In this article there were mentioned selected design aspects of sections and joints in low energy buildings. There were set legal requirements in energy saving and thermal insulation as well as for avoidance of surface and interlayer condensation. In order to select internal sections and joints which fulfil the requirements for low energy building, calculations of physical parameters were performed with professional computer programs. The usage of modern insulating materials and correct set of material systems in external partitions and their joints guarantees minimal heat loss through permeating and ensures reaching the low energy building standard.