This contribution deals with the development of a numerical approach based on discrete element method to study the hygrothermal behaviour of conventional and composite materials. For this purpose, we consider the context of magnesium aluminate and polyamide 6 reinforced with 30% of short glass fibre respectively. A coupled hygrothermal model based on boundary layer theory and the analogy between the Fickian mass and heat transfers is proposed. In addition, the original Halo approach introduced in the context of heat conduction is adapted to determine water concentration gradient fields with a suitable level of description. The proposed model is validated in terms of water concentration and water gradient fields for both materials by comparison with numerical and experimental results through the modelling of drying and absorption processes. Results exhibit the relevance of the proposed approach to provide such information with a suitable level of precision.