Residential buildings in Latvia are one of the essential heat consumers during the heating season. The majority of Latvian as well as European residential buildings were constructed within the period from 1965 to 1990. Introduction presents brief overview of current situation in Latvian and EU countries. This chapter provides overview of real energy consumption and definition of buildings technical conditions. Materials and methods are based on evaluation of standardized energy consumption in two kindergartens and multi apartment buildings including also dynamic energy simulation. Chapter on thermal performance of building envelope provides an extensive comparison of heat transfer coefficients in non-renovated buildings as well as comparison with normative values. Section on energy consumption of existing multi apartment buildings presents review of buildings real energy consumption before and after renovation. In addition this chapter evaluated indoor air quality. This study was done in order to define necessary reconstruction goals to reach European Regional Development Fund project “A New Concept for Sustainable and Nearly Zero-Energy Buildings” Nr. 188.8.131.52/16/A/007 main targets.