This book focuses on housing refurbishment as a vehicle to reduce energy consumption in the towns and cities of North West Spain. It analyzes potential energy savings in relation to climate, retrofitting strategies, original construction systems and the urban fabric. The investigation begins with a thorough study of the climate and the most common urban and constructive typologies. The thermodynamic principles associated with each retrofitting technique are then explored to gain a clear understanding of typical performance patterns in different scenarios. General trends are identified and further studied by means of multiple computer simulations, which unveiled the underlying correlation between efficiency, typology and upgrading measures. Finally, summary tables synthesize potential energy savings, as well as the embodied energy and the economic cost derived from retrofit interventions, thus offering both a method and a detailed catalog of alternatives to environmentally conscious practitioners, tenants and landowners.