Which life cycle assessment? Managing the risk of inconsistent building assessments across regions
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RambollA recent study compares commonly used building life cycle assessment methodologies in Europe. Our experts created a database of building carbon footprints to demystify LCA variations and help you break down the differences.
The built environment significantly impacts society and nature. Life cycle assessment (LCA) methods are widely used to assess the environmental impacts of buildings, yet their adoption and implementation varies widely across countries.
The result is inconsistent outcomes and environmental impacts, making it hard to compare and benchmark building LCA results. Built environment stakeholders struggle to make informed decisions for the environmental performance of buildings. Policymakers, too, are challenged to develop consistent and effective regulations.
To help the buildings industry, Ramboll experts developed a benchmarking database of building carbon footprints that accommodates LCA method variations. They conducted a mapping exercise to clarify the similarities and differences among the most used building LCA methods across our projects in Denmark, Sweden, Norway, Finland, the United Kingdom, Germany, Asia Pacific, Central Europe, and the Middle East.
“With a more comprehensive understanding of LCA distinctions, we hope LCAs become more effective in informing sustainable building design and construction practices,” says Paul Astle, Decarbonisation Lead at Ramboll.
Below we highlight the biggest discrepancies found while mapping out the differences in life cycle assessment methodologies and risks.
Different emissions results from differences in scope
Historically, LCAs were used for documentation purposes or as part of meeting environmental certification credits. Now, however, to achieve the carbon reduction targets required to meet the Paris Agreement, LCAs must become a part of the early stages and design processes of a project.
The LCA methods reviewed in the study are adaptions and interpretations of the proposed EN 15978:2011 standard guidelines. The standard’s open-interpretation and minimal scope definition leads to significant result variations.
System boundary: The system boundary determines the processes included in assessing a building. In the context of building LCAs, the system boundary constitutes the building life cycle stages, as indicated in Figure 1.
Figure 2 shows the different system boundary requirements of each life cycle assessment in this study.
Building element groups: Each LCA method defines which building elements are required as a minimum. The variation in minimum building element groups to be included in an assessment significantly contributes to result discrepancies.
Figure 3 shows the required building elements for each LCA methodology organised into element groups based on RICS elements as used in the RICS LCA methodology.
Floor area definitions and metrics: LCA results are typically provided per unit floor area, even when not required nor defined in EN 15978:2011. It is, however, a familiar industry approach. LCA methods use a variation of gross floor area (GFA), with each country having its own GFA definition. As GFA is used to calculate a building’s carbon footprint to allow comparison with other buildings and benchmarks, its definition impacts the calculated figures. Figure 4 maps respective GFAs and their corresponding building components. We group GFA definitions into two categories: (1) those which include the external wall thickness, and (2) those that do not.
Reference study periods: As indicated in Figure 2, a reference study period (RSP) represents the temporal boundary of an LCA. RSPs determine the impact during asset use (B module), including anticipated replacement cycles. Generally, cycles vary from 50-60 years but can include 75-100 years depending on building type. RSPs are particularly important where it is standard practice to provide metrics on a per year basis.
Impact categories: EN15978 defines indicators describing environmental impact, resource use, waste categories, and output flows leaving the system. These environmental indicators are selected by established LCA calculation methods. Figure 5 shows the proposed EN 15978:2011 impact categories compared to those in the LCA methods. Two impact categories not proposed by the EN 15978 standards were added: (1) “total use of energy,” and (2) “waste processing.” These categories originate from the Voluntary Sustainability Class and the BREEAM standards.
The discrepancies in definitions and requirements between the different methods clearly show different results.
