Limited empirical and qualitative studies focus on the detailed processes and obstacles for coordinating off-site prefabrication between builders and suppliers. This research aims to identify and address the obstacles that currently prevent the further expansion of off-site prefabrication, with a research scope on timber and mechanical/electrical/plumbing (MEP) services in construction projects. The focal point of this research is to highlight their obstacles. A total of forty interviews were conducted and analyzed from four builders’ organizations and four suppliers’ organizations to ascertain their obstacles in coordinating the practice of off-site prefabrication. The results found the builder’s obstacles were sustainability, quality assurance (QA), mass production, CAD/BIM, technological support, commercial arrangements, system building, buffering in supply, schedule monitoring, productivity, flexibility, engagement, risks, and multiple supply arrangements. The supplier’s obstacles were design, financing and subcontracting, coordination, recognized practices, risks, multiple supply arrangements, and constraints. Moreover, the builders and suppliers had identified some ways to harmonize off-site prefabrication of timber. Some examples of timber prefabrication technology include joinery, doors and/or windows, structural floor/wall/roof frames, partitions, trusses, stairs, balustrades, and others. MEP services with in situ construction comprise the use of power sources and working coordination. The most important outcome of this investigation is that these obstacles can be addressed through collaboration and coordination. This is because there is a traditionally a lack of collaboration amongst builders and their suppliers. Furthermore, there is a lack of coordination between them in general. The research contributes to the improved timber and MEP services collaboration and coordination in off-site prefabrication, which can be referred to by other approaches of modular construction.