This work is within the scope of thermal retrofitting, applied to old buildings’ façades (built between 1700 and 1960) located in Mediterranean climates, such as Portugal. The aim is to increase the sustainability of existing buildings, by reducing their energy consumption needs, for heating and cooling, and the corresponding gaseous emissions, while increasing their users’ comfort. Firstly, an analysis of the advantages and disadvantages of several thermal insulation solutions for façades was carried out, supported in current literature. Then, a survey of real retrofitting scenarios and interviews with experts was completed, to allow the selection of the most adequate thermal insulation techniques. Finally, as a result of this study, the discussion of retrofitting strategies was carried out to support the designer’s decision process, based on a flowchart with complementary tables, discussing the best thermal retrofitting technique to be implemented on old buildings’ façades, case-by-case.

Life cycle assessment (LCA) is a scientific method for evaluating the environmental impact of products. Standards provide a general framework for conducting an LCA study and calculation rules specifically for buildings. The challenge is to design energy-efficient buildings that have a low environmental impact, reasonable costs, and high thermal comfort as these are usually conflicting aspects. Efficient mathematical optimisation algorithms can be applied to such engineering problems. In this paper, a framework for automated optimisation is described, and it is applied to a multi-story residential building case study in two locations, Portugal and Hungary. The objectives are to minimise the life cycle environmental impacts and costs. The results indicate that optimum solutions are found at a higher cost but lower global warming potential for Portugal than for Hungary. Optimum solutions have walls with a thermal transmittance in the intervals of 0.29–0.39 and 0.06–0.19 W/m²K for Portugal and Hungary, respectively. Multi-objective optimisation algorithms can be successfully applied to find solutions with low environmental impact and an eco-efficient thermal envelope.

The purpose of this study is to explore the relationship between solar orientation, age (constructive characterization) and energy performance of Portuguese residential building stock and to assess the usefulness of exploring the Portuguese National System for Energy and Indoor Air Quality Certification of Buildings (SCE) database through multivariate analysis techniques. By using principal components technique, it was possible to condense the residential units’ features to only four principal components (PC): solar orientation; constructive characterization; geometry and energy performance, making information more workable. Grouping the entities into Clusters with favourable and unfavourable solar orientation and old buildings allowed to dilute the particularities of each entity, facilitating the interpretation of the data through generalization. A regression model was generated in order to explore/confirm which factors influence summer comfort the most. Using this approach, it was illustrated that the exploration of the SCE database through multivariate data analyses has an enormous potential to convert data into knowledge.