It's a green home-building feature particularly fitting for Southern California: a concrete tile roof that neutralizes the smog-forming nitrogen oxides spewed by automobiles.
Hoping to attract environmentally concerned homebuyers, KB Home, based in Los Angeles, has joined forces with Boral Roofing, the Irvine, Calif., manufacturer of what is being called "smog-eating tile."
KB Home, a national homebuilder, in January began offering the tile in all of its housing developments in Southern California. In a few communities, the roof comes standard, but in most it's an upgrade available for an extra $800 or so.
"Obviously, in California pollution from cars is a concern. This is the right thing to do. It is cutting edge," said Steve Ruffner, president of KB Home's Southern California division.
According to the manufacturer, the concrete tile roof on a typical 2,000-square-foot house can annually break down the same amount of nitrogen oxides as a car's engine typically produces during 10,800 miles of driving.
The magic ingredient is titanium dioxide, a naturally occurring substance incorporated into the tile surface, said John Renowden, Boral vice president of product development.
Daylight hitting the roof activates the titanium dioxide, which breaks down the nitrogen oxides in the air into oxygen and nitrates, he explained.
The tiles' smog-fighting ability was proven in extensive laboratory testing and field studies conducted by a European Union consortium of academic and industry experts from 2002 to 2006, Renowden said.
Similar roofs have been used in European home construction for about five years, Renowden said, but KB Home is introducing them in the United States. Boral acquired the license from Monier Germany to produce the tiles for the North America market. They'll be manufactured at two Boral plants in California and one in Henderson, Nev.
"In the studies conducted in Europe where they actually applied it to roadways, the air was measurably cleaner," said Michael Chusid, a building products marketing and technical consultant in greater Los Angeles.
Installed on large numbers of homes, the tiles could reduce the potential for smog, Renowden said.
And when it rains, he said, the small amount of nitrates that accumulate will flow off the roofs as a diluted fertilizer and green up the lawns. He said the tiles' smog-suppressing quality is expected to last at least 25 years. Boral is participating in a European study to determine its longevity more precisely.
Sam Atwood, spokesman for the South Coast Air Quality Management District that regulates the Southern California air basin, said, "We are aware this technology has been used in the past in various applications," such as coating automobile radiators to neutralize nitrogen oxides on roads. "We are interested to see how this works with roof tiles."
KB is offering the roof as an option at all of its new developments, Ruffner said. The tile adds about $800 to the cost of the average 2,000-square-foot house.
The payback is well worth the investment when homebuyers roll the cost into a 30-year home mortgage at today's 5 percent interest rate, Ruffner said. "For about $5 a month, they can take a car off the road each year. It is a pretty cool thing to think about."
Smog-eating roofs will be a standard feature of a Martha Stewart-inspired community of single-family homes that KB Home is building in Eastvale, Calif.