Case Studies of the Allocation and Reduction of Time Buffer through Use of the Last Planner System

Buffers are used in construction to absorb variation caused by the inherent complexity and uncertainty present in construction projects. The case studies presented here focus on time buffer added to construction task durations. For this research, time buffer is defined as extra time added during planning to individual task durations to compensate for uncertainty and protect against workflow variation. Two case studies were conducted with one involving a mechanical contractor and the other involving a large general contractor. This research contributes to the body of knowledge by: (1) investigating the time buffer impact on project performance; (2) empirically demonstrating the effect of last planner system (LPS) on reducing time buffer and increasing percent planned complete (PPC); and (3) examining the buffer trends of different trades and activity types. The findings demonstrate LPS as an example of an effective planning strategy for construction managers in improving project performance and help them understand what drives the need for buffer in their construction schedules, allowing efforts focused on strategically addressing the most critical areas of concern and uncertainty. (C) 2014 American Society of Civil Engineers.