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

A set of guidelines comprising 2-dimensional prescriptive building separation requirements was promulgated by HKSAR (Hong Kong Special Administrative Region)’s BD (Buildings Department) 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 (Computational Fluid Dynamics) 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 BIM (building information modelling) technologies. A new geometric parametrisation method—LCP (Least Cost Path) was proposed. The method evaluates FC (Friction Cost) and TC (Turning Cost), measuring building design’s airflow resistance and path complexity. These metrics are applied within a 3D (3-dimensional) 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.