BIM-Based Wind-Driven Rain Modelling Using ISO 15927-3 and Geometry-Based Exposure

• Geometry-derived wall factors replace tabulated ISO 15927-3 coefficients • BIM-integrated ray tracing computes façade-cell WDR exposure in Revit • Field measurements and CFD validation of spatially resolved WDR predictions • Exposure fractions enable façade-level moisture risk mapping • BIM workflow links WDR exposure to durability and service-life modelling Wind-driven rain (WDR) is a key source of façade moisture risk. ISO 15927-3 estimates WDR using static wall-factor tables, limited in scope and unable to capture façade-specific geometry or sheltering. This study introduces a BIM‑native workflow that dynamically computes wall factor as a geometry‑derived exposure fraction, evaluated per façade cell via ray tracing and power‑law‑based cell‑level height‑scaling factorization. Implemented in Revit, the method automates ISO corrections for terrain, topography, and obstruction, and outputs exposure fraction, wall indices, and catch ratio with façade-resolved visualization. For the cases studies presented, the BIM-Ray Tracing approach (mean absolute errors 0.03–0.06), achieved accuracy close to CFD and outperformed ISO 15927-3 with runtimes suitable for early design. While turbulence and edge recirculation remain better addressed by CFD, the workflow enables exposure mapping, rule-based checks, and integration with ISO 15686 service-life performance analysis.