Results of scientific research of heat-shielding properties of modern designs of external walls in box-shaped modules are given in this article. On the basis of thermovision quality control of thermal insulation of external walls temperature anomalies in the edge zones of enclosing structures are revealed. Using results of thermal monitoring of the object, the most significant heterogeneous fragments of external wall are allocated. Deterioration in the thermal mode of designs is caused by considerable influence of the end-to-end heat-conducting inclusions of big extent accepted in the project. For the purpose of determination of a heat-shielding level mathematical modeling of heat transfer in external walls is executed. The most precisely additional heat-losses caused by influence of edge zones can be determined by temperature fields. The specified resistance to heat transfer (R-value) of the wall is in interval of admissible values according to Russian Norms (SP 50.13330.2012) and is close to economically reasonable resistance to heat transfer. However, extremely low value of heat transfer performance uniformity factor for external walls (0.49) is caused by the inefficient design solution of a heat-shielding. Enhancement of the constructive solution of panels of external walls application instead of edges of connectors reduces additional heatlosses and increases heat-shielding properties of designs. Higher value of heat transfer performance uniformity factor in the offered option (0.64) demonstrates increase of heat-shielding of external walls. Application the connector in a wall levels the temperature field and improves the thermal mode of a wall.