The building sector’s decarbonization requires comprehensive approaches beyond conventional energy-focused methods. This chapter presents two integrated methodologies: Service Point-Based Carbon Accounting (SPBCA) and BEMS-Driven Energy Audit Method (BDEAM). SPBCA employs GIS to quantify building-level CO2 emissions across energy, water, and food sectors, covering approximately 70% of global emissions compared to 50% in traditional methods. BDEAM leverages BEMS data and industry standards to enable precise performance evaluation by space use and equipment type, identifying specific inefficiencies invisible to conventional whole-building audits. The integration of both methods through a shared resource-use intensity database enables detailed building diagnostics to inform city-wide carbon reduction strategies. However, this requires transitioning from fragmented BEMS data storage to centralized, systematically managed systems. Only through such infrastructure can evidence-based decarbonization strategies effectively bridge building and urban scales.