In this study an assessment of the energy renovation potential was analyzed for Trnsko, a neighbourhood in the city of Zagreb. The settlement model was designed by Rhinoceros 3D computer program, after which the energy simulation was done using The Urban Modeling Interface (UMI) that provides various energy analyses. UMI was used to calculate the amount of required and delivered energy for the existing building condition as well as after the implementation of energy renovation measures. Since UMI is intended for large unit modeling, the main goal of energy analyses is a fast simulation performance with acceptable result accuracy. In order to evaluate the reliability of UMI, additional energy simulation was done in TRNSYS software for Elementary School Trnsko. With the aim of determining the optimal thermal insulation thickness and the investment return period, an economic analysis was conducted for residential buildings in Trnsko, taking into account different thicknesses of external wall insulation. The obtained deviation in the accuracy of the results is 20% for the required energy for heating and cooling compared to TRNSYS. This is considered acceptable in relation to the advantages of urban modeling possibilities. After changing the thermal properties of the layer, which included the insulation of external walls and roofs as well as a window replacement, the delivered energy for heating decreased by 74%, while the delivered energy for cooling decreased by 7%. By conducting an economic analysis for different thicknesses of the insulation of the outer wall, results show that the optimal thickness of the insulation is 14 cm for which the investment return period is 31,7 years.