In this study, an experimental protocol for the quantitative diagnosis of insulated building walls of restored old constructions is developed. Active infrared thermography in step heating mode is used to estimate thermal resistance of different commercial multi-layered panels fixed onto a building wall. The experimental set-up is based on a heating reflector that allows heating the investigated wall thanks to halogen spots. Measurements of wall surface temperature are performed by infrared thermography and measurements of air temperature in front of the wall are carried out using thermocouples. The proposed heat transfer modeling uses both thermal quadrupoles method and simplified asymptotic models. These models are implemented within an identification procedure to reach the parameters of interest. The study of the influence of the heating measurement duration has led to define minimum measurement duration to obtain accurate estimations. Finally a number of experiments provided quite satisfactory estimated thermal resistances in most of the investigated cases. This method might be used in the near future for in-situ determination of building walls thermal resistance.