Energy saving in existing buildings is of vital importance. In this work, the characterization of housing stock in Spain for energy retrofitting purposes has been performed. The regulations in force when the existing stock was constructed (1980–2007) were considered to model the envelope and thermal systems of single-family and block housing. Building energy consumption and CO₂ emissions were estimated for each type of dwelling and location, ranging from 44.2 to 130.6 kWh/(m²·year) (13.6–32 kg CO₂/(m²·year)) for multi-family homes, and 85.5 to 213.5 kWh/(m²·year) (17.1–45.2 kg CO₂/(m²·year)) for single-family homes. A global picture of the energy performance and emissions for 13 different climate zones was obtained with a total of 504 simulations. Retrofitting of the envelope allowed the reduction of consumption and emissions from 37.7% to 58%, depending on the climate zone. Energy consumption per square meter in block housing was lower than in single-family housing; nevertheless, single-family houses responded more effectively to energy improvement actions. Finally, non-renewable primary energy savings seem a better indicator of the improvement by retrofitting than the energy label. The building models designed in this work may serve as a reference for subsequent research concerning energy retrofitting and energy savings of housing stock.