Creating a circular economy within the built environment plays a crucial role in society’s pursuit to become more sustainable. A building consists of building components, such as a kitchen, façade and roof. By replacing building components with more circular ones during new construction, maintenance and renovation, we can gradually make buildings circular. There are many design variants for circular building components. Knowledge on which variants are the most circular, and which are feasible to implement is lacking. In this dissertation, we develop and test 8 circular building components for housing renovation together with Dutch social housing associations and industry partners. Combining Action Research and Research through Design approaches, we generate knowledge on 4 research goals. We present a design tool for circular building components. We develop a Life Cycle Assessment model to assess the environmental impacts of circular building components. We compare the environmental performance of multiple circular design options for multiple building components and derive environmental design guidelines. Finally, we identify which stakeholder choices throughout the development of 8 circular building components led to feasible, circular building components. We conclude that not all circular design options lead to desirable circular building components; not all desirable circular design options are yet feasible. This research makes scientific contributions to circular design theories, management models for the built environment, and research methodology. We recommend 4 changes in practice to implement more circular building components.

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 environmental impacts, resource consumption and waste generation. The built environment can be made circular by replacing building components with more circular ones. There are many circular design options for building components and knowledge about which options perform better – from an environmental perspective – is limited. Existing guidelines focussed on single components, single circular design options, applied different assessment methods and provide conflicting guidelines. Therefore, in this article, we develop environmental design guidelines by comparing multiple circular design options for two building components: a kitchen (short service life) and renovation façade (medium service life). First, we synthesize design variants based on distinct circular pathways, such as renewable-, non-virgin material use, and modularity for reuse. Second, we compare their environmental performance to a ‘business-as-usual’ variant through Material Flow Analysis (MFA) and a multi-cycle Life Cycle Assessment (LCA) including extensive sensitivity analysis on circular parameters. Analysing the 78 LCAs and MFAs, we derive 8 lessons learned on the environmental design of circular building components. We compare our findings to existing guidelines, including those for circular building structures (long service life). Amongst other lessons, we found components with a short service life benefit more from prioritizing circular design options to slow and close future cycles, whilst components with a longer service life benefit more from reducing resources and slowing loops on site. However, applying circular design options does not always result in a better environmental performance. Tipping-points were identified based on the number of use cycles, lifespans and the assessment methods applied.

The built environment can be made more circular by gradually replacing building components with more circular components during construction, renovation, or maintenance. However, many different design options can be seen as circular. Although there is a growing number of studies about circular design options, research on what makes these options feasible or not feasible in practice is limited. This type of research requires intensive, long-term involvement with practitioners. Therefore, this article presents a longitudinal case study of an exemplary circular building component: the circular kitchen. The researchers actively engaged in a co-creation with industry partners to develop a circular kitchen design, supply chain model, and business model. All the choices made from initiative to market implementation were documented. Five lessons were drawn from an analysis of the stakeholder choices that can aid the future development of feasible circular building components: about ambition, aesthetics, design scale, participation, and focus.

The construction sector can become more sustainable by applying the Circular Economy concept, which distinguishes two main pathways: substituting materials for biological materials, or optimizing the use or reuse of technical materials. Practitioners sometimes choose one pathway over the other, but knowledge of which of these pathways yields the best circular performance for the building industry is lacking. To determine which pathway is the most circular, the performance of biological, technical, and hybrid variants for a circular kitchen and renovation façade are developed and compared with one another and with the linear ‘business-as-usual’ (BAU) practice components. The novel methods of Circular Economy Life Cycle Assessment (CE-LCA) and Circular Economy Life Cycle Costing (CE-LCC), and traditional material flow analysis (MFA) are used. The results show that the biological kitchen and façade consistently perform best in the CE-LCA, but perform second best and worst in the MFA respectively, and consistently perform the worst in the CE-LCC. Technical solutions perform best in the MFA. However, while the technical kitchen performs second best in the CE-LCA and best in the CE-LCC, the technical façade performs worst in the CE-LCA and third best in the CE-LCC. A purposeful, reversible, hybrid application of biological and technical materials yields the most consistent circular performance overall, performing best in the CE-LCC (saving 17 % compared to BAU), second best in the MFA (saving 23 % compared to BAU), and third best in the CE-LCA (an increase of 21 % compared to the BAU). This study shows that neither a purely biological nor purely technical solution performs best overall, but that a purposeful hybrid solution can mitigate the disadvantages of both pathways. Further research is recommended to assess more building components and other hybrid variants.

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.

Transitioning to a circular built environment can reduce the environmental impacts, resource consumption and waste generation emanating from buildings. However, there are many options to design circular building components, and limited knowledge on which options lead to the best environmental performance. Few guidelines exist and they build on conventional environmental performance assessments that focus on single life cycles, whereas the circular economy (CE) focuses on a sequence of multiple use-and life cycles. In this article, environmental design guidelines for circular building components were developed in five steps. First, examples of circular variants of a building structure were synthesized. Second, the environmental performance of these variants was compared with a business-as-usual variant through Life Cycle Assessments (LCA) and Material Flow Analysis (MFA) respectively. Circular parameters of these variants were tested using a scenario-specific approach. Third, from 24 LCAs and MFAs, a scorecard, rules-of-thumb and nine environmental design guidelines for designing circular building components were developed that provide guidance on which circular pathways and variants lead to the best environmental performance. For components with a long functional–technical lifespan, the following are promoted: resource efficiency, longer use through adaptable design, low-impact biomaterials and facilitating multiple cycles after and of use. Fourth, the design guidelines were evaluated by 49 experts from academia, industry and government in seven expert sessions. Further research is needed to validate the generalizability of the design guidelines. However, this research makes an important step in supporting the development of circular building components and, subsequently, 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.

The building industry is responsible for the highest resource use, amount of waste and emissions of all industries. The principles of the Circular Economy (CE) could offer an approach to create a more sustainable built environment. For a transition towards a circular built environment, a comprehensive assessment method is needed to support the development of circular building products. As a step towards such a method, we developed an economic assessment in the form of a Circular Economy Life Cycle Cost (CE-LCC) model. It is based on existing Life Cycle Cost techniques and adapted to meet the requirements of CE products. The model is developed to (1) consider products as a composite of components and parts with different and multiple use cycles, (2) include processes that take place after the end of use, (3) provide practical and usable information to all stakeholders, and (4) facilitate alignment of the functional unit and system boundaries with LCA. To test the model, it has been applied to the case of the Circular Kitchen (CIK). Three variants of the CIK were compared to each other and the ‘business-as-usual’ case to determine which variant is the most economically competitive on the long term. The model indicates that the most flexible variant of the CIK has the lowest LCC outcome, even when considering multiple interest, lifespan and remanufacturing and recycling scenarios. Although, the model could benefit from further research and application, it can support the transition towards a more sustainable (building) industry.

The transition towards a Circular Economy (CE) in the built environment is crucial to achieve the Sustainable Development Goals (SDGs). Theoretical frameworks and methods for circular design have been developed. Yet, there is a lack of knowledge on circular design in practice and how circular design thinking can be supported. This study aims to provide insights on circular design in practice and how this can be supported through circular design methods. First, we reviewed existing circular design methods and developed a card-based circular design tool. Next, an interactive survey and design workshop using the tool was carried out with 12 design experts to gather knowledge on circular design in practice. Finally, we derive key learnings that can support the development of circular design methods and advancement of CE in practice. Overall, circular design remains highly conceptual and is challenging due to the interconnectedness of parameters and temporal aspects such as product life cycle. Designers need ways of educating and convincing stakeholders on the value and feasibility of circular design. Advancing the CE in practice requires circular design methods that help to contextualize the design process and reduce complexity, and examples are needed of how CE can be implemented in practice.

Introduction. The building sector consumes 40% of resources globally, produces 40% of global waste and 33% of greenhouse gas emissions. The transition towards a Circular Economy (CE) in the built environment is vital to achieve the Sustainable Development Goals (SDGs) of climate action and responsible consumption and production. Metrics are needed to support this transition; previous work identified Life Cycle Assessment (LCA) as the best method to analyse the environmental performance of the CE. However, current LCA methods focus on the individual system, considering a single lifecycle. Circular assessment requires a systems-perspective: buildings, components, parts and materials have multiple lifecycles. Thus, questions arise about how benefits and burdens should be allocated between systems. Method. In this study, we compare the potential influence of applying different allocation approaches in LCA method. We calculate the environmental impacts of two 'circular building components': (1) a concrete column designed for direct reuse and (2) a recyclable roof felt. We applied four allocation approaches: (a) the cut-off approach stated in EN 15804/15978, (b) the Circular Footprint Formula (CFF) from the Product Environmental Footprint (PEF), (c) the 50:50 approach, and (d) the linearly degressive (LD) approach. Results. The allocation approaches resulted in notable differences in impact distributions thereby incentivising different CE principles (narrowing, slowing and closing). Due to the long lifespan of building components, concerns regarding uncertainty and 'green-washing' resulting from allocation of impacts between cycles arise. However, the LD approach was, for closed-loop systems (such as the ones assessed here), found to be promising: it is simple to use; it creates incentives for narrowing, slowing and closing loops and to design for these in the future; it deals with the uncertainty, material quality and number of use cycles. Conclusion. The comparison of allocation approaches and first recommendation on an allocation approach provides an important step towards circular life cycle assessment and, subsequently, helps promote the CE concept within the building industry.

Transitioning the built environment to a circular economy (CE) is vital to achieve sustainability goals but requires metrics. Life cycle assessment (LCA) can analyse the environmental performance of CE. However, conventional LCA methods assess individual products and single life cycles whereas circular assessment requires a systems perspective as buildings, components and materials potentially have multiple use and life cycles. How should benefits and burdens be allocated between life cycles? This study compares four different LCA allocation approaches: (a) the EN 15804/15978 cut-off approach, (b) the Circular Footprint Formula (CFF), (c) the 50:50 approach, and (d) the linearly degressive (LD) approach. The environmental impacts of four ‘circular building components’ is calculated: (1) a concrete column and (2) a timber column both designed for direct reuse, (3) a recyclable roof felt and (4) a window with a reusable frame. Notable differences in impact distributions between the allocation approaches were found, thus incentivising different CE principles. The LD approach was found to be promising for open and closed-loop systems within a closed loop supply chain (such as the ones assessed here). A CE LD approach was developed to enhance the LD approach’s applicability, to closer align it with the CE concept, and to create an incentive for CE in the industry.

The building sector consumes 40 % of resources globally, produces 40 % of global waste and 33 % of CO₂ emissions. Creating a circular built environment is therefore of paramount importance to a sustainable society. The housing stock can be made more circular through circular retrofitting. However, strategies and solutions integrating circularity within housing retrofit are lacking. This paper focusses on developing a circular housing retrofit strategy and solution for Dutch housing constructed between 1970 and 1990. Through literature study, potential circular retrofit approaches are identified and translated into a general strategy. By developing a concrete retrofit solution, we illustrate how this general strategy can be applied in practice. It is found that in the Dutch context 'all-in-one' sustainable retrofits are difficult to realise. By applying modular (allowing component-by-component retrofit), 'mass-customisable', and 'cyclable' retrofit products, natural maintenance moments can be employed to gradually create a circular housing stock. As an example of such a product we describe the Circular Kitchen (CIK), which was developed together with industry. The CIK applies a plug-and-play design, separating components based on lifespan. The CIK supply-chain arranges 'relooping' of the CIK in a 'return-street' and 'return-factory'. The CIK business model applies financial arrangements such as lease and 'sale-with-deposit', motivating the return and 're-looping' of the CIK after use. In conclusion, the strategy presented in this paper has the potential to support circular housing retrofit in the Dutch context and for housing with similar characteristics. However, development of more circular retrofit products is necessary to create a fully circular housing stock over time.

Purpose: The transition to a circular economy in the built environment is key to achieving a resource-effective society. The built environment can be made more circular by applying circular building components. The purpose of this paper is to present a design tool that can support industry in developing circular building components. Design/methodology/approach: The tool was developed and tested in five steps. In Step 1, the authors analysed existing circular design frameworks to identify gaps and develop requirements for the design tool (Step 2). In Step 3, the authors derived circular design parameters and options from existing frameworks. In Step 4, the authors combined and specified these to develop the “circular building components generator” (CBC-generator). In Step 5, the CBC-generator was applied in the development of an exemplary component: the circular kitchen and tested in a student workshop. Findings: The CBC-generator is a three-tiered design tool, consisting of a technical, industrial and business model generator. These generators are “parameter based”; they consist of a parameter-option matrix and design canvasses. Different variants for circular components can be synthesised by filling the canvasses through systematically “mixing and matching” design options. Research limitations/implications: The developed tool does not yet support establishing causal links between “parameter-options” and identification of the most circular design variant. Practical implications: The CBC-generator provides an important step to support the building industry in developing and implementing circular building components in the built environment. Originality/value: Whilst existing tools and frameworks are not comprehensive, nor specifically developed for designing circular building components, the CBC-generator successfully supports the integral design of circular building components. First, it provides all the design parameters which should be considered; second, it provides extensive design options per parameter; and third, it supports systematic synthesis of design options to a cohesive and comprehensive circular design.