Evaluation of efficiency in housing construction design

In housing projects a lot of time is spent for rework, entailing the risk of additional costs, time and deficient quality. As much as 50% or more of rework is originated in faulty output from the design phase. Activities within this phase are strongly interrelated and are carried out by several design consultants. Once the sequence of work in an ongoing project is interrupted the risk for loosing control is high. This results in, e.g., poor coordination of project participants, necessary changes in schedules, possible time pressure and about all a higher risk for making errors. The goal with this study is to reduce the risk of work sequence interruptions in the design phase of housing projects, or in terms of Lean, to make activities in the design phase flow. A timber housing multi dwelling building project in Sweden has been mapped in detail. In total 212 activities have been observed and recorded, spanning from the sales to the erection phase. Iterations (rework) have been identified by using process mining techniques in combination with supplemental interviews. A map of the complete design process consisting of 112 activities (exclusive of iteration) has been derived. A measurement model to detect process regions with a high share of iteration has been proposed that, together with the process map, serves as a starting point for further process optimisation. The efficiency of an activity is assessed by comparing the working hours, ignoring the time used for negative iteration (waste), with the working hours actually used to execute this activity. A Pareto-analysis of the occurring iteration with negative impact on quality then provides an indication of a suitable order for process optimisation.