The historic town hall of Aachen

From the end of the 8th century up to the present the town hall of Aachen in unity with the bordering Granus tower in the north and Aachen cathedral at the opposing south side of Katsch court have been witnesses of the former palatine complex of Carl the Great in Aachen. In addition to the archaeological verified remains of the Carolingian arrangement these buildings, despite numerous deformations and deconstruction, preserve evidence of the imperial palatine complex as well as Carolingian and medieval original substances in their foundations and ascending stonework. Whereas science and research where able to gather a lot of information from the Marien Church, the present cathedral, concerning building history, there was neither a comprehensive documentation nor a systematic building research regarding the King´s hall, on which the gothic town hall was built during the 14th century. This led to the start of a first intensive building documentation and -research in spring 2007 in the Granus tower, the former “turris regalis” (=” tower of the king”) of the Carolingian palatine complex. Within the scope of the course "Bauforschung als Grundlage denkmalpflegerischer Maßnahmen" (= “ Building Research as Groundwork of building conservational methods”) given by the research assistants Judith Ley and Marc Wietheger there have been multiple documentation campaigns in field surveys containing the buildings systematic measurement, drawing, photograph and scientific description in cooperation with students of architecture, each course lasting a period of a week. Beyond the practical teaching of several methods and techniques of examination in handling historical building substances within the student course at the Department of Historic Building Conservation and Research, the works results being exact architectonical as-built drawings and the analysis of the structural health should be capable to be used in terms of securing as well as restoring the estate. The project was supported by Aachen’s Office for Preservation of Historic Monuments from the beginning. Nevertheless, it is the work´s primary aim to evaluate the estate on-site in combinational use of analyses of historic sources to reassemble the variant construction periods into the buildings initially state and to facilitate the ability of defining the building´s original use. Using tachymetric-CAD- supported online-measurement, photogrammetrically documented stone faced surfaces, 3D-Laserscanning and manual measurement of detail areas, deformation accurate as-built drawings were created. Within a uniform measuring system (3D-Polygonal course) it was possible to generate detailed floor plans of each main and sub floor as well as six vertical section plans. This way it was possible to map the construction joints, used materials, damage patterns and special works on building material in detail enabling a succeeding analysis of the inner complex spatial structure. Especially the examination of the tower´s number of storeys, orientation, accessibility and exposure of the rooms and stairways as well as the connection to the kings’ hall and so to the whole composition of the palatine is of major interest. In short-term the advanced work on the Granus tower is going to be expanded to the historic town hall: the external viewed additive layout of building components turns out to be an integral planned complex spatial concept in the inside depending on their multitude of architectural intersections. The analysis of this internal structure is expected to lead to a deeper understanding of the original architectural plan. The interim results and targets of the present building research are being discussed in different panels by expert colleagues and people involved in the project and furthermore influence the work of the newly founded working group for palatine research in Aachen.