This study examines the application of Taiwan's Building Energy-Efficiency Rating System for New Buildings (BERSn) by analyzing its framework, evaluation criteria, and classification system to assess its impact on Energy Use Intensity (EUI) and Carbon Emission Intensity (CEI). Two types of residential buildings were selected for case analysis: (1) Jingfeng Phase II Social Housing and (2) a detached single-family house in Linkou. The results indicate that the social housing project achieved a CEI of 14.31 kgCO₂/m²·yr, meeting the BERSn Level 1 certification with a carbon reduction rate of 25.7%. The single-family house, utilizing passive design strategies, achieved a CEI of 10.67 kgCO₂/m²·yr, with a carbon reduction rate of 33.13%, approaching the Nearly Zero Carbon Building (NZCB) standard. Taiwan's transition toward net-zero residential buildings still faces multiple challenges, including high cooling demand in a subtropical climate, high carbon emissions from traditional reinforced concrete (RC) structures, and the high cost of advanced energy-saving technologies. To facilitate the low-carbon transition, this study recommends policy directions that include strengthening the regulatory applicability of BERSn, providing financial incentives for green buildings, and accelerating the integration of renewable energy. The findings of this study serve as a reference for sustainable building policies and provide empirical evidence to support energy efficiency improvement strategies for urbanized subtropical regions.