Additional or retrofitted thermal insulation systems of existing buildings appeared as the most straightforward way to achieve almost immediate improvements in heating energy consumption. Insulation reduces fuel consumption, undesirable emissions from the burning of fossil fuels, and increases thermal comfort by minimizing heat losses from buildings. The thermal performance of four residences with different external wall systems, which are located in the Unikent Housing Complex in Isparta, was analyzed in this study. The users of three residences applied additional insulation layers to the wall system. One of these buildings had no insulation system, one had internally applied insulation, and the remaining two residences had externally applied insulation systems. One of the residences with an externally applied insulation system had an enclosed balcony. Data loggers were placed in the bedrooms, which have the same sized windows and look towards the same direction and are located on the second floor of each building, to obtain the temperature and humidity values of these spaces. The buildings with insulation were found to exhibit better performance when compared with the uninsulated buildings. According to the study conducted, the building with internal insulation behaves like an uninsulated building during the period when no heating is applied. Nonetheless, during the period when heating is applied, the internally insulated building permits less exposure against external atmospheric conditions since the materials used in the internal surface of the wall store the heat. Additionally, an externally insulated building with an enclosed balcony shows better performance than the other externally insulated building with a lower U wall value. The balcony, enclosed by using glass material, did increase the heat savings and enabled the maintenance of the inner temperature of the related room.