Energy efficiency is an increasing requirement in the modern construction industry. The building envelope design plays an important role for increasing energy efficiency. The main objective of this study was to evaluate different roof and wall designs for energy efficiency in order to fulfil the future requirement for a sustainable building envelope. The comparative case studies were carried out by calculation and analysis of the different building parts. Of the roofs compared, the koljern-technique worked best. During the analysis of the wall constructs, an exterior wall with polyisocyanurate (PIR) insulation showed the best results. One of the conclusions was that better insulation is needed to meet future requirements for a sustainable building envelope. Another important finding was that the construction industry should be open to new technologies, such as the koljern-technique and PIR-insulation.