One of the primary problems solved for increasing energy efficiency of a building is increasing of the insulating properties of the building envelope. The paper describes the method for determining the coefficient of thermotechnical uniformity by analyzing a thermogram of parts of a building envelope. The method is based on obtaining temperature distribution matrix on the surface of a building envelope fragment by thermography. Two methods for assessing the coefficient of thermotechnical uniformity are proposed. One method for determining the coefficient of thermotechnical uniformity is based on obtaining mean temperature values by numerically processing thermograms, another on numerical integration along the contour lines of temperature curves.