As climate change reshapes our world, the demand for environmentally responsible building practices has never been more urgent, especially given that the architecture, engineering, and construction (AEC) industry contributes more than 37% of global carbon emissions. A new focus on sustainable construction is emerging, with a particular emphasis on the critical role of embodied carbon. Understanding and reducing this component of a building’s carbon footprint is no longer optional but a fundamental aspect of responsible construction and stewardship. This shift marks a profound evolution in how we think about, design, and construct the spaces where we live, learn, and heal.
Understanding Embodied Carbon
Embodied carbon represents the total greenhouse gas emissions associated with a building material’s life cycle. This life cycle can be broken down into five main stages: extraction, production/fabrication, construction, use, and end of life. Collectively, these are measured by a Life Cycle Assessment (LCA). Each stage contributes significantly to the material’s overall carbon footprint, underscoring the need for a meticulous approach to material selection and use. Buildings are made up of many different materials with varying embodied carbon intensities. The practice of summing up the entire embodied carbon impact of all materials contained inside a building is called a Whole Building Life Cycle Assessment (WBLCA). It is through this practice that an estimation of a building’s total impact can be formed.
Benefits of Adaptive Reuse with Respect to Embodied Carbon
The most effective strategy to mitigate embodied carbon is to minimize material usage. By reusing existing buildings, there is a direct opportunity to conserve embodied carbon already expended. Even if an existing building was constructed with materials high in embodied carbon, this carbon has already been accounted for; thus, repurposing these materials essentially incurs no additional embodied carbon compared to demolishing the structure and constructing anew with “greener” materials. It’s important to note that, today, even the most environmentally friendly new materials still contain some embodied carbon. Additionally, demolishing existing structures not only generates emissions but also necessitates the disposal or recycling of debris, each of which has its own carbon footprint. Adaptive reuse preserves the embodied carbon of the original materials and avoids the environmental impact associated with waste management and the production of new materials.
Recently, LEO A DALY undertook an important and challenging adaptive reuse project in Washington, D.C. Collaborating closely with The RMR Group, the team successfully reimagined a former federal office building into a vibrant, multi-award-winning mixed-use development that reawakened an area of the city. This development, known as 20 Mass, now includes retail spaces and a luxury hotel. By reusing the existing structure, the project saved approximately 6,905 metric tons of CO2e. This number of saved emissions is equivalent to the emissions from 1,643 cars in one year or the carbon that would be sequestered by 114,175 saplings over 10 years.
Strategic Approaches to Decarbonization
Implementing decarbonization strategies involves two primary methods: reducing the use of materials and selecting lower-impact materials.
Reducing Material Use
Reducing the use of materials involves selecting materials that are less carbon-intensive and optimizing the use of those materials throughout the building process to achieve maximum efficiency and minimal waste. Along with adaptive reuse, below are several strategies that can help you lessen your material impact:
Strategic structural system selection: Employing parametric design tools during the conceptual phase of the design will help you analyze the implications of various systems. These tools can support other early-phase decision-making processes. For instance, they can assist you in strategically placing structural elements like columns and beams to reduce material usage while maintaining structural integrity.
Detailing systems for maximum efficiency: Detailing designs to maximize structural efficiency is essential, involving critical decisions for both structural engineers and architects. For instance, allowing heavy facades, such as precast concrete, to bear directly on the foundation rather than on the structural floors can significantly reduce material usage. Similarly, opting for punched windows over continuous ribbon windows helps optimize material use. Additionally, avoiding the use of heavy, brittle materials on penthouse facades supported by roof framing can contribute to a lighter structural frame. These strategic choices collectively enhance the efficiency and sustainability of the building’s design.
Right-sizing structural elements: Ensuring that structural components are precisely scaled to their load requirements in accordance with building regulations can mitigate unnecessary material use. It is crucial to maintain tight coordination with contractors and fabricators to achieve these efficiencies cost-effectively.
Innovative technologies: The use of innovative construction technologies can achieve structural performance requirements efficiently. For example, some new foundation systems utilize low-impact aggregates instead of traditional, more carbon-intensive concrete or steel deep foundations to provide environmentally friendlier and cost-effective foundation solutions. This technique can enhance load-bearing capacities while reducing the carbon footprint associated with deep foundation work.
Reducing on-site waste: By minimizing on-site waste, such as over-excavation for foundations, which leads to larger concrete pours, you can reduce costs associated with waste disposal and material purchases while enhancing the efficiency of your material usage. Minimizing waste not only ensures more effective use of materials but also conserves essential resources and reduces the environmental impact associated with their extraction, processing, and manufacturing.
Effective collaboration between designers and contractors is crucial to successfully implementing these practices, ensuring that planning and execution align to optimize resource use and manage waste effectively.
Choosing Low-Impact Materials
Selecting materials with lower embodied carbon impacts involves analyzing the entire life cycle of materials used in construction. Although the choice of materials might be limited, there are impactful strategies professionals can employ to advocate for and utilize lower-carbon alternatives:
Prioritize materials and systems with naturally lower embodied carbon: Different materials inherently have varied levels of embodied carbon due to their production processes. By choosing material types that naturally exhibit lower embodied carbon, you can significantly influence the carbon footprint of your projects. For example, opting for a metal panel system rather than a granite masonry veneer for exterior cladding can inherently reduce the embodied carbon due to differences in how these materials are produced.
Prioritizing low-impact materials within a product category: A product category consists of a group of products that fulfill the same functional purpose. Many products can fit within one product category. For example, concrete with a strength of 3000 psi is a product category. Many different mixes from various concrete plants can meet this specification, although the ways they are mixed and the ingredients in the mix may differ greatly. Therefore, some of these functionally equivalent mixes have high embodied carbon impacts, while others have low impacts compared to their peers. Procuring lower-impact materials that meet the project’s requirements is a great way to build lower-impact buildings.
Request environmental product declarations (EPDs): While the market availability of low-impact materials can be limiting, you can exert influence by specifying that all building products must include EPDs. This not only ensures that contractors select vendors who are conscious of their environmental impact, but it also encourages more manufacturers to obtain EPDs as they recognize the growing demand for sustainable products in the industry.
Set specific carbon intensity targets: Beyond choosing types of materials with lower emissions, it is also crucial to select specific products from vendors that meet predetermined carbon intensity targets. This approach involves setting benchmarks, such as requiring that certain materials have embodied carbon intensities at least 10% below the industry average. Although the market may not yet support the specification of “zero carbon” materials, setting achievable carbon reduction targets ensures that the materials selected are at the forefront of reducing environmental impact.
As climate change continues to challenge our traditional construction practices, the architectural and engineering sectors are uniquely positioned to drive meaningful change through decarbonization strategies across the entire building life cycle. Through these combined efforts, architects and engineers not only contribute to a reduction in global carbon emissions but also set new standards for responsible design and construction that align with the environmental and sustainability goals of the future.
Edward Benes, P.E., is CEO and Jake Zach is a senior structural engineer and associate at architecture firm LEO A DALY.
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