The object of investigation is one-type neighbouring blocks of flats located in Volgograd region (Russia, N 48°). Thermophysical field testing using eco-friendly nondestructive test methods was carried out to estimate whether the level of heat protection in buildings meets requirements of the Russian construction norms SP 50.13330.2012. According to the results of thermophysical field tests of residential buildings made of autoclaved aerated concrete blocks, the following was found out. Design of double-layer exterior walls in the form of AAC blocks with front brick masonry bears thermotechnical risks due to an increase in non-uniform heat protection of buildings’ covers caused by a significant impact on heat protection of buildings’ edge zones. The designed level of heat insulation does not conform to the basic level of heat protection for the majority of regions in the Russian Federation. Two-layer exterior walls without supplementary insulation practically do not have heat protection and energy saving reserves. The reduction of the actual insulation in envelopes, compared to the designed one, can be explained by both unapproved deviations from the design project made by a subcontractor during construction and low-quality construction and assembly work. It is strongly suggested to improve the structural solution of edge zones in envelopes to reduce thermotechnical risks when designing buildings. Supplementary insulation along the surfaces of the walls can be considered as another activity to increase heat protection.