Causes of Time Buffer and Duration Variation in Construction Project Tasks: Comparison of Perception to Reality

Due to the inherent nature of the construction industry, all construction projects have some amount and type of uncertainty. This uncertainty can lead to variation in project task durations from what was originally planned. As a result, construction personnel compensate for the uncertainty by adding a time buffer to absorb variations in the work plan. For the purpose of this research, a time buffer is defined as the amount of time included in task durations to compensate for uncertainty and to protect against variation. Variation is defined as the difference between the planned and actual task duration. Although previous research acknowledges time buffer additions, the root causes for adding a buffer have not been thoroughly researched. A nationwide survey was administered to project managers, superintendents, and foremen to identify the most severe reasons for adding time buffers to construction task durations. The root causes of variation have been previously identified and are used as the comparison benchmark. Contributions to the body of knowledge include (1) comparing and contrasting the overall most severe causes of time buffers with the most severe causes of duration variation to identify disconnects between the perception of concerns about uncertainty and the reality of what causes task duration variations at different levels of management; and (2) the use of factor analysis to quantitatively identify the underlying structure of time buffer factors. The findings of this research will help construction managers understand what drives the need for buffers in their construction schedules and allow them to focus efforts on strategically addressing the most critical areas of concern and uncertainty. Furthermore, the research reveals similarities and disconnects in the effects of uncertainty on planning and task execution. © 2014 American Society of Civil Engineers.