benefits, including cutting greenhouse gas emissions, alleviating the urban heat island effect, and reducing smog. Cool roofs reduce greenhouse gas emissions by lowering air-conditioning demand, thereby conserving electricity and reducing Roofing contractors & specifiers choose Durapax coal tar roofing systems. Coal Tar: First Choice for Flat Roofs Durapax: First Choice in Coal Tar 610.579.9075 Durapax.com • Coal tar roofing provides low cost and long life (25+ years) • Many coal tar roofs last more than 50 years • Coal tar’s cold flow properties provide self-healing • Superior technical & customer support • Delivery you can depend on • Comprehensive warranties • UL & FM approved systems Specify your next flat roof with a Durapax coal tar roofing system. A U G U S T 2009 I N T E R FA C E • 3 1 power-plant production demand. Creating electricity not only wastes energy in the conversion process but also produces CO2, particulate matter, and other air pollutants. Lowering the amount of electricity produced by a power plant therefore reduces the amount of CO2 and air pollution released into the atmosphere. A city’s annual mean air temperature can be 1.8 to 5.4˚F warmer than surrounding environments, due to the large areas of dark surfaces that consist mainly of roads, parking lots, and dark-colored roofs.2 The extra heat absorbed through dark surfaces during the day is then reemitted at night, raising the day- and nighttime air temperature averages, a phenomenon referred to as the urban heat island effect. Cool roofs help mitigate the intensity of the urban heat island effect by maintaining cooler urban temperatures during the hot summer months. Lower ambient air temperatures resulting from cool roof applications also reduce the production of smog. Smog is created by photochemical reactions of air pollutants, a process accelerated by warmer temperatures. Reduced greenhouse gas emissions and smog production also benefit public health by reducing the prevalence of asthma and other respiratory health conditions aggravated by air pollution. Figure 4 – A cool roof is defined by two properties: solar reflectance and thermal emittance. 32 • I N T E R FA C E A U G U S T 2009 Figure 5 – Advancements in pigment technology increase solar reflectance across a broad spectrum. Photo courtesy of American Rooftile Coatings. How to Find a Cool Roof A specifier might want to verify that a product meets a code requirement, an architect might be interested in a Leadership in Energy and Environmental Design (LEED®) credit, or a building owner might need accurate information for a utility rebate, but searching through all of the products that are available can be overwhelming. A fair, accurate, and credible rating system that provides the radiative properties of roof surfaces was needed to satisfy this continually growing demand within the building industry; hence, creation of the Cool Roof Rating Council (CRRC). What Is the Cool Roof Rating Council? The CRRC was established in 1998 as an independent, nonprofit rating organization that measures the surface radiative properties of roofing products. As the incentives for saving energy, money, and the environment continue to grow, third-partyverified data allow for product comparison to occur on an even playing field. The CRRC publishes the reflectance and emittance ratings of products that have been tested through the program, but it does not set minimum requirements used to define a cool roof. It is up to the code bodies, green building programs, and utilities to set and define cool roof minimum requirements. The CRRC’s Product Rating Program allows roofing manufacturers to accurately label their roof surface products with independently rated “initial” and “aged” reflectance and emittance values. These product ratings are listed on the Rated Products Directory, available at www.coolroofs.org/products/search.php. Independent Testing and Verification Testing of product samples is performed at one of the CRRC’s six Accredited Independent Testing Laboratories (AITL). The CRRC’s Product Rating Program also maintains a random testing program whereby roughly 10% of rated products are randomly selected each year to undergo retesting. Random testing samples are either obtained directly from the marketplace through distributors and contractors or they are collected at the manufacturing site. Random testing provides assurance that CRRC-rated values for initial reflectance and emittance are accurate. Initial and Aged Ratings Initial testing for solar reflectance and thermal emittance is first conducted at a CRRC AITL and then submitted to the CRRC to be added to the Rated Products online directory. Once initial testing is performed, the product samples are sent to test farm locations in three different climate zones (hot/dry, hot/humid, and cold/ temperate) to weather for three years. The samples are then removed and retested, unwashed, for their radiative property values. The purpose is to simulate how products age and change in performance over time as affected by soot, algae growth, oxidation, natural weather, and environmental conditions. The aged values, using an average of the results from the three sites, are then added to the CRRC online directory. How to Use the CRRC as a Resource: CRRC-Rated Products Directory The Rated Products Directory is a free online resource with several search features to help locate specific products, including product type, manufacturer, brand, model, color, slope, minimum initial or aged solar reflectance, and thermal emittance (Figures When you really need your equipment covered, call RoofScreen! A U G U S T 2009 I N T E R FA C E • 3 3 6 and 7). Currently, there are over 1,400 rated products in the directory. Cool Roof Codes and Programs Developed from an understanding of the benefits of cool roofing, numerous building codes, green building programs, and rebate programs now include a cool roof requirement or incentive. The following section provides a selection of cool roofing codes, green building programs, and rebate programs. For more information, please visit www.coolroofs.org. Cool Roofs in Energy Codes Two primary organizations – the International Code Council (ICC) and the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) – have developed national model energy codes. These codes are not mandatory or enforceable until a jurisdiction adopts the documents as part of regulation or law. In the U.S., many states and jurisdictions have adopted these codes, while others, such as California, have developed their own. California’s Title 24, The California Energy Commission’s Building Energy Efficiency Standard, includes a cool roof prescriptive requirement. A new version went into effect on August 1, 2009, and includes prescriptive requirements for lowand steep-slope roofs and for residential and nonresidential building applications. Minimum radiative property requirements are detailed in the standard and must be met in order to be considered cool roofs. Title 24 designates the CRRC as the supervisory entity for radiative properties of roofing materials. See Table 1. Please note that there are many exceptions to the ratings listed in this summary table. For more information, visit www.coolroofs.org or the California Energy Commission’s Title 24 Web site at www.energy.ca.gov/title24/. Other locations, including Austin, Dallas, and Houston, Texas; Chicago, Illinois; and the state of Florida all have cool roof building codes with minimum solar reflectance and thermal emittance properties that reference Slope Type Minimum Three-Year Minimum Thermal Minimum Solar Aged Solar Reflectance Emittance Reflectance Index (SRI) Low Slope 0.55 0.75 64 Steep Slope 0.2 0.75 16 ≤ 5 lb/ft² Steep Slope 0.15 0.75 10 > 5 lb/ft² Table 1 34 • I N T E R FA C E A U G U S T 2009 Figures 6 and 7 – On the CRRC-Rated Products Directory search page, users can search by a number of different criteria to find a product that meets their needs. the CRRC or U.S. Environmental Protection Agency’s Energy Star® Reflective Roof Program. Several states, including Arizona, Arkansas, Georgia, Hawaii, Louisiana, New Mexico, North Carolina, South Carolina, and Texas, have adopted ASHRAE 90.1 as their state building energy code, which includes a cool roof credit. ASHRAE 90.1 is also called the Energy Standard for Buildings Except for Low-Rise Residential Buildings. In the 2004 edition, section 5.3.1.1 allows reduced roof insulation (Ufactor) if a cool roof is used. It defines a cool roof as having a minimum solar reflectance of 0.70 and a minimum thermal emittance of 0.75, an allowance applicable only for U.S. climate zones 1, 2, and 3. Green Building Programs In 2009, the U.S. Green Building Council updated its LEED® program. LEED® 2009 includes significant structural changes to the rating program as well as changes to individual credits. The LEED® cool roof credit requires that at least 75% of the roof surface be covered with a material that meets or exceeds the minimum SRI value (low slope = 78, steep slope = 29). Rebate Programs As the green building movement sweeps the country, more utilities across the U.S. are providing incentives for cool roofs. Some states with current utility rebate programs include Arizona, California, North Carolina, South Carolina, Colorado, Florida, Idaho, New Jersey, New York, and Texas. Check with your local utility company to see if it offers a cool roof rebate program. Many codes and programs reference the CRRC or the Energy Star® Reflective Roof Program. The Energy Star® label is widely recognized by consumers as an indication of energy efficiency. Manufacturers can choose to rate their products with Energy Star® as long as they meet Energy Star’s® minimum specifications. The Energy Star® program accepts manufacturer-provided data, as well as CRRC ratings. In order to obtain an Energy Star® rating, a manufacturer must have three-year data. Another way cool roofs are being incentivized is through a federal tax credit. Through December 31, 2010, the IRS will provide a tax credit for Energy Star® metal and asphalt roofing products. The tax credit is for 30% of the cost of the roof, up to $1,500. Visit the Energy Star® Web site at Test your knowledge of building envelope consulting with the follow ing ques tions devel – oped by Donald E. Bush, Sr., RRC, FRCI, PE, chairman of RCI’s RRC Examination Develop – ment Subcommittee. 1. Building envelopes consist of opaque components and fenestration components. What are the opaque components in a building envelope? 2. Which fenestration components are included in the building envelope? 3. An envelope component can be either an exterior or semiexterior type. What is the purpose of exterior envelope components? 4. What is the purpose of semiexterior envelope components? 5. The building envelope design must take into consideration both external loads and internal loads. What do the external loads include? 6. What do the internal loads include? Answers on page 36 A U G U S T 2009 I N T E R FA C E • 3 5 Michelle van Tijen is the marketing coordinator for the CRRC. She answers the cool roof hotline, writes articles for publications, and coordinates the CRRC newsletter. Michelle keeps up to date on green building codes and programs containing cool roof credits and is currently overseeing the process to have the CRRC-1 Standard become approved as an ANSI National Standard. In the past, she has worked as the sustainability coordinator for the UC Davis Architects and Engineers Office and has also worked on green building campaigns with the California Student Sustainability Coalition. She holds a bachelor’s degree in design from the University of California at Davis. Michelle van Tijen www.energystar.gov for details on how to receive a rebate. Cool roofs can both dramatically improve the energy efficiency of a building and help reduce a building’s environmental impact. As codes, standards, programs, and rebates steer the green building movement towards cool roofing, the CRRC-Rated Products Directory has become a useful and essential tool for manufacturers and architects alike. Energy savings, cost savings, increased roof durability, reduced air pollution, and improved public health are all excellent reasons to consider a cool roof. It certainly pays to stay cool. REFERENCES 1. “Reflective Roof Products for Consumers,” Energy Star®, May 14, 2009, www.energystar.gov/index .cfm?c=roof_prods.pr_roof_products. 2. “Heat Island Effect,” United States Environmental Protection Agency, May 14, 2009, www.epa.gov/heatisland /index.htm. Answers to questions from page 35: 1. Walls, roofs, floors, slabson- grade, below-grade walls, and opaque doors. 2. Windows, skylights, and doors that are more than one-half glazed. 3. To separate conditioned space from outdoor conditions, including ventilated crawl spaces and attics. 4. To separate conditioned space from unconditioned space or from semiheated space. Semiexterior envelope components also separate semiheated space from exterior conditions or from unconditioned space. 5. Solar gains, conduction losses across envelope surfaces, and infiltration. 6. Heat gain from lights, equipment, and people. REFERENCE: User’s Manual for ANSI / ASHRAE / IESNA Standard 90.1 – 2004. RCI Foundation Mission To support research, education, and the dissemination of information for issues important to the industry. 800-828-1902 www.rcifoundation.org 36 • I N T E R FA C E A U G U S T 2009
