Examining Off-Site Construction from a Flow Viewpoint

The theoretical connections between off-site construction (OSC) and lean have only been marginally addressed in existing literature. This study analyses how distinct OSC strategies (1) affect flow and completion times, and (2) support simplification in construction (by reducing the number of parts and/or steps). Flow, which entails the smooth and reliable transfer of work across trades, is at the heart of lean whereas simplification is one principle of this management philosophy. Industry data based on three residential projects built in Australia using traditional construction or OSC strategies (panels/cassettes, and/or bathroom pods), and 15 hypothetical scenarios were used to develop a simulation exercise. The results show that OSC can substantially reduce schedule durations, particularly when different prefab elements are jointly used, but flow variability [measured by coefficient of variation (COV)] remains unchanged when compared to traditional construction. OSC was found to minimize the number of parts on-site by having building materials and components aggregated off-site and delivered as subassemblies. Yet, the number of steps did not reduce substantially, and the reductions only occurred when panels/cassettes were used. Alternative perspectives explaining the numerical results obtained are also discussed. The main contribution of this paper lies in measuring the impact of distinct OSC strategies from a flow viewpoint as well as in empirically examining their benefits from a simplification viewpoint. The study extends existing knowledge by leveraging industry data to quantify such impacts utilizing a tailored simulation approach. This provides an important addition to the still limited number of investigations measuring and comparing flow under different conditions.