Bioshaders are plants used mainly as external shading devices of buildings such as vertical climbing plant canopies. In this research, the numerical modeling of the thermal performance of a bioshader is investigated in terms of its shading effect on building’s external walls. A dynamic, one-dimensional model is developed, describing heat and mass transfer in building envelope. The numerical modeling is utilized as a simple method in order to manifest the shading effect of the selected plant canopy in the hot arid climate. The effects of temperature and moisture concentration is considered along with the vegetation canopy layer properties of air and foliage. Then at a later stage, this numerical modeling will help in designing a controlled experiment of a real bioshader erected on external building façade and verifying the obtained results. The developed model will be useful to simulate and predict the cooling effect of external plants on building external surfaces. It is considered an important stage of a broader study that emphasizes on the thermal performance of bioshaders.