Previous experience shows that renovation of ventilation systems is not a typical component of renovation of multi-apartment buildings (MAB) in Latvia. The typical solution for ventilation of the existing MAB – with natural exhaust channels from the toilet facilities and kitchen premises, and air inflow through gaps between the window frame and window carcass – does not ensure return of heat from the exhaust air and cannot ensure a maintenance of room microclimate that would be independent of weather conditions and would correspond to the human comfort requirements. As a consequence, rooms are not ventilated enough and indoor air quality (IAQ) is reduced. This, in turn, leads to progression of the so called sick building syndrome (SBS). IAQ measures within energy audit inspections in13 unrenovated MAB shows that CO2 concentration level in 19 of the examined 30 apartments was ≥1000, indicating insufficient ventilation. Reduced temperature on the sourface of building constructions create enable environment for a mold growth. The results of measures and inspections affirm necessity to realize only complex renovation activities in existing MAB to enhance energy efficiency and indoor microclimate of buildings.