*4.2. Ongoing Research Tracks and Developments on Design Support Tools for Circular Building*

Next to the available tools, there are ongoing research tracks on the development of design support tools for circular building design. These trends show that the circular economy still has a significant traction in academia and in the building practice. Most developments are focusing on (1) the integration of BIM with LCA; (2) the integration of BIM with circular design strategies; and (3) developing tools to measure circularity in a building. In this study, BIM was not seen as a design support tool as such but as a concept and method to enhance creating and managing information of a construction project by its linked database of geometric and nongeometric data attached to building elements. The main reason to integrate BIM with design support tools is to deliver accurate and adequate information of the building design, to decrease the (calculation) effort and to speed up the project process [86,87]. Additionally, in Belgium, 29% of the architect officesalready used BIM in their projects and 67% are aware of its functionalities in design practice [88]. This awareness could lead to a large implementation percentage of tools linked to BIM.

The first research track, the integration of BIM in LCA, has been progressively published in scientific literature in the last five years and new tools have been developed [86,89,90]. Building information modelling tools can facilitate quantitative assessments of design options, with automated inventories of material flows and waste [24,91]. This trend answers to the need of making LCA user friendlier (Figure 3). This is an important aspect, as ease of use is considered essential (85%), even more than the cost of a tool (63%) according to a survey done with 224 Flemish architects [20].

Similarly, the second research track concerns circular design strategies tools that become increasingly BIM compliant. For example, the disassembly network analysis method uses BIM and network analysis to analyse the interdependency between building elements to define which elements are recovered and lost during the disassembly of a building and to calculate how long the disassembly takes [91]. Other examples are the BIM-Based Deconstructability Assessment Score, which determines the extent to which a building could be deconstructed [24], and the disassembly planning method of Sanchez et al. [92]. Integrating BIM in design tools for reversible buildings is a result of the support that BIM can offer in this respect: efficiently developing three-dimensional representations of a reversible building, identifying spatial conflicts in the design and collaboratively resolving them with clash detection software [93].

A third development path contains tools and methods that aspire to quantify circularity in buildings. They do so in two different ways. First, the research on circularity indicators in construction is growing [94–96]. For example, Verberne et al. [95] developed a tool that determines the degree of circularity. However, also in this case, the comment was made that the assessment model is meant to provide guidance in concretising the ambitions and should not be seen as an absolute outcome. In the same vein, Flanders developed the GRO tool which is based on sustainability criteria and performance levels [45]. Second, adaptive capacity quantification tools arise as well [97]. For example, the Spatial Assessment of Generality and Adaptability (SAGA) method uses weighted graphs to quantify a building's capacity to support changes [98], the FLEX 4.0 uses a point-based system to assess the adaptive capacity of buildings [99], and the AdaptSTAR model is based on a weighted checklist scoring system to evaluate future adaptation potential in newly designed buildings [100].

Next to those three main research tracks, there are also several tools that do not fit a well-developed research track. There are some initiatives to develop collaboration tools for circular economy in the building sector that is published in the scientific literature such as by Leising et al. [101] and Simons et al. [102]. The conceptual tool "Circular Building Components"-generator aims to support designers in creating and reviewing circular design options [103]. Furthermore, when looking at a broader perspective than the construction sector, more tools on circular design are being researched and developed. For example, the tool of Gehin et al. [104] on implementing sustainable end-of-life strategies in the product development phase, the value mapping tool for sustainable business modelling by Bocken et al. [105], the Circular Material Library of Virtanen et al. [106] and the assessment tool for end of life product recovery strategies by Alamerew et al. [107] are studies aiming to develop design support tools for all kinds of circular products.
