What is our assessment?

Our analysis concludes that the projected climate impact of using cool roofs on buildings is not large enough to be globally significant (>0.1 Gt CO₂‑eq/yr ). However, we consider it “Worthwhile” because it helps reduce electricity consumption in buildings, makes indoor spaces more thermally comfortable, and lessens the urban heat island effect.

What is it?

Using cool roofs reduces the amount of electricity needed to cool indoor spaces, thereby cutting GHG emissions from electricity generation. Cool roofs are generally defined as light-colored roofs designed to reflect more sunlight and transfer less solar energy into the interior compared to traditional roofs, thereby reducing cooling loads. Cool roofs can be achieved by applying coatings or using roofing materials with a high solar reflectance index (SRI), which results from high solar reflectance and thermal emittance. These properties ensure that surface temperatures on cool roofs remain substantially cooler than conventional roofs.

Does it work?

Using cool roofs can effectively reduce the amount of air conditioning needed to cool indoor spaces, though their potential to cut annual electricity use in buildings and resulting GHG emissions is minimal. Nonetheless, evidence from real-world applications demonstrates that the surface temperatures of cool roofs can be as much as 28–30°C cooler than conventional roofs on extremely hot afternoons. Other studies have shown that cool roofs can decrease indoor air temperatures by 2–3°C while simultaneously reducing surrounding outdoor air temperatures by about 10°C, thereby minimizing the urban heat island effect.

Several organizations are deploying initiatives to drive cool roof adoption as a passive cooling strategy in the building sector. For example, C40 Cities previously launched a cool roofs program across New York City. Over a six-year period (2009–2015), the initiative resulted in nearly 530,000 m² of building roof tops being retrofitted as cool roofs. As of 2023, the United States is estimated to have over 232 million m² of installed cool roofs. Recently, the Million Cool Roofs Challenge organized by the Global Cool Cities Alliance resulted in 1.1 million m² of additional cool roofs in 2022 across 10 countries, including Indonesia, Mexico, and Rwanda.

Some studies estimate that about 229 billion m² of roof space existed as of 2022. Given the existing building stock – and the fact that the bulk of projected new construction by 2050 is expected in regions with hot climates – the impact of this potential solution could grow.

Why are we excited?

There are several advantages to using cool roofs in buildings. First, it is cheap to implement, and the incremental cost of applying new coatings or selecting light-colored roofing materials during construction is often minimal compared to conventional roofs. Second, it is expedient as a cooling strategy when buildings are not mechanically air-conditioned or designed to be naturally ventilated. This is important because many countries in hot climates (where cooling is generally required for indoor thermal comfort more than heating) also lack access to reliable electricity, thereby necessitating the use of passive measures in building design. 

In addition, a recent analysis of 77 low- and middle-income countries determined that cooling systems are not readily available, sustainable, or affordable, especially for building applications, placing nearly 4 billion people at risk. Deploying scalable strategies such as cool roofs in buildings helps reduce exposure to these risks, which could lead to greater adoption and climate impact. Several studies have also shown that using cool roofs can help reduce indoor heat stress, especially in hot and humid environments. Others are exploring the concept of cool-colored roofs, where non-white roof materials can provide similar cooling effects while preserving aesthetic choice for building owners and developers. 

Why are we concerned?

Despite the advantages of using cool roofs as a potential climate solution, a few challenges exist. Some studies have shown that cool roofs can slightly increase heating loads during winter, especially in cold climates. However, other studies conclude that the increase is marginal and often inconsequential. Another concern is that cool roofs can produce glare as the incident sunlight is reflected. This could adversely impact building users if the buildings with cool roofs are surrounded by taller structures with daytime occupancy, such as offices, which is an increasing reality in urban spaces. Lastly, we found examples of pilot projects and resources for cool roofs, but could not find reliable datasets for a comprehensive assessment of their current impact. Addressing such data gaps could help drive cool roofs research, integration into industry practices and building codes, and, ultimately, greater adoption.

What is our assessment?

We found strong evidence that improving the thermal performance of building envelopes reduces heating and cooling loads. However, effectiveness typically varies depending on the climate. While the solution’s potential climate impact is likely globally significant (>0.1 Gt CO₂‑eq/yr ), data are not available to confirm this. We consider the solution “Worthwhile” because it can reduce energy use in both retrofits and new construction, and helps provide thermally comfortable indoor spaces.

What is it?

Improve Building Envelopes cuts GHG emissions from 1) burning fossil fuels to provide direct or indirect space heating and 2) generating electricity to power heating and cooling systems. Thermal performance upgrades to the envelope can be achieved through various design and material interventions. Our assessment focuses on thermal insulation added to the roofs, external walls, and floors of buildings (Conley et al., 2018; McDiarmid et al., 2024). Such upgrades give the envelope a higher thermal resistance, which means that the envelope reduces heat gain better in hot periods and minimizes heat loss in cold seasons (Brunoro, 2024; Gupta & Deb, 2023).

Does it work? 

Improving the thermal resistance of building envelopes is widely used and has been strongly demonstrated to enhance indoor thermal comfort and reduce GHG emissions. Since the emission intensity of fuels (International Energy Agency (IEA), 2024), and heating and cooling demand vary, so does this solution’s potential effectiveness. Various studies provide evidence of substantial heating energy savings. For example, work in China, Australia, Denmark, and Canada demonstrated that energy use reduced 17–62% due to added insulation in external walls and roofs (Abuseif et al., 2023; Jradi et al., 2017; Khayrullaev et al., 2026; Luo et al., 2024). Evidence also substantiates that envelope improvements significantly reduce cooling loads in warmer regions (Abdeen et al., 2024; Shittu et al., 2020). Despite the benefits, thermal improvements to building envelopes tend to have diminishing returns (Luo et al., 2024). For example, adding insulation to a building that has none will have a greater influence on reducing energy use than it would if some insulation is already present in the building, and even less if the envelope has a lot of insulation.

Why are we excited?

Improve Building Envelopes and other climate solutions that enhance buildings’ thermal performance (see Improve Windows and Glass) can offer both climate mitigation and adaptation benefits. First, they are applicable to existing buildings and new construction, help save heating and cooling energy costs, and improve occupant comfort. Studies show that the lower energy costs often offset the price of the improvements, with relatively low payback periods depending on the scope of intervention and insulation materials. For example, work in Türkiye, Italy, Morocco, and Saudi Arabia determined payback periods fewer than two years, reaching up to five or seven years (Akyüz, 2025; Dlimi et al., 2019; Makawi et al., 2025; Scrucca & Palladino, 2023). Second, improving the thermal performance of building envelopes increases resilience to heat waves and power outages in cold climates, especially for vulnerable populations like the elderly (Howden-Chapman et al., 2007; Ham et al., 2024, Jain 2024). Third, it could help reduce energy poverty, as well as noise infiltration and mold growth, improving the quality of lived spaces (Evin & Ucar, 2019; Janssen et al., 2023; Kattenberg et al., 2026). Finally, it reduces air pollution by lowering the demand for energy generated using fossil fuels (Levy et al., 2016).

Analysis of building energy codes across 88 countries shows that some regions (largely in colder climates, which are often high-income countries) have stringent or mandatory thermal performance requirements for building envelopes (World Bank, 2024). Thus, the greatest opportunities may be in countries that lack codes or minimum thermal performance requirements for building envelopes, or where such requirements are poorly implemented and enforced (Gaum, 2023; Gaum et al., 2026; World Bank, 2024). This highlights the potential for greater future adoption and ample opportunity to scale the solution’s climate impact, where it is globally significant.

Why are we concerned?

Improve Building Envelopes carries a few challenges and tradeoffs. First, it typically requires using more building material (e.g., to achieve better insulated walls or roofs). This often leads to buildings with greater embodied emissions, depending on the materials (Füchsl et al., 2022). Other climate solutions have explored alternatives which could potentially alleviate this concern (see Deploy Alternative Insulation Materials and Improve Other Building Materials). Second, insulation may be easily added to a new building during construction but can require extensive renovations in existing buildings such as opening up walls, and could include losing living space in the process (Conley et al., 2018). If not done well, adding insulation can create new problems with moisture control (Craven & Garber-Slaght, 2014). This is particularly significant in regions (especially high-income countries in cold climates) where the rate of new construction has slowed compared to that of low- and middle-income countries (IEA, 2023) and building energy codes already specify high thermal resistance requirements. In such cases, greater heating and cooling energy efficiency improvements in buildings may be derived from implementing other solutions such as Use Heat Pumps. Third, building energy codes can either be mandatory or voluntary and are not always enforced effectively (Gaum et al., 2026). This means that buildings may not always be developed with the specified envelope requirements, which could limit the solution’s adoption. Despite these challenges, the solution likely has a climate impact that is globally significant (>0.1 Gt CO₂ eq/yr). However, our analysis could not arrive at a conclusive climate impact estimate because the data required to determine current adoption and estimate future adoption scenarios are severely limited.