The paper describes the problem of building envelope investigation with active thermography. Mainly emphasized is its application to detect different material of wall inclusions. Examples of active thermography application and description of experimental investigation has been shown on a model envelope, with inclusion of significantly different thermal conductivity and heat capacity materials; XPS polystyrene, steel and granite. Thermograms received for every kind of inclusion have been compared and analyzed. Finally, the summary and conclusion have been shown along with the prospects of development and practical application of this kind of investigation in construction.