This work involves the study and the modeling of heat transfer in a wall subjected to a condition of solar radiation in winter on the outside. An optimal proposal is cleared from this study based on the searched objectives. We also analyzed the influence of heat transfer on materials selection and optimization of the thickness of such a building envelope in southwest Algeria. The operation of the numerical code developed on cases related to the problem in the home. The simulation results are presented examples of building in real operating conditions (solar input, temperature, accumulated heat, etc.) and are in good agreement with those of the literature. In the established periodic regime, the temperature of the outer face varies from 21.23°C to 56.01°C, the temperature in the middle of the wall varies from 14.96°C to 22.02°C. Therefore, the amplitude of the quasi-steady state is 17.39°C. The heat stored and returned inside the room varies from 136.61 W/m² to 177.73 W/m²; the amplitude of the quasi-stationary regime is 20.56 W/m².