A complex at the crossroads

The post-pandemic context has reinforced the trend away from business districts such as La Défense, which were designed according to the functionalist zoning vision of modernist urban planning. Younger generations aspire to work in flexible, less vertical organizations, while enjoying the amenities of a rich urbanity, more in tune with the porosity of their lifestyles. As a result, La Défense is working to enrich and diversify its urban fabric, with a mixed-use approach that can be applied to every single building.

In the historic part of the La Défense slab, adjacent to Courbevoie, CB3 is a typical example of a high-rise building in the district, albeit discreet due to its smaller size than the surrounding towers. Classically composed around a large patio, it’s a rather functional building, suffering from the usual symptoms of this type of tertiary complex from the Trente Glorieuse era, now obsolete. In particular, it features a curtain-wall facade that is typical of the period, outdated and not very energy-efficient. Previously cleaned out, the building remained empty, awaiting a project that would take advantage of its advantageous location. Right next to the emblematic CNIT building, CB3 is highly visible from the boulevard circulaire, benefits from unobstructed views over Courbevoie and will soon be served by an Éole station, an extension of the RER E.

The programmatic mix

PCA-STREAM has decided to make CB3 a beacon of the possible future of La Défense by reenchanting it with a number of key principles, notably the introduction of a programmatic mix, a rationalization of distributions, and the addition of numerous services and outdoor spaces, all in keeping with a responsible approach. A large central street has been added to the building’s dense, dimly-lit ground-floor. This interior street reorganizes the existing flow of traffic and creates transparency towards the slab. On either side of the street are shops, restaurants, a coworking space and a bike club, all accessible from both inside and outside, providing a mixed-use environment shared with the neighborhood. A business center on the first floor is also accessible to building users and the general public. On the upper floors, the office space has been rationalized and enhanced with outdoor areas and walkways. The complex is topped by two extensions of differing heights, due to the impossibility of carrying out structural alterations: a light office extension on the parvis side, and a five-storey hotel facing Courbevoie, organized around a shared terrace. The hotel itself boasts a number of exteriors, topped by an exceptional panoramic restaurant overlooking the Arche. The self-sufficient office building thus becomes an iconic heart of the district.

A post-carbon vision

The approach developed by PCA-STREAM to reenchant CB3 is part of a post-carbon vision for La Défense, via an ambitious environmental strategy, which begins with the choice of restructuring (with 86% of floors retained), which is inherently more efficient than new construction. It is complemented by new, energy-efficient facades, as well as by equipment and features encouraging soft mobility and virtuous behavior. The hotel section features a double skin that acts as a thermal buffer and offers accessible loggias. On the office floors, the facades that were removed have been replaced by high-performance facades, enhanced by accessible outdoor spaces that act as passive protection. These corridors, like all the exteriors, are extensively planted, helping to enrich the biodiversity of a mineral district. A reuse approach is complemented by the choice of elevations made of mixed concrete and wood structures from bio-sourced sources. Last but not least, the sharing of functions between the various programs is part of a virtuous circular logic.