Abstract Off-site construction is a popular construction technique due to improvements in construction time and efficiency. However, a typical construction will incur several air emission substances which can be categorised as direct and indirect emissions. The effect of these pollutant substances may have severe health impacts on the immediate surrounding environment of the construction site. The study attempts to quantify direct and indirect emissions associated with off-site construction and compare with traditional on-site construction. Two case studies in Chengdu, China is used to investigate the direct and indirect impacts of off-site construction as compared to conventional construction. The results indicate GHG emissions reduction of 8.40% for off-site construction. Impact assessment revealed pre-fabrication having more reduction on global warming and oxidation formation at global level and eutrophication, human toxicity and acidification at regional and local environment. Further analysis revealed a strong relationship between the transportation distance and the level of pre-fabrication on total carbon emission reduction. The methodology provided in the current study exemplified the importance of conducting a well-articulated assessment to help decision making on environmental impact reduction in off-site construction. The results conclude the importance of developing a structured decision making platform to assist the sustainable decision makings in future.