Despite the increasing efforts made by the construction sector to reduce the environmental impact of their processes, construction sites are still a major source of pollution and adverse impacts on the environment. This paper aims to improve the understanding of construction-related environmental impacts by identifying on-site causal factors and associated immediate circumstances during construc- tion processes for residential building projects. Based on the literature and focus group fi ndings, we have developed a construction-related Environmental Impact Causal Model consisting of a process-oriented causal network of thirty-nine environmental impacts, forty- fi ve causal factors and over two hundred causal relationships. It is intended to contribute to a reduction in construction-related environmental impacts on building sites by supporting contractors and other decision-makers in the early identi fi cation of factors that are likely to lead to impacts or to exacerbate their consequences, as well as the later environmental performance evaluation and control. The causal model is validated by investigating over a hundred environmental incidents. Finally, possible methods to improve construction-related environ- mental performance are suggested.