In addition to reducing the energy consumption in residential buildings, the Rulebook on the energy efficiency of buildings, which was recently enacted in Serbia, also pays special attention to the issue of energy performance of the existing buildings. On the other hand, in the course of a few decades researchers all around the world are showing tendencies towards inclusion of embodied energy into the calculation of the overall energy consumption in the residential sector instead of just employing the most frequent and widespread calculation of operational energy. Thus, the aim of the paper is to determine the quantity of embodied energy on the example of the external wall of selected residential buildings, before and after the process of energy performance optimisation, in four different scenarios including four different insulation materials. A selection of seven house types, which were deemed representative for this research, was conducted on the example of Sombor, a typical town in Vojvodina, i.e. a typical town in Northern Serbia. Two criteria were involved: the applied materials and the representation of buildings constructed in different time periods. The issue of improving the thermal features of the external walls is analysed, since it was previously determined that none of the selected buildings satisfy the maximal value of thermal transmittance U, as stipulated by the latest Rulebook from 2011 (Ministry of Environment, Mining and Spatial Planning MEMSP 2011a). The methodology for the embodied energy evaluation in 1 m(2) of the external wall was created on the basis of the grouping of life cycle phases into building's energy use categories: initial embodied, operational, recurrent embodied and demolition energy; and into the system boundaries: cradle to gate, cradle to site, cradle to grave and cradle to cradle. After taking into consideration, the life cycle phases of the external walls' building materials and subsequently installed insulation materials, it was determined that in terms of consumed recurrent embodied energy, the local insulation materials typical for the region of Vojvodina, are more preferable in relation to the widespread artificial materials.