The building envelope is subjected to climatic influences by its individual orientation and composition. The main function of the building envelope in hot climates is to minimize external heat stress. Indoor thermal control can only be achieved through understanding of the thermal performance of the building envelope in relation to relevant weather parameters. It is also becoming increasingly realized that much can be done to mitigate heat stress in unconditioned buildings and to reduce cooling and heating loads and the energy consumption of air conditioned buildings, through a proper choice of building envelope materials and envelope design. The envelope's response to climatic conditions is a major determinant of the amount of energy required to maintain the building's thermal environment. Also, he building envelope directly influences the cooling peaks and air conditioning system capacity requirements. The thermal properties of the envelope are determined by the combination of wall mass, thermal resistance; insulation location, external surface colour, texture, and size.