The history of restorations and renovations on the octagonal apse or Shrine Chapel of the Nidaros Cathedral in Trondheim began already soon after the construction of its lower inner wall and main arches, directly after a first major fire in 1328, and it has continued even if irregularly in all its areas, especially in two major constructive phases during the early 16th, with the archbishop Valkendorff, and the late 19th centuries, with the origin of the Restoration Office and Workshops Nidarosdomens Restaureringsarbeider on 1869. A multidisciplinar and heterogeneous approach of the research of archival documentation, historical photographs and notes on the architect journals has been graphically located through photogrammetry and 3D-Scanning elevations, confirmed by mortar sample analysis and an exhaustive mapping on site of all the surfaces of the octagon, in a Building Archaeological analysis. The example of this methodological procedure is to be shown in general terms for the whole building, whilst concretizing with a deeper level of details in the case of the north-western bay of this apse, an area which contain and can illustrate all these diverse restoration and renovation phases and its characteristics. Further analysis in other areas and the combination and merging feasibility among historical-artistic, archaeological-architectonic and geometrical-modelling data are also included in this article, yet in a second term.