Height-Responsive Balcony-Integrated Envelope Design for High-Rise Residential Buildings: Sensitivity Analysis and Clustering Based Optimization Approach

Balconies function as essential shading elements within the building envelope, playing a critical role in regulating occupant comfort and energy efficiency. Despite their importance, balconies are often designed repetitively across floors without accounting for the variation in environmental conditions at different elevations. Therefore, this study aims to optimize the envelope design of residential bedrooms with balconies to improve visual and thermal comfort, and energy performance across three representative floor positions: lower (3 m), middle (18 m), and upper (33 m), considering the surrounding context in hot-humid tropical climate of Dhaka, Bangladesh. The proposed research framework combines parametric-based multi-objective optimization using the NSGA-II algorithm with multi-criteria decision-making through K-means clustering and Sobol sensitivity analysis. Design variables are grouped into three categories: envelope geometry, balcony geometry, and material types. The four performance objectives include maximizing spatial daylight autonomy (sDA300/50%), spatial glare autonomy (sGA40%/5%), and thermal comfort percentage (TCP), while minimizing energy use intensity (EUI). Results reveal that optimal solutions vary significantly by floor. Lower floors benefit from wider glazed openings and higher parapets to control reflected glare, while middle floors achieve balanced performance with smaller openings and moderate balcony features. Upper floors prioritize deeper shading and reflective materials to manage intense solar exposure. It also challenges conventional recommendations by identifying parapet height, not glazed door width, as the key variable for visual comfort on lower and middle floors. In contrast, glazed door width is more influential on upper floors through Sobol sensitivity analysis. In addition to this, second-order interactions, particularly among balcony-related parameters, were strongest on lower floors, moderate on upper, and minimal on middle floors. This study contributes to the current knowledge on climate-responsive high-rise design by demonstrating the importance of floor-specific strategies for a hot-humid tropical context. The proposed approach aids designers in making informed decisions not only during early design phases but also for renovation and code development in a similar climatic context.