Using Last Planner and a Risk Assessment Matrix to Reduce Variation in Mechanical Related Construction Tasks

Variation, defined for this research as the time difference between what was planned and what actually happened, is important as it can affect the productivity performance of construction tasks. The construction process is complex and consists of a large number of interdependent tasks. When the starting time and/or duration of one task varies, it can affect other downstream tasks and result in disruptions to the schedule and/or decreased productivity. This research examined the effect of using a risk assessment matrix in conjunction with the Last Planner System (LPS) method to reduce and/or eliminate task duration variation. A case study was conducted involving a mechanical contractor who specializes in plumbing, heating, ventilation, and air conditioning. The company compared the performance of two separate, but similar projects. The LPS method was used with one of the projects and the company’s traditional planning system was used with the other (i.e., not using the LPS system). A total of 16 weeks’ worth of data was collected for each project. Variation, productivity, and cost savings were analyzed using a risk assessment matrix and benefit–cost procedures. The project that used the LPS method had a 35% higher productivity performance than the traditionally planned project and resulted in a benefit–cost ratio of $13:1$. The research findings fill a gap in the body of knowledge by analyzing how planning can reduce variation with real project data. The results of this research illustrate the effect the LPS method can have on reducing variation and improving project productivity performance. The findings also serve as an example of an effective planning strategy for project managers and field managers in their efforts to improve project performance.