Shared vertical ventilation shafts are commonly used to ventilate bathrooms in multi-story residential buildings, yet weak pressure gradients and unseparated airflow paths can reduce exhaust effectiveness and allow air exchange between connected bathrooms. This study used computational fluid dynamics to evaluate passive bathroom ventilation shaft configurations in a multi-story residential building in Irbid, Jordan. A conventional shared-shaft baseline was compared with alternative duct configurations, including a bottom opening, an increased duct size, roof extensions combined with bottom openings, a roof extension with dual bathroom windows, and a proposed ventilation pathway incorporating a basement extension. The simulations were performed using a building model developed in Autodesk Revit and analyzed in Autodesk CFD under a 3 m/s wind inlet condition and a zero pressure outlet. The baseline shared shaft produced weak airflow, with a readable velocity magnitude of 0.076127 m/s over a measured region of 53,718.3 cm². The proposed three-channel configuration increased velocity magnitude to 0.147702 m/s over a comparable region of 52,890.2 cm², representing an approximately 94.0% improvement. Vector-field interpretation showed that the proposed configuration produced a clearer directional pathway from lower fresh-air entry through side supply channels and bathroom openings toward the central exhaust shaft and outdoor discharge. The findings indicate that separating supply and exhaust paths is more effective than relying only on shaft enlargement or roof extension. The proposed configuration can support low-energy ventilation design by reducing stagnation and lowering the likelihood of inter-bathroom air exchange in dense residential buildings.