Abstract Many studies have been conducted on the contributions of the construction industry to greenhouse gas (GHG) emissions. However, these studies focused on the embodied GHG emissions of buildings and were restricted by limited system boundaries due to a lack of detailed on and off-site process data, especially data for assembly and miscellaneous works as well as construction related human activities. This study therefore analyzed GHG emissions during the construction phase of a case study building on the basis of an extended system boundary in the context of China by utilizing detailed onsite process data. The results show that indirect emissions accounted for 97% of all GHG emissions. On-site electricity use and building materials production were the two greatest contributors to direct and indirect emissions respectively. Recombining the construction activities revealed that construction related human activities generated significant GHG emissions (385 tCO 2 e), which have been ignored in previous research. The findings also reveal that although some materials used during the construction process are negligible in terms of weight, such as polyamide safety nets and aluminum (