## 1 Introduction  
In Europe, a large number of buildings are constructed with stone coverings. Stone panels are supported only by certain anchorage points, leaving a joint on each of the four edges of the stone. When the wall is designed according to the 'rainscreen principle' [1], air pressure inside the cavity will be the same as that outside the cavity. For all enclosures of buildings, thermal behaviour and possible condensation are studied in order to avoid problems related to humidity and deterioration of the materials. Any enclosure has important functions to perform, requiring stability, thermal insulation, and air- and watertightness, among other things. A good hygrothermal functioning of the enclosure depends on the construction materials, and above all on a good construction design. Today, enclosures of buildings with stone cladding are constructed comprising an interior sheet that serves as a support for thermal insulation, and an open air chamber, ventilated through the joints of the outer sheet. The outer layer is composed of stone cladding. Different research works have addressed the study of temperature and natural convection in building facades for decades. Numerical solutions have been carried out for natural convection heat transfer in a square cavity [2], the natural convection problem in an enclosure with one thick vertical wall [3], and heat transfer with two vertical walls, one conducting and one insulated [4]. Conduction along with the natural convection of fluid flow in enclosures has also been studied [5]. Already in 1984, [PERSON] and [PERSON] [6] had performed one- and two-dimensional calculations under various temporal conditions. Theoretical calculations of thermal resistance, albeit in other types of enclosures, have also been studied [7]. However, thermal calculations have already been made with finite elements in specific parts of buildings, such as in the encounter between enclosures, slabs and cantilevers [8]. Only the effect of air and thermal radiation is considered, not, for example, rainwater, which has also been studied previously [9]. It is therefore a great novelty to use a finite element program for modelling using Computational Fluid Dynamics (CFD) and applying it to the enclosure of a building to study the hygrothermal behaviour of the ventilated air chamber. Some of the advantages of cavity walls include [10]: the reduction of construction time, the possibility of using materials from the area to reduce transport costs, increased energy efficiency. The thermal contribution of the air chamber is small, but it has an essential function in the control and drying of rainwater. In the air chamber, there is an upward movement of the air due to the difference in temperature that occurs between the outer and inner leaf [11]. The air cavity between both layers acts as a capillary break and a channel for drainage and drying [12]. Various parameters can influence the air conditions in the chamber, such as building exposure, exterior leaf, wind speed and direction, type of openings, or chamber dimensions [13; 14; 15], as well as environmental conditions [16; 17]. Vertical air flows depend on density; however, if forced convection occurs, the flow can be multidirectional and highly turbulent [18]. Simulations were performed with the software Autodesk Simulation CFD 2019. This is finite element software for fluid flow analysis and thermal behaviour with steady or transient modes for 2D and 3D models. This program is very powerful, and is used in other fields of engineering for the design of aircraft, racing cars, and engines. All parameters and characteristics of the simulations were carried out in accordance with the Autodesk application manual [19]. Infrared thermography (IRT) is a powerful non-contact imaging technique, suitable for the protection of cultural heritage [20]. The appropriate conservation measures for a particular building can only be planned and carried out when an accurate damage diagnosis is made.