## 2 Materials and Methods
### Data Collection
#### 2.2.3 Semi-Structured Interview  
Semi-structured interviews are a valuable qualitative research method for collecting rich data and conducting in-depth explorations of topics without being constrained by a fixed number of questions or answers [76]. These interviews can take various forms, ranging from structured formats resembling questionnaires with opportunities for follow-up probing to broader discussions focused on key topic areas, capturing respondents' detailed perspectives [77]. Following the completion of the PIQ, face-to-face semi-structured interviews were conducted with 10 sustainability experts representing different areas within the building sector. A purposive sampling approach was employed to select participants, ensuring that individuals with the most relevant expertise were included. The selection criteria required participants to have at least eight years of experience in roles related to sustainability practices in the building sector. Stakeholder diversity was ensured by including representatives such as owners, contractors, consultants, designers, and academics to offer research-based \begin{table}
\begin{tabular}{c c c} \hline \hline
**Section** & **Question** & **Format** \\ \hline \multirow{4}{*}{Interviewee Background} & Name & Open-ended (Free Text) \\ \cline{2-3}  & Organization & Open-ended (Free Text) \\ \cline{2-3}  & Years of Experience & Open-ended (Free Text) \\ \cline{2-3}  & Level of Education & Open-ended (Free Text) \\ \hline \multirow{4}{*}{Circular Geometry} & Importance of CE strategies for fostering circular & \\  & economy across the building sector (Design, & \\  & Procurement, Operation, and End-of-Life Phases) & Likert Scale (1–5) \\ \cline{2-3}  & Faaibility of adopting CE strategies in the Saudi & \\  & Arabian building sector (Design, Procurement, & \\  & Operation, and End-of-Life Phases) & Likert Scale (1–5) \\ \hline \multirow{4}{*}{Building Types} & Feasibility of applying CE principles to building & \\  & types (Residential, Commercial, Business, & \\  & Educational, Healthcare, Industrial, and Storage) & Ranking (1 = Highest; 7 = Lowest) \\ \hline \multirow{4}{*}{Building Life Cycle} & Identification of critical lifecycle phases for & \\  & embracing CE principles (Initiation, Procurement, & \\  & Design, Construction, Operation, and End-of-Life) & Ranking (1 = Highest; 6 = Lowest) \\ \hline \multirow{4}{*}{Stakeholders} & Prioritization of stakeholder impact on CE & \\  & adoption (Owner, Manufacturer, Contractor, & \\  & Consultant, Sub-contractor, Designer, and & \\  & Demolition Contractor) & Ranking (1 = Highest; 7 = Lowest \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Pre-interview questionnaire questions. perspectives and theoretical insights. Participants were chosen from organizations with significant construction projects and academic institutions engaged in sustainability and CE-related research. The semi-structured interview allowed participants to expand on their PIQ responses, providing deeper insights into their reasoning and perspectives. The questions in the interview focused on gaining a deeper understanding of participants' reasoning behind their rankings of key aspects of CE adoption in building construction.