The heterogeneous and transient features of indoor thermal environment play an important role in thermal comfort dynamics but remains difficult to predict accurately. This contribution presents the development and validation of a detailed 3D building thermal model with high-resolution description of heat conduction in the envelope and surface balances. The model is applied to the evaluation of operative temperature distribution in a room with heterogeneous and transient radiative assymetry. It is intended to couple the model with computational fluid dynamics (CFD) in further works. The coupling would improve the numerical prediction of indoor thermal environments and could be used to study thermal comfort dynamics with high resolution boundary conditions.