Process waste analysis for offsite production methods for house construction – A case study of factory wall panel production

There is a growing interest in the use of offsite manufacturing (OSM) in the construction industry disregarding criticisms of lacking real improvement from some offsite approaches adopted by housebuilders as compared to their onsite counterparts. Quantitative performance measures from previous studies are based on conventional onsite methods, with little attention paid to the performance and process improvements derived from various OSM methods. In response, a case study was conducted based on two OSM methods using standardized and non-standardized processes for the production stage of a factory-manufactured wall panel. Value system analysis and root cause analysis using the 5Whys method was adopted to evaluate possible improvements in terms of process waste. The study reveals that OSM production methods that replicate site arrangements and activities involving significant manual tasks do not necessarily provide a marked improvement from the conventional onsite method. Thus, there is a need to re-evaluate the processes involved to eliminate such embedded process wastes as non-value-added time and cost and to consider automating critical activities. The analysis adopted in the case study provides measurable evidence of the performance gained from having a structured workflow over a non-structured workflow. It also reveals how process wastes are generated in the production process of wall panels offsite.