## 1 Introduction  
Modular and offsite construction (MOC) involves the process of designing, fabricating, transporting and assembling building elements for rapid site assembly to a greater degree of finish than in on-site construction. MOC, also called prefabrication or preassembly has been widely adopted by many countries and regions (such as the United States, the UK, Sweden, Australia, Malaysia and China) as a new construction method to improve the construction productivity [1; 2; 3; 4; 5; 6; 7]. Various benefits (e.g., quality improvement, waste reduction, and savings in construction time etc.) of prefabrication have been addressed in previous studies. Because of these proven benefits, mechanical, electrical, and plumbing (MEP) contractors adopted MOC as a new approach to strengthen its profitability and competitiveness. Several studies were performed to analyze different management aspects of MEP construction. These studies include: construction schedule and planning [8; 9]; safety and risk management in MEP construction [10; 11]; coordination and integration strategies among various sub-systems and trades [12; 13; 14]; assessment of the built status of MEP works and quality inspection [15]; building information modelling (BIM)-based application in MEP layout design and construction [16; 17; 18]; and waste management of materials such as pipes used in MEP construction [19; 20]. A few studies were performed to investigate the application of prefabrication in MEP construction. [PERSON] and [PERSON] [21] presented a case that has used prefabrication technology for the distribution of heating, ventilation, and air-conditioning (HVAC) systems. [PERSON] et al. [22] presented the process of pipe spool fabrication in the industrial construction project. This study focused more on the value stream improvement in the spool fabrication shop. [PERSON] et al. [23] combined modular assembly with postponement strategy to improve productivity and reduce the on-site operations that involve risks of injury in MEP construction including cutting and drilling. [PERSON] et al. [24] developed a method to design the modular standardized industrial plant. Ten types of advantages were identified when modularization and design standardization were combined. [PERSON] et al. [25] proposed a quality management model for construction quality management that employs automated technologies such as photogrammetry and laser scanning to detect defects during piping prefabrication. The model has the potential to decrease the overall cost of a project by reducing the fabrication rework. [PERSON] [26] identified best practices in electrical prefabrication construction and improvement opportunities for electrical contractors' industrialization, and presented a prediction model of prefabrication feasibility for electrical contractors and found that prefabrication feasibility was dependent mainly on industry-related determinants. The surveys [27; 28] have indicated that prefabrication was most widely adopted to manufacture structural components and building envelope of buildings, followed by MEP systems. Building superstructure, exterior walls, and ducts are the most prefabricated building components. Prefabrication of complicated ductwork can help reduce the space requirement on site. In addition, assembly off-site can positively impact the overall project schedule. As to how to make decisions and what challenges would be faced during implementation of modularization and off-site in MEP construction, a decision framework named prefabrication, preassembly, modularization, and off-site fabrication (PPMOF) [29] developed by the Construction Industry Institute (CII) needs to be concerned. This framework focuses on identifying the requirements for effective use of PPMOF on industrial projects. PPMOF contains a preliminary decision guide and a quantitative analysis as well as suggestions for tactical analysis in the PPMOF decision process [30].