The project consists of the renovation of an existing 16-storey high-rise office building dating from the late 1960s, above the Paris Montparnasse station concourse, while retaining its general three-dimensional geometry, with a few exceptions.

The project provides for a significant upward extension of the building with a kitchen garden on the roof, and a restaurant. The additional loading will have to be offset by the surplus service loads of the office storeys. The grid at each end of the building is demolished in order to construct glazed boxes. The loadbearing structure for these boxes will require special study, in respect of both the nature of its attachment to the existing structure and the comparative load distributions.

The facades are demolished in order to construct the new sawtooth facade.

The flat roof of the station podium is intended to be remodelled with a landscaped garden and some buildings.

Double-height areas are envisaged and will require examination of localised reinforcement of loadbearing members and perimeter structure.