Especially for wooden wall constructions, ventilated rain-screen walls have been used for many decades to prohibit moisture-induced damage. The air gap behind the façade cladding provides drainage, enhances ventilation, and thus facilitates drying of wetted façade components. The conditions in the air gap behind different cladding materials, however, are still an object of research. In the presented study, the interim findings after more than two years of ongoing measurements in the air gap behind different cladding materials of a zero-emission office building in the high-latitude city of Trondheim, Norway are presented. The results provide valuable insight into the temperature conditions in the air gap of ventilated claddings in order to determine the in-use conditions of building materials and develop improved testing schemes. The results indicate that the air and surface temperature in the air cavity of the walls is strongly influenced by the solar radiation incidence on the facades. Both the highest and lowest values were observed on the roof with 81 °C and -21.9 °C, respectively, at the back side of the building integrated photovoltaic modules, resulting in a total temperature range of almost 103 °C.