The external walls of the original building were not straight. At the back side of the building the walls bended inwards. Therefore, the insulation had to stick out a little near the windows of the first floor in order to attach them taking into account airtightness on the outside of the wall.
As some of the old brick-walls had to remain visible from the inside, the air tightness of the building envelope has to be assured from the outside. Therefore it was decided to insulate using 2 layers of Foamglas, which allows for an airtight layer.