Over the past three decades, performance-based design has pursued the development of a methodology that anticipates the impact of a design solution in order to evaluate its performance. According to this methodology, designing can be considered as an iterative process of exploration, where desired performance requirements are defined –problem space–, design alternatives are proposed –solutions space–, and a process of evaluation is used to determine the confluence of the predicted solutions performance to the stated performance requirements, i.e. the solutions space can be refined through iterative simulations. Energy efficiency is one of the fundamental issues to evaluate the performance of buildings. This paper summarizes a research work which seeks to apply a performance-based design methodology to support the decision-making process in order to improve the energy performance of buildings. A case study of a social housing building recently built in Cerdanyola del Vallès, Barcelona, has been used to explore the application of performance-based design to make better informed decisions in the design process.