A roof solar chimney (RSC) is inclined in the roof of a building wherein solar radiation is employed to heat the air the channel. The hot air flows up the channel which can be used to induce flow out of the building in order to ventilate it. In this study, parameters that affect the performance of this natural ventilation system were investigated numerically, namely: inclination angles, channel gaps, solar intensities, vertical chimney attachment heights and channel expanding angles. The two last parameters were new concepts that seem to have never been studied before. All of the mentioned parameters were found to exhibit positive effects on the ventilation. Relative merits of these techniques were compared and discussed.