In Spain, a significant percentage of the residential building stock presents deficient indoor conditions regarding current energy standards, due to having been constructed before the Norma Básica de la Edificación in 1979 (NBE CT 79) regarding thermal conditions in buildings. Current environmental policies pursue a cut in energy consumption and seek improvements in indoor conditions by refurbishing current stock, mainly that constructed between 1950 and 1980. Before any retrofitting action, housing monitoring has become essential for a better understanding of real and passive environmental behavior. This paper aims to present the monitoring in hourly intervals, real-time and post-occupancy conditions of a residential building in Seville, built in the 1950s and belonging to national heritage. The results obtained show major discrepancies between thermal indoor data collected and comfort conditions, both in summer and winter, which are solved by the sporadic use of cooling and heating devices present in the dwellings, thus leading to less energy consumption than expected. This is a common occurrence in multi-family housing units from the Mediterranean arc: there are many periods of the year in which a vast number of the population lives in poor energy conditions.