The global imperative to combat climate change has placed an unprecedented focus on the built environment. While operational carbon emissions—those generated by a building’s heating, cooling, and lighting during its use—have historically been the primary concern, attention is now rapidly shifting to embodied carbon. Embodied carbon refers to the greenhouse gas (GHG) emissions associated with the entire lifecycle of building materials, from raw material extraction, manufacturing, and transportation to construction, maintenance, and eventual demolition and disposal. For structural engineers, this represents the next significant challenge, demanding a fundamental rethinking of design practices, material selection, and project delivery.
Understanding Embodied Carbon’s Criticality
Embodied carbon is often described as the “upfront” carbon, as a significant portion of these emissions occur before a building is even occupied. These early emissions have an immediate impact on the climate and, over the building’s lifespan, can account for a substantial part of its total carbon footprint, especially as operational emissions decrease due to energy efficiency improvements and cleaner energy grids. Globally, embodied carbon in the building and construction sector accounts for approximately 7% of global emissions, or 3.5 billion tonnes of CO2 annually. The production of key structural materials like cement, steel, and aluminum alone represents a staggering 23% of all global emissions.
As the world anticipates a doubling of its building stock by 2060—equivalent to constructing an entire New York City every month—the urgency of addressing embodied carbon becomes clear. There is no way to renovate or reduce these emissions once a building has been constructed. This highlights why structural engineers, who directly influence material choices and structural systems, are at the forefront of this climate change challenge.
Why Embodied Carbon is a Unique Challenge for Structural Engineers
Structural engineers are uniquely positioned to influence a building’s embodied carbon footprint because they specify the type, quantity, and grade of materials used in a project’s skeletal system. A building’s structure can account for up to 50% of its embodied carbon. This influence, however, comes with several complexities:
Material Intensity and Carbon Footprint
The primary structural materials—concrete, steel, and to a lesser extent, timber—are inherently carbon-intensive in their production.
- Concrete: The production of cement, a key ingredient in concrete, is particularly carbon-intensive, responsible for 8% of the world’s CO2 emissions. Concrete often represents the largest contributor to a structure’s embodied carbon.
- Steel: While highly recyclable, the initial production of steel is energy and carbon-intensive.
- Aluminum: Aluminum production also has high energy requirements and significant carbon emissions.
These materials are fundamental to modern construction, making their decarbonization a monumental task.
Hidden Emissions and Data Scarcity
Unlike operational energy use, which is measured during a building’s lifetime, embodied carbon emissions are often “hidden” within the supply chain, making them less discernible. Tracking and quantifying these emissions requires detailed data on material extraction, manufacturing processes, and transportation distances. While Environmental Product Declarations (EPDs) are becoming essential sources of product information, providing transparent and standardized data on a material’s environmental performance, their widespread availability and consistency are still evolving. Without standardized data, comparing the embodied carbon of different materials and design options can be challenging.
Complexity of Life Cycle Assessment (LCA)
Life Cycle Assessment (LCA) is the most widely recognized and crucial tool for evaluating the environmental impact of buildings, materials, and construction methods across their entire lifespan. While essential for a comprehensive understanding of embodied carbon, conducting a full LCA can be time-consuming, costly, and requires specialized expertise. This complexity can be a barrier for structural engineering firms, especially smaller ones, to integrate embodied carbon analysis into their standard workflows.
Design Optimization vs. Carbon Optimization
Structural engineers traditionally optimize designs for safety, cost, and efficiency in terms of material quantity and structural performance. Now, they must also factor in embodied carbon as a critical design parameter. This requires a shift in mindset and potentially new analytical tools to compare the carbon implications of different structural systems, material choices, and design geometries. What might be structurally efficient in terms of material volume might not be carbon-efficient if highly carbon-intensive materials are used.
Upfront Carbon’s Immediacy
Emissions released during the production and construction of materials have an immediate impact on the climate, in contrast to operational emissions that accrue over decades. This “time value of carbon” emphasizes the urgency of reducing upfront embodied carbon emissions to meet short-term climate targets, such as halving emissions by 2030 and reaching net-zero by 2050.
Strategies for Structural Engineers to Address Embodied Carbon
Despite the challenges, structural engineers possess significant agency in mitigating embodied carbon. Their influence extends to key decisions made early in the design process, which have the greatest impact on a project’s overall carbon footprint.
1. Material Selection and Specification
Choosing materials with lower embodied carbon is a primary lever.
- Concrete Optimization: Specifying concrete mixes with a lower proportion of Portland cement by incorporating supplementary cementitious materials (SCMs) like fly ash and slag can significantly reduce embodied carbon without compromising performance. Allowing for longer cure times (e.g., specifying strength at 56 days instead of 28 days) can also facilitate the use of lower-carbon mixes. New technologies that sequester carbon in concrete are also emerging.
- Timber as a Carbon Sink: Responsibly grown and harvested timber can be a carbon-sequestering material, making mass timber an increasingly attractive option for reducing embodied carbon, even in taller structures.
- Recycled Content: Prioritizing materials with high recycled content, such as steel produced from electric arc furnaces with low-carbon electricity, can substantially reduce embodied carbon. Structural engineers should demand Environmental Product Declarations (EPDs) from manufacturers to compare and select lower-impact products.
2. Design Optimization and Efficiency
Minimizing the quantity of material used is one of the most reliable ways to reduce embodied carbon emissions.
- Efficient Structural Systems: Selecting an efficient structural system for the building type and usage can lead to significant material reductions. For instance, certain steel and concrete lateral systems can reduce embodied carbon impacts. Utilizing composite action between steel or timber floor framing and concrete decking can also reduce floor system weight, which often accounts for the majority of embodied carbon in a structure.
- Performance-Based Design: Applying performance-based design approaches can optimize structural designs, potentially leading to lower design loads and reduced material usage.
- Minimizing Spans and Material Overdesign: Designing to limit spans (e.g., by reducing column spacing) can minimize the thickness of spanning elements. Avoiding overdesign and optimizing member sizes can lead to substantial material savings.
3. Reuse and Adaptive Reuse
The most impactful strategy often involves avoiding new construction altogether.
- Building Reuse: Encouraging the reuse, renovation, and retrofitting of existing buildings rather than demolition and new construction can yield significant embodied carbon savings, potentially up to 44% less environmental impact. Structural engineers are integral in evaluating existing structures for their capabilities to meet new programmatic requirements.
- Material Salvage: Incorporating salvaged materials into new construction can dramatically reduce embodied carbon, as the emissions associated with their initial production may be disregarded, with only transportation and refabrication emissions considered.
4. Collaboration and Early Engagement
Embodied carbon reduction requires a holistic approach and close collaboration across the project delivery team, including architects, contractors, and owners. Structural engineers should be engaged early in the design process to facilitate these strategies. This early involvement allows for more informed decisions regarding material selection and structural systems, which have a profound impact on embodied carbon.
5. Tools and Methodologies
- Life Cycle Assessment (LCA) Tools: Utilizing LCA software and tools can help quantify and track embodied carbon reductions throughout the design process, enabling comparison of different options and informed decision-making.
- Carbon Databases: Leveraging databases like EC3 (Embodied Carbon in Construction Calculator) and other carbon metrics warehouses provides valuable data for benchmarking and comparing project carbon performance.
- Environmental Product Declarations (EPDs): Requesting and analyzing EPDs from manufacturers is crucial for understanding the environmental impact of specific products and making informed choices.
Policy and Industry Initiatives
The growing awareness of embodied carbon has spurred policy developments and industry initiatives worldwide.
- Mandatory Reporting and Limits: Countries like Holland have mandated embodied carbon reporting since 2013 and introduced limits on emissions. The European Union will require embodied carbon reporting for major construction projects from 2028, extending to all projects by 2030, with specific limits to follow. Sweden has required calculation and reporting of embodied carbon for new building permits since 2022.
- “Buy Clean” Policies: Policies such as “Buy Clean California” aim to reduce GHG emissions associated with the production of certain building materials used in state-funded projects by setting Global Warming Potential (GWP) limits for materials like structural steel, rebar, and flat glass.
- Industry Commitments: Initiatives like the Carbon Leadership Forum’s Structural Engineers 2050 Challenge (SE 2050) are inspiring engineers to work towards embodied carbon benchmarks and contribute essential data. Organizations are setting targets for embodied carbon reduction, with goals ranging from 40-65% reductions by 2030 to net-zero by 2050.
Conclusion
Embodied carbon is undeniably the next significant challenge for structural engineers. As operational carbon emissions continue to decline due to advancements in energy efficiency, the relative impact of embodied carbon becomes increasingly critical. Structural engineers, with their pivotal role in material specification and structural design, hold immense power to drive down these emissions. By embracing strategies such as intelligent material selection, design optimization, advocating for reuse, leveraging advanced tools like LCA, and actively participating in policy development, the profession can lead the charge towards a truly decarbonized built environment. The shift from a focus solely on structural integrity to a holistic approach that prioritizes both safety and environmental impact is not just a trend but a fundamental evolution of structural engineering practice.
