Dark roofs and urban heat are physically linked: a conventional dark asphalt or membrane roof reflects only about 5 to 10 percent of sunlight, so its surface can climb to 150 to 190 degrees Fahrenheit on a 90-degree afternoon, roughly 50 to 70 degrees hotter than the surrounding air (Lawrence Berkeley National Laboratory Heat Island Group, 2024). Multiplied across the roughly 20 to 25 percent of urban land that rooftops cover, that absorbed heat helps push city air 1 to 7 degrees Fahrenheit above nearby rural areas during the day (U.S. EPA, 2024). This report quantifies how roof color drives city temperatures and how much a switch to reflective roofs could cut heat-related deaths.
Headline finding: In peer-reviewed modeling studies, converting a city’s dark roofs to reflective (high-albedo) surfaces lowered peak heatwave air temperature by up to about 3 degrees Celsius and reduced urban heat-related mortality by an estimated 5 to 32 percent, depending on the city, its baseline roof reflectance, and its climate. The single largest modeled outcome is New York City, where citywide roof-albedo increases were associated with roughly 219 avoided heat deaths over a decade (about 10 percent of the heat toll), per urban-albedo mortality modeling summarized below.
How hot does a dark roof actually get?
A dark roof gets far hotter than a reflective one because color governs albedo, the share of sunlight a surface bounces back. Dark roofing typically has an albedo near 0.07, meaning it absorbs about 93 percent of incoming solar energy, while a white or coated cool roof can reflect up to 80 percent (albedo 0.8) (LBNL Heat Island Group, 2024). That difference shows up directly at the surface.
At solar noon on a clear day, LBNL measured conventional roofing running about 40 degrees Celsius (72 degrees Fahrenheit) hotter than the air, while high-albedo coatings sat only about 5 degrees Celsius above air temperature (LBNL Heat Island Group, 2024). The EPA reports conventional roofing can reach as much as 66 degrees Fahrenheit above surrounding air on a warm day (U.S. EPA, 2024).
| Roof surface | Approx. solar reflectance (albedo) | Sunlight absorbed | Typical peak surface temp on a 90°F day |
|---|---|---|---|
| Black asphalt shingle / dark membrane | ~0.05 to 0.10 | ~90 to 95% | 150 to 190°F |
| Medium / weathered gray roof | ~0.15 to 0.25 | ~75 to 85% | ~120 to 150°F |
| Los Angeles average rooftop | ~0.17 | ~83% | city-wide mean |
| White or reflective cool roof / coating | ~0.65 to 0.80 | ~20 to 35% | ~95 to 120°F |
Sources: LBNL Heat Island Group (2024); U.S. EPA Heat Islands (2024). Surface temperatures vary with slope, ventilation, humidity, and cloud cover.
How roof color feeds the urban heat island
Roof color scales into a city-wide effect because rooftops are one of the largest surfaces in the built environment. Roofs account for roughly 20 to 25 percent of urban land cover (Akbari et al., EPA Urban Heat Island Pilot Project, 2003), so the heat they absorb and re-radiate is a meaningful share of the total urban heat budget.
The measured result is the urban heat island. U.S. cities average 1 to 7 degrees Fahrenheit warmer than outlying areas during the day and 2 to 5 degrees Fahrenheit warmer at night (U.S. EPA, 2024). The LBNL Heat Island Group was the first to show that raising roof albedo at the neighborhood scale is associated with lower near-surface air temperature, not just cooler roof surfaces (LBNL Heat Island Group, 2024).
Los Angeles illustrates the room to improve: its average rooftop albedo is only about 0.17 (LBNL, 2024). Simulation reviews find that applying cool roofs city-wide can lower average ambient air temperature by 0.3 to 3 degrees Celsius, and that raising roof albedo to about 0.7 produces a cooling effect comparable to converting half a city’s roofs to vegetated green roofs (Environmental Research Letters, 2014).
The heat-death connection
Extreme heat is the deadliest weather hazard in the United States, and the toll is rising. CDC WONDER records show heat-related deaths climbed from 1,156 in 2020 to 2,415 in 2023, then held near 2,394 in 2024, with 21,518 heat-related deaths logged from 1999 through 2023 (CDC WONDER, analyzed 2024 to 2026). In 2023 alone there were about 119,605 emergency-department visits for heat-related illness, 92 percent of them between May and September (CDC, 2024).
The burden is uneven. From 2019 to 2023, age-adjusted heat mortality rose fastest among Hispanic (average annual increase about 28.7 percent) and non-Hispanic Black (about 28.6 percent) populations, versus about 5.8 percent among non-Hispanic White populations (CDC WONDER analysis, 2025). Dense, low-tree, dark-surfaced neighborhoods tend to run hotter, which is where roofing intersects with public health.
Ranked: modeled heat-mortality reduction from reflective roofs
The table below ranks cities by the modeled reduction in heat-related deaths attributable to raising roof reflectance, drawn from peer-reviewed urban-albedo and cool-roof mortality studies. These are modeled estimates under specific heat scenarios, not observed death counts, and they assume wide or full roof conversion.
| City / region | Modeled heat-death reduction | Scenario | Source |
|---|---|---|---|
| London, UK | ~32% (about 249 of an estimated 655 to 920 deaths avoided) | Cool roofs on all roofs, summer 2018 heatwave | Nature Cities (2024) |
| Brussels, Belgium | up to ~25% of heat deaths preventable | Cool roofs, July 2019 heatwave | European cool-roof modeling (2018 to 2021) |
| West Midlands, UK | ~25% of UHI-linked heat mortality | Cool roofs during a heatwave | Macintyre & Heaviside, Environment International (2019) |
| Los Angeles, CA | ~21% (about 22 lives / 10 years) | Increased urban albedo | Urban-albedo mortality modeling |
| New York, NY | ~10% (about 219 lives / 10 years) | Increased urban albedo | Urban-albedo mortality modeling |
| Baltimore, MD | ~5% (about 32 lives / 10 years) | Increased urban albedo | Urban-albedo mortality modeling |
New York shows the largest absolute number of avoided deaths because of its population size, while Los Angeles shows a larger percentage reduction, reflecting its hot, sunny climate and low baseline roof albedo. Percentages and climates are not directly comparable across studies, which use different heat scenarios and methods.
What a reflective roof physically changes
A reflective roof cuts the heat entering both the building and the air above it. Cool roofs can stay 50 to 60 degrees Fahrenheit cooler than conventional dark roofs during peak summer conditions (EPA / DOE ENERGY STAR data, 2024), which reduces the re-radiated heat that warms the surrounding air.
At the city scale, cool roofs modeled across an urban area lowered daytime center-city air temperature by about 0.5 degrees Celsius on average and up to roughly 3 degrees Celsius during heatwaves (Nature Cities, 2024; Environmental Research Letters, 2014). Building-level cooling energy is a separate benefit: swapping a dark roof for a reflective one can cut annual air-conditioning energy use by about 5 to 20 percent (LBNL / DOE, 2024). One caveat is season: reflective roofs give up a small amount of useful winter heat gain, though studies find the winter penalty is minor relative to the summer mortality benefit in most temperate and hot climates.
Methodology
This report synthesizes primary data from the Lawrence Berkeley National Laboratory Heat Island Group (albedo and surface-temperature measurements, Los Angeles rooftop albedo), the U.S. EPA Heat Islands program (urban-rural temperature differentials, conventional-roof heat gain), the U.S. CDC WONDER mortality database (heat-related death counts and disparities, 1999 to 2024), and peer-reviewed cool-roof mortality modeling published in Nature Cities (2024), Environment International (2019), and Environmental Research Letters (2014). Surface-temperature ranges are drawn from field measurements and industry testing on a nominal 90-degree-Fahrenheit day. The ranked table aggregates modeled mortality-reduction estimates; figures were normalized to a common format (percent reduction and, where reported, avoided deaths over the study period) but not re-computed. Every statistic is cited inline to a named source and year.
Limitations
The mortality figures are modeled outcomes under specific heat scenarios and roof-conversion assumptions, not observed death counts, and they should be read as directional rather than exact. Studies differ in method, baseline albedo, climate, and the fraction of roofs converted, so cross-city percentages are not strictly comparable. City-scale air-temperature reductions of 0.3 to 3 degrees Celsius depend heavily on how widely reflective roofs are deployed. Reflective roofs carry a modest cold-season heating penalty in some climates. Field surface temperatures vary with slope, color, ventilation, aging, soiling, and weather. None of these figures should be treated as a guarantee for any single building or jurisdiction.
For the building-energy side of this question, see our companion research report on how much reflective roofs save by climate. For material and color context, see black shingles and heat, the most popular roof colors in America, sustainable roofing options including cool roofs, and green roof cost and load.
Frequently asked questions
Do dark roofs really make cities hotter? Yes, measurably. Dark roofs reflect only about 5 to 10 percent of sunlight and can reach 150 to 190 degrees Fahrenheit, re-radiating heat into the air. Because roofs cover roughly 20 to 25 percent of urban land, this contributes to the urban heat island that leaves U.S. cities 1 to 7 degrees Fahrenheit warmer than rural areas by day (EPA, 2024; LBNL, 2024).
How much cooler is a reflective roof than a dark roof? A reflective cool roof can stay 50 to 60 degrees Fahrenheit cooler at the surface than a conventional dark roof during peak summer conditions. At solar noon, LBNL measured dark roofing about 40 degrees Celsius above air temperature versus only about 5 degrees Celsius for high-albedo coatings (LBNL, 2024; EPA/DOE, 2024).
Can cool roofs actually reduce heat deaths? In modeling studies, yes. Widespread cool-roof adoption was associated with an estimated 5 to 32 percent reduction in urban heat-related mortality, including about 249 avoided deaths in London’s 2018 heatwave and roughly 219 over a decade in New York (Nature Cities, 2024; urban-albedo modeling). These are modeled estimates, not guaranteed outcomes for any one city.
How much can cool roofs lower city air temperature? City-wide cool-roof deployment lowered modeled daytime center-city air temperature by about 0.5 degrees Celsius on average and up to roughly 3 degrees Celsius during heatwaves. Simulation reviews put the general range at 0.3 to 3 degrees Celsius, depending on how many roofs are converted (Nature Cities, 2024; Environmental Research Letters, 2014).
Are heat deaths in the US actually rising? Yes. CDC WONDER data show heat-related deaths rose from 1,156 in 2020 to 2,415 in 2023, staying near 2,394 in 2024, with 21,518 recorded from 1999 through 2023. Increases have been steepest among Hispanic and non-Hispanic Black populations from 2019 to 2023 (CDC WONDER analysis, 2024 to 2026).
Do reflective roofs cause a winter heating penalty? A small one. Reflecting sunlight reduces useful winter solar heat gain, which can slightly raise cold-season heating demand. Peer-reviewed studies find this winter penalty is minor relative to the summer heat-mortality benefit in most temperate and hot climates, though the balance shifts in very cold regions.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.