Diagnosing Barrier Interrelationships in International Modular Construction Supply Chains: A Hierarchical Grey DEMATEL Framework

International modular construction can improve quality, schedule performance, and labor efficiency, but its supply chains are exposed to cross-border barriers that remain insufficiently understood as an integrated construction-management problem. Existing barrier studies are useful for identifying salient constraints, yet they provide limited insight into how barriers interact and propagate across international modular delivery systems. This study investigates these interrelationships in international modular construction supply chains using a hierarchical grey decision-making trial and evaluation laboratory (G-DEMATEL) framework. Based on literature review, contextual analysis, and expert consultation, 26 barriers were identified and organized into four categories. The framework integrates grey linguistic assessments to capture uncertainty in expert judgments, objective expert-weighting schemes based on certainty and consensus, and hierarchical reconstruction of the global interaction matrix to reduce elicitation burden while preserving systemic interdependence. The results show that supply chain, production reliability, and skills barriers constitute the most prominent category, whereas international regulatory and financial barriers exhibit the strongest causal role. At the global level, Incoterms and risk-transfer ambiguity, shipment-classification ambiguity, and uncertain customs-clearance time emerged as the most prominent barriers, while fragmented regulations and jurisdiction across countries acted as the strongest upstream causal driver. These findings indicate that visible operational disruptions are often downstream effects of upstream regulatory, commercial, and governance uncertainty. The study contributes by explaining barrier propagation in international modular delivery as a cross-border engineering-management system and by providing a scalable decision-support approach for prioritizing earlier interventions related to contracting clarity, customs readiness, coordination, and logistics planning.