A field study of 10 social housing dwellings in the north of Spain is presented in this paper. Knowing the building stock is the first step to set up priorities in a global strategy to improve the energy efficiency of the existing building stock. Moreover, improving the energy efficiency of buildings is one of the most effective ways to tackle fuel poverty, which is increasing in Spain in the last years, being social housing one of the most vulnerable sectors of being at risk of fuel poverty. The aim of this research is to describe a methodology for analysing the thermal performance of buildings under a holistic approach. An overview of the thermal performance of the social housing stock in a city with mild climate in Spain is presented. Social housing stock in Bilbao is classified by means of selecting 10 representative dwellings. A field study was performed during 10 months. Results of heating consumption as well as indoor conditions are presented. Results show that energy consumption in winter is not as high as expected, due to the low indoor temperatures. Amongst other factors, the influence of the occupants plays an important role in the final thermal performance of dwellings. (C) 2013 Elsevier B.V. All rights reserved.