Cool Roofs: An Underused Tool for Reducing Heat

Cities and towns in the Mediterranean and the Middle East have long used white or light-colored roofs and walls to help keep people cool. Today, cities from Ahmedabad to Singapore are also turning to cool roofs to reduce urban heat and lower energy demand.

By reflecting rather than absorbing the sun’s energy, cool roofs can lower temperatures inside buildings and, when deployed citywide, reduce heat across entire neighborhoods.

It’s a relatively simple solution to extreme heat in cities, yet it can bring big benefits to public health and energy use. Lower temperatures can save lives: A 2024 study estimated that heat-related deaths in the record-breaking summer of 2018 could have been 32% lower if all London roofs had been cool roofs.

By lowering indoor temperatures, cool roofs also reduce the need for air conditioning, which, in turn, lowers energy use and associated emissions and household cooling bills. Additionally, they can be relatively inexpensive to install when included as part of roof replacement or repairs, since the building owner is already paying for materials and labor and installing a cool roof on a new building is comparable to the cost of a non-reflective roof.

The need is especially urgent in low-income and informal settlements, where homes can trap dangerous levels of heat and residents often have few options for mechanical cooling. In many parts of the Global South, homes are also workplaces, making extreme indoor heat a threat not only to health and sleep but also to people’s ability to earn a living. Women can face additional burdens because they are often responsible for caregiving and household work.  

Cities can use a range of strategies to reduce urban heat, including trees, other forms of shade and cool roofs. These strategies work in different ways: trees lower air temperature through evapotranspiration, while shade from trees and other structures reduces people’s exposure to solar radiation. Cool roofs, by contrast, lower both indoor and outdoor air temperature by reducing the amount of solar energy absorbed by buildings.

The most effective approach is often a combination of strategies, deployed where each makes the most sense. Unlike trees, which need soil, water and years to mature, cool roofs can provide cooling benefits as soon as they are installed. This is especially beneficial in dense, built-up neighborhoods with little room for vegetation.  

Yet despite being relatively simple to implement, cool roofs remain uncommon in cities around the world, according to a WRI analysis conducted earlier this year. We explore the opportunities for tackling extreme heat with cool roofs and how cities can put them into practice.

Cool Roofs, Cool Cities

When sunlight strikes a surface, some of its energy is reflected and some is absorbed.  Dark surfaces absorb a lot of radiation, which warms them and the surrounding air. Surfaces continue releasing that stored heat even after the sun goes down, contributing to higher temperatures in cities, especially at night. Light-colored and other reflective surfaces absorb less solar energy, reflecting more of it away and preventing it from becoming heat.

This quality, which scientists call albedo, is expressed as a value between 0 and 1 representing the fraction of incoming sunlight reflected by a surface. The difference between a conventional dark roof — made from heat-absorbing material like asphalt shingles or bitumen — and a cool roof is stark. Dark roofs can have albedo values as low as 0.04, meaning they absorb up to 96% of the sunlight that hits them. Cool roofs, by contrast, can achieve albedo values of 0.65 to 0.90, reflecting up to 90% of that energy rather than absorbing it and converting it to heat.

As more of a neighborhood is covered by reflective roofs, its overall albedo increases, reflecting more incoming sunlight and reducing the solar energy available to heat the built environment. A review of modeling studies from across the globe  found that a 0.10 increase in neighborhood albedo — equivalent to increasing reflectivity by 10 percentage points — could lower summer afternoon air temperatures by up to 0.6 degrees C (1.1 degrees F). Another study found peak reductions of up to 0.9 degrees C (1.6 degrees F) on the hottest days.  While it may not sound like much, every degree makes a difference. The 32% modeled reduction in deaths during the London heatwave was associated with an estimated decrease in air temperature of only 0.8 degrees C (1.44 degrees F).

Reducing the solar energy absorbed by buildings also leads to indoor cooling. A study in South Africa found that applying a reflective coating to the walls and roof of a building reduced indoor temperatures: The average daily high temperature was reduced by up to 4.3 degrees C (7.7 degrees F) and the average daily low temperature by 2.2 degrees C (4 degrees F). Minimum temperatures often occur at night, an important time for the body to recover from heat stress experienced during the day and tropical nights (minimum temperature of at least 20 degrees C/68 degrees F) are an increasingly severe health threat. More strikingly, the annual frequency of days on which indoor temperatures exceeded 40 degrees C (104 degrees F) — an extreme level of heat that can pose serious health risks — dropped from 19% to just 1%.

Reducing Costs

Because they lessen the need for air conditioning, cool roofs can cut energy demand and reduce energy costs for building owners and occupants. A study modeling the effects of cool roofs on energy consumption across six cities with a range of climates — Cairo, Hong Kong, Seoul, London, Los Angeles and São Paulo — found energy-use reductions between 67% and 87%.  And because they reflect heat rather than absorbing it, cool roofs expand and contract less than their darker counterparts, which can extend their lifespan.

What about places with cold winters? Cool roofs can increase heating needs by reflecting sunlight that could otherwise warm a building. But the effect is often smaller than you might expect: In winter, the sun is lower and days are shorter, so less solar energy reaches the roof. At higher latitudes, snow can also cover roofs for much of the winter, making the underlying roof color largely irrelevant. These factors can substantially reduce the winter heating penalty of cool roofs. 

A Big Opportunity

Roofs comprise 25% to 30% of a typical city’s urban surface area, making them one of the largest single surfaces available for heat management. Yet in the 78 cities WRI analyzed, cool roofs (see Methods below) made up, on average, less than 1% of roof area.  

By comparing maps of buildings and albedo, we found that the median roof albedo across cities was only 0.21, meaning that half the roofs reflect less than 21% of sunlight. Making roofs more reflective with shingles, tiles, membranes, or coatings could increase citywide albedos by 0.04 to 0.12 across these cities, making them up to 12 percentage points more reflective. 

Because many cities start with relatively low albedos, even seemingly modest increases can mean a significant rise in reflectivity. The relative change from cool roofs varies by city — from 22% more reflective than baseline conditions in Columbia, South Carolina, to 57% more reflective in Barranquilla, Colombia. In Fortaleza, Brazil, for example, fully realizing the city’s cool roof potential could increase albedo by 41% relative to baseline levels. 

These increases in roof reflectivity can translate into real temperature reductions. By applying generalized estimates of how much increased reflectivity can lower air temperatures, we estimate that cool roofs could lower overall air temperatures by approximately 0.25 to 0.7 degrees C (0.45 to 1.26 degrees F).  

In Boston, WRI’s Cool Cities Lab is taking a more comprehensive approach by directly modeling how changes in land cover affect air temperature. For an area near Boston Common, the model estimates that increasing albedo by 0.17 through cool roofs could lower air temperatures by about 0.7 degrees C (1.26 degrees F), consistent with the upper end of our broader estimates.

Commercial, industrial and other non-residential buildings can be particularly good candidates for cool roofs. They often have large, flat roofs that are well suited to reflective coatings, meaning a single building can make a meaningful contribution to reducing heat. Implementation can also become easier as policies such as building codes can reach many non-residential buildings at once, rather than relying on individual homeowners to opt in.

Among 33 of the 78 cities we analyzed, non-residential buildings made up just 10% of all buildings but accounted for 32% of total roof area. On average, prioritizing cool roofs on these buildings could yield more than 20% of a city’s total potential increase in albedo, a substantial impact. 

Related

Cities

Urban Trees: An Underused Tool for Keeping People Cool

Insights April 16, 2026

Cities

Most Cities Are Getting Hotter. Not All Residents Feel It Equally

Insights March 17, 2026

Cities

Cities Are Heating Up. Better Infrastructure Can Cool Them Down.

Insights July 16, 2025

Turning Opportunity into Action

Programs to implement cool roofs exist, but they remain niche. Using cool roofs more widely will require regulatory, market and financing structures that make them the default rather than the exception. Here are some practical recommendations that could help: 

• Requiring cool roofs for new buildings and roof replacements can be a cost-effective way to expand their use. Building codes are typically updated every three years, giving cities regular opportunities to strengthen these requirements. Existing standards, such as ASHRAE 90.1, provide benchmarks for roof reflectivity that cities can incorporate into their building codes. Increasingly, cities are choosing this route: In June 2025, Atlanta passed an ordinance requiring most roofs on new buildings, as well as replacement roofs, to include reflective coatings or materials.
• Use green building certifications to incentivize commercial and institutional building owners to adopt cool roofs. Green building certification schemes can encourage the use of cool roofs. LEED, a widely used rating system for green buildings, awards points for measures that reduce heat islands — areas where buildings, roads and other city surfaces absorb and retain heat, making built-up areas hotter than their surroundings — including highly reflective roofs. EDGE, a green building certification system created by the International Finance Corporation, also recognizes reflective roofs as a cost-effective way to reduce energy use and help buildings meet efficiency requirements.
• Make cool roofs the standard for government properties, especially for social housing and schools. Governments — often significant landholders — can also accelerate adoption by requiring cool roofs on buildings they own or manage, while directing those measures toward communities most exposed to heat. Singapore's Housing and Development Board, for instance, is extending heat-reflective coatings to all existing public housing estates islandwide by 2030.
• Involve communities and build trust. Cool roofs are more likely to be adopted when residents understand their benefits and have a role in shaping how they are implemented. Cities can build trust by working with community organizations, demonstrating the benefits of cool roofs and involving residents in identifying where they are most needed. In India, the Mahila Housing Trust has used model homes and temperature monitoring to demonstrate the benefits of reflective roofs, while training women as community leaders who help neighbors understand heat risks and bring local priorities to city governments. This community-driven approach has helped MHT scale cool roofs while building support for broader heat-resilience efforts.
• Make it easy and affordable for building owners to say yes. Installing cool roofs costs money. Rebates, utility incentives and financing options that let owners repay costs through energy savings can increase their attractiveness. Directories like the Database of State Incentives for Renewables & Efficiency in the U.S. can help building owners find financial support.
• Design projects to attract investment. Cities can increase their chances of securing financing for heat adaptation by designing projects to meet funders’ requirements. Programs like WRI Brasil's Urban Heat Solutions Accelerator, launched in September 2025, are supporting cities in developing heat-adaptation projects, including cool roofs, that can attract financing.
• Prioritize large buildings for maximum impact. Large commercial, industrial and institutional rooftops offer a high-impact entry point: fewer owners to engage, larger surfaces per intervention and faster citywide albedo gains. Converting the largest buildings — those in the top 10% by building footprint area, which are often low-slope — could achieve more than half the cooling benefit of converting every roof in each of 12 global cities, according to a 2026 analysis by WRI and Google.
• Use building-level data to identify low reflectivity roofs in priority areas. Urban reflectivity can now be mapped at higher resolution thanks to advances in remote sensing. Data recently published by Google Research that draws on the above analysis, maps rooftop reflectivity building-by-building across more than 50 cities, including London, Athens, São Paulo, Los Angeles and New York. The accompanying Heat Resilience Earth Engine App allows planners to identify the least reflective buildings in those cities and download data that can be used for local policy development.

Cool roofs won’t solve urban heat on their own. But few interventions offer so many benefits at once: they can cool buildings from the inside, reduce temperatures across neighborhoods and lower energy demand for air conditioning. They can be added when roofs are built, repaired or replaced, often without requiring additional land or major changes to how cities are built. Cities can also prioritize cool roofs in vulnerable communities where heat exposure is highest. The opportunity now is to make cool roofs a routine part of building codes, public investments and renovation decisions.