The thermal performance of a monozone building located in Lisbon is studied when night ventilation combined with radiative cooling is used in order to remove the heat from indoors. For simulating the thermal behaviour of the building, a commercial energy building software is used. The potential for radiative cooling in Lisbon, as well as the efficiency of the radiative cooling system were investigated previously. A validated numerical model is used in order to predict the temperature of the air at the outlet of the radiative system. The outdoor night air cooled by the radiative system is then used to cool the building by ventilation. Various simulations are performed using, as weather source, averaged values derived from the typical reference year of Lisbon. It is concluded that when properly designed, a radiative cooling system such as described here, may enhance the effectiveness of night cooling.