A successful construction project is determined when it is completed within the expected budget and time, ensuring the required levels of quality and safety. For a project to be successful, it is essential to plan properly and have a reliable monitoring system in place. Furthermore, the building construction sector has a negative impact on the environment by generating waste, increasing carbon emissions, polluting the air and water, and accelerating climate change. This study intends to investigate cost overrun prevention strategies in Sri Lanka using sustainable building materials. Accordingly, a mixed-method research approach was selected, and an e-based closed-ended questionnaire survey and semi-structured
expert interviews were carried out to collect data from construction industry professionals. In the questionnaire survey, a total of 80 construction industry experts were selected from different job categories as the respondents, and 53 responses were received with a response rate of 66.25%. On the other hand, 10 construction professionals participated in the semi-structured interview. The study has identified 15 factors that significantly impact cost overrun in the Sri Lankan building construction sector based on the mean weight ratings. The study found that using sustainable alternatives to natural resources at a lower cost is preferable. The most workable solutions to control the identified critical factors were determined to be new policies for sustainable construction, new financial frameworks for importing sustainable materials, new construction methods and technologies associated with sustainable materials and controlling the monopoly of sustainable material suppliers or manufacturers
