Due to the current environmental situation, energy saving has become the leading drive in modern research. Although the residential houses in tropical climate do not use air conditioning to maintain thermal comfort in order to avoid use of electricity. As the thermal comfort is maintained by adequate envelope composition and natural ventilation, this paper shows that it is possible to determine the thickness of envelope layers for which the best thermal comfort is obtained. The building is modeled in EnergyPlus software and HookeJeves optimization methodology. The investigated house is a typical residential house one-storey high with five thermal zones located at Reunion Island, France. Three optimizations are performed such as the optimization of the thickness of the concrete block layer, of the wood layer, and that of the thermal insulation layer. The results show optimal thickness of thermal envelope layers that yield the maximum TC according to Fanger predicted mean vote.