Design of Work in Process Buffers in Repetitive Building Projects: a Case Study

Variability in construction projects usually leads to schedule delays, cost overruns and productivity losses. Among the different techniques and tools employed to manage a construction project the use of buffers is a common approach to handle variability and to protect production processes from its negative impact. Time float, resource inventories and budget contingencies are examples of buffers used in construction in an intuitive and informal way. Empirical evidence recently collected about existing inefficiencies in the use of WIP (Work-in-Process) in construction projects highlights the double-opportunity to improve current practice of WIP and variability management by using WIP as buffers. The paper addresses the use of WIP buffers in construction schedules of repetitive building projects and proposes an approach for WIP buffer design. A discrete simulation model to study the impact of the optimum WIP buffer size on construction schedule was developed and this paper presents its application to a real project (case study). Finally, simulation results and the potential of WIP buffers to implement production strategies based on Lean Construction principles in construction projects are analyzed.