The European roadmap towards a competitive low carbon economy in 2050 raised the awareness
about buildings energy performance due to their potential for cost-effective energy consumption and carbon emissions reductions. For the evaluation of the levels of energy performance of buildings, the European Commission presented the Cost Optimal Methodology allowing comparing different energy performance levels of buildings and buildings components and identifying those with the lowest associated cost considering the building life cycle. This study, using four reference buildings from the Portuguese building stock, where some scenarios for the improvement of their energy performance were analysed with the purpose of identifying the cost-optimal levels, compares the economic performance of different measures. Results provide guidance for the assertive combination of elements for new buildings and for building packages of renovation of measures, as well as for the choice of individual measures in partial renovation scenarios, which, beyond common, are usually performed
without the control of the national energy certification system.