## 4 Discussion
### Circularity Assessment Frameworks--Scopes and Objectives  
The application of CE principles in real estate, building design, and use (adaptability, durability, waste reduction, and high-quality management according to the European Commission [68]) is mainly focused on new buildings where circularity can be embedded and facilitated since the early design stage and consequently throughout the whole life cycle of a building and its components and materials. Conversely, circularity in the context of existing buildings is not yet defined [69]. The multitude of definitions of CE, particularly circularity in the built environment, does not contribute to a coherent, systematic approach. CE needs to be viewed as a business strategy, not only waste management or a design strategy. Optimizing buildings' use should also be spotlighted instead of only viewing those as potential material banks where components and materials can be recovered, reused, or recycled for new constructions [14; 69]. Still, recovered materials from existing buildings face a critical barrier in their technical compatibility and quality appraisal, which put their direct reuse in question, leading to down-cycling processes, engaging extra resources, and energy flows. On the other hand, less has been said about the design aspect of circularity integration in buildings (e.g., design for disassembly (DfD), design for adaptability (DfA), design for change (DfC), etc.) and the role of building professionals and supply chain elements in embodying the CE principles into the building sector [38]. In other words, existing practices and concerns focus on the CE principle of \"closing the loop\" which assumes intensified reuse and upcycling of materials and components. Meanwhile, the CE principle of \"slowing the loop\" that suggests increasing building and product longevity by preserving their value, quality, and efficiency to the highest possible extent has received less attention so far. This can be justified by the influence of the prevailing construction and design culture during the last decades of viewing buildings as temporal products of limited life service and predefined desthus--demolition. Another key principle of CE that is rarely addressed by existing frameworks is \"narrowing the loop\" which relies on using fewer resources per product. This principle is inspired by nature's processes that mainly use a limited chemical palette, often consisting of six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur, while industrial manufacturers follow a different approach, seeking out rare and toxic elements to reach the desired functional properties. Narrowing the loop delivers conditions for recycling by allowing efficient and facilitated material separation and recovery. Moreover, several tools have been developed to support the decision-making of designing or/and assessing buildings for circularity. However, many of these tools serve the same purpose with slight differences in goal and scope. The majority were developed to focus on specific aspects of circularity without considering other aspects, such as supporting products and materials choice by only substantiating material-related indicators based on their environmental impacts (e.g., aspects of health, non-toxic composition) and reuse and recycling potential, such as Materials Passports (MP), Circular Materials Platforms, Material Circularity Index (MCI) developed by the Ellen McArthur Foundation [13], and material flow analysis (MFA) tools. However, these tools fail to address a comprehensive circularity conception and lead to a loss of criticality when used individually since they do not appraise all the other important design aspects, e.g., building composition and connectivity between elements, durability, and service life of building components. This is because circularity values come up when specified intrinsic properties (material and product characteristics) cross with relational properties (building design and use characteristics) [25].