Volumetric Criteria and An Automated Assessment Tool Development for Optimizing Building Permeability Design in High-Density Urban Environments

Better urban ventilation can significantly contribute to achieving UN SDGs through better liveability for sustainable cities and communities (SDG 11), better air quality for health and well-being (SDG 3), and more climate-responsive building design for climate action (SDG 13). Aligning with the said goals, a set of guidelines comprising 2-dimensional prescriptive building separation requirements was promulgated by HKSAR's Buildings Department (BD) in 2011 to promote better urban ventilation. However, some practitioners have concerns about applying the guidelines for projects with complex geometries. Projects may adopt alternative assessment methods using wind tunnel or CFD simulations to demonstrate compliance, but the required time and cost are also a concern. Given the concerns and stakeholders’ collective experience using the guidelines, BD commissioned a study in January 2024 to establish an alternative automated assessment tool for cost-effective evaluation of building permeability design using building information modelling (BIM) technologies. A new geometric parametrisation method - Least Cost Path (LCP) was proposed. The method evaluates Friction Cost (FC) and Turning Cost (TC), measuring a building design's airflow resistance and path complexity. These metrics are applied within a 3D assessment grid system for a building project's low, middle and high zones. Normalised CFD and LCP performances were reviewed, showing a strong correlation (R² ~ 0.8). The study also identified a cost threshold under the LCP method that differentiates “good” from “poor” ventilation designs. An automated BIM-integrated assessment tool using the LCP method will be further developed in Phase B of the Study.