Optimizing glass material and overhang performance in building envelopes through OTTV analysis to reduce building’s thermal load

Abstract Global warming and the energy crisis are pressing global issues, with buildings contributing significantly to energy use, especially through air conditioning and ventilation systems. Optimizing the building envelope is a passive strategy to reduce cooling loads from solar radiation and heat transfer. Based on SNI 6389:2020, building envelopes must achieve an OTTV not exceeding 35 W/m 2 . In existing buildings, performance improvements can be made through fenestration adjustments, particularly glass type and overhang design. This study applies a quantitative comparative method to analyze OTTV performance under variations of glass materials and overhang dimensions. Calculation were conducted to evaluate their effect on reducing heat transfer and to assess compliance with SNI 6389:2020. The case study is an architectural studio building, yet its current envelope does not compile with thermal performance standard. The results indicate that clear glass combined with a 0.75 m overhang lowers OTTV compared to existing conditions but still fails to meet the required standard. In contrast, treated glass such as Panasap 5 mm, Sun Energy 5 mm, and Stopsol 5 mm significantly decrease OTTV values, proving more effective in achieve thermal performance standard. The findings underscore the importance of glass selection and shading optimization in designing building envelopes.