Green walls can act as natural thermal regulators, reducing solar radiation on surfaces and providing cooling due to shading and evapotranspiration. Several studies have investigated the cooling effects of a bare wall, in contrast to a vegetated wall, as well as the correlation between temperature reduction and system characteristics. In the present work, we analyze the influence of the orientation of a green wall on its ability to reduce surface temperatures in a Mediterranean climate. Environmental variables such as irradiation and air temperature have been considered. A real-time monitoring system has been used, with a database of three years of measurements. Results show that on average, the control temperature is greater than the green wall temperature with maximum differences of 20 °C in summer and 8 °C in winter in the south wall surface. During the summer, the temperature reduction in the south façade occurs mainly in the central hours of the day, while in the west façade it occurs mainly in the afternoon. Being the summer the most relevant season for the use of green walls, this information is very valuable as it allows the designers to know at what time of day the façade provides a temperature reduction, depending on the orientation. •Effect of green walls on the surface temperature under different orientations.•Experimental study done on a real building located at Madrid under real conditions.•More than three years of monitored data by means of a real-time monitoring system.•The temperature behind the green wall is up to 20°C lower than on the control one.•The effect of the green wall is different depending on the orientation.