Cool Roof Benefits

Substituting cool roofs for traditional dark roofs can provide benefits for your buildings, your city, and our planet.

On the building level:

• Cool roofs absorb less sunlight and therefore heat up less on a sunny day, which reduces the transfer of heat into the top floor of buildings and lowers indoor air temperatures.[1]
• Lower indoor air temperatures translate to energy and cost savings by reducing the need for air conditioning.[2]
• In buildings without air-conditioning, lower indoor air temperatures provide enhanced indoor comfort, which promotes increased productivity and wellbeing.[3]

On a summer afternoon, the black roof at left was measured to be 30°C (54°F) warmer than the white roof at right (source: U.S. Department of Energy)

On the city level:

• Because cool roofs absorb less sunlight and heat up less than dark roofs, they transfer less heat to the local atmosphere, which leads to cooler outside air.
• Lower outside temperatures mitigate the urban heat island effect, which can lead to reduced heat-related illness and mortality.[4]
• Lower outdoor temperatures lead to improved air quality by slowing the formation of smog.[5]
• Air quality will further improve because of lower power-plant emissions of greenhouse gases and other pollutants owing to reduced electricity demand, particularly during peak times (e.g., hot summer afternoons) when the most polluting plants operate.[6]
• This reduction in peak electricity demand can also ease strain on the electricity grid, which lessens the risk of power outages.

On the global level:

• Cool roofs decrease the amount of heat that is absorbed at the Earth's surface and thus lower surface temperature. This decrease in surface temperature reduces the transfer of heat into the atmosphere, which offsets a portion of the warming from greenhouse gases and thereby delays climate change (see Figure 6).[7],[8]

White roofs absorb less sunlight, which allows them to transmit less heat to the city air and atmosphere. (source: LBNL-Heat Island Group and Global Cool Cities Alliance)

Notes

• It is important to keep in mind that these benefits vary depending on the solar reflectance value of the roofing product. Traditionally, higher reflectance values confer greater benefits.
• During winter months, cool roofs increase the need for heating energy in cold climates because they absorb less of the sun’s energy. However, in winter the sun stays low, the days are short, and the skies are often cloudy, limiting the amount of sunlight available to a roof. In addition, when snow covers roofs, the color of the roof beneath the snow becomes irrelevant. In the United States, this winter heating penalty is typically small compared to the summer cooling benefit.[9]
• Bright, solar-reflective roofs can produce glare, which may disturb occupants of taller neighboring buildings. In such situations, a cool-colored (nonwhite) roof may be more appropriate for the shorter building to stay cooler while avoiding visual concerns.
• While implementing cool roofs is a good first step, local entities that wish to capture significant cooling benefits should consider coupling cool roofs with cool pavements and vegetation. A cool community program/plan is most effective when combining these strategies to achieve maximum benefits. To learn more about cool pavements visit HERE and urban vegetation HERE.

The cooling energy savings from cool roofs should outweigh the winter heating penalty in all but the very  Northern-most locations in the US (source: Levinson and Akbari 2010)

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Footnotes:

[1] Levinson R, Akbari H. 2010. Potential benefits of cool roofs on commercial buildings: conserving energy, saving money, and reducing emission of greenhouse gases and air pollutants. Energy Efficiency 3:53-109.