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

There is growing interest in the use of offsite manufacturing (OSM) in the construction industry despite criticism that some offsite approaches used by housebuilders do not offer real improvement compared with 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 nonstandardized 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 over the conventional onsite method. Thus, there is a need to reevaluate 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 this case study provides measurable evidence of the performance gained from having a structured workflow over a nonstructured workflow. It also reveals how process wastes are generated in the production process of wall panels offsite.