The Polish cadastral model was finally defined (after modifications) in 2015, within the regulation of Ministry of Administration and Digitization. According to this legal act, cadastral model comprises information on land, buildings and premises (apartments) being independent estates. These data generally concern two dimensions, whereas chosen information on third dimension for buildings and premises are included within its attributes. The concept described in the paper bases on introduction of classes defining new 3D objects into the model of Polish cadastre. Firstly, they are EGB_GeneralObject3D, EGB_CadastralParcel3D, EGB_BuildingLegalSpace3D and later EGB_RegisterUnit3D, EGB_BuildingBlockUnderground3D and EGB_BuildingBlockAboveground3D. It results in creation of five new diagrams within Polish cadastral model. As new objects (with suffix 3D added to the name) are connected with relationships with already existing ones, they become part of the whole cadastral model. The research described in the paper shows how 3D objects may be introduced into already existing model of Polish cadastre, in order to create 3D cadastral model. This method may be also used for building 3D cadastre in Poland applying solutions proposed by other authors.