For the purpose of supporting urban planning strategies, 3D models of large urban areas are nowadays on high demand. Due to their weather and daylight independency, SAR systems are of high interest for this task. Moreover, the new SAR sensor generation enables acquiring images of wide areas at high resolution that makes the analysis of urban areas possible. Especially, the tandem mission of TerraSAR-X and TanDEM-X offers the opportunity of single-pass interferometry, reducing noise and leading to better data quality. In this paper, we want to show the sustainability of such data for building reconstruction in urban area.