In order to estimate air change rates (ACH) on Natural Ventilation (NV) processes a number of factors should be known as general and openings dimensions, pressure distribution over the facades, internal heat sources (or sinks) and head losses. The atmospheric boundary layer (ABL) characteristics change with the terrain roughness and affect the pressure distribution. Construction features determine infiltration rates, flow regimes through openings and its head losses so affecting the internal airflow. The present paper concentrates on one of the external factors affecting air change rates - turbulence - and it's inclusion on VENTIL, an integral model for NV estimates. As a result an increased knowledge of NV capabilities is obtained. Some results will be presented as an application to an industrial building under different ABL.