The Circular Economy (CE) paradigm has been gaining momentum. However, the tools and methods used to design, measure and implement circularity are not immediately suitable for decision making and practice by key stakeholders. This article details a qualitative and a quantitative method to evaluate characteristics such as circularity, adaptability and reuse of building elements amongst others in order to provide decision-makers, such as building clients, architects, investors and policy makers, an objective way to assess the benefits and constraints of circular buildings and elements. The study implements the method in the case study, the Circular Retrofit Lab in Belgium, and uses a multi-criteria decision approach to evaluate qualitative parameters and life cycle assessment and life cycle costing to quantitatively evaluate the circular solutions proposed in this study. As such, the paper shows how a multi-criteria decision approach can be applied to evaluate circular building solutions in the context of practical architectural projects, in this case assessing the suitability of three interior wall systems for applications with different turnover rates. The study shows that the overall performance of the evaluated wall systems varies largely from one expected user scenario to the other.

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In 2018, the construction sector was responsible for 39% of the worldwide energy and process-related carbon dioxide emissions (Global Alliance for Buildings and Construction et al., 2019). This is partly due to the embodied carbon, which represents the carbon emissions related to building construction and material production (LETI, 2020). While zero energy buildings and zero energy renovations start to get the operational carbon down, the circular economy aims to do this by closing material loops and stimulating the reuse of discarded materials in building construction (Ellen McArthur Foundation et al., 2015). Although it is not a new phenomenon, material reuse does require a substantially different approach and is at this point not yet common in the building industry. This is especially true for load-bearing components. This article presents a pilot project for the reuse of discarded timber formwork for the construction of the façade and (load-bearing) substructure of a new house. Through this pilot case and by reflecting on a series of similar cases, it studies the remaining challenges for material reuse but also proposes and assesses redesign strategies that will allow upscaling the reuse of timber formwork. The project shows that although waste, material, and money can be saved by using reclaimed materials, it does complicate the design and construction process and, as such, does not necessarily reduce the total project budget. Moreover, for reuse to become a current practice, new design approaches and collaborations will need to be established. Finally, socio-economic factors must be considered to increase the acceptance of reclaimed materials in new building construction.

Living in an age of rapid changes, designers are challenged to create solutions that remain sustainable in a continuously evolving environment. Since most of our earth's resources are finite, these solutions should incorporate efficient material use and reuse. Buildings and structures are always in transition. Facilitating these transformations is vital to the sustainable development of our built environment. With our group we study, develop and assess transformable structures on different scales, in different contexts and for various time-spans and purposes. This paper presents our work on transformable structures, based on four case studies: a kinetic curved-line folding component, a temporary and rapidly assembled structure, a dynamic wall assembly and a BIM tool for material flow assessment of adaptable buildings. Although varying in scale or purpose, these cases demonstrate the same key principles of transformability. Reducing the complexity of the connections and structural system facilitates an easy and rapid assembly, but also allows users and locals to participate in the assembly, maintenance, reconfiguration and deconstruction of the structure. Apart from benefits during the assembly and adaptability, it is important to assess transformable structures and building solutions on their material and cost effectiveness. With BIM tools it is possible to incorporate this assessment already in the conceptual design phases of a project, as illustrated in the fourth case. Keywords: BIM, deployable structures, design for change, kit-of-parts structures, material flows, prototyping, transformable structures. INTRODUCTIONThe complex nature of our built environment subjects it to continuous evolutionary processes. The subsequent changes in cultural trends, global markets and technological innovation increasingly lead to resource depletion and waste production, and thus endanger the self-sustaining nature of our planet. Because most of the earth's mineral and fossil resources are finite, they should be used and reused wisely. Designers are challenged to create solutions that remain sustainable in a continuously changing context. The structures of the built environment in which we operate are never end states, but phases of a process. Facilitating transformations is vital to sustainable development. This requires holistic approaches that take change into account and help alleviate future problems.By introducing transformational capacity at different design levels, we want to maximise the sustainability of settlements, structures and components through time while minimising the waste of resources. We believe that transformability can act as an important catalyst for sustainable development because of the social, economic and ecological qualities it generates over time and the life-cycle resource management it incorporates. With our research group, we study, analyse, design and assess transformable structures varying in scale, context, timespan and purpose. This paper discusses the main principles of the develop...

As opposed to conventional, static structures, transformable structures possess a transformational capacity enabling them to efficiently respond to altered boundary conditions, such as climatic conditions, different locations, varying functional requirements, or emergency situations. Generally, this capacity is provided through built-in mobility (structural mechanisms) or by means of assembly/disassembly of its constitutive members (kit-of-parts systems). The former group demonstrates kinematic properties that allow them to rapidly respond to changing needs by folding, expanding, or by any other form of deployment. Generally they come in the form of lightweight deployable structures that can easily transform between different configurations. This makes them fit for temporary, mobile applications or for adding adaptable sub-structures to buildings. In what follows, the research performed at the Vrije Universiteit Brussel by the Transform Research Group, the Lightweight Structures Lab, and the Mechanics of Materials and Constructions research group (MeMC), all collaborating on lightweight deployable structures, is presented. Through six case studies, diverse possibilities of deployable structures in architectural and structural engineering are explored. Key aspects concerning the design, analysis and construction of mobile, as well as adaptable constructions, are explained. Finally, conclusions are drawn on the intricate relationship between the geometric configuration, the kinematic behaviour and Mobile and Rapidly Assembled Structures IV 1

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