Comparing the Amount of CO2 Emissions from a Commercial Building with a Traditional Design and a Sustainable Design

The building sector's substantial contribution to global CO2 emissions necessitates the urgent adoption of sustainable construction practices. This study employs life cycle assessment (LCA) methodology through One Click LCA software to quantitatively compare the environmental performance of conventional versus sustainable commercial buildings, while also evaluating three prominent certification systems: BREEAM, LEED, and DGNB. Results demonstrate that the sustainable design achieved an overall CO2 emission reduction of 49.7% (from 961 to 483 kg CO2/m2) compared to the traditional design. This included 42% lower operational CO2 emissions and 28% decreased embodied carbon. Certification assessments revealed notable disparities: the building scored 78% under BREEAM (which gives significant weight to energy efficiency), 85% under LEED (which emphasizes operational energy and renewable energy), and received approximately 15% lower ratings under DGNB, reflecting DGNB's comprehensive lifecycle approach and strong focus on embodied carbon (25% material weighting). These variations highlight fundamental methodological differences in sustainability evaluation that may affect market perceptions and policy effectiveness. The findings provide empirical evidence for two critical conclusions: sustainable building design delivers measurable environmental benefits, and current certification systems exhibit inconsistent assessment frameworks that could hinder standardized progress toward net-zero targets. This research underscores the need for greater alignment among certification methodologies to ensure consistent, transparent evaluation of building sustainability and offers valuable insights for architects, policymakers, and certification bodies.