||The up to date state and the consistency of shared building model data are of utmost importance for the achievement of efficient model-based collaborative work. However, in engineering design these are not easy tasks. Design activities are typically carried out in long transactions that are characterized by the following three subtasks: check-out of the needed design data into a private workspace, making design changes within the private workspace, and check-in of a new model state into the shared model repository to make changes and decisions visible to the other designers. As a result of various existing semantic interoperability problems, in the new model state both actual design changes and data loss have to be considered that cannot be easily distinguished. To help tackle these problems we suggest a delta-based versioning approach whose essence is in storing design changes instead of complete design states. This approach is then used as basis to support the three data processing stages of a design step within a collaborative work environment, namely (1) creation of the needed and manageable model subset by removing all irrelevant design data, (2) storing the design changes, and (3) restoring the removed data by an ""undo"" operation of the first step. In the paper we present the used semantics for describing design changes, their transformation to deltas and the scope and limits of the suggested undo operation. At the end we provide an example of the use of the suggested approach with the industry standard IFC model and discuss its potential and needed further research.""