Mercedes Beaudoin
June 12, 2023
Which life cycle assessment? Managing the risk of inconsistent building assessments across regions
A 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.
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.
Click through the most important differences in LCA method scopes below:
Different emissions results
Figure 1: Building lifecycle stages used to define a system boundary. Reproduced from EN 15978:2011 with B8 module added.
Ramboll
Figure 2: Comparison of system boundary requirements of life cycle assessments
Ramboll
Figure 3: Comparison of building element groups by life cycle assessment, by country.
Ramboll
Figure 4: Comparison of gross floor area definitions by life cycle assessment, by country.
Ramboll
Figure 5: Comparison of impact categories of life cycle assessments
Ramboll
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.
To illustrate a practical example of the magnitude of difference on resulting carbon and environmental impacts, the study’s authors calculate a theoretical building’s GWP using two different national LCA methods.
Imagine designing identical 3,000 square metre, three-storey timber-framed office buildings on each side of the Øresund Bridge spanning the strait between Denmark and Sweden. The office in Denmark is evaluated using Danish building regulations (Danish building regulation 2023), while the office in Sweden uses Swedish regulations (Klimatdeklaration). The results organised by building element group are shown in Table 1.
Floor area definitions are similar in Denmark and Sweden, meaning the variation in results are due to differences in system boundary and building elements. The greater number of building elements and lifecycle stages included in the Danish regulations produce a higher total GWP, even when operational energy is excluded. When emissions from operational energy are included, the GWP of the Danish building is nearly three times the Swedish building.
Figure 6 compares these buildings, where the authors descope the comparison to common life cycle stages (A1-A3) and building element groups. Even with descoping, there are still outcome differences, as the Danish calculations include biogenic carbon in A1-A3. A fairer comparison would remove biogenic carbon from scope., however, it is currently impossible with the Danish environmental product declarations (EPD) data. Consequently, it is only possible to compare A1-A3 of substructures not containing any biogenic carbon elements. Despite this, significant differences persist due to differing data sets and applying the penalty value to the generic data used in the Swedish method.
This example of an identical building demonstrates the potential distortion created when comparing different LCA approaches. Depending on definitions and scope, either the Danish or Swedish building could be perceived as more environmentally friendly. Both theoretical buildings are not different and their embodied carbon should be near identical, yet they are not.
The number and inconsistency of LCA methods used, and their different interpretations, create significant conflicts when reporting carbon values. The long-term solution is to improve multi-method harmonisation, particularly using common scope definitions for building and construction stakeholders. For now, the ability to distinguish life cycle scopes and boundaries remains, especially when assessing building performance and comparing solutions.
Want to know more?
Paul Astle
Decarbonisation Lead
+44 7436 545367
Astrid Eriksen
Student Assistant