With the growing complexity of construction projects, design changes are inevitable. As many of the construction projects in Sri Lanka follow standard contractual documentation which will also result in frequent changes, variations are generally considered a major cause of cost and time overruns in residential construction projects. Therefore, this study aims to explore the causes and mitigation strategies for variations in residential projects in Sri Lanka. In achieving this aim, a mixed approach of both quantitative and qualitative approaches was followed. A comprehensive literature review was undertaken initially followed by a questionnaire survey. A sum of 51 responses were received which were valid and used for further analysis using the mean and RII formula. The findings of the quantitative study were validated using semi-structured interviews and analysed using content analysis. The results suggested that the unstable financial status of the client is the primary cause of variations in residential projects in Sri Lanka. Further, it was noted that most of the factors related to variations were consultant-related and contractor-related causes. Accordingly, proper project planning and maintaining the document quality by the consultants and technological adaptions by the contractor were revealed to be the most effective strategies in mitigating the variations in residential projects in Sri Lanka. The study highlighted the necessity of adopting new technologies in the planning and construction stages of residential building projects.