Thermal imaging cameras are the basic measurement tool used to examine the quality of thermal insulation of walls of various objects, especially building walls. However, the thermal imaging measurement result is very sensitive to the correct adjustment of values of measurement parameters. These measurement parameters include the emissivity of the tested object, the radiant ambient temperature, atmospheric air parameters including its temperature and moisture content as well as the distance between the object and the infrared camera. All parameters mentioned above, except the ambient radiation temperature, can be determined by the measurement using known measuring devices. The radiative ambient temperature of the tested surface is the second parameter after the emissivity of the tested surface in terms of the impact on the thermal imaging measurement result. Hence, it is important for the accuracy of infrared camera temperature measurement. In the case of measurements in open atmospheric space, for the simplest case, the surroundings of the tested object consist of the ground surface and a hypothetical hemispherical surface of the sky. This case of determining the radiative equivalent ambient temperature has been described in previous publications. The problem is more complex in the case of thermovision diagnostics of objects (especially those of large height) located in close proximity to other similar objects (for example, buildings located in dense housing estates). The work proposes a solution to the problem of determining the ambient radiation temperature of the tested objects, especially its vertical differentiation along the external walls of buildings. This phenomenon was observed during infrared camera inspections of relatively tall buildings in housing estates. Sample charts have been developed for selected examples.