Cool ideas for roofs cut energy bills, smog

November 18, 1994

By Mike Wooldridge, MAWooldridge

For years, researchers in LBL's Energy and Environment Division have been building the case that "painting it black" in sunny climates burns money.

Typically two-thirds of metropolitan landscapes are covered by asphalt-shingled roofs, black-paved roads, and other dark, heat-absorbing materials. The radiation they capture from the sun, researchers say, is an important reason why summer afternoon temperatures in cities average 5deg.F higher than those in nearby rural areas.

The warmer temperatures in these so-called "heat islands" translate into an extra $4 billion in cooling costs in the United States each year, studies estimate. They are also an indirect contributor to air pollution, since warmer temperatures boost chemical reactions that produce smog.

Now the heat island problem has also been taken up by President Clinton. Much of the cool communities approach that began at LBL--which seeks to decrease temperatures in heat islands with reflective roofs, lighter pavement, and shade trees--has been integrated into Clinton's Climate Change Action Plan (CCAP). The comprehensive plan seeks to cut the nation's energy use 10 percent by the year 2000 with about a dozen energy-saving strategies, including cool communities measures.

Members of E&E's Heat Island Project met with other government researchers, roofing and pavement industry representatives, and utility officials at conferences in February and July of this year to formulate a national plan for the CCAP's cool communities approach. What emerged was a 10-year, $30 million program that aims to bolster research on cool materials as well as bring the cool communities philosophy to the marketplace.

"The approach is very down-to-earth," says E&E's Hashem Akbari, who heads the Heat Island Project at LBL and chaired the steering committee at the two conferences. "We are looking at the available resources. We are trying to get into the culture of the manufacturer and the consumer, and educate them about the benefits of using cool materials." E&E's Sarah Bretz, Paul Berdahl, and Art Rosenfeld also participated in the conferences.

Currently, the status of cool materials in the roofing industry ranges from fair to poor, says Akbari. While there exist cool materials for use on commercial buildings--light-colored roofing membranes and such--they are often viewed as a more expensive alternative rather than a practical first choice. The picture is much bleaker in the residential market: reflective materials are practically non-existent.

Central to the committee's goals is the creation of a nationwide computerized resource covering the philosophy and technology behind cool communities. The information system would integrate databases and simulation models about cool paints, shingles, asphalts and other materials. Researchers, architects, and manufacturers could call up the information electronically, potentially over the Internet. Similar information would be spread to consumers through such means as interactive kiosks at retail outlets.

Plans were also set up by the committee for a nationwide product rating and labeling system for cool materials, similar to the energy savings figures now attached in stores to refrigerators, water heaters and other appliances. Controlled tests would assign products such as roofing shingles a rating based on the temperature they rise to on an average sunny day. With the labels, homeowners could weigh the air conditioning costs of choosing different shingles when reroofing a house.

The plan proposes specific research projects to answer some of the long-term questions associated with cool materials. How will more reflective materials withstand the elements compared to those currently on the market? Many experts expect cool roofing materials will actually extend the life of roofs, since a cooler roof would tend to undergo less expansion and contraction, and thus experience less wear and tear under the sun.

The CCAP plan also recommends more studies of heat islands and air quality to present a clearer picture of what effect cooler cities will have on smog. Current computer simulations at LBL estimate that a 3deg.F drop in air temperature in a major heat island like Los Angeles--a change considered feasible with cool community measures on a wide-scale--could cut smog 10 percent, equivalent to converting about a million conventional cars on the road to electric.

"We believe energy efficiency, including heat island measures, is moving into the market to a certain extent just by the natural market forces," Akbari says. "However, in some cases the natural market forces have to compete with the cheap energy prices, and they may not initially compete very well. We're just trying to give the natural processes a push."

Researcher beats roof heat with style

The push to lower temperatures and save money in communities with more reflective construction materials may find its toughest hurdle not with manufacturers but with the average homeowner.

"It's a question of aesthetics," says Paul Berdahl, an LBL materials scientist who works on cooling buildings at the molecular level. "Though it varies somewhat from place to place and over time, white is basically regarded as an unsuitable color for roofs in residential areas."

Even the lighter conventional asphalt shingles on the market today, Berdahl says, are relatively hot. "The ones on the shelf that are called "white" are essentially black in the sun, since their material absorbs most of the solar radiation that strikes them," he says.

But if research at LBL pans out, having a cool roof may not necessarily require you to cover your home with unstylish materials. This is because half of the sun's rays are invisible to the eye, and have no effect on a material's color. A clear, low-emissivity coating tested at LBL, for example, has been shown to reduce temperatures of the darkest, hottest shingles 20 degrees by reflecting invisible light.

Lab researchers are also looking to tinker with the molecular structure of paints to make them more reflective. For instance, the pigment hematite, which is used on shingles, contains impurities of magnetite that absorb light in the near infrared part of the spectrum. Finding a way to get rid of the magnatite, Berdahl says, could create a more reflective paint without noticeably changing its rust-red color.

"It comes down to a question of understanding how the structure of a material contributes to its performance in the sun," he says. In the end, consumers may be able to keep their dark shingles and tiles, and have cooler homes, too.

What color is your roof?

On a sunny day, roof temperatures can range from comfortably warm to egg-frying hot, depending on how much sunlight they reflect. Different roofing materials were tested side-by-side by LBL researchers; their peak temperatures are listed below. Ambient air temperature at the time of the test was 55deg.F.