A really cool idea: As temperatures rise, so does the demand for cool roofing

by sadia_badhon | May 27, 2020 10:52 am

by Amanda Boyer

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The 2010s were marked by shorter winters, longer heat spans, and record-setting temperatures around the globe. According to the European Union’s Copernicus Climate Change Service, 2019 was the second hottest year on record[2], beaten by 2016 by less than ³/₅₀ C (¹/₁₀ F). As greenhouse gas (GHG) emissions continue to trap heat and make homes and businesses more difficult to cool, cities are struggling to keep up with the demand on local energy grids.

While the late 2010s experienced a construction boom, higher cooling demands are making owning a home, running a business, or staffing an office building more costly in ways that threaten to dampen industry growth[3]. It is incumbent upon designers, architects, and specifiers to factor in the costs of rising temperatures, and incorporate temperature-lowering cool roofs into their recommendations. The incentives, as well as the technology to do so, have been steadily improving.

Cool roofing and energy use

Americans are by far the most prolific users of air-conditioning[4] (87 percent of all homes), more than the rest of the world combined. According to the U.S. Energy Information Administration[5] (EIA), air-conditioning accounts for 12 percent of the country’s total energy use. Long before the advent of modern air-conditioning units, builders understood the roof’s capacity to retain heat and make living conditions unbearable.

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Roofs have the most exposed surface area of any part of the building, so it makes sense the materials and coatings used on it have a big impact on the comfort of occupants. If white tunics have worked to keep the sun off desert travelers for several millennia, then why not apply the same tactics to roofing? Throughout the Mediterranean and Middle East, buildings with white exteriors have been common for centuries. Examples include the labyrinth of Byzantine-influenced buildings in Ostuni, Italy, and the stunning white-washed villas of Santorini, Greece.

When light touches any surface, some of its energy is reflected and some absorbed. Individual colors are how the brain perceives the wavelength of the reflected light. White light[7] contains all the wavelengths of the visible spectrum, so when the color white is reflected, all wavelengths are also reflected, making it the most reflective hue.

In the 1980s, the U.S. Department of Energy (DOE) began researching the benefits of reflective roofing[8] in urban environments with the goal of reducing high temperatures caused by dark roofing, asphalt roads, and other heat-absorbing building materials (known as the ‘heat island effect’). They found white or reflective roofs[9] typically only increase 6 to 14 C (10 to 25 F) above ambient air temperatures during the day, which translates up to 15 percent savings on air-conditioning use over the course of a year for a typical one-story residence.

In 1998, the Cool Roof Rating Council[10] (CRRC) was established to develop credible and universal methods to evaluate and classify the solar reflectance and radiative properties of roofing products, and share that information publically. “Coolness,” as defined by CRRC, is measured by two properties:

• solar reflectance[11] (the fraction of solar energy reflected by the roof); and
• thermal emittance (the relative ability of the roof surface to radiate absorbed heat).

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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[13] 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[14]” 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[15] 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[16], 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[17] 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.

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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[19]. 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[19] 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[20] 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[21] 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[22] 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.

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Choosing cool roofing from the outset

There are many reasons for architects and specifiers to consider incorporating cool roofing into their plans from the beginning. For one, people are moving less[24]. Deep changes in the economy and housing market, growing post-college debt, and the availability of telecommuting options are encouraging potential homebuyers, especially millennials, to stay put longer.

Additionally, older Americans are living longer and often choosing to age in place[25] rather than downsize or move into retirement communities. When people do buy, they are often looking for a ‘forever home’ and materials that are both long-lasting and capable of saving money over time. Cool roofing is a huge potential growth area in retrofit construction and a valuable savings tool to attract buyers to new construction.

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As mentioned earlier, the key benefit of cool roofs is lower summer utility bills. Less demand for cooling could enable owners of large buildings and complexes to decrease the size of the air-conditioning units. According to the Lawrence Berkeley National Laboratory’s Urban Heat Island Group, retrofitting 80 percent of commercial buildings in the U.S. with cool roofs[27] would yield $735 million (15 percent) in annual energy cost savings. Additionally, homeowners can increase the lifespan of existing air-conditioning systems[28] by lowering the demand placed on each unit.

There are also public benefits to cool roofs[29], such as improved grid stability, reduced GHG emissions, and fewer heat wave-associated public health risks. Reduced air-conditioning lowers peak electrical demand and use, decreasing the likelihood of brownouts and blackouts during heat waves. Lowering energy use also reduces the amount of power plant emissions[30] in the atmosphere. Philadelphia’s senior-focused Cool Homes Pilot Project[31] found reducing the urban heat island effect and lowering temperatures, particularly in the top floors of buildings, can improve a person’s ability to regulate body temperature and to avoid heat stroke. The ambient temperatures around cities employing cool roofing materials[32] tend to be lower. Moreover, as vehicles require less air-conditioning and gasoline, smog decreases and public health improves.

There are some arguments cool roofing is not always the best choice for extremely cold climates. The winter months bring fewer hours of sunlight, and since cool roofing causes the sun’s natural heat to deflect off the roof rather than be absorbed, this may moderately increase the heating costs. However, with more communities being impacted by climate change, one can argue winter is becoming more elusive, and architects and specifiers should prepare for futures with higher temperatures. In addition to ceiling fans, shaded windows, and proper insulation, cool roofs can have an impact on homes and businesses as well as the communities around them.

[33]Amanda Boyer oversees product management for CertainTeed’s West Coast operations, fully supporting sales teams and manufacturing plants in the region. She joined CertainTeed in 2014 and has served in various roles supporting the roofing supply chain, including serving as a former production planner for three manufacturing plants. Boyer has a bachelor’s degree in communication studies from Millersville University, and a master’s degree in political science from East Stroudsburg University.

Source URL: https://www.constructionspecifier.com/a-really-cool-idea-as-temperatures-rise-so-does-the-demand-for-cool-roofing/

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