Abstract Examined here are the effects of cross-ventilation when a porous hedge is placed ahead of a residential building. Parametric studies include the hedge porosity ( 0 ⩽ η ⩽ 1.0 ) , the space between the hedge and the building ( 0.25 ⩽ L / 2 H ⩽ 3.0 ) and the hedge height ( 0.1 ⩽ h / 2 H ⩽ 1.0 ) . A computational fluid dynamics (CFD) simulation is carried out to predict the airflow characteristics around both the porous hedge and the building. Results show that the porous hedge could modify the flow structures behind it, and thus can alter the cross ventilation of the building. In addition, the shelter effect of the porous hedge is increased when the hedge porosity is decreased. It is also discovered that there exists a critical hedge porosity below which the cross ventilation in the building becomes inverse.