CRRC helped develop the American National Standards Institute (ANSI)/CRRC S100, Standard Test Methods for Determining Radiative Properties of Materials. Formerly known as CRRC-1, it enables cities, states, and other entities to reference cool roof standards in building codes and rating programs worldwide. After experiencing a series of rolling blackouts in the summer of 2001, California helped lead the cool roof movement by changing its code to require cool roofing on all low-slope buildings, including large apartments and commercial complexes.
Since then, many cities and states have established codes and programs prioritizing and incentivizing cool roofing on new and retrofit construction. As such, cool roofing products and reflective materials now boast a formidable presence in the residential and commercial roofing market. Examples include San Antonio’s (Texas) “Under 1 Roof” residential cool roof repair program, which identifies seniors, veterans, and low-income homeowners for cool roof replacement. Nearly $3 million has been allocated to the program since 2015, with each new roof reducing home energy use by an average of 7.3 percent. The program expects to replace a total of 700 roofs by the end of 2020 for qualifying San Antonio homeowners, with another 4000 roofs replaced over the next five years. Other examples include the Los Angeles Department of Water and Power’s cool roof rebate program, which provides funds for cool roof repair or replacement when the roof area being replaced is equal to or less than 50 percent of the total roof area. According to CRRC, the program has permitted 18,000 new cool roofs and issued an additional 2200 repair rebates since 2010, resulting in 3 million m2 (33 million sf) of cool roofing, equating to 5.1 GW a year in energy savings.
New choices for cool roofing
Low-slope cool roofing has been popular for quite some time. Most commercial business owners will not bat an eye at the idea of painting their roof white or some other light color, as most low-slope roofs are invisible from the street level. Breaking into the U.S. residential space has been more difficult due to the proliferation of dark roofs, most popularly represented by asphalt shingles. In 1903, Henry M. Reynolds began marketing cut rolls of shingles made from asphalt, an inexpensive byproduct of petroleum refinement. By the 1920s, the asphalt shingles were so popular they were sold in mail-order catalogues. Cut to the 1950s, most asphalt shingles were sold in squares with tab-forming cutouts, much like today. Currently, asphalt shingles cover about 80 percent of American homes.
Asphalt shingles are popular because they are relatively lightweight, low in cost, and easy to install and maintain. However, standard dark roofs can reach temperatures of 65 C (150 F) or more in the height of summer. A cool roof under the same conditions is typically 10 C (50 F) cooler, saving both energy and money by reducing the use of air-conditioning. White is no longer the only cool roof color, as manufacturers have created solar-reflective shingles in dynamic shades, including darker hues like gray and black. Cool roof asphalt shingles are formulated by pressing light, medium, and dark pigmented mineral granules with high near-infrared reflectance into an asphalt-impregnated fiberglass mat. These granules cover the sheet so completely that only a small fraction of the asphalt is exposed, sidestepping the natural solar-absorbing properties of darker hues (even black) without sacrificing color to the naked eye.
Metal panel roofing is also giving design professionals a wealth of cool roofing options previously unavailable for residential and light commercial applications. The surface of smooth metal panels is the perfect canvas for solar-reflecting polyvinylidene difluoride (PVDF) paint coatings. PVDF coatings are durable, lightweight, resistant to chemicals and solvents, and possess low thermal conductivity. Newer metal panel roof systems also install in much the same fashion as asphalt shingles, are comparatively lighter and stronger than most roofing products, can mimic traditional roofing profiles (e.g. wood shake, slate, and clay tile), have a life expectancy of 50 years or more, and are recyclable at the end of their life cycle. While more of an upfront investment than asphalt, metal roofing continues to grow in popularity due to its durability, design versatility, and sustainability/energy-efficiency benefits.
Amanda might have mentioned that green vegetative roofs are significantly cooler than reflective roofs that merely reflect heat back up into the atmosphere. In fact, vegetated roof surfaces are typical several degrees cooler than ambient temperatures due to the plants transpiration cooling affects.
This reduction in the urban heat islands from roof surfaces is only one of dozens of green roof benefits most importantly including storm water management and reduction in carbon dioxide emmissions.