Imagine this: it's peak summer, your fan is running at full speed, and your electricity bill still looks like a phone number. Now imagine living under a dark, sun-soaked roof that turns your attic into an oven every single day. That was the reality for many low-income families in San Antonio, Texas, not long ago. Then the city tried a simple approach: swapping conventional dark roofs for light-colored, reflective ones. According to a 2018 University of Texas at San Antonio (UTSA) study of homes in the city's roofing program, during peak summer afternoons, attic temperatures dropped by an average of 10.1°F, while homes overall saw their Electricity Use Intensity fall by an average of 7.3%.A city that knows what real heat feels likeSan Antonio was the fourth fastest-growing city in terms of population increase in the United States from 2023 to 2024, according to the data provided by the U.S. Census Bureau, and 17% of its population live below the poverty level. The maximum heat index of 117 degrees Fahrenheit was registered in San Antonio on June 4, 2024, by the National Weather Service and is considered the highest in its history. In 2017, San Antonio pledged to follow the agreement set forth by the Paris Climate Agreement and in 2019 made it a citywide goal to become carbon neutral by 2050. For families that struggle to pay for the rent and buy food, a hot summer creates hard decisions about air conditioning. It is exactly what San Antonio has attempted to tackle through the roofing program "Under One Roof."What "Electricity Use Intensity" actually measuresThe 7.3% figure mentioned earlier refers to a specific metric called Electricity Use Intensity, or EUI, which measures energy consumption per square foot of building space over a set period, rather than a household's total electricity bill. The choice of this metric is preferred among researchers and building engineers since it provides a way of fair comparison of houses of varying size: while the bigger house will consume more total electricity in comparison with the smaller one regardless of the color of the roof, EUI eliminates this factor and shows the efficiency of the energy consumption. This fact, in turn, makes the results of the UTSA study relevant beyond San Antonio specifically. A percentage drop in EUI reflects a genuine efficiency gain from the roofing change itself, not just a coincidental drop in usage tied to smaller homes or milder weather during the study period.So, what exactly did they do?Beginning in 2016, the city started replacing the old roofs of homes of low-income families, senior citizens, veterans, and people living with disabilities. Instead of standard dark shingles, the city used Owens Corning reflective shingles in Shasta White, along with a radiant-barrier underlayment. In other words, these materials reflect sunlight rather than absorbing it. From a pilot project with a budget of $200,000 in a city council district in 2016, the program has expanded into a citywide project with a budget of $2.25 million expansion in 2018 and more than $5 million of joint public and private funding as of 2020. Under the program's official rules, the city places a five-year restrictive covenant on each property, requiring homeowners to keep owning and living in the home for five years afterward, which keeps homes affordable and protects families from being displaced.San Antonio's reflective roofs cut average electricity use by 7.3% (representative image). Image Credits: ChatGPTWhy a lighter roof makes such a big differenceIt's more than just a hunch in San Antonio. Dark roofs absorb solar rays, turning them into heat that transfers into the building below. Reflective roofs, by contrast, send more of that solar energy back to the sky, so less heat enters the building and the air conditioner does not have to work as hard. This basic mechanism has been documented elsewhere too: a Lawrence Berkeley National Laboratory study of two small buildings found measurable electricity savings after their roofs were painted white, though at a much smaller scale than San Antonio's residential program. That may be why San Antonio's own electricity use intensity, measured per square foot, decreased by 7.3% after the roof replacements.Heat isn't shared equally, and that's the bigger storyNot all neighborhoods receive the same amount of heat within the same city. A 2020 study published in the journal Climate by researchers Jeremy Hoffman, Vivek Shandas, and Nicholas Pendleton looked at 108 American cities and found that in 94% of them, neighborhoods affected by 1930s housing discrimination, known as redlining, are still warmer than other neighborhoods. Some cities had a temperature difference of up to 7°C (12.6°F), while the average difference between these neighborhoods was 2.6°C (4.7°F) across all 108 cities examined in the study. The same researchers point out that this gap is partly explained by less tree canopy and more paved, impervious surface in these neighborhoods. San Antonio's program targets high-heat, low-income areas, which makes its results especially relevant.Why this should matter to us, not just TexasCities around the world are becoming warmer, and low-income neighborhoods often feel it first because older buildings can have dark roofs that trap heat. San Antonio's approach offers a low-tech model that other cities could adapt. A lighter shingle or a coat of reflective paint isn't glamorous, but it can lower indoor temperatures and electricity bills for the people who can least afford them. San Antonio's project suggests that small-scale interventions can make a difference for those who need it most. In this case, at least, part of the solution really was as simple as picking a different color for a roof.