The cooperative housing sector is directed at low and medium income residents who cannot afford to buy their homes in the regular private market. Due to social housing legislation, it is possible to build cooperative housing below regular market costs and use tax benefits, therefore providing affordable dwellings to their owners. Traditional cooperative housing used to provide less comfort and higher running costs in indoor and domestic hot water heating than in standard construction. However, cooperative housing has started to change its method of traditional construction towards sustainable construction, in order to benefit from the savings on energy consumption and domestic water as well as to provide an improvement as far as the comfort of its residents is concerned. Therefore, in this article, the savings in electricity and natural gas in different building settlements, calculated for Madalena building—sustainable construction—and for Azenha de Cima building—traditional construction—will be presented, according to two different criteria of calculation: efficiency of dwellings at a pre-determined standard level of indoor comfort opposed to real consumptions made by residents. For each building under analysis, an energy audit and further monitoring were brought in, in order to issue an energy evaluation according to the Portuguese energy agency rules. Results showed an expected decrease of the operational costs of natural gas and electricity, obtained by the use of efficient building systems and equipment, as well as a decrease of the payback period for each situation.