Optimizing residential density based on water–energy–carbon nexus using UTilités Additives (UTA) method

High-density housing is primarily constructed to decrease per capita civil infrastructure and land resource. Multi-family residences are preferred to single-family residences for neighbourhood densification changing per capita landscaping, affecting residential water and energy demand. These alterations also affect energy-associated carbon emissions and landscaping-associated carbon sequestration, revealing the existence of the water–energy–carbon (WEC) nexus. This study has developed a holistic framework for optimal residential density based on WEC nexus. The conflicting criteria water footprint, energy use, net carbon emissions, life cycle cost, aesthetic value, and government priority, associated with the WEC nexus in various densities, were evaluated using the UTilités Additives method. The developed framework was applied to a planned neighbourhood in the Okanagan Valley (British Columbia, Canada) by preparing 11 alternative designs with different residential densities. Neighbourhood scenarios with different criteria weights were studied. Results show that per capita water footprint, energy use, net carbon emissions, and life cycle cost have a power relationship with net residential density despite a linear relationship between population and net residential density. The estimated optimal net residential density is approximately 260 persons/ha for most of the scenarios. The findings present the benefits of building medium- to high-density housing to achieve an optimal WEC nexus.