CFD Analysis for Design Principles of Sub-Floor Ventilation Cavities in Historic Buildings

Sub-floor ventilated cavities represent a widely used remediation method for structural moisture reduction, yet their performance is often assumed to be automatically functional without evaluating internal airflow dynamics. This study presents a detailed Computational Fluid Dynamics (CFD) analysis supplemented by in situ experimental monitoring to evaluate cavity airflow performance and optimize parameters for moisture control in building structures. The CFD simulations demonstrated high predictive accuracy, revealing that systems strictly reliant on natural ventilation exhibit severe instability, with airflow velocities dropping to near-zero values during calm wind. Parametric evaluations confirmed the critical impact of protective grille permeability: grilles with a low free area ratio generate significant pressure drops that virtually disable air exchange, whereas higher permeability values are required to minimize resistance. Furthermore, effective drying requires targeted airflow along moist structural surfaces to enable continuous evaporation, whereas radon mitigation primarily relies on establishing a negative pressure field relative to the interior to prevent radon ingress. Improper mechanical ventilation configurations without adjusting all flow pathways can induce backdraft effects, disrupt internal airflow distribution, and fail to maintain the required negative pressure field, thereby compromising the moisture reduction process. The research demonstrates the necessity of CFD modeling to prevent aerodynamic failures and design reliable sub-floor ventilation systems.