When discussing the construction industry, the term "embodied carbon" refers to the greenhouse gas (GHG) emissions that are produced throughout the extraction, processing, transportation and installation of building materials. The United Nations Environment Programme (UNEP) estimates that the construction industry contributes an astonishing 37% to global emissions. As sustainability in construction becomes a priority, accurate embodied carbon assessments are crucial for assessing and lowering a project's environmental impact.
Embodied Carbon in Construction
Embodied carbon accounts for a significant portion of a building’s total lifecycle emissions. Unlike operational carbon, which is generated from energy use during a building’s lifespan, embodied carbon is released prior to the building being operational, so the emission value is locked in from the outset. Understanding embodied carbon at the beginning of a construction project, during the design phase, will help determine appropriate reduction strategies that contribute to overall carbon footprint reduction.
A good case study for this is Tunley Environmental’s work with Extrudakerb, a leading specialist in horizontal slipforming for concrete barriers. In a bid to demonstrate their commitment to sustainable construction, Extrudakerb employed the services of Tunley Environmental to assess the embodied carbon of their operations in a project. Tunley’s expert sustainability scientists conducted a comprehensive Embodied Carbon Assessment (ECA) for the project, identifying key carbon contributors and assessing the emissions of the whole project. In addition, Tunley Environmental also carried out a separate assessment to quantify the emissions of an alternative, more conventional practice (using precast concrete barriers); this was to highlight Extrudakerb's good practice. Overall, using Extrudaberb's onsite method resulted in 24.3% carbon reduction per metre of barrier, compared to the conventional method.
Read More: Extrudakerb Case Study with Tunley
Steps to Calculate Embodied Carbon in Construction
The initial steps in this process involve defining the goal and scope of the assessment and establishing the system boundaries. These steps ensure that the assessment is comprehensive, accurate, and aligned with the intended objectives. Below are the detailed steps to define the embodied carbon general preparations:
Step 1: Define the Goal and Scope of the Assessment
Purpose and Objectives:
- Clearly articulate the purpose of the embodied carbon assessment. This could include objectives such as reducing the carbon footprint, complying with regulatory requirements or achieving sustainability certifications.
- Identify the specific goals of the assessment, such as quantifying the carbon emissions associated with the production and transportation of building materials.
Intended Audience:
- Determine the primary audience for the assessment results. This could include stakeholders such as project developers, regulatory bodies, investors or sustainability consultants.
- Tailor the assessment approach and reporting format to meet the needs and expectations of the intended audience.
Assessment Type:
- Decide whether the assessment will be cradle to gate (A1-A3) or cradle to store (A1-A5).
- Cradle to Gate (A1-A3): Includes the extraction of raw materials (A1), transportation to the manufacturing site (A2) and manufacturing processes (A3).
- Cradle to Store (A1-A5): Extends the assessment to include transportation to the construction site (A4) and construction and installation processes (A5).
Functional or Declared Unit:
- Define the functional or declared unit for the assessment. This is a quantified performance measure of the building or its components, such as 1 m² of building floor area or 1 tonne of concrete.
- Ensure that the functional unit is consistent with the goals and scope of the assessment and provides a clear basis for comparison.
Geographical and Temporal Scope:
- Specify the geographical scope of the assessment, including the locations of raw material extraction, manufacturing and construction sites.
- Define the temporal scope, including the time period over which the data will be collected and the assessment will be conducted.
Step 2: Establish System Boundaries
Inclusion of Processes:
- Identify and include all relevant processes within the system boundaries. This includes raw material extraction, transportation, manufacturing and construction activities.
- Ensure that the selected processes align with the defined goal and scope of the assessment.
Exclusion Criteria:
- Clearly state any exclusion criteria for processes or activities that will not be included in the assessment. Justify these exclusions based on their insignificance to the overall carbon footprint or practical limitations in data collection.
Cut-off Criteria:
- Define cut-off criteria to determine the significance of material or energy flows that will be included in the assessment. This helps in focusing on the most impactful processes and avoiding unnecessary complexity.
The embedded carbon assessment can offer insightful analysis of the environmental impact of building materials and techniques by precisely defining the purpose and scope and setting unambiguous system limits. This foundational work sets the stage for a robust and credible assessment that supports informed decision-making and sustainability initiatives.
Step 3: Data Collection and Quality
Data Collection:
- Bill of Quantities (BoQ): The first and most crucial step in the data collection phase is to prepare a detailed Bill of Quantities (BoQ). The BoQ provides comprehensive details on the supply chain for each component, including the origins and the materials used in each component. This document is essential for identifying the sources of data and ensuring the accuracy of the embodied carbon assessment.
- Primary Data: Collect primary data for processes under your control, such as material production, transportation, and construction activities. This data should be specific to the project and obtained directly from suppliers, manufacturers, or contractors.
- Secondary Data: Use secondary data for processes where primary data is not available. This data can be sourced from generic databases, industry reports, or published literature. Ensure that secondary data is relevant and representative of the processes being assessed.
Data Quality:
- Time-Related Coverage: Ensure that the data collected is recent and covers an appropriate time period. Data should reflect current practices and technologies.
- Geographical Coverage: Data should be representative of the geographical locations where the processes occur. Consider regional variations in energy sources, transportation distances, and manufacturing practices.
- Technology Coverage: Data should accurately represent the technologies and processes used in the production, transportation, and construction of materials.
- Precision and Completeness: Aim for high precision and completeness in data collection. Quantify the variability and uncertainty in the data to understand its reliability.
- Representativeness and Consistency: Ensure that the data set reflects the true population of interest and is applied consistently across all processes.
- Reproducibility: Provide sufficient detail about the data sources and methodologies to allow independent verification and reproduction of the results.
Relating Data to the Functional Unit:
- Functional Unit: Relate all collected data to the defined functional or declared unit (e.g., the one-unit building or 1 m² of building floor area). This ensures that the assessment results are comparable and meaningful.
- Aggregation: Aggregate data appropriately to match the functional unit. This may involve converting raw data into per-unit values and summing contributions from different processes.
Step 3: Calculating Emissions
Carbon Emission Factors:
- Databases: Obtain carbon emission factors from reputable sources such as the Inventory of Carbon and Energy (ICE), government websites and Environmental Product Declarations (EPDs).
- Verification: Verify the emission factors to ensure they are up-to-date and relevant to the specific materials and processes being assessed.
Raw Material Emissions:
- Extraction and Processing: Calculate the emissions associated with the extraction and processing of raw materials. This includes activities such as mining, refining, and manufacturing.
- Emission Factors: Apply the relevant emission factors to the quantities of raw materials used in the project.
Transportation Emissions:
- Transportation Modes: Identify the modes of transportation used to deliver materials to the manufacturing site and construction site (e.g., road, rail, sea).
- Distances: Calculate the transportation distances for each mode.
- Emission Factors: Apply the relevant emission factors for each transportation mode to the distances and quantities of materials transported.
Construction Emissions:
- Construction Activities: Calculate the emissions associated with construction activities, including on-site energy use, machinery operation, and waste management.
- Emission Factors: Apply the relevant emission factors to the quantities of energy and materials used during construction.
Summarising Emissions:
- Total Emissions: Sum the emissions from raw material extraction, transportation, and construction to obtain the total embodied carbon for the project.
- Documentation: Document all calculations, data sources, and assumptions used in the assessment. Ensure transparency and provide sufficient detail for verification and reproducibility.
By following these steps, you can ensure a comprehensive and accurate calculation of embodied carbon emissions for your building project. This process provides valuable insights into the environmental impact of building materials and processes, supporting informed decision-making and sustainability initiatives.
Benefits of an Embodied Carbon Assessment
Conducting an embodied carbon assessment provides multiple benefits:
- Regulatory Compliance: Helps businesses meet sustainability regulations and certifications like BREEAM and LEED.
- Cost Savings: Identifying low-carbon materials can lead to long-term financial savings.
- Enhanced Reputation: Demonstrating commitment to sustainability improves corporate image and investor confidence.
- Competitive Advantage: Companies prioritising sustainability in construction gain an edge in an increasingly eco-conscious market.
- Informed Decision-Making: Provides clear insights into emissions hotspots, helping stakeholders make data-driven sustainability improvements.
- Carbon Reduction Targets: Supports organisations in setting and achieving carbon reduction goals in line with global sustainability initiatives.
Reducing Embodied Carbon in Construction
Once embodied carbon is quantified during the design phase, strategies that are backed by data and scientific expertise can be implemented to reduce emissions. Ultimately the carbon hierarchy should be followed. This can be seen in the figure below.
Specific examples of emission reductions include:
- Using low-carbon materials such as recycled steel, engineered timber and low-carbon concrete.
- Incorporating passive design principles, reducing material use through efficiency, and designing for adaptability and future reuse.
- Adopting modular construction to reduce waste and energy consumption.
- Sourcing materials locally to minimise transportation emissions.
- Maximising material reuse and recycling at end-of-life stages.
- Employing energy-efficient construction methods such as prefabrication.
Read More: How Organisations Can Reduce Embodied Carbon
The Bottom Line
Calculating embodied carbon in construction is a critical step in reducing the environmental impact of the built environment. Tunley Environmental provides expert embodied carbon assessment services, helping businesses and developers measure and reduce the carbon impact of their construction projects.