This study describes an experiment to investigate the effect of a ventilated interior courtyard on the thermal performance of a house in a hot-arid region. The site of the experiment is Al-Oyyena village, situated in the countryside around Riyadh, Saudi Arabia. Statistical analysis of data recorded during the summer of 1997 was carried out. The results indicate that the courtyard gives high efficiency in providing cool indoor air through cross-ventilation. A statistical module and its validation for natural ventilation are presented. The aim is to estimate the indoor daily average dry-bulb temperature as a function of outdoor temperature and wind speed.