Changing Black Roof to White or Green Creates Natural Building Cool Down Effect, Says Study

Intensive green roof system at Chicago City Hall. Photo courtesy of Elements Roofing, LLC.

It’s common sense to most of us that if we wear lighter colored breathable clothes, we’ll feel cooler when we’re outside in the summer heat. Well as it turns out, the same principle also applies to the buildings that we live and work in.

Testing this idea on its own properties, the energy company Con Edison in its effort to create both more energy efficiency within its own corporate structure and combat global warming, commissioned a study by Columbia University to measure temperature differences and other data from the three roof types.

The three different roof types were monitored and tested (and are continuing to be tested) as part of a long term study of there effectiveness. The white roofs were installed at the company’s headquarters in Manhattan and its Learning Center in Long Island City, N.Y., where the green roof was also installed.

Photo by the www.infrastructurist.com.

The black and white roofs are made of the same material, ethylene-propylene-diene-monomer, with color being the only difference. The green roof consists of 21,000 plants in four-inch deep modular sedum systems.

The sedum is a large plant group containing around 400 species found throughout the northern hemisphere, varying from creeping herbs to shrubs. The plants have water-storing leaves.

The Columbia study found that, “The white membrane temperature peaks are on average 30 °F (17 °C) cooler than black in summer. [The] green roof membrane temperature peaks are on average 60 °F (33 °C) cooler than black in summer.”

Researchers in the study said, “We estimate that the 10,764 sq. ft green roof on the Con Ed building is saving roughly $400/yr in heating costs and $250/yr in cooling costs. If this area had been a white roof instead, we estimate that cooling savings would have been $200/yr.”

The green roofs also have other benefits that the other roofs lack, including:

• direct air quality improvements
• water runoff control
• water quality improvements
• urban biodiversity
• noise reduction
• building amenity value

The European Federation of Green Roof Associations - EFB elaborates on these benefits, saying, “Plants reduce carbon dioxide in the atmosphere and produce oxygen. Green roofs reduce the heat island effect (a metropolitan area which is significantly warmer than its surrounding rural areas), which is the main cause of ozone production.

Biting Stonecrop (sedum acre). Photo from Wikipedia.

“Plants roofs remove heavy metals, airborne particles, and volatile organic compounds. Being absorbed into the green roof system, these polluting particle do not enter the water system through surface run off leading to improvement in water quality.”

There are major benefits to installing a green roof, but homeowner and businesses still need to keep in mind the installation and maintenance requirements.

“A green roof system is an extension of the existing roof, which involves a high quality water proofing and root repellant system, a drainage system, filter cloth, a lightweight growing medium, and plants,” according to the nonprofit Green Roofs for Healthy Cities.

In North America, green roofs are slowly taking hold, while the European markets are exploding with technologies becoming well established. Green Roofs explains that, “This has been the direct result of government legislative and financial support, at both the state and municipal level.

“This support has lead to the creation of a vibrant, multi-billion dollar market for green roof products and services in Germany, France, Austria, and Switzerland among others.”

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