## 1 Introduction  
The new Energy Performance of Buildings Directive (EPBD) [1] promotes sustainable, economical and comfortable buildings for their residents. There are requirements for lower energy consumption, and more attention is being given to the use of hygroscopic materials from renewable sources [2; 3], which are characterized by a lower negative impact on the environment. User comfort and indoor air quality have become important parameters to take into account when choosing building materials [4]. This approach is also promoted by green building rating tools as the Building Research Establishment Environmental Assessment System (BRESAM), Leadership in Energy and Environmental Design (LEED) or voluntary standards such as Passive House. Therefore, research on renewable, hygroscopic materials has acquired much more importance than in the past. In recent years, numerous studies of hygric materials have been conducted, showing that these materials can contribute to improvements in indoor air quality by passively controlling the indoor humidity level [5; 6; 7] and reducing energy consumption [8; 9]. These materials usually have very good moisture-buffering capacities; they can effectively take up and release moisture from the air when they are exposed to different moisture loads [10]. The literature reports several studies, conducted at the materials scale, where the moisture buffering was quantified using the moisture buffer value (MBV). At the Technical University of Denmark, [PERSON] [11] compared the MBVs of different materials using an experimental flux chamber. A theoretical MBV, determined by measuring the water vapour permeability and sorption isotherm, was calculated for clay masonry by [PERSON] at al. [12], [PERSON] et al. [13] and [PERSON] et al. [14]. [PERSON] et al. [15] reported the MBV results for six different bio-based materials: hemp lime, hemp fibre, wood wool, wood fibre, barley-straw starch and corn pith-alginate. Novel bio-insulating particleboards made from bamboo powders and various bio-adhesives were investigated by [PERSON] [16], and [PERSON] et al. [3] studied bio-based insulating materials based on various hemp and shive-fibre ratios. The moisture-buffering phenomenon is not limited to the materials scale. The definition of the moisture buffer value is also applicable to the wall scale [10]. [PERSON] and [PERSON] [17] determined the MBVs of lime-hemp composite wall assemblies, using WUFI simulations and adopting the Nordtest protocol [10]. A series of experiments in a full-scale test facility, aimed at determining the moisture buffer effect of interior walls of cellular concrete and plasterboard construction, was carried out by [PERSON] et al. [18]. [PERSON] et al. [19] investigated the hygrothermal behaviour of a hemp-coated concrete wall using cyclical absorption/desorption tests and compared their simulation results with the experimental data. The MBVs of vapour open wall assemblies containing hemp-lime with inner linings and surface treatments were compared with that of the exposed hemp-lime by [PERSON] et al. [20]. The experimental method, based on diurnal cycles with two relative humidity levels (upper and lower) corresponding to occupied and unoccupied periods, was studied by [PERSON] and [PERSON] to determine the moisture-buffering effect of structures and building components [21]. At the same time, numerical studies on the hygrothermal behaviour of hygroscopic materials and walls have increasingly been undertaken by researchers and designers, as this is a cheaper and more easily available method. However, to have confidence in the model used, it is necessary to validate the prediction of the numerical model using the measurement data. The latest studies comparing measurement and simulation results on the hygrothermal behaviour of building materials and investigating potentially emerging trends for all building materials, thus validating the simulation tools, are reported in [22].