Scientists develop formula to calculate CO2 savings from 'cool roofs'

Sacramento Business JournalGreen may be the color of money, but white could prove to be the color of savings when it comes to roofs.

California scientists announced today that they have developed a formula to calculate how much carbon dioxide (CO2) can be offset by using more reflective surfaces, such as rooftops, in urban settings.

“White roofs can cut a building’s energy use by 20 percent and save consumers money,” California Energy Commissioner Art Rosenfeld said in a prepared statement. “The potential energy savings in the U.S. is in excess of $1 billion annually. Additionally, by conserving electricity, we are emitting less CO2 from power plants,” he added.

The announcement was made at the California Energy Commission’s fifth annual Climate Change Research Conference at the Sacramento Convention Center this week.

In a study to be published in the scientific journal Climate Change, Rosenfeld, along withLawrence Berkeley National Laboratory Scientists Hashem Akbari and Surabi Menon, estimates that replacing nonreflective, dark roofing materials with white ones on an average house with 1,000 square feet of roof surface would result in an equivalent CO2 offset of 10 metric tons annually. With an offset value of $25 per metric ton, according to European CO2 markets, that could be worth $250.

Scientists have long known that putting white roofs on homes and buildings is a simple and effective way to reflect the sun’s rays. Similarly, cool-colored pavements aid in the reduction of “urban heat islands” which contribute to global warming, according to the energy commission.

Since 2005, commercial buildings with flat roofs in California have been required to have white roofs. Beginning in 2009, new residential roofs and retrofit constructions in California will be required to have “cool-colored” roofs which reflect more of the sun’s rays than current roofing materials of the same color.

In an effort to increase the use of reflective roofing and pavement materials, Akbari, Menon and Rosenfeld propose an international campaign to organize 40 of the world’s largest cities in tropical and temperate zones to develop programs to require white roofs and “cool pavements” when roofs are initially constructed and pavements installed.

The projected estimate for worldwide CO2 emissions in 2025 is 37 billion metric tons; a proposed global CO2 offset for cool roofs and cool pavements would be 44 billion metric tons, valued at more than $1 billion, and enough to offset more than one year of the total global CO2 emissions, according to the study.

“This idea of a ‘cool cities’ campaign could lead to significant energy savings, improved air quality, reduce the heat island effect in summer, and more importantly, cool the globe,” said Akbari in a prepared statement.

“This simple and effective idea can organize the world into taking measured steps to mitigate global warming. Our findings will help city leaders and urban planners quantify the amount of CO2 they can offset using white roofs and cool pavements.”

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