Operational and embodied emissions associated with urban neighbourhood densification strategies

Urban densification increases the number of people living in urban areas and is hypothesized to be a more efficient use of available land than urban sprawl. The objective of this study was to quantify the operational and embodied emissions created as a result of densification. A ‘Business as usual’ and a ‘Concentrated’ densification strategy were investigated. When densifying at the neighbourhood level, existing buildings can either be replaced or extended to accommodate the additional inhabitants. The densification strategies were applied to two reference urban design neighbourhoods in Switzerland. The ‘Typical’ approach assumed that all the buildings were demolished and rebuilt and the ‘Preserve-existing’ approach involved the extension of existing buildings as much as possible. Construction material choice and modification of the built form were the sources of embodied emissions considered for each strategy. Urban building energy modelling was used to calculate the emissions incurred by heating the buildings and the embodied emissions were calculated using building standards. The operational performance was simulated assuming both a gas boiler and an electric heat pump to determine the influence of the heating system type on the operational emissions. This study found that savings of approximately 30% in embodied emissions can be achieved by extending the existing building stock rather than rebuilding. However, these savings represent a relatively small percentage of the total emissions incurred throughout a building's lifetime and the savings further diminish in the concentrated densification strategies.