Stephan's problem of a freezing front propagation inside a multilayer objects is discussed. For to solve this problem in practice numerical methods are used to integrate moisture and heat transfer equations while calculation of the current frost pane's coordinate inside external multilayer building envelopes whose surfaces' temperatures are measured over a while. When the Stephan's equation integration takes place, the phase transformation is taken into account by means of a sharp jump of the material's specific heat capacity at the point of the phase transformation. Examples of such calculation of the frost pane coordinate dependency of time inside multilayer constructions are presented. An algorithm of the current dew point coordinate determination inside multilayer objects is suggested.