Methods based on the stochastic apparatus technical diagnostics are put forward to solve problems concerning determination of the structural elements technical condition. Diagnosis is performed using probabilistic methods of recognition of technical conditions of complex technical systems. The diagnosis is conducted with the help of probabilistic methods of the complex engineering systems condition recognition based on the Bayesian analysis. 

The aforementioned approach and information theory methods are applied to run the multilevel diagnostics of elements and systems of floor slabs in old urban buildings. Multilevel diagnostics was done in the concepts of information entropy. 

During the analysis of the results of forward and reverse traces on the hierarchical diagnostics structure the next conclusion was made. The forward trace allows to determine the technical condition and category for the each element of each level in the hierarchical structure and the reverse trace gives a possibility to evaluate the contribution of each element condition to the information about the whole building condition. The last point can be an argumentative basis for the account of physical depreciation of building structures.