The detection of changes in SAR images is important for many tasks. However, because of the long revisit times of SAR satellites, usually only amplitude change detection is performed. This situation has changed significantly with the advent of TanDEM-X, because with this formation single-pass interferograms from space can be achieved. In this paper we present an approach for urban change detection in time series of TanDEM-X interferograms, aiming at the detection of changes of large buildings. The approach has been developed on synthetic interferograms simulated with the parameters of the TanDEM-X data.