During the last few decades an increased attention has been directed towards reduction of building energy use. This paper presents results of a simulation study to achieve deep energy retrofit in a five story dormitory of about 3825 m2, located in Latvian capital Riga. Simulation was carried out within the framework of Annex 61 “Business and Technical Concepts for Deep Energy Retrofit of Public Buildings” of program “Energy Conservation in Buildings and Communities” by International Energy Agency. A software “Riuska” was used for comfort and energy simulation. Following scenarios have been used in modelling: Scenario 1 (baseline) represents the pre-1980 standard to describe the building envelope and systems before renovation. Scenario 2 (base case) is the country specific “business as usual” retrofit to meet requirements of minimum current national standards. Scenario 3 is related to application of core energy technology bundles to achieve approximately 50% energy use reduction against the baseline (scenario 1). Scenario 4 targets to achieve a current national “dream energy standard”. Energy improvement measures for scenarios 2 to 3 focused on the reduction of transmission and infiltration losses through insulation of building envelope and replacement of windows. These measures are one of the most frequently implemented ones in Latvian public buildings, where most energy is used for heating. Building’s energy need for space heating was 143 kWh/(m2·a) before renovation as for scenario 1 (pre-1980 standard) and has