According to the Intergovernmental Panel on Climate Change (IPCC) the building sector is responsible for 40% of greenhouse gas (GHG) emissions.Since most of the global electricity comes from fossil fuels, most of the GHG emissions from buildings are caused by the consumption of electric power during the operation phase.Hence energy efficiency in buildings has been identified as one of the main strategies for climate change mitigation.In Colombia, this strategy is part of the National Plan for Low Carbon Development.Although in this country 70% of electricity is produced from hydropower, a renewable source with low GHG emission factors.On the other hand there is a high deficit of social housing and an accelerated process of urban growth in Colombia, where the building systems are characterized by a low level of industrialization, a high intensity of materials (2.5 ton/m 2 ) and a substantial production of construction waste (1.0 ton/m 2 ).By using emission factors for construction materials in Colombia, recently calculated by the United Nations Environmental Programme and the National Unidad de Planeación Mineroenergética, this study conducted at The Metropolitan Area of the Aburrá Valley shows that production of materials for the construction of new buildings produces 2.4 times more GHG emissions annually than the total electricity consumption of all existing buildings.There are no emission factors from construction activities and construction waste disposal specific to the Aburrá Valley, but these would evidently be directly related to the total weight of materials involved.Although electricity efficiency of buildings is an important