In this article, a new technique for identification of the thermal parameters of simplified mathematical model for an existing building is presented. This thermal simulation model allows the performance analysis of a building. The model is based on the electrical analogue with resistances and capacitors (RC) used for the simulation of the unsteady heat flow in the building. The model is validated with the results of a TRNSYS simulation. The obtained accuracy lies within a 7% interval. This tool is then used in an inverse method in order to determine the value of the electrical (RC) equivalent thermo physical characteristics of the building envelope. The model for the determination is based upon the least squares method, between the indoor measured temperatures and the model response, using an inverse iterative algorithm (Reflective Newton). (C) 2015 Elsevier B.V. All rights reserved.