Off-site manufacturing (OSM) has implied capabilities that could enhance housing supply in Australia. The OSM system requires the efficient management of two concurrent working locations: the off-site fabrication facility and the construction site. Client order behaviour impacts on the OSM system. Accordingly, client order information flow is an essential component for efficiently managing this system. This paper investigates the effects of client order behaviour on the performance of OSM within the Australian housebuilding context using discrete-event simulation (DES). The data used to develop the conceptual model were based on a review of 21 related technical documents and interviews with 13 OSM experts in Australia. The operational data used for executing the simulation model were collected through a questionnaire survey of 30 builders as well as three one-day site visits to the fabrication facilities and construction sites of three major building organisations in Australia. The simulation model assisted in experimentation with four scenarios that represent client order interaction in the OSM system in Australia. The model simulation results showed noteworthy improvements in house completion time and the number of completed client orders per year.