LONG-TERM MAINTENANCE COST FORECASTING AND WARRANTY BUDGET PLANNING FOR RESIDENTIAL BUILDINGS IN BANGKOK, THAILAND

Abstract

This study evaluates the adequacy of current warranty budget allocations in residential developments and proposes differentiated, data-driven percentages based on long-term maintenance cost projections and project characteristics. Empirical defect data from five condominium projects in Bangkok, varying in unit type, scale, and market positioning, were collected between 2019 and 2023 and used to model 30-year cost projections through linear regression. The findings show that maintenance costs consistently increase over time, with annual cost slopes ranging from USD 10,162 to USD 30,857 and R² values between 0.90 and 0.99, while projected lifetime maintenance costs represent 5.56% to 11.26% of total project values. The widely adopted 2% warranty allocation was found to be inadequate, depleting as early as year 11 in high-density or lower-cost projects. Based on cumulative cost behavior and project conditions, differentiated warranty budgets of 6% to 11% are recommended to ensure financial sustainability. While the analysis is limited to five projects in Bangkok and linear forecasting methods, the results underscore the importance of empirical, context-sensitive approaches to warranty planning. By integrating real defect data with long-term cost modeling, this research provides a practical framework for improving financial foresight, construction quality, and asset management in rapidly urbanizing regions.