Efficient use of energy is important since the global energy resources are finite and power generation using fossil fuels has adverse environmental effects. As buildings are the biggest users of energy in Europe, representing approximately 40% of energy consumption in the European Union (EU), it is vital that we make our buildings more energy efficient. The measures are being applied across all EU countries and are in line with the European Directive for the Energy Performance of Buildings (EPBD). The paper investigates whether different design approaches were considered when designing energy efficient buildings and what criteria for design were used in accordance with architectural research to constructing low energy buildings. It also examines if there were any implications to constructing such low energy building designs compared to the traditional designs besides cost budget and resource use. In the paper, this is demonstrated with a case study of a residential building where the building is constructed as a low energy house and various thermal assessments were carried out in relation to its design and energy balance in order to improve building energy efficiency. Furthermore, a comparison study was prepared between this selected passive house with improved standards and the same house design with common standards in order to justify the energy efficiency levels achieved, which is also presented on a graphical scale known as energy labelling of buildings as part of EPBD implementation throughout the EU countries.