## 4 Discussion  
### Adaptability Assessment Frameworks--Scope and Objectives  
Existing adaptability assessment frameworks in large part, act in support of the decision-making at a lifecycle point when a building reaches obsolescence due to different factors (physical, social, economic, environmental, legal, technological, etc.). At this point, it is critical to choose between two alternatives (to demolish or to adapt) in terms of which would be more beneficial and economically viable. Adaptive reuse frameworks often apply to buildings that were not designed for future adaptability in the first place. These buildings often require huge interventions to be adapted to new functions or rehabilitated to carry out similar functions. Adaptive reuse tools are important to advance the circularity of existing buildings. However, other considerations are required to make more efficient decisions (e.g., the possibility of material recovery and waste management). The majority of the reviewed adaptability tools, particularly adaptive reuse models (e.g., ARP, ABD, PAAM, and ARAM), rely on the analysis of obsolescence causes being the trigger to take an adaptive reuse action (see Table 1). They, therefore, use the obsolescence criteria in their methodologies to address future uncertainties (ARP, ABD, IconCUR, AdaptSTAR, PAAM, ARAM). The literature places technical, physical, and economic factors on top of the most influential on a building's useful life. However, this study shows that prioritizing factors mainly depends on the building typology and function, tool purpose, and stakeholders' willingness to preserve it. For example, social, political and economic factors are prioritized over physical aspects for heritage buildings (as shown in the ARAM model). Table 1 presents a comparative analysis of the reviewed tools in terms of indicators' categories, prioritization and weighting methods in addition to the tools' outcomes and lifecycle stage intervention. Predicting future changes is a common attribute in adaptability assessment frameworks. However, from a circular economy perspective, the future is unpredictable. Buildings should therefore be prepared to accommodate any type of change that might run at any stage against making the maximum use of the full potentials of its life and the life of its components. Adaptive reuse tools target a later use stage of buildings to make decisions between two end-of-life options adaptation or demolition. Meanwhile, design-support tools for new  
buildings considering a whole lifecycle perspective are still in short supply (see Table 1). Existing ones only focus on specific dimensions of adaptability (e.g., layout adaptability in SAGA model) or specific typologies of buildings (e.g., commercial and office typology in ABD, office, and school building in FLEX 4.0). Table 2 synthesizes the results of the analysis of existing frameworks and methods in terms of target building typology and status, indicator type, and methodology's system and validation. The consideration of residential building typology is another shortcoming of existing models and only addressed in general adaptability frameworks with no specific tool or framework addressing the specific requirements of residential building adaptability. The focus is mostly given to commercial and office buildings because adaptations in these cases do not imply large transformations as those usually use simple layouts. Moreover, existing tools have not addressed radical functional shifts as the adaptability in these tools addresses alterations within the original use of the building. Criteria and indicators in the reviewed tools are often of qualitative and/or qualitatively quantified nature. Moreover, tools' frameworks were only tested on illustrative single case studies representing certain scenarios. Some of the frameworks also used inter-model comparisons for validation. As a result, most of the tools do not provide evidence on which design strategies/indicators most influence the overall adaptability performance.