Thermal performance and carbon reduction potential of phase change material-based building roof in extreme summer conditions

Global building energy consumption accounts for nearly 40% of total energy use and one-third of carbon emissions, driving an urgent need for climate-resilient and energy-efficient infrastructure. The integration of phase change materials (PCMs) into building envelopes has emerged as a promising passive strategy to improve thermal regulation and energy efficiency in buildings. Given that the built environment contributes a significant share of global carbon emissions, the adoption of thermally adaptive materials represents a critical pathway toward low-carbon and climate-resilient construction. This study presents a comprehensive experimental evaluation of PCM-enhanced RC roof slabs under hot summer climatic conditions, quantifying their influence on indoor thermal stability, energy savings, and economic performance. Two hollow slab configurations, one incorporating PCM macroencapsulation and a reference slab without PCM, were tested under identical boundary conditions. Key performance indicators, including Indoor Temperature Reduction (ITR), thermal load reduction (TLR), heat flux reduction (HFR), energy cost savings (ECS), and the payback period, were analyzed to assess the thermo-economic viability of PCM integration. The results revealed that PCM incorporation effectively stabilized indoor temperatures, achieving a peak ITR of 7.2 °C and a maximum TLR of 32.94%. The PCM slab also demonstrated an HFR of up to 60.6% and a daily ECS of 4.67 INR, corresponding to the shortest estimated payback period of 5.7 years. These findings confirm that PCM-integrated hollow slabs offer a technically and economically feasible pathway for enhancing passive cooling performance and energy sustainability in subtropical building applications.