This research investigates parametric design efficiency implemented into the conventional green infrastructure (GI) interface curb by comparing water retention volume and flow. The objective of this study is to investigate innovative methods to advancing urban sustainability through design. The Urban Heat Island (UHI) phenomenon continues to remain an urban challenge, contributing to increased energy consumption, poor air quality, and increased public health risks. In context, the research evaluates passive parametric design strategies implemented via street elements, focusing on geometric strategy to increase rainwater retention and promote directional flow. A typical sample segment of the South Korean street was modelled digitally. This model facilitated a systematic assessment of several curb design variations, each subjected to different parametric adjustments. The simulation quantified the volumetric retention of rainfall associated with each configuration, enabling a robust comparison of performance outcomes. The results showed that increasing curb extrusion showed higher rainwater retention, with the tallest profiles (Design C, 210 mm) achieving peak retention. However, it also exhibited the most variability, whereas Designs A and B showed moderate retention capacity with more stable retention capacities, with the mid-range inclinations around 3°. These results underscore the importance of curb typology and overall, an insight into integrating passive design into streetscape level. Ultimately, the study highlights the implications for urban planning, offering a pathway for integrating water retention strategies into existing infrastructure. Such advancements not only support climate adaptation efforts but also contribute to the expansion of green infrastructure and the mitigation of urban hazards.