**1. Introduction**

In recent years, a growing academic, political and industrial interest has been arising in transitioning from a linear to a circular economy (CE) [1,2]. A CE can be defined as "an economic system that is based on business models which replace the 'end-of-life' concept with reducing, alternatively reusing, recycling and recovering materials [...] with the aim to accomplish sustainable development [...].", according to Kirchherr et al. [3], who identified 114 different CE definitions.

The construction sector has an important role in the transition to a CE, as it accounts for about 50% of all extracted material and for over 35% of the EU's total waste generation [4]. Therefore, the European Commission identified "construction and buildings" as one of the seven key product value chains in its Circular Economy Action Plan [4]. Also, subsequent Flemish Governments have set the transition of the construction sector to a circular economy as one of their priorities [5,6].

Since 2014, the policy programme "Material-Aware Construction through Circular Supply Chains—A Sustainable Materials Management Prevention Program for the Construction Sector 2014–2020" [7] aims to establish an economy of closed material loops through socio-technical innovations in the Flemish construction sector [8]. The programme is governed by the Flemish Government's Agency for Public Waste, Materials and Soil (Openbare Vlaamse Afvalstoffenmaatschappij OVAM) under the auspices of the regional government of the Belgian region Flanders. As stated by Silva et al. [9], "the Flemish Sustainable Material Management program initiated by OVAM, was the first larger scale

waste to materials policy restructure in the world, [ ... ] and won a Circular award at the World Economic Forum for its dedication to shift towards a circular economy". Paredis [10] explained earlier:

"All in all, the change in discourse from waste to sustainable materials management is undeniable. It is not only taken up in the Materials Decree and propagated by OVAM as main government actor, it also seems to find support with all actors involved in the waste/materials system: advisory councils, different sectors of the industry, knowledge actors, such as universities and VITO, and NGOs. Politically, the build-up of the discourse coalition benefited from the possibility to link it to ongoing developments at European level and to the innovation and green economy debate at Flemish level".

More recently, to accelerate the implementation of the Flemish policy programme and to increase its impact, sector-oriented initiatives were set-up to foster new demolition and design practices, for example, waste management organisations (e.g., Tracimat) and design instruments [11], or so-called green deals [12] and project calls [13].

When taking a broader look at the rather complex landscape of the circular economy, one can notice that multiple pathways and directions are taken in various regions [14]. Circular economy has become a political ambition in the European Union and other countries worldwide, such as China and Japan [2], where each country or region has its own focal points. Even with given direction from the EU [4] and international standards [15], variations among different continents and even among EU-member states can be noticed in various sectors, including in construction. Whereas, in Portugal, for example, the CE concept is mostly applied in the area of waste management, in countries like Belgium and The Netherlands they also emphasise the implementation of CE principles in the design stage.

This diversity and divergence was also identified by Bauwens et al. who posit "that a CE can be conceptualized in very different ways and that it is essential to better examine the trade-offs between these conceptual models and their societal consequences" [16]. This diversity is not uncommon for challenging sustainability transitions. Transition Management researchers Geels and Schot name these multidimension processes "co-evolution" or "co-construction" and argue that the conjuncture of multiple developments is important for any transition's success [17].

Given that Flanders can be considered as one of the forerunners in the transition towards a circular construction economy (with varying success), it makes the region and its ongoing initiatives a well-documented and instructive case for reflection and learning about the transition itself.

Furthermore, in addition to the different directions of CE, today, many innovative experiments are being performed and various collaborations are taking shape. Also, in Flanders, experimenting with CE principles and exchanging knowledge and experiences is encouraged by, amongst others, the Flemish transition hub Circular Flanders. As a result, applications and analytical studies are each taking their own approach, and different practitioners have to navigate the increasing "methodological noise" and try to make sense of the available information and means for their own working context.

Hence, the transition to a CE within the construction sector still faces major challenges. The transition implies radical changes at different levels and scales: from organisational changes within the sector to new building design methods [14,18,19]. Due to the numerous challenges and the rather complex landscape of the circular economy, and even though there is a demand from Belgian construction stakeholders to implement circular building concepts [20], the construction sector still struggles to effectively put circularity into practice. For example, building designers find it difficult to design circular construction products or buildings, when there is a lack of interest, knowledge, skills or incentives [21,22].

As an answer to the struggles of this specific stakeholder group (i.e., the building designers and advising engineers), the demand and supply of design support tools for circular building is rising [21–23]. Design support tools intend to facilitate the design process. They can be defined as instruments of any form or kind that address architects and/or advising engineers, include circular design principles and/or evaluation criteria, and aim to make better informed design choices. These tools can be an important enabler in the transition towards a circular building sector [24] through providing guidance on, for instance, waste generation, material selection, making reversible connections between building elements, and on the reuse and recycling potential [25]. However, when using existing design support tools for circular building, or before developing new ones, one should know which tools are available, what their effectiveness and limitations are, and which tools or features are still missing. Due to the lack of an overview of the available tools [20] and a comparative framework, it remains unclear for designers and advising engineers which tools fit their way of working and the context of their projects. Further, there is a lack of understanding of what designers need of (features in) design tools [20]. Addressing the needs of these stakeholders is crucial to understand the potential uptake of tools, and it lowers the risk of putting effort into developing new design support tools without answering any need [26].

The present study was set-up to classify available design support tools for circular building, to identify building designers' and advising engineers' needs and expectations from such tools, and to reveal which research tracks on design support tools for circular building are currently being developed. The tools as well as the needs were classified per building design aspect and by design stage. This way, the tools and the needs could be compared. Subsequently, conclusions could be drawn on the effectiveness and limitations of the available design support tools, on opportunities to improve available tools, and on prospects to develop new tools for circular building.

We assumed that guiding the practitioners through this experimental phase, with finding the tools and methods that support their specific situation best, can accelerate the learning and transition process, or at least make it as effective as possible.

### **2. Method**

This study was done in five phases (Figure 1). The first phase entailed the selection and review of relevant design support tools for circular building. The design support tools were initially collected based on the authors' own knowledge of existence of such tools, enlisting other researchers and practitioners on their awareness and attending various events and presentations where design support tools were (partly) discussed. The relevant tools for this study were selected by using four criteria in line with the adopted definition mentioned earlier: instruments of any form or kind that address architects and/or advising engineers, include circular design principles and/or evaluation criteria and aim to make better informed design choices. The first selection criterium was "relevant for the Flemish building sector", related to the location context of this study, where tools were selected that are developed by Flemish or Dutch developers or by internationally known developers (e.g., The Ellen MacArthur Foundation, the European Commission and Pré (SimaPro)). The second selection criterium was "(claim to) support circular building". The tools were screened on the adoption of the circular design principles "closed-material loops" and "life cycle design". The third selection criterium was "available for use". Only tools which were ready for immediate use were selected. Tools that were still in the research phase or in the development were eliminated. The fourth and last criterium was that they should "address building designers and advising engineers". For example, written documents without a coupled action were considered redundant for this stakeholder group, and 38 tools remained after the selection process.

The process of categorising the tools was similar to defining themes in transcribed interviews [27]. A predetermined list of categories was set-up before defining the categories of the selected tools. This list contained general categories such as assessment tools, principle tools, economic tools and describing tools. This list was subsequently complemented during the review of their role in the design process. The six resulting categories were: Circular design strategies, Circularity score, Environmental impact, Product and material choice, Practical examples and Circular business models.

**Figure 1.** Diagram that shows the actions and results of the five research phases. RIBA is the Royal Institute of British Architects.

In the second phase, a framework that allows the consistent mapping of tools and needs was set-up. On the horizontal axis of the framework different building design stages were listed. Those stages were based on the Royal Institute of British Architects' (RIBA) Plan of Work [10] which is the definitive UK model for the building design and construction process and which was translated and verified for Flanders by Lespagnard [28]. On the vertical axis, the identified and abovementioned design tool categories were lined up.

During the third phase, stakeholders were interrogated through face-to-face, semi-structured interviews. The aim of the interviews was to obtain a preliminary but thorough idea of what the needs were of building designers concerning design support tools for circular building. Through in-depth individual interviews, valuable information could be provided on the personal thoughts and perspectives of the stakeholders on these needs. Seven interviews were conducted with different interviewees: a researcher on sustainable buildings (15 January 2019, Heerlen, The Netherlands), a facade contractor/designer (21 January 2019, Velp, The Netherlands), an architect (22 January 2019, Antwerp, Belgium), a sustainability engineer (23 January 2019, Louvain-la-Neuve, Belgium), an architect (03 September 2019, Antwerp, Belgium), an architect (04 November 2019, Brussels, Belgium) and an architect (06 November 2019, Brussels, Belgium). The interviewees were Flemish or Dutch

forerunners active in Flanders and were selected by the researchers on the basis of their familiarity with circular design principles and their practical design experience. This was assessed by reviewing their portfolio and their explicit circularity ambitions in various media. Although not representative for the whole sector, working with forerunners, as advised by Geels et al. [29], was important to have an in-depth understanding of the needs in design support tools for the still uncommon but generally envisioned practice of circular building. Concretely, interviewees were asked about their perceived needs and motivations related to the abovementioned tool categories in order to be able to proceed in designing circular buildings. The interview guide is available in Appendix A.

The fourth phase consisted of filling out the developed framework twice: once with the identified needs and once with the reviewed tools. To determine to which design phase(s) the tools belonged, three questions of the RIBA Plan of Work were adopted:


During the fifth and last phase, the two filled-out frameworks were compared with each other. The similarities and mismatches among the tools and the needs were identified, reviewed and analysed. Additionally, the ongoing main research and development tracks on the development of design support tools for circular building design were outlined. These research paths were also compared with the needs of the building designers and advising engineers. Last, further research and development paths were identified and proposed for practitioners, tool developers and researchers, based on a synthesis of the previous phases.
