For years, researchers in Lawrence Beckley Laboratory’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 sunny afternoon temperatures in cities average -15deg C higher than those in nearby rural areas.
The warmer temperatures in these so-called areas 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.
Currently, the status of cool materials in the roofing industry ranges from fair to poor. While there are 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.
A nationwide computerized resource covering the philosophy and technology behind cool communities was created by a committee. The information gathered will be inputted into a system that 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 labelling 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 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
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 colour. 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 magnetite could create a more reflective paint without noticeably changing its rust-red colour.
“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.
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 researchers; their peak temperatures are listed below. Ambient air temperature at the time of the test was 13°C. Your roof colour of choice is now up to!
- Black acrylic paint: 61°C
- Galvanized steel: 58.8°C
- Black acrylic paint infrared-reflecting film : 50.5 °C
- Common “white” fiberglass/asphalt shingle : 47°C
- Clay terra cotta tile : 44 °C
- Red acrylic paint: 41°C
- Light green acrylic paint: 40°C
- White acrylic paint: 23°C
- Hyper white” acrylic paint : 18°C