The research problem has emerged in the weak efficiency of the external envelopes in existing buildings, affecting the rate of energy consumption, as it has become involved in the largest proportion of the total energy consumption. The research aims to present a method for classifying techniques for increasing the efficiency of the building envelope, based on two aspects: energy conservation and renewable energy production, especially for middle-income residential buildings, and to clarify their impact in reducing the rate of energy consumption. The study conducted theoretical studies to clarify the problems of energy consumption in existing buildings, the importance of the envelope's contribution to saving it, and knowledge of the most important technologies that increase the efficiency of the envelope. Then, presented a case study for one of the existing middle-income residential buildings in Egypt and simulated it using Design Builder to determine the energy-saving rates. The research has reached a set of results that confirm the extent to which saving energy consumption in existing buildings is linked to raising the efficiency of their envelope through a set of technologies that can be integrated with the envelope to conserve energy and produce renewable energy.