Buildings

Construct zero-carbon buildings

Understanding carbon emissions from building construction

The construction of new buildings contributed 10% of global carbon dioxide (CO2) emissions in 2022. These emissions, sometimes referred to as “embodied emissions,” come from the construction process itself as well as the emissions associated with producing the materials used in buildings, including cement and steel, aluminum, bricks and glass. Analyzing these emissions reveals connections between buildings, the power system (particularly the supply of energy for material manufacturing), the industry system (particularly the manufacturing of cement and steel for use in buildings) and the circular economy system (particularly the reuse of building materials and waste).

Strategies to reduce embodied emissions from building construction

There is an opportunity to maximize the impact of decarbonizing the material itself to make progress in reducing emissions from heavy industry and the embodied emissions of buildings. At the same time, reducing the amount of steel, cement and other building materials needed for a particular building will also help reduce embodied emissions from buildings. Both approaches, as well as using alternative materials, will be necessary to drive rapid declines in embodied emissions.

The importance of decarbonizing building operations

Much of the current effort to decarbonize buildings is focused on either reducing operational energy use or decarbonizing equipment, and both are important. As a result of the lack of focus on embodied emissions, data to assess progress is sparse. Many actors involved in the construction and operation of buildings can help reduce embodied emissions: chiefly, architects and engineers in the design phase, property owners and manufacturers in the procurement phase and developers and construction companies in the construction and demolition phases.

Data Insights

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Embodied emissions in new buildings

“Embodied emissions” come from the materials used in buildings and the process of constructing them. Reducing embodied emissions in buildings is fundamental to decarbonizing the sector and contributing to change in other sectors.

Most of the carbon emissions that can be attributed to buildings come from day-to-day operations, meaning from the energy used to power services like heating, lighting and cooling. The rest of emissions associated with buildings are known as “embodied emissions,” which come from the construction industry and the production of key materials — cement, steel, aluminum, bricks and glass — used in the construction of buildings. Embodied emissions accounted for 3.7 Gt of carbon dioxide (CO2) emissions in 2022, or around 10% of global energy and process emissions. The World Green Building Council calls for a 40% reduction in embodied emissions in new construction by 2030 and net-zero embodied emissions by 2050.

The generation of embodied carbon emissions refer to the emissions generated during a building’s life cycle outside of its operations. This can be broken into three key stages. The first is the construction stage, in which emissions come from the production of materials used, the transportation of these materials and construction equipment, the energy needed to run construction machinery and the waste that is generated. Then, in  the operation stage, emissions are produced from retrofitting, including replacing insulation and upgrading equipment and other components. The final stage is demolition, with emissions coming from the transportation and use of machinery as well as the waste from this process.

Tackling embodied emissions will require a “Build nothing, build less, build clever, build efficiently, and minimize waste” approach. This means considering the necessity of construction and emphasizes retrofitting and repurposing existing buildings before constructing new ones.

When buildings are constructed, it is also important to design them in a way that improves the reusability of the materials (known as designing for disassembly) and reduces the emissions associated with the demolition process. During construction, it is critical to improve material efficiency by optimizing the amount of materials used (known as lean construction) and reduce transport emissions by using local and zero-carbon materials where possible.

Currently, it is difficult to track embodied emissions due to a lack of centralized and methodologically consistent data. Collecting more data on buildings and conducting standardized life cycle assessments (LCAs) can help fill this gap. Based on such LCAs, Circular Ecology's ICE Database provides data on embodied carbon (in kilograms of carbon dioxide equivalent, kgCO2e, per unit) for materials such as steel, aluminum and glass. While this database does not contain direct data for buildings, it can serve as a starting point for calculating the embodied carbon of buildings.

In the United Kingdom (UK), a suite of initiatives helps to cover these data gaps for the UK context, including the Net Zero Whole Life Carbon Roadmap (from the UK Green Building Council), the Net Zero Carbon Building Standard (in development by a coalition of industry organizations) and the Built Environment Carbon Database (a free, collaborative resource for collecting and sharing data).

Average lifetime of buildings

Safely extending the average lifetime of buildings can be done through design and retrofits, which helps to maximize the use of existing structures and avoid additional embodied emissions from new construction.

Several factors determine the lifetime of buildings (the amount of time a building is operating): the type of materials used and the durability and lifespan of those materials, effective construction management, structural and architectural design choices, the type of climate and local environment (specifically, extreme heat or humidity), properly evaluated extensions or renovations (designing for adaptability), safety considerations and maintenance.

There is no global dataset to track progress on this indicator. At the national level, censuses and surveys can help build this data. For example, information on the construction year of buildings is collected by the American Housing Survey (AHS) in the United States and by the EU Building Stock Observatory in the European Union.

Action is needed to extend the lifetime of buildings and deliver reductions in embodied emissions. First, new buildings should be designed and constructed with the long term in mind — this means considering the materials used and designing buildings for multiple uses. Second, increasing the rate of deep retrofits of the existing building stock is crucial to prolonging the life of existing buildings and meeting net-zero emissions goals.

Despite anticipated building stock and floor area growth, more than two-thirds of current buildings will still be here in 2050 and the retrofit challenge is immense: currently, less than 1% of existing buildings are renovated each year to improve energy efficiency.

Reuse and recycling rate of construction and demolition waste

The reuse and recycling of construction and demolition waste can help reduce the need for virgin materials such as concrete and steel for new buildings, as well as the emissions that would be generated from producing these materials.

The construction sector generates one-third of the world's solid waste. Increasing the reuse and recycling of construction and demolition waste (CDW) would help reduce the need for virgin materials such as concrete and steel for new buildings.

Many developed countries have already achieved a high recovery rate, but some developing countries are still struggling with the large amount of CDW. CDW from buildings can be particularly difficult to recycle because it can include a mix of non-hazardous waste like concrete and brick and hazardous waste such as insulation and wires.

There is no publicly available global dataset or target for the reuse and recycling rate of CDW. The European Union, however, set a target to achieve a 70% recovery rate of CDW by 2020.

Unfortunately, it is difficult to assess progress toward this target with the available data, which includes not only reuse and recycling, but also backfilling, the use of materials to fill holes in excavated areas and building foundations. A 2017 report commissioned by the European Union proposed a 70% recycling rate target for 2030 that excludes backfilling. Countries such as Denmark are also attempting to make reuse and recycling of CDW easier by encouraging sorting of wastes before disposal.

Enablers and barriers

We also monitor change by tracking a critical set of 9 enablers and barriers enabler or barrier that can help spur or impede change. Explore the data and learn about key actions supporting systems change.

Investments in research and development of alternative building materials

Investment into researching and developing alternative building materials, together with using existing materials in innovative ways, is necessary to increase the sustainability of the construction sector and reduce its environmental impact.

Developing new building materials and using existing materials in innovative and more efficient ways are crucial to mitigation and adaptation goals and to increasing the sustainability of the construction industry. Investment in research and development (R&D) around building materials will be necessary to achieve these goals, though at the moment there is no data to track the current level of such investment or how much is needed. The OECD statistics database has data for R&D spending for different industries but covers only OECD countries.

These developments are not applicable to the informal housing sector; however, progress is being made in developing countries and for the informal housing sector by the campaign Roof Over Our Heads (ROOH). The campaign works to increase the resilience of urban housing and infrastructure, particularly in the informal housing sector, while also achieving low carbon aims.

Currently, research is underway to create climate adaptive building shells, which respond to the external environment to support energy goals by helping to reduce demand — for example, by providing shade or heating with the sun — while at the same time maintaining a comfortable indoor experience.

Similarly, supercool and smart materials can help buildings stay cool even in hot temperatures, which also reduces the amount of cooling they require. Upgrading existing insulation materials and using them more efficiently can also support goals of improving energy efficiency while reducing embodied carbon.

Share of new buildings that undergo a whole life carbon assessment

Whole life carbon assessments look at the emissions produced over a building’s lifetime, including embodied emissions from construction and demolition and operational emissions from day-to-day use.

Life cycle assessments (LCAs) are a tool used to assess a system or product (or in this case, a building) for its impact on the environment. Whole life carbon assessments (WLCAs) look specifically at the carbon emissions produced over a building’s lifetime, including embodied emissions from construction and demolition and operational emissions from day-to-day use.

It is estimated that less than 1% of building projects quantify and report their full carbon footprint, despite the fact that embodied carbon contributes up to 50% of the whole life cycle carbon emissions from buildings. There is no global data to track progress on this indicator.

In a survey of 28 countries on buildings and climate policy conducted by the OECD in 2024, methodologies for assessing the whole life carbon emissions via LCAs were in development in 54% of the country respondents and databases to store and track the data from LCAs were in the process of being established in 46% of the countries. Some countries, such as France, already require WLCAs for all new buildings.

Increasing the share of buildings that undergo a WLCA, providing finance to cover the cost of the evaluations and standardizing these assessments would increase the amount of data existing on buildings, which at the moment remains a challenge. Data from WLCAs provides a picture of where emissions come from, empowering stakeholders (including architects, builders and owners) to make decisions about key stages of a building’s lifetime, including its design, the materials used, the construction process, renovations and demolition.

Number of companies with targets to reduce whole life cycle carbon emissions

Whole life cycle carbon emissions are those produced over a building’s lifetime (from construction to demolition). They should make up part of companies’ emissions profiles, whether they are involved directly in the construction industry or they own or procure buildings to carry out their business activities. However, not all companies include these emissions in their profiles.

Companies make up a key subset within the network of stakeholders that need to take action to reduce embodied and operational emissions from buildings. Whole life cycle carbon emissions should make up part of companies’ emissions profiles, whether they are involved directly in the construction industry or they own or procure buildings to carry out their business activities. However, not all companies include these emissions in their profiles. Targets adopted by companies raise ambition and push decarbonization within the sector.

While there is no data to track progress on this indicator, the World Green Building Council’s (World GBC) Net Zero Carbon Buildings Commitment can serve as a proxy to track companies’ progress toward reducing whole life carbon emissions, committing to energy efficiency in buildings and committing to zero-carbon buildings/decarbonization of their own buildings. As of July 2024, 143 companies had signed the commitment, alongside 29 cities and 6 states and regions. Some of these signatories agree to reduce emissions in their assets and to minimize embodied carbon in new construction, with attention to the design and construction of buildings and consideration of the building’s operational phase and demolition.

Number of countries with building codes that include restrictions on embodied carbon

The provisions of building codes that concern emissions currently focus on the performance of building operations. To help reduce embodied emissions, they could be adapted to incorporate the emissions from the production of building materials and construction.

Building codes are a common regulatory instrument used in many countries. They specify health, safety and energy standards, among other criteria, for new and existing buildings.

Currently, building codes are focused on operational performance, but they should also be adapted to require embodied emissions reductions. This requires an understanding of a building’s embodied emissions, so jurisdictions incorporating embodied emissions into their building codes should also ensure that those emissions are measured accurately.

Although many countries have building codes, particularly for energy efficiency, codes that account for embodied emissions are still emerging. An OECD survey on buildings and climate policy in 28 countries found that 21% had regulations about declaring or limiting whole-life carbon. However, building codes are adopted by different levels of the government, including at the subnational level, such as municipal and city levels. These levels are not tracked by this indicator, but they remain crucial for regulating buildings where national codes do not exist.

For example, in the United States, Marin County, California, incorporated a requirement for low-carbon concrete in new commercial buildings into the building codes in 2021. Adding requirements like this one could be one possibility for other jurisdictions to adopt, although a larger step would be to require reductions in embodied emissions more broadly.

Number of countries with a requirement for public buildings to be zero-carbon (whole life)

Building energy codes underpinned by government regulations will be necessary to achieve net-zero emissions pledges and global climate goals. Governments have additional agency over public buildings and can lead by example by requiring them to be zero-carbon.

As of 2022, approximately 90 countries had established mandatory or voluntary building energy codes. Many countries have developed building performance regulations to reduce energy use intensity and use sources of energy with lower carbon emissions. These codes must be expanded to include embodied emissions in order to cover whole life cycle carbon emissions from buildings.

A 2024 OECD survey of buildings and climate policies in 28 countries found that there were more stringent policies for public buildings compared to private buildings in 53% of the country respondents. Governments have additional agency over public buildings and can lead by example by requiring them to be zero-carbon, while also creating a demand for jobs and expertise in making this transition.

While there is no data to track this at the global level, 21 cities that have signed C40 Cities’ Net Zero Carbon Buildings Accelerator have additionally committed to making all municipal and government buildings zero-carbon in operation. This applies to both existing public buildings and any plans for new constructions. Only nine cities have signed C40 Cities’ Clean Construction Accelerator, pledging to conduct life cycle assessments and reduce emissions throughout the construction process, among other commitments.

In the European Union, by 2028, the Energy Performance of Buildings Directive will require new public buildings to be net-zero carbon in operation and undergo a whole life carbon assessment.

Use of cement for buildings

Alongside steel, cement is one of the key materials used in the construction of buildings, as it is a core ingredient in the production of concrete. Cement production is highly emissions-intensive, so minimizing the use of cement in buildings contributes to reducing overall emissions. Global demand for cement for buildings was almost 2 million tons in 2021.

In 2020, 40% of concrete produced was used in the construction of residential buildings, and the global demand for cement — a core ingredient in the production of concrete — is expected to increase with urbanization and construction needs. According to the IEA, global demand for cement for buildings was almost 2 million tonnes (Mt) in 2021, up from 1.6 Mt in 2010 and 0.9 Mt in 2000.

Currently, there is no dataset to track progress on this indicator; however, global demand for cement for buildings serves as a proxy for the amount of cement used in buildings. Floor area is projected to grow and new construction will be necessary to meet housing needs. Cement production is highly emissions-intensive, so minimizing and optimizing the use of cement in buildings and construction contributes to reducing overall emissions. The IEA Net Zero by 2050 scenario calls for a 50% reduction in the use of cement and steel by 2050.

Reducing the overall use of cement in buildings requires action across the supply chain. Designers can start by choosing alternative, lower-carbon materials. Cement producers can take steps to improve material efficiency and lower the carbon intensity of cement. Builders and construction companies can procure low-carbon cement and use the materials more efficiently in the construction process, reducing the amount of cement used per square meter of floor area. Prefabrication can also reduce waste, as well as recycling cement into new construction at the end of a building’s lifetime.

Use of steel for buildings

Like cement, steel is a crucial material for constructing buildings, with 30% of steel demand coming from the construction sector. However, roughly 25% of emissions attributed to the construction process come from steel as a result of the energy needed to produce it in the first place. Global demand for steel for buildings was around 0.5 million tons in 2021.

The production of steel is currently responsible for around 25% of construction emissions. However, the IEA’s Net Zero Emissions scenario shows that embodied emissions resulting from the use of steel need to reduce by 25% by 2030 in order to stay on track for meeting global climate goals, and the IEA’s Net Zero by 2050 scenario calls for a 50% reduction in the use of cement and steel by 2050.

Currently, there is no dataset to track progress on this indicator. However, around 30% of steel demand comes from the construction sector, and global demand for steel for buildings serves as a proxy to measure the amount of steel used in buildings. According to the IEA, global demand for steel for buildings was around 0.5 million tonnes (Mt) in 2021, up from 0.4 Mt in 2010 and 0.2 Mt in 2000. Projected increases in floor area will require new construction, which is fundamental to ensuring access to adequate housing.

Reducing the amount of steel used in the construction of buildings helps to reduce those emissions, as does reducing the carbon intensity of steel production. In order to mitigate growth in demand for steel, a suite of material efficiency measures is needed along supply chains, as well as finding alternatives to using steel in the construction processes, using steel more efficiently (reducing the amount of steel used per square meter of floor area), extending buildings’ lifetimes and recycling materials after demolition. These actions could help to reduce global steel demand by around 20% by 2050, relative to baseline projections.

Carbon intensity per tonne of cement

The carbon intensity of cement remained at about 660 kg CO2/tonne of cement from 2012 to 2020, as producers had already maximized energy efficiency in existing processes. Further decarbonizing cement is required to meet the 2030 and 2050 targets.

Cement is a major component of concrete, one of the most prevalent materials used in buildings. The carbon intensity of cement measures the average amount of carbon dioxide (CO2) emitted for each tonne of cement produced. That includes direct emissions from fuel combustion, process emissions and indirect emissions from electricity consumption.

The carbon intensity of global cement production remained virtually constant at about 660 kilograms of carbon dioxide per tonne (kgCO2/t) of cement from 2012 to 2020. It is posited that this is due to the energy efficiency of the equipment used for cement production nearing optimum levels. Therefore, further decarbonizing cement production is needed to meet the 2030 target of 360-370 kgCO2/t of cement and the 2050 target of 55-90 kgCO2/t of cement.

Meeting these targets requires new approaches and materials, such as material substitution in the cement production process and zero-carbon heat. These could include reducing the ratio of clinker (the “glue” that binds the raw materials of cement together) to cement — about 40%-50% of cement emissions could be avoided through clinker substitution.

Alternatively, using sustainable biomass sources, hydrogen or electricity to provide the heat needed to make cement or applying carbon capture, utilization and storage (CCUS) would reduce CO2 emissions from the production process.

Carbon intensity per tonne of steel

The carbon intensity of global steel production increased from 1,800 kilograms of carbon dioxide per tonne (kgCO2/tonne) of steel in 2007 to 1,910 kgCO2/t in 2022. Alternative production techniques and carbon capture technologies can help reverse this trend in order to meet the 2030 target of 1,340-1,350 kgCO2/t of steel.

About half of the steel produced annually goes into construction, and about two-thirds of that goes into constructing buildings. The carbon intensity of steel measures the average amount of carbon dioxide (CO2) emitted per tonne of steel produced, and considers both primary and secondary steel production. Primary steel production refers to steel produced through the reduction of iron ore which is then processed into steel, while secondary steel production refers to the recycling of scrap steel into useful steel again. It includes direct emissions from fuel combustion, process emissions and indirect emissions from electricity consumption.

The carbon intensity of global steel production increased from 1,800 kilograms of carbon dioxide per tonne (kgCO2/t) of steel in 2007 to 1,910 kgCO2/t of steel in 2022.

Changing the trajectory of steel sector emissions intensity will require an increase in secondary steel production, and a far greater share of primary steel production will need to rely on new technologies. These include using green hydrogen and an electric arc furnace instead of the traditional coal-fired blast furnace or adding carbon capture, utilization and storage (CCUS) and eliminating all residual emissions.

Alternative production techniques and carbon capture technologies can help reverse this trend in order to meet the 2030 target of 1,340-1,350 kgCO2/t of steel and the 2050 target of 0-130 kgCO2/t of steel.

Data Challenges

Embodied emissions are not well studied and the data deficit on whole life carbon emissions is a barrier to tracking progress (all of the indicators for this shift are classified as “Insufficient Data”). Even when data is available, it can be difficult to attribute emissions to individual buildings, especially if the construction process is not well documented.

If building owners and managers are encouraged to track the performance of their buildings, it can help make the data collection and aggregation process more manageable. One proposed method for this is the “building passport” model, which encourages actors in the construction and operation of a building to collect data at every step, store it in a repository and share it with fellow stakeholders. 

Photo credits

Photo by Zac Wolff on Unsplash