A theoretical investigation of a combined wall-roof solar chimney to improve night time ventilation in buildings is presented. A spreadsheet computer program is used for the parametric study to find out the optimum configuration of the wall-roof chimney. It has been reported that a roof solar chimney alone can induce an air flow rate of 0.81 m(3)/s when the average incident solar radiation is 850 W/m(2). The maximum air velocity induced is 1.1 m/s when the 25 degrees inclined chimney plates are 0.25 m apart. The aim of the paper is to predict the induced air flow rate as a result of the combined effect and to find the best height. The wall chimney height is varied from 1.95 to 3.45 m to determine the optimum length in relation to the chimney inlet. The results show that the air flow rate is three times more than that of the roof solar chimney alone (0.81 to 2.3 m(3)/s). The maximum air flow rate of 2.3 m(3)/s occurs at 3.45 m wall height. ACTION Psychrometrics Software (Sunshine Technology, USA, 1995) is used to predict the mean cooling load corresponding to the induced ACH. An air change per hour up to 26 could be achieved for a flat volume (321 m(3)). Such ACH could be utilized to improve night ventilation to reduce indoor air temperature and cool low-rise heavy buildings with large diurnal outdoor temperature variations.