*4.3. The Relevance of Design Tools*

In the busy and increasingly complex practice of building designers, the question is to what extent tools are picked up and used to steer design choices. In general, design practice is largely based on experience and less on tools. This statement is confirmed by the survey of Weytjens et al. [20]. They concluded that design decisions are mainly based on experience, the client's demands and on regulations. Intuition and reference projects are taken into account by over 35% of the respondents when making design decisions, whereas only 21% use design decision tools as a deciding factor [20]. This does, however, not mean that tools do not have an unconscious impact on the considered alternatives and course of the design process.

Similarly, the development and use of design support tools cannot only guarantee the creation of circular buildings. Several other enablers and barriers that have an influence on the transition to a circular economy in the construction sector have been outlined too [21,22,108,109]. Furthermore, users and developers must be aware about every project's specific context [2,14] and the broad scope every design process entails.

## **5. Conclusions**

The present study was set-up to classify available design support tools for circular building, to identify building actors' needs and expectations from such tools and to reveal which research tracks on design support tools for circular building are currently being developed. This section divides the conclusions drawn and the actions to be taken for three types of actors: practitioners (building designers and advising engineers), tool developers and researchers.

First, from a practitioner's perspective, the present study categorises available design support tools for circular building and identifies designers' needs for such tools. This way, it offers an overview and reference to building designers and advising engineers which tools fit their particular needs, their way of working and the context of their projects(?), accelerating the tools' purposeful adoption in practice. Concretely, this study resulted in eight subcategories of tools each having its specific added value during different design stages: Design principles tools, Material flow analysis tools, Life cycle assessment tools, Material and product labels, Reused material platforms, Material passport tools, Life cycle cost tools and Knowledge sharing platforms.

Second, from a developer's perspective, this study reveals opportunities to work on new design support tools, to improve the already available tools and further accelerate their adoption. By comparing the identified needs through the set-up framework with ongoing developments on design support tools for circular building, it became clear that the needs of designers are only partially reflected by the available design support tools and the ongoing developments, and it is now better understood which features are overrepresented and which needs have received little attention so far. When developers create additional design support tools, they should investigate the tools already available, the support base of potential users and the added value of their tool. The resulting research agenda therefore includes these recommendations:


Third, from a researcher's perspective, the frameworks in Figures 2 and 3 are a first attempt to compare systemically the "supply and demand" in this field. This framework allows to further monitor the lack and oversupply of certain design support tools for circular building and guide researchers and developers further in their endeavours. Nevertheless, it also needs further refinement and validation. Concretely, possible research paths are:


Some of the shortfalls of this study include the focus on the region Flanders, which is a small region that has a specific construction sector culture and political landscape, and the small interview sample. However, given that Flanders can be considered as one of the forerunners in the transition towards a circular construction economy, makes the region and its ongoing initiatives a well-documented and instructive case for reflection and learning about the transition itself. The main limitation of the interview sample and the in-depth interviews is that generalizations about the results cannot be made because a small sample was chosen and random sampling methods were not used. These in-depth interviews, however, provide valuable information for a preliminary idea of what the needs are concerning design support tools for circular building and to be able to compare these needs with the available tools and research directions. Furthermore, this study focused on design support tools as a possible aid to provide guidance for the practitioners in the design process. Other tools and institutions can also be of significance as guidance, where the expertise of policy makers, researchers and consultants can be employed.

Through these insights and recommendations, this research wants to contribute to a much needed debate within the building sector supply chain to better understand and prioritise the key issues concerning supply and demand of design support tools for circular building practice and, consequently, supporting the construction sector in its transition to a circular, sustainable economy.

**Author Contributions:** The conceptualization, the outlining of the methodology, the original draft preparation and the making of the figures was performed by C.C.; For writing—review and editing, C.C. and W.G. were involved. The study was supervised by N.D.T. and W.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Fonds Wetenschappelijk Onderzoek (FWO), grant number 1S55518N.

**Conflicts of Interest:** The authors declare no conflict of interest.
