The paper presents study on existing building stock energy consumption for country of LaLvia. Especial attention is paid to the analysis of typical Soviet type multi-apartment buildings' specifics. The study analyses theoretical as well as real measured multi-apartment building heat consumption before and after renovation. Based on dynamic simulation precise energy balance was calculated for typical multi-apartment building. Results shown that simple thermal insulation of building insulation can ensure 50% reduction of building heat consumption. however, practical measurements have shown significant increase of indoor air relative humidity and CO2 concretion level. Evaluation of cost effective deep complex retrofitting solutions should take into account not only theoretical heat losses/heat gains but also human behavior. Paper does not take into account primary energy. Primary energy factors varies in EU countries. In some case primary energy factors was assumed without clear methodology. Thus, comparison of reduction of primary energy consumption in building stock could be incorrect.