Decision support for the implementation of low-carbon measures in the building sector
Abstract: The building sector is responsible for about a fifth to a third of global greenhouse gas (GHG) emissions. Therefore, a successful mitigation of GHG emissions over the entire life cycle of buildings is particularly important to achieve climate targets such as the Paris Agreement. This requires measures at multiple levels and from multiple actors, including broad roadmaps for the building sector, policies and regulations, certification and green procurement criteria, and new practices among property owners, architects, developers and manufacturers. Such initiatives are sometimes supported by the introduction of tools and methods to quantitatively assess environmental performance. Life cycle assessment (LCA) is one such tool, used in certification and increasingly in procurement and regulation. To reliably steer towards lower environmental impacts, environmental performance assessment tools need to be precise, accurate and well-adapted to the decision contexts in which they will be used. While a tool like LCA can provide valuable decision support, some methodological issues remain unresolved, and its effect in real decision situations remains understudied.This thesis aims to support decisions and initiatives to mitigate environmental impacts in the building sector, with a particular focus on fulfilling ambitious climate targets. The thesis addresses two facets of this overarching issue. First, it investigates challenges to the implementation of relevant sustainable practices, at various levels and in various decision contexts. Second, the thesis considers to what extent environmental performance assessments could steer towards low environmental impacts (and in particular low global warming potential (GWP)).The thesis is based on a combination of quantitative and qualitative approaches. At a strategic level, a quantitative model of buildings’ GWP linked to four backcasting future scenarios is used to spotlight issues for the fulfilment of ambitious climate targets. This helps challenging existing paradigms and images of the future about how buildings are constructed and operated. At a more operational level, multiple qualitative studies explore barriers to specific practices to mitigate environmental impacts, and the roles played by environmental performance assessments. An interview- and workshop study explores important factors for the adoption of space sharing, as a way of optimizing the use of indoor space. A survey- and interview study highlights challenges to the use of requirements by Swedish municipalities to promote low-GWP construction. A third interview study shows how various artefacts mediate work with sustainable design in housing projects. Finally, the thesis addresses more directly the accuracy of environmental performance assessments, and investigates how choices of data and method related to maintenance and replacement affect LCA results, exemplified for façade materials.The modelling of buildings’ GWP in backcasting scenarios helps challenge current paradigms by drawing attention to some less-discussed issues, such as reducing embodied emissions (including by avoiding new construction) as well as the demand for indoor space. Space sharing can help optimizing the use of indoor space, but several factors limit its adoption. It requires different practices among building users and property managers, including different business models and performance metrics considering occupancy. Ambiguities in national legislation and municipal plans regarding the status of shared and multifunctional buildings also hinder space sharing initiatives (e.g. unclear rights and responsibilities of tenants and property owners, conflicting requirements for fire safety or ventilation, etc.). Similarly, the thesis highlights important regulatory ambiguities regarding to what extent municipalities can set requirements to promote low-GWP construction. Environmental performance requirements in construction also entail barriers related to limited in-house skills, access to data, time and resources. Using such requirements would first require bridging skill and data gaps. Similar barriers are highlighted regarding the use of LCA in public housing projects. In such projects, artefacts such as national regulations, local development plans and internal requirements of the housing organization enforce a certain level of work with sustainable design while limiting the range of design options. Other artefacts simplify the design work and provide standardized default options. In such cases, design choices that strongly influence environmental performance are taken upstream of the project, when these criteria, requirements and default options are developed.The thesis highlights ways in which quantitative assessments of environmental performance could directly influence building design and management, e.g. through the introduction of environmental performance criteria in regulation and procurement. Besides challenges related to skill, data, time and resources mentioned above, the thesis draws attention to the variability of LCA results due to choices of method and data sources. In the particular case of maintenance and replacement processes, the choice of reference study period (RSP) influences the relative significance of these processes, and longer RSPs favor more durable products. Discrepancies exist between different sources for service life data, indicating a need for more reliable data. The use of a round-up or annualized number of replacements makes little difference in average, but can lead to different outcomes in specific cases. This shows a need to carefully harmonize methodological choices as LCA becomes used more and more broadly in procurement and building regulation.Furthermore, the thesis also draws attention to more complex effects of environmental performance assessments in housing projects. Widespread certification systems can become de-facto definitions of sustainability for actors, influencing design even in projects that are not certified. Environmental performance assessments can hide or reveal certain aspects of sustainability. Widely used assessment tools can act as “black boxes”, where criteria for what constitutes a sustainable building are hidden and no longer contested. This process helps operationalize sustainability in building projects. However, it can lead to some important aspects being disregarded. For instance, conventional energy performance metrics are often normalized for floor area, ignoring occupancy and space efficiency. On the other hand, quantitative assessments can also highlight important aspects of the multifaceted issue of sustainability. The thesis exemplifies this by using a quantitative model of buildings’ GWP to draw attention to key mitigation strategies, and by reviewing energy metrics highlighting occupancy and space efficiency.
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