Optimization of Urban Block Form by Adding New Volumes for Capacity Improvement and Solar Performance Using A Multi-Objective Genetic Algorithm: A Case Study of Nanjing

During urban renewal, multi-story residential blocks face a contradiction of balancing residential capacity improvement and solar constraint. This paper constructed a set of automatic workflows for adding new volumes to existing buildings, and a multi-objective optimization was applied with a Wallacei plug-in in Grasshopper to optimize the solar radiation, solar hours, and block capacity. First, this study established three building addition modes of existing blocks in the horizontal direction, vertical direction, and mixed direction, respectively. Three optimization objectives—maximum floor area ratio, maximum average radiation amount, and minimum solar shade—were defined. Second, the net increase in the floor area ratio of the block was calculated to balance capacity improvement and solar constraint. Third, the advantages of the three addition modes under different orientations were discussed. Among all three modes, the mixed addition mode had the best capacity improvement effect, with a 70% increase in floor area ratio. The vertical addition mode had the least impact on the solar shade of existing buildings. The horizontal addition mode could further improve the floor area ratio in areas where building height was strictly limited. The results can provide insights and inspiring guidelines for the renewal of the existing residential blocks to solve the floor area ratio constraint from solar radiation, as well as achieve urban function reconstruction and vitality regeneration.

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