## 4 Focus Group Study  
After exploiting a comprehensive literature review, a preliminary list of constraints in modular construction was established. It was then followed by a focus group study to refine critical constraints. According to [PERSON] [70] and [PERSON] [71], a focus group study is an efficient method to observe a large amount of interaction and add related data to a topic in a limited period. In this study, a face-to-face focus group study recruited 12 experts, including two from the academy, three developers, two designers, two manufacturers, two contractors and one transporter. All of these interviewees had practical experience and relative research surrounding modular construction for at least five years (Table 2). The overall process of the interview was recorded by the author. The audio record was transcribed as well as analysed utilising NVivo systematic coding and data retrieval. \begin{table}
\begin{tabular}{c c c} \hline
**Code** & **Constraints** & **Key Reference** \\ \hline C1 & Lack of experience and expertise & [36; 52; 53; 54; 55] \\ C2 & Lack of government support & [33; 35; 36; 38] \\ C3 & Poor market and society acceptance & [32; 55; 56] \\ C4 & Higher capital cost & [8; 20; 34; 43; 46] \\ C5 & Higher construction cost & [37; 46; 57] \\ C6 & Additional transportation cost & [8; 47] \\ C7 & Additional crane cost & [8; 58] \\ C8 & Lack of R\&D and resource support & [59; 60] \\ C9 & Lack of coordination and communication among stakeholders & [30; 54; 55; 61; 62; 63] \\ C10 & Lack of building codes and standards & [32; 33; 38; 43; 44] \\ C11 & Unable to freeze design early & [41; 42; 63; 64] \\ C12 & Poor design flexibility & [42; 62] \\ C13 & Complexity of design on seismic performance & [17; 65] \\ C14 & Complexity of design on fire-resistant performance & [66; 67] \\ C15 & Incompetence of suppliers and manufacturers & [36; 40; 68] \\ C16 & Unable to achieve economies of scale & [32; 44] \\ C17 & Lack of skilled labour & [8; 33; 43; 45] \\ C18 & Limitation of weight and dimensions & [31; 48; 61] \\ C19 & Damage to modules during transportation & [50; 55; 62] \\ C20 & Limitation of transport routes & [55; 63] \\ C21 & Limitation of cranes to lift modules & [34; 51] \\ C22 & Complexity of connection & [32; 51; 69] \\ C23 & Demand for on-site modules storage & [33; 55] \\ C24 & Lack of quality inspection standard & [31; 38; 62] \\ \hline \end{tabular}
\end{table} 
Table 1: The preliminary list of constraints hindering the development of modular buildings. \begin{table}
\begin{tabular}{c c c} \hline
**Role** & **Job Title** & **Years of Experience** \\ \hline Academic Researchers & Professor & 8 \\  & Senior Lecturer & 6 \\ Developers & Design Manager & 5 \\  & Business Manager & 10 \\  & Operations Manager & 6 \\ Designers & Senior Architect & 8 \\  & Architect & 5 \\ Manufacturers & Design Manager & 7 \\  & Operations Manager & 6 \\  & Project Manager & 8 \\ Contractors & Site Manager & 12 \\  & Transporters & General Manager & 8 \\ \hline \end{tabular}
\end{table} 
Table 2: Information on experts for focus group study. The 24 constraints were reviewed and discussed by 12 interviewees, who endorsed that these constraints can portray general issues in modular construction. Combining with practical experience, experts pointed out some critical constraints that emerge in multiple phases throughout modular construction, such as lack of coordination and communication, which hamper the widespread application of modular buildings and should be addressed urgently. Aside from 24 constraints, experts supplemented three factors, namely poor supply chain integration, weather disruptions and lack of relevant application and technical support. Comparing with traditional construction, modular construction highly depends on the reliability and sustainability of supply chain comprising procurement, design, manufacture, transportation, and assembly.