## 1 Introduction  
The reliability of building structures is closely connected to various physical phenomena, among which moisture can be undoubtedly considered one of the highly relevant factors. Moisture affects the number of material properties, from thermal conductivity to the mechanical properties in terms of strength, etc. There are more parameters that describe the behavior of the material from a moisture perspective. The structure and material base [1] determine which phenomena will be applied during moisture transport and moisture binding. Capillary and porous materials are often used for building construction; however, they interact with moisture intensely. In building construction, autoclaved aerated concrete (AAC) is a frequently used material and can be considered a representative of a sustainable building material, considering its specific structural, mechanical and thermal insulation properties. This allows forming the building envelope structure with no additional thermal insulation layer and thermal bridges; its thermal conductivity ranges from 0.09 to 0.2 W\(\cdot\)m\({}^{-1}\).K\({}^{-1}\)), with bulk densities ranging from 450 kg/m\({}^{3}\) to 750 kg/m\({}^{3}\)[2]. On the other hand, the properties of this material are strongly dependent on moisture content, which also affects the strength characteristics and compressive strength [3, 4]. In general, the moisture transport in concrete is determined by the moisture gradient as well as the temperature gradient [5]. The effect of moisture content on the thermal conductivity of the AAC is significant, with a critical value of 15% moisture content [6]. Other studies, focused on lightweight concretes, expressed a linear dependency of the increase in thermal conductivity and moisture [7]. However, the hygrothermal behavior of AAC masonry walls is a subject absent in discussions of the scientific community [8]. Moisture transport by diffusion and capillary conduction is used in AAC. The ability to express moisture binding at a low saturation is expressed by the sorption curve. When dry porous material with an open-pore structure is exposed to a humid environment, moisture binds in its pores and even in some pore groups, getting completely filled. This state takes place gradually, characterized by a gradual and very slow weight gain, which in a certain time reaches the so-called equilibrium state. Measurements show that relative humidity varies instantaneously and linearly with the temperature at locations where the moisture content is supposed to be constant. These variations were found consistent with the temperature dependence of the sorption isotherm. [9]. Similarly, desorption, exposure of a moist material to a lower humidity environment, results in the gradual release of moisture from its porous structure, causing weight loss. Most materials are characterized by a very significant deviation between sorption and desorption, called hysteresis. The measurement of building material moisture, using well-established methods as well as the inclusion of new approaches [10; 11], are one of the current relevant research challenges to establish more detailed studies of the basic physical processes fundamental to moisture transport. The results of measurements by standard stead-state procedures for moisture transfer in AAC building materials may show slightly underestimated data compared to the methodologies using dynamic effects [12]. In case of highly hygroscopic materials, such as AAC, the samples going through different preconditioning methods (especially in wet cup tests) may have a statistically different moisture content and permeability [13]. Therefore, adequate material parameters and their characterization are currently an important factor for identifying the reliability of the development and verification of theoretical models, such as the numerical prediction of heat, air and moisture transport (HAM) in porous building materials [14; 15].