In this work we present a systematic tool for the optimal retrofit of buildings that considers several economic and environmental criteria simultaneously at the design stage. Our approach is based on a rigorous mixed-integer linear program (MILP) that identifies in a systematic manner the best alternatives for reducing the environmental impact of buildings. These include the use of different insulation materials and windows as well as the installation of solar panels. Environmental concerns are explicitly accounted for in this MILP by means of Life Cycle Assessment (LCA) principles, which allow evaluating the impact of each alternative being assessed considering all the stages in its life cycle. We illustrate the capabilities of our approach using a case study that considers weather data for Central Portugal. (C) 2014 Elsevier B.V. All rights reserved.