The project for the new State Administrative Centre in Lyon is part of the Part-Dieu urban district in Lyon, France. La Part-Dieu is France's second-largest business district, after La Défense. It is a particularly densely populated area, with 60,000 jobs, 2,500 businesses, shops, offices and a railway station. Today, this part of Lyon is the subject of a vast renovation plan that includes the redevelopment of public spaces and the creation of new public buildings, housing and offices. The existing buildings, which are old and obsolete, will be demolished to free up space for urban developments such as the new Centre Administratif d'Etat (CAE).

A singular situation - This urban district was created in the 1970s and has had a strong identity and constant development ever since. It is marked by the presence of several iconic buildings, with simple shapes and an architectural style characteristic of the period, forming a significant part of Lyon's urban and architectural heritage. Already highly urbanized, land is scarce. The Cité Administrative d'État was built on the last vacant lot in the district. It's a small hollow space with eight century-old plane trees, a vestige of Lyon's history in the last century and of the former barracks that used to occupy the site. The project, with its simple, uncluttered massing representative of the architecture of Part-Dieu, is built around a landscaped pocket formed by the two rows of plane trees that have been preserved. This core will weave landscape connections at ground level that are currently non-existent. The building will be laid out in a U shape around this green core, fragmenting the 19,000m² of office space into several volumes. This fragmentation into several volumes will reduce the visual impact of the building, increase the number of facades to benefit from as much natural light as possible and encourage the creation of outdoor spaces (terraces, gardens) to provide breathing space in a very mineral environment.

Volumetric and layered organization of spaces - An active, living plinth is built on the available land to enliven the public space on either side of the plot. In direct contact with the landscape of the green heart, this plinth, which houses the building's public and communal functions, opens out generously to the north onto the future urban park, which could eventually become the main entrance to the staff. To the south, a new dynamic is offered to the district with the development of a lively and animated façade. The building is made up of three wings, two wings extending over six levels around the plant heart and linked together on five levels by the footbridge, and a third wing extending over five levels. The project is based on a rigorous programmatic compartmentalization, enabling the public reception areas to be grouped on the ground floor and the functions accessible only to CAE staff and invited guests to be installed on the upper floors.

Two wings of office space - Two 5-story office wings are built on top of this active base, on either side of the green heart. This layout means that most workspaces have a view of the garden and trees and are protected from overlooking views. The planted core acts as a filter, making these workspaces more intimate and separating them from the public areas. It also has undeniable climatic and energy benefits, as the plane trees cast shade on the south-facing façades in summer, while providing generous amounts of sunlight and light in winter. The density of vegetation also helps to limit the heat island effect.

The footbridge - These two entities are linked along the blind facade of the shopping centre by a volume of internal walkways that close off the all-encompassing shape of the building around the central garden. This walkway offers high-quality, intimate social spaces extended by outdoor balconies. It is also of interest in terms of flexibility of layout, circulation, operation and programmatic division over time for the project. Its position set back from the Part-Dieu shopping centre also makes it possible to create a large terrace on the south side of the active base.

A third wing of office space - To complete the urban integration of the project, a third wing has been created to the south. This four-story office wing, deliberately built lower to limit the height of the future residential tower to the west, is the same width as the other two wings, ensuring the functionality and flexibility of all the office floors, whose layout is thus systematized across all the CAE buildings.

A constrained site - Appropriate technical solutions - The small size of the plot, with its century-old trees, and the many other worksites in the immediate vicinity, meant that on-site storage facilities were limited during the works. Similarly, the lack of space and the traffic problems in the vicinity of the site meant that a major logistical effort was required, which was a major challenge on this project, more so than on others. The location and size of the plot also justified an essential construction choice in the project: the use of numerous prefabricated elements.

A kinetic façade - The façade concept is directly inspired by the architecture of Part-Dieu and its repetitive system of façades, articulating the same module throughout the volume, using the same palette of materials. The use of a modular façade system for this project offers several advantages (repetition, screening, prefabrication, assembly, economy of means), while at the same time reinterpreting the vocabulary of the iconic buildings of the district's architecture. The architecture of the Part-Dieu district is also marked by its color palette, which is made up of neutral tones ranging from grey to more saturated or darker sandy tones. This discreet color expression, adapted to the context, also guided our thinking in terms of reinterpreting and integrating the building into its urban environment. The geometric modules are hen divided into different categories according to criteria specific to the facades: exposure to the sun - limiting exposed glazed surfaces that could lead to overheating in summer, natural light requirements - enlarging glazed surfaces to ensure sufficient natural light in areas that need it, and safety constraints - passage width required for emergency services. There are two types of façades based on this principle of modularity.

Façades on the outer periphery of the project - These façades, which are more exposed to the elements, are made up of four different modules. These modules are based on the same external grid, within which a colored oblique upright varies in angle from one module to the next. The width of the glazing can be adjusted according to requirements for solar exposure, light gain and passage width. The arrangement of four identical modules across all the façade grids means that the construction system remains flexible and fast. The ingenious design of these façades means that entire modular façade blocks can be prefabricated in the workshop, contributing fully to the environmental performance of our project.

Facades around the green heart - The same principle of modularity is applied to the façades overlooking the vegetation. The north and south façades, which are less exposed thanks to the presence of the vegetation, are made up of modules whose vertical and horizontal decorative elements are gradually reduced to become smooth as the façades extend westwards. The façade of the gateway building, located at the bottom of the planted area, has no raised modeling.

An urban green oasis - The concept of the planted core around the plane trees is complemented by the creation of outdoor areas on terraces and roofs, planted and accessible to all. Like hanging gardens, these areas form part of the extension to the square and make up a planted area with a total surface area of 1,300m2, in addition to the 1,800m² of the green heart. Together, these areas contribute to the development of biodiversity and the creation of a cool island in a dense urban area. To the south, a vast terrace has been installed on the roof of the active base. Facing south, this 600m2 outdoor space is accessible to all users of the CAE (ground floor +1). The Passerelle roof is also equipped with a long 350m² accessible terrace linking the two wings on the ground floor, +5 story from the outside. The Passerelle's loggias will also add an element of greenery to the Passerelle building's facades. Lastly, on the rue du Docteur Bouchut side, the top floor will feature an accessible south-facing terrace of 180m² that is both discreet and striking. Set within the overall massing of the building, this terrace will be an outdoor area accessible to users of the building. Finally, the public reception, training, meeting, catering and work areas are grouped around the green heart, offering all civil servants and residents a veritable urban oasis where nature and natural light are omnipresent.