The escalating demand for sustainable urban development has increased the focus on energy efficiency, particularly within the building sector; our research dives into the specific topic of green roofs, investigating their potential to enhance building performance through advanced heat and moisture transfer modelling. Our research addresses the problem of how green roofs, as a building technology, can be effectively modelled to predict their impact on building energy consumption. We modified the existing heat air and moisture transfer model (HAMFit) implemented in COMSOL Multiphysics to simulate heat and moisture dynamics in green roofs. We integrated vegetative effects, moisture transfer, and thermal conduction into the model, validated against empirical data from an extensive field study in a marine climate. Results indicate that green roofs moderately enhance thermal performance, with the benefits observed in heating-dominated climates. The results also underline that evapotranspiration contributes to additional cooling effects under favourable moisture and temperature conditions. The findings suggest that green roof design shall be optimized for each climate and design, offering an additional component in pursuing sustainable building design.