Implementing circular building components can contribute to the transition to a circular economy. There are many possible circular design options for building components. Knowledge on which options are feasible to implement remains limited. Existing feasibility studies do not compare multiple circular design options, building components and/or are based on interviews rather than observation. They list barriers but do not identify their relative importance throughout a development process. In this article we present a longitudinal study on stakeholder choices in 5 development processes of 8 circular building components. The researchers co-created with stakeholders from initiative up to market implementation. Through process reflection and analysis, we identified choices which influenced the perceived feasibility of circular design options within different building components throughout their development. We found that circular design options perceived as feasible vary between different building components. Specific applications and context influence their feasibility. Moreover, perceived feasibility changes throughout the development process.

The transition towards a Circular Economy (CE) in the built environment is vital to reduce resource consumption, emissions and waste generation. To support the development of circular building components, assessment metrics are needed. Previous work identified Life Cycle Assessment (LCA) as an important method to analyse the environmental performance in a CE context. However, questions arise about how to model and calculate circular buildings components. We develop an LCA model for circular building components in four steps. First, we elaborate on the CE principles and LCA standards to identify requirements and gaps. Second, we adapt LCA standards and propose the ‘Circular Economy Life Cycle Assessment’ (CE-LCA) model. Third, we test the model by assessing an exemplary building component: the Circular Kitchen (CIK). Finally, we evaluate the CE-LCA model with 44 experts. In the CE-LCA model, building components are considered as a composite of parts and materials with different and multiple use cycles; the system boundary is extended to include these cycles, dividing the impacts using a circular allocation approach. The case of the CIK shows that the CE-LCA model supports an ex-ante assessment of circular building components in theoretical context; it makes an important step to support the transition to a circular built environment.

Introduction. The building sector consumes 40% of resources globally, produces 40% of global waste and 33% of all emissions. The transition towards a Circular Economy (CE) in the built environment is vital to achieve Sustainable Development Goals (SDGs) such as responsible consumption and production. The built environment can gradually be made circular by replacing the current 'linear' building components with circular ones during maintenance and renovation. However, there are many possible design alternatives for circular building components; knowledge on which variants perform best - from an environmental perspective - is lacking. Methods. In this article, we develop environmental design guidelines for circular building components. First, we synthesize design variants for an exemplary circular building component: the Circular Kitchen (CIK). Second, we compare the environmental performance of these variants and a 'business-as-usual' variant by applying a Material Flow Analysis (MFA) and Life Cycle Assessment (LCA). Finally, from the results, we derive design guidelines. Results. We synthesized four design variants: (1) a kitchen made from bio-based, biodegradable materials, (2) a kitchen made from re-used materials, (3) a kitchen which optimises lifespans and materials, and (4) a modular kitchen in which components (with varying lifespans) are re-used by the manufacturer. From the LCA and MFA, we derived 7 design guidelines, which include: consider building components as a composite of sub-components, parts and materials with different and multiple use-, and life-cycles; match the materialisation of each part with the expected life cycle (merely substituting for re-used or low-impact materials does not provide the most circular design); facilitate various loops (e.g., repair, re-use, recycling) simultaneously. Conclusions. The presented design guidelines can support industry in developing circular building components and, through implementation of these components, support the creation of a circular built environment.