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White roof paint cools houses down

DOING something as simple as painting a roof with white reflective paint saves a lot of energy and reduces electric bills and carbon dioxide. When it's time to replace a roof, using heat-reflective materials means even more savings. Sean O'Driscoll reports.

Herb Van Gent points his infrared gun at a square of still unpainted gray shingle and clicks the trigger. He gets an immediate temperature reading: 62 degrees Celsius and rising. Then he aims it 1.5 meters away to a square of roof I have just painted: 37 degrees Celsius and decreasing.

He smiles, announcing 26-degree difference on the first coat. That means it also will be cooler inside the building, he says, which saves energy.

It is 11am, and we are on the roof of a New York retirement home, rolling out a thick, shiny white paint. Van Gent is one of a volunteer group that has come up here to paint the roof as part of a city-sponsored "cool roof" program.

The idea of painting roofs white is catching on across America; Energy Secretary Steven Chu has said it could contribute to the fight against global warming.

"Cool roofs are one of the quickest and lowest-cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change," Chu said in July as he announced that Department of Energy buildings would be painted white wherever possible.

While white roofs keep homes cool in summer by letting less heat in, they have little impact on winter heating bills, according to the Cool Roof Rating Council, a nonprofit group created in 1998 to research and implement the technology.

That generally is because the sun is less intense in winter, the group said, and less important as a heat source. The roofs do not let any more heat escape than other roofs, it said.

In the state of Arizona, cool roofs are mandatory for state and state-funded buildings, while Philadelphia, Pennsylvania, has an ambitious green energy plan that put cool roofs at its center.

In New York City, with Mayor Michael Bloomberg's blessing, the Department of Buildings and other public and private groups have vowed to paint 90,000 square meters of roof on city-sponsored community buildings. Organizers have advertised on Craigslist for volunteers, promising that the painting is rewarding and fun.

I decided to give it a try.

There were half a dozen volunteers on the roof that day from New Jersey-based GAF Materials, which supplied the reflective white paint. Among them was technical specialist Steve Hecht, who showed me how to spread the paint.

Proponents say the idea is as sound for private homes as it is for big, residential apartment buildings. The Cool Roof Council provides information on materials and resources at its website,

Philadelphia recently held a "cool roofs for free" competition, and a block of row houses won.

"The biggest difference is definitely when we wake up in the morning," says Terry Jack, who organized her block's winning entry. "I noticed the difference the very next morning after they painted the roof."

Workers are painting the roofs on both sides of her street with reflective white paint, while also insulating the houses.

City officials hope to show that a white roof will reduce the amount of air conditioning used, saving energy and reducing electricity bills.

According to former California energy commissioner Arthur Rosenfeld, an average, 93-square-meter roof painted white can save 10 tons of carbon dioxide, the equivalent of emissions from one car for about 20 years.

On a national scale, turning roofs cool could eliminate 2 billion tons of carbon dioxide, roughly the same as taking 20 million cars off the road for 20 years, according to Rosenfeld, who carried out his experiments with Hashem Akbari at the Lawrence Berkeley National Laboratory, in California.

So far, many cities have been limited in their response. New York's 90,000 square meters of white roofs is a "very, very, very, conservative target," says Akbari, who advised the city on its NYC Cool Roofs project.

"When you consider that a large box store or mall can have a roof of 18,500 square meters, the entire New York program is the equivalent of painting five of those stores," he says.

But Akbari stresses it is not just about white paint.

"Certainly, the white color helps, especially if it is special reflective paint, but ultimately we want to see people using cool roof material when they have to change their roofs," he says. "There are a whole range of materials that can reflect the heat."

Sophisticated white roofing material can lie underneath a roof's visible surface, he says, reflecting the sun's heat while allowing a wider choice of colors on the surface.

"Definitely, aesthetics has held back the cool roof movement until now, but that is changing. You have a longer lasting roof without having to look bad," says Akbari.

According to the Department of Energy, there are no federal tax credits for roof coatings, but there is a tax credit for using cool materials when replacing a roof.


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