Environmental Leader

California scientists say white roofs can cut a building’s energy use by 20 percent, and they say they have a formula to calculate how much CO2 can be offset by increasing the reflectivity of rooftops.

“The potential energy savings in the U.S. is in excess of $1 billion annually,” said California Energy Commissioner Art Rosenfeld.

Along with Rosenfeld, Lawrence Berkeley National Laboratory scientists Hashem Akbari and Surabi Menon have successfully quantified the effects of white roofs in populated settings in terms of CO2 offset.

In a study, the scientists estimate that replacing nonreflective, dark roofing materials with white ones — on an average house with 1,000 square feet of roof — would result in an equivalent CO2 offset of 10 metric tons annually. At the current offset value of $25 per metric ton on the European CO2 markets, that could be worth $250.

Beginning in 2009, new residential roofs and retrofit constructions in California will be required to have “cool-colored” roofs which reflect a higher fraction of the sun’s rays than current roofing materials of the same color.

The scientists are also proposing an international campaign to organize 100 of the world’s largest cities to require white roofs and “cool pavements.”

Worldwide CO2 emissions in 2025 is projected to be 37 billion metric tons. The proposed global CO2 offset would be 44 billion metric tons, valued at $1,100 billion.