Globally mental health is a serious concern, particularly in construction. According to the Health and Safety Executive (HSE, 2021), stress, anxiety, and depression are the second biggest cause of work-related ill health in the UK construction industry. Occupational stress and mental health issues should, therefore, be treated with the same level of significance as physical health and safety risks in construction. To the authors' knowledge, there are very few, if any, published empirical IGLC papers that have explicitly focused on this concern. This study was conducted using case-study interviews and a focus group with industry experts, to explore and promote the concept of 'occupational stress' in construction. The study provides novel contributions to knowledge, which include: identifying seven main sources of stress (i.e. stressor) in UK construction projects, revealing 'workflow interruptions' as a prevalent and severe source of stress in construction, shedding some empirical light on the inadequacies of the critical path method, and generating new questions and proposals to pave the way towards a future IGLC research agenda for tackling occupational stress and mental health issues in construction.