To improve living conditions of biodiversity and humans, urban forms must reconcile density with vegetation to meet the dual challenge of sustainability and liveability. This sustainable urbanism paradox is a dilemma for practitioners and researchers, stressing the crucial need for comprehensive analyses. Multi-family residential (MFR) housing could achieve balanced density-greening, proximity ecosystem services and people-biodiversity interactions, but meeting such objectives relies on finding balanced morphologies and metrics at the operational scale. Based on a systemic approach of 11,593 MFR plots in the Lyon metropolitan area (France), we identified critical tipping points in morphology and greening. Density explained 6% of plot greening, while open space ratio and open space greening explained 94%. Open space ratio >0.5 was found to be a tipping point to achieve sustainable green supply. Operational morphologies balancing density and greening were modelled and illustrated across building heights, providing guidelines for emerging regulatory tools in sustainable urban planning.