The main question studied during this study was what does it takes conversion of conventional building built according minimum energy efficiency requirement by existing building code to nearly zero energy building (nZEB). The aim of this study is to work out technical requirements to reach nZEB level in Latvia and test them in real building project. Real energy consumption data and indoor climate conditions have been analysed to understand building energy performance after construction. At the moment no official low energy building guidelines exist how to reach very low energy standard in Latvia climate conditions. This study also helps to identify challenges and future development needed for building components to reach nZEB level.