The awareness of users about the benefits provided by the energy retrofitting of buildings is mostly related to the measurable return on investment in each energy efficiency measure. The environmental and economic assessment of the benefits depends on the quality of information (which usually has to be collected for each case). However, in the absence of data decisions tend to be postponed or taken on a subjective level. This paper assesses the preference of occupants about energy efficiency measures applied to Portuguese residential buildings, following cost optimality criteria. Six alternatives were created for the reference building and presented to twenty-five interviewees. These alternatives encompass different combinations of energy efficiency measures arrived at by changing four elements (insulation, glazing, equipment and renewable energy systems). The reference building is representative of the housing stock built between 1961 and 1990 which has high potential for improving energy efficiency. Two Multi-Criteria Decision-Aiding (MCDA) methods were applied: one additive method based on Multi-Attribute Value Theory (MAVT) and an outranking method (PROMETHEE). These methods enabled decision-makers’ preferences to be established and gave a final ranking of the alternatives being assessed. Moreover, this study also looks at the results from four rankings of building conservation measures: Spontaneous (obtained through simple sorting of alternatives by interviewees), MAVT, PROMETHEE and Cost-Optimal (sorting given by interviewees after knowing the cost-optimal analysis).
