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Urban Heat Islands
As anyone who lives or works in the city will attest, it’s hotter in the concrete jungle than it is in surrounding urban areas. Dark colored roofs and pavement, along with fewer trees and shrubs to shade buildings are a few of the major factors contributing to the “urban heat island effect.”
Hot roof surfaces are being targeted because they are unnecessary sources of heat that contribute to elevated air temperatures and increased demands on air conditioning which in turn, lead to smog formation. Green roofs and white reflective roof surfaces can both help lessen the urban heat island effect and improve air quality.
How Green Roofs Help
On an average summer day, a city like Chicago can actually be 10 degrees warmer than its suburban neighbors due to the urban heat island effect. To help reduce the urban heat island effect in Chicago, the city installed a green roof on their city hall. As a result, when summer temperatures reach 90 degrees in Chicago, City Hall’s green roof reflects the temperature outside, while its neighbor’s roof can reach nearly 160 degrees. By installing a green roof, the improved insulation properties can lessen the requirement from the building’s heating and air conditioning systems by as much as 30%.
Click here to learn more about Chicago City Hall’s green roof.
Chicago City Hall's Green Roof
How White Reflective Roof Surfaces Help
Highly reflective roof surfaces, such as Sika Sarnafil’s EnergySmart Roof®, are being recommended by both the scientific and environmental communities as a way to help mitigate increases in urban air temperatures and to help improve air quality.
Nasa Investigates the Heat Island Effect
In July, 1998, two NASA scientists, Dr. Jeff Luvall and Dr. Dale Quattrochi conducted research to see if they could identify surfaces that exacerbate oppressive urban air temperatures and accelerate the formation of smog. The NASA team used a specially equipped airplane to record photographic and thermal infrared images in order to detect all the “hot spots” in Salt Lake City, Utah.
The physical and reflective properties of the roofing membrane on the RC Willey building illustrate the specific cooling impact that reflective roofs can have in reducing air temperatures within urban heat islands. The air temperature in a heat island is typically 5 to 10 degrees (F) warmer than in surrounding rural areas. Higher temperatures foster an increase in energy demand to run air-conditioning equipment. Consequently, a rise in energy demand leads to a corresponding increase in power-plant generation.
- Above left: RC Willey building. This 865,000 square foot roof utilizes a Sika Sarnafil EnergySmart Roof membrane.
- Above center: Salt Lake City from space
- Above right: NASA thermal imaging proves the building is not absorbing solar radiation, unlike surrounding urban buildings shown in red.
Studies have shown that the urban heat island effect costs the United States in excess of $2 billion a year and represents five to 10% of the peak electric demand across the country ("Urban Heat Islands and the Roofing Industry,” RSI magazine, 1998).
Click here to learn more about energy efficiency
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