How Reflective Paint Brings Down Scorching City Temperatures

Cities across the U.S. have found relief from this summer’s record-setting heat with the help of technologies that shield roofs, pavement and other surfaces from the sun’s scorching rays.

Some of these technologies have been around for more than a decade but are experiencing greater demand as global temperatures rise. Washington, D.C., for example, has built more than 3,200 green roofs covering 9 million square feet—up from about 300,000 square feet in 2006, according to federal and city officials.

Other technologies, such as super-reflective coatings for pavement, streets and windows, are just now becoming effective and affordable enough for widespread use.

The Los Angeles neighbourhood of Pacoima, a densely packed location sandwiched between freeways and an industrial area, has created a partnership with GAF, a New Jersey-based roofing manufacturer, to paint a basketball court, local park and neighbourhood streets with a reflective coating.

“There’s a lot of asphalt and lack of investment for tree canopies,” said Melanie Paola Torres, 24 years old, a community organiser with the group Pacoima Beautiful. “Given the fact that we are in an industrial zone, that contributes to the urban heat-island effect.”

The reflective coating has reduced air temperatures in the test area at 6 feet above ground by 3.5 degrees Fahrenheit during extreme heat days, and surface temperatures by 10 degrees, according to Jeff Terry, GAF’s vice president of corporate social responsibility and sustainability.

Sweltering conditions are worse in urban heat islands, which can be 10 degrees hotter than surrounding suburbs and occur as buildings, roads and other infrastructure absorb and re-emit the sun’s energy.

Cooling technologies mitigate this. Green roofs absorb heat before it penetrates the buildings beneath. Super-reflective coatings reflect the sun’s visible light and invisible infrared radiation away from surfaces to keep them cooler. And an ultra-white paint developed at Purdue University promises even more protection, although the product isn’t commercially available yet. Each strategy helps reduce energy use.

“The important thing is to help people cool their homes and workplaces affordably,” said Jane Gilbert, chief heat officer for Miami-Dade County, which experienced a record 46 straight days of a 100-degree-plus heat index this summer. “The more efficient we can make both the buildings and the AC systems themselves, the less we’re contributing both to greenhouse gases and also waste heat that goes to our urban heat islands.”

Miami is one of the most vulnerable cities to the urban heat-island effect, along with San Francisco, New York, Chicago and Seattle, according to an analysis by Climate Central, a New Jersey-based nonprofit that researches the effects of climate change. Its analysis found that 41 million people living in 44 cities face an urban heat-island effect of at least 8 degrees. Nine U.S. cities had at least one million people exposed to urban heat of 8 degrees or higher because of the local built environment.

To fight the heat, some cities are leveraging federal money and other incentives to persuade local builders to turn office buildings greener and cooler.

In Miami-Dade County, officials used federal funds to outfit 1,700 public housing units with new low-energy air-conditioning units. Local officials also offered a successful amendment to the Florida state building code requiring cool reflective roofs on all new commercial buildings beginning in 2024, and enrolled 150 structures in a voluntary energy-audit program to track improvements to cut energy use and keep temperatures down.

New York, Chicago, Philadelphia, Toronto and other cities are pushing green roofs with tax breaks and other incentives in an effort to lower energy bills and reduce ambient temperatures, according to Steven Peck, president of Green Roofs for Healthy Cities, a Toronto-based green-roof and -wall industry association. Peck said green roofs can be 30 to 40 degrees cooler than a similar-size blacktop roof, while also cutting waste heat from air-conditioning units.

In the Los Angeles neighbourhood of Pacoima, Torres says residents tell her the streets and playgrounds feel cooler since the reflective coating was completed in August 2022.

“The number-one thing that always comes up is the heat waves when you’re looking down the street,” Torres said. “They don’t see those anymore.”

The next step is to install reflective roofing material on a handful of homes as part of the neighbourhood cooling effort. “We want to keep stacking the solutions to overall create a cool community with multiple strategies,” Torres said.

Altering the urban landscape to adapt to extreme heat requires money and technical know-how, according to city leaders and academic experts. But they also acknowledge the need to keep people safe as global temperatures rise.

“Any one solution is not going to necessarily be able to address the entire problem, but by systematically applying solutions that work in each individual location, we can make a dent in the urban heat-island effect,” said David Sailor, professor of geographical sciences and urban planning at Arizona State University.