In this work, we numerically investigate coupled heat and moisture transfer in a bio-based mortar wall containing micronized miscanthus fibers. The physical property inputs and their dependencies on temperature and moisture content were determined from literature data. A heat and moisture transfer model, based on the Künzel approach, was implemented in COMSOL Multiphysics. Simulations were compared with experimental data, demonstrating accurate estimations of temperature and relative humidity variations at different material depths. A maximum temperature deviation of 0.6 ℃ between experimental and numerical data was observed at a depth of 5 cm, while a maximum relative humidity deviation of 5% was obtained at a depth of 7.5 cm. Despite these discrepancies, the results are considered acceptable, given the inherent heterogeneity of bio-based materials and sensor accuracy. The developed numerical tool is adaptable, allowing the integration of additional physical models and phenomena to enhance the estimation of coupled heat and moisture transfer in complex bio-based building materials.