Embodied carbon in construction refers to the carbon emissions associated with manufacturing and transporting construction materials, as well as the construction process itself. While much attention has been given to operational emissions, the embodied carbon footprint is often overlooked. Buildings contribute a staggering 39% of global greenhouse gas (GHG) emissions: 28% from building operations and 11% from embodied carbon.
In some cases, embodied carbon can represent nearly half of a building’s total carbon footprint over its lifetime, primarily due to carbon-intensive material manufacturing and the heavy use of fossil fuels before materials even arrive at a construction site. Addressing this hidden culprit is essential for the construction industry to mitigate its environmental impact and achieve climate targets.
1. The Need to Understand Embodied Carbon
Unlike operational carbon, embodied carbon cannot be reduced once a building is constructed. As operational efficiencies improve with advanced technologies, embodied carbon will constitute an increasingly significant proportion of a building’s lifetime emissions.
Awareness of embodied carbon is growing, but meaningful action is still in its infancy. Without addressing this issue, the construction industry will struggle to meet the emission targets required to keep global warming within 2°C. Incorporating embodied carbon reduction into construction practices is no longer optional but essential for mitigating climate change.
2. Assessing Embodied Carbon
To reduce embodied carbon effectively, it is critical to assess it accurately. This involves identifying the carbon “hotspots” within a project—materials and systems that contribute the most to embodied emissions—and prioritizing changes that deliver the most impact.
Tools and Methods
- Whole-Building Life-Cycle Assessment (WBLCA): The most comprehensive method for analyzing embodied carbon, WBLCA examines a material’s entire life cycle, from extraction and manufacturing to its end of life, such as recycling or landfill.
- Free Resources:
- The Bath Inventory of Carbon and Energy (ICE) provides detailed embodied carbon data.
- The Quartz database offers insights into the environmental impact of 102 common materials.
- Environmental Product Declarations (EPDs): Product-specific data tools based on functional units, offering a detailed breakdown of carbon footprints for various materials.
Using these tools provides project teams with a clear understanding of how materials compare in terms of environmental impact, helping them make informed decisions to minimize embodied carbon.
3. Strategies to Reduce Embodied Carbon
Avoid New Construction
The most effective way to reduce embodied carbon is to minimize the need for new materials. Reusing and incorporating salvaged materials can eliminate the emissions associated with manufacturing and transporting new products. By extending the lifespan of existing buildings through adaptive reuse, emissions from repeated construction cycles can be avoided.
Focus on Longevity and Adaptability
Before construction begins, teams should assess how buildings can serve multiple purposes over their lifespan. Designing for flexibility and eventual deconstruction allows materials to be reused in future projects, reducing waste and the need for new resources.
4. Optimizing Structural Systems
Structural systems account for approximately 80% of a building’s embodied carbon. This makes them a critical focus area for reducing emissions. Here’s how different materials can be optimized:
Concrete and Cement
Concrete has a significant carbon footprint due to the production of portland cement, which contributes to 5% of global CO2 emissions. To mitigate this impact:
- Replace some cement with supplemental cementitious materials (SCMs) such as fly ash or blast-furnace slag.
- Reduce cement usage by specifying higher-quality aggregate and optimizing water content.
- Work closely with ready-mix suppliers to tailor mixes that meet both structural and environmental requirements.
Steel
Steel has a higher embodied carbon footprint per ton than concrete, with its production responsible for 6.6% of global GHG emissions. Despite some advancements in cleaner production technologies like electric arc furnaces (EAF), challenges remain:
- Composite Design: Use steel and concrete together to reduce the amount of steel required.
- Structural Systems: Opt for braced frames with diagonal braces, which use less steel than moment frames.
- Involve structural engineers early in the project to identify opportunities for reducing steel quantities while maintaining performance.
Structural Wood
Structural wood offers a sustainable alternative, as it sequesters carbon rather than emitting it. Mass-timber products like cross-laminated timber (CLT) are gaining popularity for their presumed lower embodied carbon impacts. Using wood instead of steel or concrete can significantly reduce emissions, making it a compelling choice for sustainable construction.
Conclusion
The construction industry must prioritize reducing embodied carbon to achieve sustainable building practices. By leveraging advanced assessment tools, rethinking material choices, and designing with adaptability in mind, it is possible to lower emissions significantly. Optimizing structural systems, embracing innovative materials, and reusing existing resources are essential steps.
Collaboration between designers, engineers, and suppliers will be key to implementing these strategies effectively. Addressing embodied carbon is not just about meeting climate goals; it is a vital step toward a more sustainable future for the planet.