In a unanimous vote on June 2, the Atlanta City Council approved a significant ordinance requiring all new and replacement roofs to be built with light-colored, reflective materials, commonly known as “cool roofs.” The ordinance, set to take effect in one year, is part of a growing effort to reduce the city’s vulnerability to extreme heat.

Georgia Tech researchers say the new policy marks a major step forward in climate adaptation, especially for heat-vulnerable communities, and could help position Atlanta as a national leader in urban resilience.

How Cool Roofs Can Help Hotlanta 

”On any given summer afternoon, temperatures in Atlanta’s intown neighborhoods can be as much as 15 degrees Fahrenheit higher than in the city’s most forested areas,” said Brian Stone, professor in the School of City and Regional Planning and associate director of Georgia Tech’s Center for Urban Resilience and Analytics.

That spike is partly due to the urban heat island effect — a phenomenon driven by heat-trapping materials like concrete, asphalt, and dark rooftops, combined with the loss of trees and natural landscapes. The impacts are not just uncomfortable — they’re dangerous. Extreme heat is now one of the deadliest forms of weather in the U.S., with disproportionate effects on low-income communities, elderly residents, and those without access to air conditioning.

According to Patrick Kastner, assistant professor in the School of Architecture, rooftops are key contributors. “A major driver [of heat buildup] is dark, heat-absorbing material that stores solar energy during the day and then re-radiates it at night. If you look at a satellite image, for most of the day rooftops have more exposure to the sun than building facades — so the material choice there matters a lot.”

The Power of Reflective Roofs — and Trees

Stone and his students conducted modeling that found that widespread adoption of cool roofs across Atlanta could lower summer afternoon temperatures by more than 2 degrees Fahrenheit in many neighborhoods. That’s comparable to findings in other global cities like London, where cool roofs have reduced average temperatures by up to 2 degrees Celsius (3.6 F).

But cool roofs are only one part of a broader urban cooling strategy. In the same study, Stone’s team showed that planting trees in just half of Atlanta’s available planting zones could yield an even more dramatic effect, reducing temperatures by 4 F or more in some areas.

“Cool roofs are highly effective, but pairing them with increased urban tree cover would multiply the benefits, especially for neighborhoods currently lacking shade,” Stone said.

Equity and Energy Impacts

Atlanta’s ordinance requires cool roofing materials on new commercial construction and when existing commercial roofs are replaced. While that may sound like a technical design tweak, Stone emphasized its equity implications.

“Residents in South and West Atlanta, where tree canopy is sparse, and energy costs take up a larger share of household income, stand to gain the most,” Stone said. “When a cool roof is installed as part of a required roof replacement, those households will see meaningful reductions in cooling costs month after month.”

Kastner added that cool roofs could ease pressure on the electrical grid, lowering peak energy demand required for cooling during extreme heat and possibly reduce the risk of outages.

Durability, Maintenance, and Design Trade-offs

Stone noted that cool roofs tend to extend the life of roofing materials by limiting thermal degradation. However, he and Kastner also flagged some trade-offs.

For example, highly reflective coatings can create glare, especially on sloped roofs near neighboring buildings. The ordinance accounts for this by setting different standards for flat and pitched roofs. Maintenance is another consideration: over time, reflective coatings may degrade or become dirty, requiring periodic cleaning to maintain performance.

“Aesthetics and material compatibility may also challenge adoption when it comes to historic buildings or for roofs already outfitted with solar panels,” Kastner said. “But advancements in roofing technology, including high-performance materials that aren’t plain white, offer more flexible options than ever before.”

A Cool Roof Policy With National Impact

While cities like New York and Chicago have implemented cool roof programs for over a decade, Atlanta’s proposed ordinance is one of the most comprehensive in the country — applying to all roof types, not just flat industrial ones.

“Atlanta is steadily emerging as one of the most climate-resilient cities in the U.S.,” said Stone, pointing to the city’s urban forest and growing network of floodable parks as complementary resilience strategies. “Adding a best-in-class cool roofing ordinance to that portfolio is a bold step forward.”

And it could spark innovation across the region.

“Georgia Tech is uniquely positioned to help advance climate-resilient design,” Kastner said. “From research on advanced coatings to urban planning tools that target the most heat-vulnerable areas, we’re bringing science and policy together to shape cooler, healthier cities.”

As the planet warms, changing weather patterns are only one effect. Warming air is often more toxic, leading to asthma and even heart attacks. A better understanding of these air quality changes can help society mitigate their consequences. Georgia Tech researchers are innovating ways to study air quality — beginning with prehistoric insights and zooming all the way to satellites in our orbit.

Read more »

Lithium-ion batteries power everything from electric cars to laptops to leaf blowers. Despite their widespread adoption, lithium-ion batteries carry limited amounts of energy, and rare overheating can lead to safety concerns. Consequently, for decades, researchers have sought a more reliable battery. 

Solid-state batteries are less flammable and can hold more energy, but they often require intense pressure to function. This requirement has made them difficult to use in applications, but new research from Georgia Tech could change that. 

The research group of Matthew McDowell, professor and Carter N. Paden Jr. Distinguished Chair in the George W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering, has designed a new metal for solid-state batteries that enables operation at lower pressures. While lithium metal is often used in these batteries, McDowell’s group discovered that combining lithium with softer sodium metal results in improved performance and novel behavior.

McDowell and his collaborators presented their findings in the paper, “Interface Morphogenesis with a Deformable Secondary Phase in Solid-State Lithium Batteries,” published in Science on June 5.

Stackable Solution

Lithium-ion batteries have been the industry standard because they combine compact size, reliability, and longevity. However, they contain a liquid “electrolyte,” which helps lithium ions move in the battery but is also flammable. In solid-state batteries, this electrolyte is a solid material that is less flammable. The challenge is that when the battery is used, the lithium metal in the battery changes its shape, potentially losing contact with the solid electrolyte, which degrades performance. A common way to ensure the metal doesn’t lose contact is to apply high pressure to these batteries.

“A solid-state battery usually requires metal plates to apply this high pressure, and those plates can be bigger than the battery itself,” McDowell said. “This makes the battery too heavy and bulky to be effective.”

The researchers, led by Georgia Tech research scientist Sun Geun Yoon, sought a solution. The solid-state batteries would still require some pressure to function, but they found that by also using a softer metal, less pressure is required. The researchers decided to pair the commonly used lithium metal with a surprising element: sodium. 

“Adding sodium metal is the breakthrough,” McDowell noted. “It seems counterintuitive because sodium is not active in the battery system, but it’s very soft, which helps improve the performance of the lithium.”

How soft can sodium be? In a controlled environment, a person could stick their gloved finger into sodium metal and leave an imprint. 

From Biology to Battery

To understand the enhanced performance of their battery, the researchers borrowed a concept from biology called morphogenesis. This concept explains how tissues or other biological structures evolve based on local stimuli. Morphogenesis is rarely seen in materials science, but the researchers found that the combination of lithium and sodium behaves according to this concept. 

McDowell’s research group has been working on applying morphogenesis to battery materials as part of a project funded by the Defense Advanced Research Projects Agency in collaboration with several other universities. Their battery is among the first viable demonstrations of this concept — effectively, the sodium deforms readily at the low pressures needed for solid-state batteries to function. 

Battery Boon

The possibilities of a viable, smaller solid-state battery are vast. Imagine a phone battery that could last much longer or an electric vehicle that could drive 500 miles between charges. With this in mind, McDowell and his team have filed for a patent for this battery system.

While solid-state batteries still have some way to go before commercial use, results like these could mean that solid-state batteries can compete with lithium-ion. McDowell’s lab continues to experiment with other materials to further improve performance. 

Funding from the Defense Advanced Research Projects Agency.

Sarah Roney studies oysters — and coastline restoration, wave energy, erosion, blue crabs, and predator chemical cues. A Ph.D. candidate in Georgia Tech’s Ocean Science and Engineering program and a Brook Byers Graduate Fellow, Roney has spent the past four years studying how strategically placing oyster reefs along Georgia’s coast could yield significant benefits.

Georgia’s coastal ecology is being degraded by several threats. Erosion caused by a combination of traffic from water vessels, sea-level rise, increased storm intensity and frequency, and property development, are negatively impacting both coastal living systems and the state’s economy. Tourism, agriculture, recreation, fisheries, property development, and trade (through the Port of Savannah) all rely on healthy coastlines.

Roney’s interest in coastal ecology and oysters drew her to focus her doctoral thesis on this problem. She divided her project into two parts. The first involved understanding how much oyster reefs reduce the erosion caused by wave energy (ship wake) from water traffic. The second part demonstrated a method for making young oysters resistant to predation — increasing their survival rates and that of the reef colonies they call home. Roney focused her research on two major waterways in the Savannah area. The Intracoastal Waterway and the South Channel of the Savannah River, which leads to the Port of Savannah, are both subject to heavy ship and boat traffic. According to Roney’s collaborators at Georgia Tech, 65% of the wave energy lashing the South Channel’s shores is generated by cargo vessels navigating to and from the Port of Savannah. Because traffic along the Intracoastal Waterway is subject to very few speed restrictions, there is plenty of erosive wave energy there also, even though the vessels are almost exclusively small.

Roney chose one site in each waterway to place her reef structures. Mesh bags of oyster shells were seeded with young oysters by personnel working at a University of Georgia Shellfish Research Lab. Roney created her reef structures by placing these bags in a row 15 to 20 meters long and a meter wide. Once established, Roney found that constructed reefs dissipate 40% of the wave energy before it reaches the marsh edge. “This is an experimental pilot study, so the reefs are on the smaller side,” Roney explained. “Reefs as large as 100 meters long may be necessary to protect certain areas — which sounds like a big investment. But because these are living shorelines, they are self-sustaining, and will keep growing and building on themselves.”

Establishing oyster reefs can be challenging, however, because predators feast on young oysters. Blue crabs are among the most voracious. The second part of Roney’s research was to develop a method that improves adolescent oysters’ chances of surviving to adulthood — when they infrequently succumb to predation. Roney and her collaborators at Georgia Tech identified two compounds found in blue crab urine, called trigonelline and homarine, that induce young oysters to devote more energy toward growing their shells, which become 25-60% stronger than normal. Roney found that after four to eight weeks of exposure to these compounds in hatchery conditions, their overall survival rate improved by 30% once placed in a reef. Her method not only helps constructed reefs to become established, but can also help existing oyster reefs become more resilient by slowing, or reversing, their decline.

While coastal restoration projects are not new in Georgia, the techniques Roney developed are relatively novel. Conventional shoreline restoration projects involve excavation, placing gravel beds, and extensive plantings, mostly with sea grasses. Roney has shown that using living shoreline strategies are less intensive and less expensive to establish and are also effective in reducing wave energy in waterways vulnerable to erosion. Perhaps most significantly, these techniques also restore the foundational functions of the ecosystems in which they are placed. The reefs become nurseries, incubating fish, bird, plant, and crustacean species.

Roney engaged several partners over the four years of her project, many in the communities along Georgia’s coast. Over 35 coastal residents, business owners, citizen scientists, and students volunteered their time and resources to help Roney’s project succeed. Roney said, “I think the most rewarding part of the project has been seeing how many people are truly invested in our coastal resources and want oyster reefs to thrive.”

This project isn’t likely to end once Roney earns her PhD. For living shoreline restoration practices to catch on, several other problems require investigation. Roney wants to devise a way to slowly release predator cue compounds into the water near oyster reefs, so baby oysters won’t need to spend as much time in a hatchery before being placed in the wild. Perfecting such a time-release mechanism could also help rejuvenate naturally occurring oyster reefs under threat from erosion and predation.

Roney also wants to try combining constructed oyster reefs with oyster farms, integrating one of the most sustainable ways that protein can be raised with living shoreline restoration. “As the mariculture industry in Georgia grows, there will be lots of opportunities to investigate the possible intersections between the ecological benefits, engineering benefits, and cultural benefits of oyster farming,” Roney said. “Food might be a continuous byproduct of shoreline restoration projects.”

Roney’s research shows that economic development and preserving, or even regenerating, diverse and productive coastal habitats for future generations don’t have to be mutually exclusive propositions.

Roney’s thesis advisor is Marc Weissburg, Brook Byers Professor in the School of Biological Sciences. Kevin Haas, professor in the School of Civil and Environmental Engineering, helped Roney map and measure the hydrodynamic forces in her study zones. The Coastal Resources Division of the Georgia Department of Natural Resources, the National Parks Service, and the University of Georgia Marine Extension and Georgia Sea Grant program provided access, permitting, funding, and resources.