## 1 Introduction
On the one hand, condensation water can occur inside construction components; on the other hand, it can be formed on the surfaces of construction components when their surface temperature is lower than the dew-point temperature of the surrounding air [18]. Roof surface temperatures can fall below the ambient air temperature due to radiative effects. This leads to condensation of air moisture on cold surfaces. Water and vapour are absorbed by wood, which causes swelling and shrinking when the moisture dries off. Surface temperatures inside ventilated roofs were shown to be below ambient temperatures for approximately half of the time during spring and autumn in Trondheim, Norway [19]. During the warm season, the moisture input into a construction from the outside air can be significantly larger than that from the inside. Especially problematic is when the air in the ventilation system on the southern roof side is warm and wet and is transferred to the northern roof side, which is cold during spring and autumn. Under these circumstances, intense ventilation was shown to be disadvantageous due to condensation and increasing the moisture content of wooden construction elements [20]. It was shown that, in cold attics, ventilation adds moisture when its relative humidity is higher than 70% [21]. In north-facing cold attic spaces under the eaves, infiltration of moisture from conditioned spaces, as well as ventilation, can lead to increased moisture levels in the construction; hence, existing construction rules have to be evaluated [22]. Moisture is only removed from the inside air or building component by ventilation air when the absolute moisture content of the introduced air is lower than that of the inside air [23]. In this respect, it was shown that the risk of mold growth can be higher in ventilated attics when the climate gets milder and wet due to climate change. Under these circumstances, mechanically ventilated attics are recommended [24]. In ventilated walls, the introduced air can also wet the construction during moist weather conditions [25]. It was shown that transient hygothermal models are suitable to predict the temperature and moisture conditions in cold roofs [26]. The authors stated that the definition of reliable in- and outdoor climate boundary conditions are especially crucial when creating hygothermal models, which is also the most important reason for a model's potential deviation from real values. The reason for this investigation is the assumption that the durability of wooden shingles on ventilated roof (cold roofs) constructions could be shorter than that on constructions with a cold attic space [27]. It is assumed that deficient flow in the ventilation gap and condensation of humid air might be the reason. The research question for this investigation is whether it is recommended to apply wooden shingles on a ventilated roof construction or if their application should be limited to buildings with uninhabited cold attics without ventilation of the roof cladding. The effect of cardinal orientation is also evaluated in this respect. Moreover, it is discussed whether the partial closing of the ventilation gaps results in a lower wood moisture content. This is a relevant question, because historic buildings, which originally had cold attics, are increasingly equipped with roof ventilation in the course of roof refurbishment. The research question is addressed using the example of a historic building, which originally had no ventilation layer under its wooden shingle roof and which was refurbished applying a ventilation layer under a new wooden shingle roof cladding. Air temperature, humidity, and air speed in- and outside the ventilation layer were measured throughout a year. A hygothermal model of the construction was set up and the measured data were used to validate the model. Finally, the model was used to simulate the effects of varying cardinal orientation of the roof, varying airflow in the ventilation layer, and partial closing of the ventilation layer on the dry-out of the shingles.