The Drive Behind Mission #3: Cool Roofs

The Benefits of Cool Roofs

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Photo: Duro-Last Roofing
Cool roofs or light colored, reflective surfaces reflect more sunlight than dark ones, turning less of the sun's energy into heat. Increasing the reflectance of our roofs can can reduce the temperature of buildings, cities and even the entire planet. White roofs, and other cool surfaces, are an efficient and affordable tool to help alleviate some of the stress caused by rising local, regional and global temperatures. A cool roof is a roofing system, consisting of materials of white or light-color, which effectively reflects the sun's energy from the roof surface. Reflective surfaces do not need to be white. The term "cool roofs" is used to exemplify how materials of high solar reflectance come in a range of colors, including many shades of grey and even light red. Learn more.

Cool roofs...
    • Reduce the roof surface temperature by up to 100 degrees Fahrenheit, thus reducing the heat transferred into the building below. A white or reflective roof typically only increases 10-25 degrees Fahrenheit above ambient temperatures during the day. Learn more.
    • Save on annual electricity bills by reducing summer air conditioning costs. Creates an average of 20% savings, but can reach over 40% and there have even been electrical savings recorded nearly up to 50%. Learn more.
    • Significantly cut greenhouse gas emissions and combats global climate change by reducing energy needs and cooling cities and the world. This is done through principles of solar radiation management and geoengineering, which show that cool roofs are not only used to reflect solar energy but emit infra-red radiation to cool the planet and reduce global warming. Learn more.
    • Reduce the "Heat Island" effect. Learn more.
    • Save peak electricity demand costs. Learn more.
    • Reduce roof maintenance and replacement expenses by extending roof life. Learn more.
    • Increase indoor comfort by the reduction of infrared conversion from visible light. Learn more.
    • Reduce air pollution. Learn more.
    • Increase the thermal conductivity of the roofs insulation. Learn more.
    • Receive utility rebates in some locations. Learn more.
    • Maintain aesthetics of a roof that performs and looks good. Learn more.
    • Increase the life expectancy of the buildings cooling equipment. Learn more.
    • Reduce smog formation. Learn more.
    • Are an effective alternatives to bulk attic insulation in humid tropical and sub tropical climates. Bulk insulation can be entirely replaced by cool roofing systems. Learn more.
    • Reduce roofing waste added to landfills. Learn more.
    A study by Lawrence Berkeley National Laboratory showed that if cool roofs were widely adopted, the Greater Toronto metropolitan area could save more than $11 million annually on energy costs. Learn more.
    According to
    Global Cool Cities Alliance:
    When Sunlight Hits a White Roof...
    10%heats the environment
    8%heats the city air
    80%is reflected
    1.5%heats the building
    When Sunlight Hits a Dark Roof...
    38% heats the atmosphere
    52% heats the city air
    5% is reflected
    4.5% heats the building
    Cool Roofs
    Easy. Cheap. Efficient.
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    Image : White Tops NYC | Click to enlarge
    If all urban, flat roofs worldwide were whitened, the reduction in carbon emissions would be 24 Gigatonnes, or equivalent to taking 300 million cars off the road for 20 years. Learn more.
    Quick Facts About Cool Roofs
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    The latest research shows that cool roofs and pavements can help cool the entire planet. Permanently retrofitting urban roofs and pavements in the tropical and temperate regions of the world with solar-reflective materials would have an equivalent effect on global temperatures as stopping the emissions of 44 billion tonnes of CO2, or over one year’s worth of humanity’s CO2 emissions.

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    Reducing air-conditioning demands in the U.S. by installing cool roofs on 80% of the 2.58 billion square meters of commercial building conditioned roof area could save 10.4 terawatt hours of electricity and $735 million annually.

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    Pavements and roofs comprise approximately 60% of city surfaces. Cool roofs and cool pavements can help reflect away the sweltering temperatures of summer urban heat islands, improving air quality and comfort. Widespread installations of cool roofs and pavements can reduce summer air temperatures in cities by 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit).

    After cool pavements were installed in a city park in Greece, surface temperatures were reduced by 12°C and ambient temperatures were reduced by 1.9°C. 'Cool' paving materials helps lower city temperatures
    Even School Buses Are Catching On!
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    Photo: LemonReese/Flickr | Click to enlarge
    "In a typical city, pavements account for 35 to 50 percent of surface area, of which about half is comprised of streets and about 40 percent of exposed parking lots. Most of these streets and parking lots are constructed with dark materials. Because dark pavements absorb almost all of the sun’s energy, the pavement surface heats up, which in turn also warms the local air and aggravates urban heat islands.” Like cool roofs, which are lighter-colored roofs that keep the air both inside and outside the building cooler by reflecting more of the sun’s energy, cool pavements reflect as much as 30 to 50 percent of the sun’s energy, compared to only 5 percent for new asphalt (and 10 to 20 percent for aged asphalt)." ~ Heat Island Group, 'Berkeley Lab researchers showcase cool pavement technologies'
    The True Cost of Dark Roofs

    • Image: Patrick Theiner, Creative Commons

      Image Credit: Patrick Theiner, Creative Commons

    Most of the roofs in the world, including 90% in the United States, are dark-colored. In the heat of a full sun, a black roof surface can increase temperatures as much as 122 degrees Fahrenheit, reaching temperatures of 150-190 degrees Fahrenheit. This massive heat increase contributes to:
    "A new study of how different white roofing materials performed “in the field” in New York City over multiple years found that even the least expensive white roof coating reduced peak rooftop temperatures in summer by an average of 43 degrees Fahrenheit. If white roofs were implemented on a wide scale, as the city plans to do, this reduction could cut into the “urban heat island” effect that pumps up nighttime temperatures in the city by as much as 5 to 7 degrees Fahrenheit in the summer, said the study’s lead scientist, Stuart Gaffin of Columbia University." ~ NASA
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    On a sunny summer afternoon the annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C), according to the EPA. The elevated air temperatures associated with this summer “urban heat island” (UHI) make air conditioners work harder to keep buildings cool, which can strain the power grid. They also accelerate the formation of smog, degrading air quality. Image courtesy of Heat Island Group, Lawrence Berkeley National Laboratory
    The "Heat Island" Effect
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    On May 11-12, 1997, NASA used a specially outfitted Lear Jet to collect thermal data on metropolitan Atlanta, Georgia. Nicknamed “Hot-Lanta” by some of its residents, the city saw daytime air temperatures of only about 26.7 degrees Celsius (80 degrees Fahrenheit) on those days, but some of its surface temperatures soared to 47.8 degrees Celsius (118 degrees Fahrenheit). In this image, blue shows cool temperatures and red shows warm temperatures. Pockets of especially hot temperatures appear in white. Image courtesy of NASA/Goddard Space Flight Center Scientific Visualization Studio
    For hundreds of millions of people living in or near cities, urban heat islands are a growing environmental and health concern. If you turn on the local weather report, you'll most likely notice a strange trend. Temperatures are often higher in cities in comparison to their surrounding areas. According to the EPA, the annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C). This is a result of a phenomenon known as the urban heat island effect. "Heat Islands" are mainly caused by dark surfaces, which absorb and hold more heat from the sun, and from less vegetation, which would provide shade and cool the air. Elevated temperatures from urban heat islands, particularly in the summer, affect a communities environment and quality of life. Although the heat island impacts lengthen the plant-growing season, the EPA outlines the many detrimental effects of urban heat islands:
    • Increased energy consumption : Higher temperatures in the summer increase energy demand for cooling and adds great pressures to the electricity grid during peak periods of demand. One study estimates that the heat island effect is responsible for 5-10% peak electricity demand for cooling buildings in cities.
    • Compromised human health and comfort : Higher air pollution levels and warmer days and nights contribute to general discomfort, respiratory difficulties, non-fatal heat strokes, heat cramps and exhaustion and heat related mortality.
    • Elevated emissions of air pollutants and greenhouse gases : Increased energy demands generally result in greater emissions of air pollutants and greenhouse gas emissions from power plants. Higher air temperatures also encourage the formation of ground-level ozone.
    • Impaired Water Quality : Hot pavement and rooftop surfaces emit massive excess heat to stormwater, which drains into storm sewers and raises water temperatures as it is released into streams, rivers, ponds, lakes and oceans. These rapid temperature changes are stressful and damaging to aquatic ecosystems.
    • Perhaps the worst result of the heat island effect is the number of  heat related deaths . The National Oceanic and Atmospheric Administration reports that heat is usually more deadly in the U.S. and typically kills more people each year than hurricanes, tornadoes, floods and lightning put together.
      EPA: Reducing Urban Heat Islands
      With the current rate of greenhouse gas emissions, studies by the National Academies of Sciences in the United States, show that that by 2100, a hot summer day would reach temperatures of roughly 137°F. Learn more.
      New York Times: White Roofs Cut Energy Costs

      What About Winter?

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      Roof covered with snow/Wikipedia Commons
       While it may seem that white roofs do more harm than good in colder climates, research shows that the heating benefits of a dark roof in the winter are very minor because the days are shorter, the angle of the sun is low, the skies are cloudier and sometimes the roofs are covered in snow. The amount of heat energy you may lose in winter may be at maximum 30% of the summertime savings. Also, hot air always rises. Thus, whatever heat is transmitted into the attic or into living areas from a dark roof will stay very near the ceiling trying to get back out again instead of circulating through the house. Aside from energy savings, a white roof also saves money on roof repairs. Since black or dark roofs become overheated in the sun, they are prone to warping and cracking .  This means more roof repair. A white roof saves money on roof repair because it is more durable. A white roof can also extend the life of a buildings cooling equipment by decreasing use. If you live in a four-season climate where you need cooling in the summer and heating in the winter, a white roof will most likely save you money. For more information, see the Global Cool Cities Alliance Q&A page and how the White Roof Project answers the question, "What about the Winter?According to the Cool Roofs Rating Council and other sources, "The roof is an insignificant source for heat gain in winter. While cool roof owners may pay slightly more to heat their homes, this amount is usually insignificant compared to the cooling energy savings during the summer". However, In much colder climates where annually there are far more heating days than cooling days, such as in parts of Alaska, cool roofs are not typically a worthwhile investment, in terms of energy efficiency and savings. In these much cooler locations, the cooling benefits of a reflective roof surface do not outweigh the winter months heating benefits on a less reflective, or dark roof surface. Learn more.
      Calculate Your Cool Roof Savings
      Cool roofs are not just flat and white. There are many options for cool roofs, including cool asphalt shingles. Learn more.
      In addition to cool roof systems, communities and individuals can take four other main steps to reduce the heat island effect and help cool cities and the planet:
      1. Increase tree and vegetative cover.
      2. Create "green roofs" (rooftop gardens).
      3. Use cool pavements.
      4. Use alternative energy and install solar panels.
      The idea of white roofs isn't a new one. There are many locations in the world which fully utilize the benefits of cool roofing systems, especially in the Mediterranean and Middle East:
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      Houses with white roofs, like these in Greece, would be able to reflect light back through the atmosphere. Image: Alamy
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      In California, flat-roofed premises are now required to have white roofs. Image: Alamy
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      White-roofed, colourful houses dot Bermuda's hills. Image: Wikipedia Commons
      Cool Your Building. Cool Your City. Cool Our Planet.
      Cool Roof Resources and Articles
      Technical Guides to Cool Roofing Systems
        U.S. DOE: Guidelines for Selecting Cool Roofs Have a Difficult Roof to Paint? Find a Contractor Within Your Area
        Cool Roof Academic Papers