## 1 Introduction  
Rapid urbanization during the last decades has had several environmental, economic, and social consequences. Among these, an issue of great concern has been the development of the so-called urban heat island (UHI) phenomenon, characterized by higher temperatures in the density of built areas than the ones of the rural surroundings, which is both directly and indirectly related to serious energy, environmental, health, and economic problems [1]. Apart from that, some other causes include materials with high thermal storage capacity and anthropocentric sources, such as the emissions from air-conditioned buildings, which are related to the building's operational performance. In the European context, this phenomenon is especially intense in the Mediterranean basin, with a fast growth of energy consumption in the last years due to the widespread use of air-conditioning systems and the increase of cooling demand. This situation becomes even more worrisome in the face of global warming and the significant rise of heat waves (HWs) [2]. Especially in Athens, Greece, UHI has been present already since the 1980s. Research studies have shown that there has been an increase of the energy building demands, thermal risk, and vulnerability of urban population [3; 4; 5] and it has been reported that during the HWs, there is even an intensification of the average UHI magnitude by up to \(3.5\,^{\circ}\,\mathrm{C}\), an outcome of a study reporting the heatwaves in Athens in 2012 [6]. The heat that is dissipated from the buildings to the external environment increases the UHI phenomenon, and, therefore, has a strong indirect impact. More specifically, in Athens, an average increase of the cooling load of about 13% is estimated, with an annual global energy penalty for unit of city surface and degree of UHI intensity of 0.74 kWh m\({}^{-2}\) K\({}^{-1}\)[7]. The UHI is a complex phenomenon and is directly and indirectly related to serious energy, environmental, health, and economic problems [3,8]. When it comes to the influence of buildings, it has been established that there is both a direct and an indirect impact of the building's energy performance on the increase of the UHI in the cooling-dominated areas, such as Athens [8]. More specifically, the direct impact which is examined in the current research relates to the reflected solar radiation directed from the building's surface towards the urban microclimate, whereas the indirect one concerns the released heat which is generated from the building's cooling systems and is then accumulated in the urban environment. Other aspects that could also be considered part of the direct impact, such as the infrared thermal transmission due to the surface temperature of external facades, were out of the scope of the current study. An improvement of the building envelope and the energy efficiency might, therefore, reduce the ambient temperature and building's impact and, consequently, decrease the amplitude of the phenomenon. In this direction, a certain level of climatic responsiveness and adaptiveness to extreme heat changes in an energy-efficient way can arise as a promising strategy, in order to reduce the building's energy consumption. This gives way to the broad development of responsive technologies, such as passive dynamic adaptive facade systems, which are favored due to the real-time responsiveness to the also dynamic and unpredictable environmental changes, acting as the threshold between building and exterior environment. The abovementioned framework is the direction that was followed in the current research study. This was further explored and developed with a focus on the incorporation of smart and shape memory materials (SMMs), such as shape memory alloys (SMAs), by means of a case study in Athens, Greece, and design concept to evaluate their potential for facade application.