Lighter Roofs That Can Soothe Ever-Warming Urban Environments: Wouldn’t That Be Cool?

Patricia Derocher, COO, AlterEcho

Let’s check in on cool roofs—an answer to the urban heat island effect, whereby built-up areas in urban areas absorb and retain more of the sun’s heat than surrounding rural areas, primarily as a result of replacing green spaces, native vegetation, and other natural landscapes with intensive human development.¹ This phenomenon is especially pronounced in nights and evenings, after the sun’s heat has accumulated in the urban landscape over the course of the day, disproportionately impacting historically redlined areas which remain predominantly populated by Black, Indigenous, and People of Color (BIPOC) and/or low-income residents. The temperature differential between urban and wealthier suburban/rural areas can be quite profound—sometimes to the tune of a 24-degree Fahrenheit difference on a given day.² Indeed, the urban heat island effect is so distinct, some have argued that climate change observations are largely a function of earlier movements of weather stations from rural to urban areas over the course of the Industrial Revolution (spoiler alert: they’re not).³ The good news is that not only do we know how to address the urban heat island effect—at least on a regional level—but also some of the solutions have a high payoff for relatively little time and cost.

Chief among these interventions are so-called “cool roofs,” which are often as simple as repainting a black or otherwise dark-colored roof to white or another light color. In the 2010s, cool roofs gained extensive media attention, as cities from Los Angeles⁴ to New York⁵ started implementing cool roof programs, whether by requiring them in city building codes or providing funding for building owners to convert their roofs and employment and training for jobseekers to implement the conversions. Around that same time, cool roofs started gaining traction and coverage in the media, including industry and mainstream publications alike.⁶ While it seemed like cool roofs came out of nowhere, cities had been looking into the benefits for years, and the US Environmental Protection Agency published studies on the subject as long ago as 2008.⁷ The benefits are more than just environmental—especially for individual property owners and residents. By reflecting rather than absorbing the sun’s rays (and accompanying heat), light-colored roofs cool down cities and the surrounding areas, and it follows that they do so by cooling down each individual building, thereby saving on energy and HVAC costs, especially in warmer climates and in warmer months.⁸ Lower interior temperatures are also beneficial for people living or working in the buildings; so much better, in fact, that researchers believe that cool roofs could reduce mortality in future heatwaves (close to 250 lives could have been spared in London’s record-breaking summer of 2018, for example).⁹

Of course, virtually nothing is without tradeoffs, but in the case of cool roofs, most evidence indicates that they are limited. For instance, while heating costs may increase in cooler weather, research suggests that savings in the warmer months more than offset increased winter costs.¹⁰ There is also the theoretical possibility that replacing large swathes of the urban landscape with cool roofs, and thereby significantly reducing temperatures, could reduce evaporation and subsequent downwind rainfall.¹¹ While studies suggest that implementing cool roof-like technologies across enormous areas, such as deserts, could indeed have this effect, the consensus is that interventions on a city level are unlikely to have such negative externalities.¹²

These benefits, however, are not enough to persuade everyone. In recent years, a concerted lobbying effort has arisen, driven by entrenched interests in the roofing industry. Specifically, the move toward cool roofs has driven a move away from EPDM, a synthetic rubber material that is usually black or gray, and toward TPO, a white thermoplastic that is durable, flexible, and compliant with the large majority of cool roof requirements.¹³ EPDM manufacturers are not going quietly. In Denver, industry representatives successfully lobbied to water down the city’s cool roof ordinance, arguing in part that the city’s cold climate would lead to increased heating costs.¹⁴ (Denver’s average high in July is somewhere around 90 degrees Fahrenheit.¹⁵) In Tennessee, a prime example of a region that would benefit from cool roofs, lobbyists managed to get the state legislature to entirely repeal the state’s cool roofing requirement for commercial buildings.¹⁶ The EPDM industry hasn’t won every battle. In 2023, for example, Baltimore passed a comprehensive cool roof ordinance, notwithstanding lobbyists’ pressure.¹⁷ Nevertheless, an underlying truth remains: Even in the face of consistently, almost overwhelmingly, positive data about cool roofs, organized opposition still exists, and that opposition has been successful. It is, in other words, a lesson for environmental advocates, that part of being able to do their jobs and meet their missions
is the ability and willingness to communicate that vision to the public and policymakers alike, even
in the face of fierce opposition.

The cool roof movement is far from dead, however; just look at Baltimore and other cities that have maintained their programs, repeatedly demonstrating that cool roofs are effective and relatively easy to implement in climates across the United States. If people are persistent and willing to ask leaders to better explore scientific approaches that might ruffle some feathers along the way—whether it is pushing for cool roof requirements in new construction or participating in local action groups—it is entirely possible that sensible environmental solutions like these can be a practical way to cool a warming planet.

Lighter Roofs That Can Soothe Ever-Warming Urban Environments: Wouldn’t That Be Cool?

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