Policies for energy efficiency requirements in buildings have become more stringent according to EU2020 goals. Despite policy regulations, requirements for energy efficiency are not met in many new buildings. Some of the reasons for this energy performance gap are related to the building process. The aim with this paper is to describe a purposed method for quality assurance of sustainable buildings according to energy efficiency. The proposed method is called ByggaE, where 'Bygga' is the Swedish word for 'build' and E is the first letter in 'energy efficient'. It is a tool intended to lower the energy performance gap related to the building process by guiding the client and providers through the process to fulfill goals. The essence of ByggaE is the formulation of requirements by the client and the working process of identifying, handling and following up critical constructions and key issues. This working process involves all participants in the building project by using appropriate quality guidelines and checklists for documentation, communication and verification. ByggaE is a step forward ensuring that the building fulfills the defined functions and that conscious decisions are taken when goals have to be changed during the building project. The next steps are to ensure the usefulness of the method in practice by more testing and to spread knowledge about the method.