In this paper, a new model used to compute the outdoor to indoor signal strength emitted by a base station is presented. This model is based on the combination of 2 existing models: IRLA (Intelligent Ray Launching), a 3D geometric-like model especially optimized for outdoor predictions, and MRFDPF (Multi Resolution Frequency Domain ParFlow), a 2D FDTD-like model initially implemented for indoor propagation. The combination of these models implies the conversion of the ray launching signals on the border of the buildings, into virtual source flows that will be used as an input for the indoor model. The performance of the new combined model is evaluated via measurements, and it appears to be an efficient solution for radio network planning, both in term of accuracy and computational cost.