AIM: This research examines the important issue of energy efficient improvements to the existing building stock through building envelope upgrade. To facilitate this, the energy performance characteristics of the existing building stock were identified with a view to establishing an existing building stock type, where building envelope upgrades can contribute to a higher level of energy efficiency improvements. The literature review along with the selected building precedents was used to establish the best current practice for building envelope upgrades.MATERIAL AND METHODS: Established building precedents and identified best practice for building envelope upgrade, a high rise block of flats was identified and used as a case study, with the current and predicted, following building envelope upgrade, energy performance of the building calculated. This has allowed us to identify the possible energy efficiency improvements for this type of building following the building envelope upgrade. RESULTS: In the projected case, the building with energy class - "D" become class "B". In addition, increased quality of the living room in the attic was enabled. It was possible to obtain a decrease of the heating energy from 130.76 kWh/m²a to 37.73 kWh/m²a or to jump in the class "B" of energetic passport.CONCLUSION: This research contributes to the local implementation of the global agenda for sustainable development, design and construction, and it demonstrates the possible way and level of energy efficiency improvements to the least efficient building stock through existing building envelope upgrade.