Cost overruns remain a critical issue in the Philippine construction industry, particularly in vertical building projects within the private sector. These budget exceedances can significantly disrupt project timelines, reduce profitability, and erode stakeholder trust. This study aims to investigate the root causes of cost overruns by collecting empirical data from 40 construction professionals, including engineers, project managers, architects, and contractors. Using a structured survey and statistical analysis, the study identifies and ranks both internal and external factors that contribute to budget deviations. The results show that internal issues such as inappropriate planning (85%), poor project management (78%), design errors (65%), and financial difficulties (60%) are the most significant contributors. External causes, including raw material price fluctuations (50%) and unforeseen site conditions (45%), were acknowledged but deemed secondary in severity. A key insight is the variation in perception across stakeholder roles: senior managers emphasized communication and financial controls, while field professionals highlighted operational planning and risk assessment. The paper proposes several mitigation strategies, including the adoption of digital project management tools, stronger communication protocols, rigorous financial oversight, and proactive risk management practices. By addressing these issues comprehensively, construction stakeholders in the Philippines can significantly reduce the frequency and impact of cost overruns. The study not only contributes to the limited body of local literature but also provides actionable recommendations for enhancing cost performance and overall project success.

Keywords: cost overruns, construction projects, project management, risk factors, Philippine construction industry