Residential sector
The average age of buildings and the share of new buildingsin the total stock represent a
good indicator of the quality and standards of construction. 36% of the buildings were
constructed in the period 1960-1980. The first normative requirements for thermal insulation
in Bulgaria were applied from 1961.The main requirement is the achievement of minimal
value of the total thermal resistance of heat transfer in order not to cause condensation of
water vapors on the internal surface of the building shell during the coldest winter day, which
is a hygienic requirement. After the oil crises in the end of 1970s the energy performance
characteristics of panel buildings were improved. In 1987 new normative requirements were
applied and the thermal requirements were increased with about 35-40%.