The aim of this study is the numerical investigation of the capacity of porous hygroscopic building materials to damp indoor humidity variations due to external environmental loads and internal sources due to heat and moisture exchange. By means of numerical simulation, building material moisture content is computed by using a basic approach based on a diffusion model. Subsequently, a model incorporating the isothermal sorption curves of materials and complete thermal analysis is elaborated. The first modelling approach is more appropriate for material characterization even though it requires more time for modelling implementation and involves greater computational costs. The second modelling approach is useful for the assessment of hygro-thermal behaviour and energy performance of complex building components made of different materials. Moreover, this second approach can be easily applied to a 3D solid model of complex geometrical and architectural layouts. Results involve two different geometries. The first geometry belongs to a 1cm sized cube and represents the test system used in our study. The second one is representative of a usual building wall with a thermal bridge, consisting of different layers. From results analysis, it can be deduced that a more accurate numerical approach, using thermos-physical properties, porosity and hygroscopicity of materials and their corresponding sorption isotherm curves as input data, could be proposed for material characterisation and hygrothermal behaviour evaluation, in relation to the real physical indoor and outdoor transient climatic conditions. On the other hand, in many practical technical applications, our two proposed approaches can comprehensibly describe the investigated process combined with building-plant system energy performances, depending on the implementation process and computational costs we can implement.