The extension project was activated in 2013, with the Ströher family as clients. A feasibility study undertaken by Herzog & de Meuron explored the potential of the site under current conditions. The resulting project constitutes a radical new start. The original idea of an illuminated cube balanced on the silo towers and visible from afar has been jettisoned. Instead, we propose to erect a building whose dimensions and materials accord with the sequence of historic brick structures lining the dockside. The new structure thus completes the existing museum complex in a visually appropriate way and forms a suitable conclusion to the row of buildings along the dock. At first glance, it might seem as though the new building had always been there.

The new structure consists of three parts with a height of approximately 33.5, 30.5 and 27.5 metres respectively. In terms of mass, height and materials they take their cue from the existing buildings, continuing them and rounding them off to form a harmonious whole. Two parts contain the exhibition areas, the third provides access and houses utilities and art handling facilities. With five levels, one below ground, floor space amounts to some 4,900 square metres, in addition to exhibition areas of roughly 2,500 square metres.

Massing was crucially influenced by a ban on building within forty metres of the autobahn. Optimum use is made of the available area. The arrangement of the exhibition structures – the tallest of the three parts and the smaller one adjoining it – echoes the course of the building-free zone, while one elevation of the third part runs along its boundary. The additively composed parts remain distinctly legible. At its tallest point (the uppermost level of the larger exhibition component), the new structure is related in height to the main existing building.

The extension is to be linked directly to the existing exhibition spaces by bridges through the silos at the first and second upper levels, facilitating uninterrupted visitor access throughout the museum. Similarly, the height of the new exhibition areas takes its cue from the existing galleries. The silos will not only be converted into elements connecting the old with the new; they will also house distinctive exhibition spaces. Their original materials are to be retained, however, because the silos are an indispensable ‘sculptural’ component of the Küppersmühle as an industrial monument. Long reduced to this historical and aesthetic aspect, they acquire a new function through refurbishment as access links and display areas. Six inner silos had already been removed. Now, with the ground-floor ceiling opened up and the insertion of the bridges, the entire space will be visible to visitors. In addition, the silos can be seen from some of the exhibition areas.

As in the existing galleries, windows in the elevations facing the dock and Philosophenweg offer varied and striking views of the site and its surroundings. The material of the elevations echoes the brick of the existing buildings.

A staircase permits continuous visitor circulation and the arrangement of all the exhibits in a consecutive sequence. In conception and spatial context, the staircase is related to that featured in the museum project of 1999.

The new exhibition areas echo the overall additive character of the Küppersmühle as a typical industrial facility of the nineteenth and twentieth centuries. In their architecture and interior design, the galleries echo the existing exhibition spaces. The uppermost display area, which is not directly accessible from the existing building, consists of a visible shed construction with top-lighting. All exhibition levels have a spatial arrangement facilitating flexible multiple uses.

The silos are to be fitted out with a superstructure, as they were original, in the 1930s. Featuring a viewing platform accessible from the dockside promenade, the superstructure will grant the silos yet another new function.