A parametric workflow for multi-objective optimization of solar-access trade-offs in neighborhood-scale infill design: a case study of Gorgan, Iran

Solar access in dense infill neighborhoods is shaped by building morphology and surrounding context, making climate-responsive housing design difficult under real planning constraints. This study developed a parametric multi-objective optimization workflow for neighborhood-scale infill design in Gorgan, Iran, under explicit morphological and development-capacity constraints. Solar performance was defined through two annual indicators evaluated during 06:00–16:00: incident solar radiation (ISR) on building envelopes, treated as a maximization objective, and mean direct sun hours (DSH) in ground-level open spaces, treated as a minimization objective. The workflow integrated parametric massing generation in Rhino/Grasshopper, solar simulation in Ladybug Tools, and evolutionary optimization in Wallacei using NSGA-II. The optimization used a population of 50 over 100 generations, producing 5000 solutions. Stable convergence was observed in final generations, with 12 Pareto-optimal solutions identified. Results revealed an ISR–DSH trade-off rather than a single universally optimal solution or uniform improvement across both indicators. Relative to the baseline reference scenario, used only for post-optimization comparison, selected Pareto-optimal solutions reduced annual mean ground-level DSH by about 22.2%, while annual envelope ISR decreased by 17.2–17.6%, quantifying the trade-off between improved ground-level solar control and reduced envelope-level solar access. Across the selected solutions, ISR ranged from 669.344 to 672.043 kWh/m² and DSH from 1168.81 to 1169.88 h/point. Building height emerged as the primary driver of the ISR–DSH trade-off, while typology and footprint acted mainly as secondary tuning variables. Overall, the workflow supports early-stage infill design by identifying Pareto-efficient alternatives that clarify how feasible configurations negotiate envelope-level solar access and ground-level solar control.