Results of numerical modeling of stationary heat exchange in three-dimensional model of a site of the panel building of the OD-4 series are presented in article. Dependence of thermal losses on physical parameters of construction materials of a protecting design is shown. Results of modeling are well coordinated with data of the thermovision shooting carried out by authors. Calculation for justification of technology of recovery of heatphysical characteristics of protecting designs of panel buildings due toapplication of polysulphidic tapes for sealing of interpanel seams is executed. External conditions for the climatic region of St. Petersburg arechosen. The increase in heatlosses through protecting designs at decrease in their heatphysical characteristics of rather design indicators reaches 30%. Economic efficiency of sealing of seams isdefined.