Located in Paris La Défense, Trinity is a 32-story tower, built ex nihilo on a concrete slab poured above a seven-lane roadway, a first in France. A major feat of civil engineering, the slab is planted, providing 3,500 square meters of landscaped public space and linking the previously disconnected neighborhoods of the CNIT (National Center of Industries and Techniques) and Coupole-Regnault: a concrete solution for enhancing the quality of life of its users on an urban scale. Trinity is La Défense’s first tower to develop an offset core, yielding a “heart of life” with exterior glass-walled elevators running along the façade. Diverging from the traditional office building format, Trinity is a tower conceived to facilitate open interaction with its environment, and promotes a new way of working, through its shared spaces, its 43 planted terraces and balconies, its rooftop and its 4,000 m² devoted to services.
A CONTEXTUAL PROJECT
In an environment as dense and constrained as that of La Défense district, which houses 16 of France’s 20 tallest buildings but where very little area is still available for new construction, the first challenge was to invent the landholding on which the tower would be built. The solution was a feat of civil engineering: a concrete slab poured over seven traffic lanes, providing an ex nihilo land for the construction of a high-rise building. Then, the project had to be integrated into the existing heterogenous surroundings, counting a number of architectural icons (the CNIT and the Tour Areva), and smaller buildings such as Notre-Dame de la Pentecôte Church and residential buildings. Furthermore, continuous exchanges with the neighborhood through public consultation meetings throughout development process enabled the project to mature and better meet the expectations of its inhabitants.
Following a previous collaboration on renovating the CNIT in La Défense, the project owner Unibail Rodamco Westfield commissioned Cro&Co Architecture to consider this unusual project over the roadway. A relationship based on trust and exchange enabled the creation of an exceptional project, combining the client’s ability to carry ambitious projects with the architects’ creativity. The duo quickly enrolled the expertise of an engineer to fully exploit this extremely complex site. The local development agency Paris La Défense and the State then joined the project, motivated by the shared desire to make a major contribution to the neighborhood.
Trinity was designed as a comprehensive and 9 contextual urban project. In order to successfully integrate into an atypical site, it combines three major axes in a single construction program: the erection of a building, the creation of major urban links, and a large-scale intervention to enclose highways.
MAJOR URBAN LINKS
The concrete slab built over the highway provides real solutions for creating urban connections and enhancing the quality of life of its users. It links the previously disconnected neighborhoods of the CNIT and Coupole-Regnault, through broad stairways and public, panoramic elevators, connecting the various levels with the ground and facilitating access to the largest transit hub of La Défense. It contributes to transform the former mono-functional business center of La Défense into a meshed city district. This fertile slab, offering 3,500 m² of landscaped public space, has metamorphosed the former congested, noisy roadside landscape, into a pleasant environment, a fresh haven propitious to strolling, enjoyed as much by the tower’s users as the inhabitants of the neighborhood. The project also provides new premises for community services managed by the town, and restaurants open to the general public.
The first gesture of sustainability for Trinity is hidden below its site. As it is built above a roadway, it enables the reuse of the existing sealed soil, and can therefore be defined as a restructuring. In addition, the construction of a tower, on this site in particular, contributes to furthering urban densification rather than urban sprawl.
AN OPEN, OFF-CENTER CORE
Trinity is a living tower, and clearly expresses its ambition to support real interaction with its surroundings. Its off-center core brings a new architecture to La Défense. Usually enclosed fully within, and presenting an obstacle in the middle of the floor plate, here the core is opened up and becomes the main expressive element of the project. Animated by the occupants, activity is revealed in the façade: the movement of the panoramic elevators, the terraces, the suspended meeting rooms, the kinetic façades. The off-center core enables natural light to bathe the elevator landings, thanks to the panoramic, glassenclosed shaft. This openness provides comfort of use, ease of orientation within the building, and a very human architectural experience. The large glazed openings also offer exceptional views of La Défense’s landscape.
SOCIABILITY AND SERENDIPITY: ARCHITECTURE FOSTERING ENCOUNTERS
Imagined as a place of exchange, Trinity breaks with the conventions of the office tower and its standardized and monofunctional spaces by privileging serendipity, flexibility and pooling. It enables users to take full advantage of the tower’s spaces thanks to their reversibility and wide range of uses. Inside the tower there are 45,000 m² of flexible work areas, 4,000 m² of services including reception, waiting areas, cafés and bars, and 1,500 m² of terraces and loggias accommodating nearly 4,500 employees. Particular attention was paid to the design of the furniture, created by the architect and manufactured by a French boat-hull builder. Three custom-made, 43-meter-long curved and sculpted aluminum furniture pieces structure the hall, providing sitting areas, reception desks, a bar desk, and more.
The planted terraces and the areas of conviviality are located close to the elevators, ensuring they become improvised meeting points that can serve several floors. These reimagined horizontal common circulations are part of a series of other informal spaces. Altogether, the tower numbers 8 terraces with trees planted, 12 planted loggias and 23 balconies, for approximately 1,500 m² of exterior space. At the top of the tower, six floors are joined to form three duplexes whose levels are linked by open communicating stairs, the le 25th floor being equipped with a Business Center benefiting from a panoramic terrace. A deliberate choice was made to locate these shared spaces on the tower’s upper levels to offer a view to all users. In addition, a broad range of services are available (concierge, wellness center, varied dining possibilities, bicycle storage local).
By incorporating high environmental standards, Trinity Tower has received both Haute Qualité Environnementale (HQE) Exceptionnel and BREEAM Excellent certifications. It is the first office tower in France to obtain a faultless HQE certification with a total of 14 targets reaching the High Performing level (Très Performant).
ENERGY SAVINGS AND CARBON REDUCTION
Beyond certification, sustainability in the meaning of common sense was always part of the design development. Cutting-edge technologies are used, including decentralized air handling units (AHUs) on each floor, heat recovery systems, retention tanks, generalized leak detection, CO2 detection, dimmable lights, light sensors, presence detection, and a fully automated building management system (BMS). The bioclimatic facades include operable windows in each second bay. On each floor, necessary resources are measured in order to modulate energy consumption thanks to presence, temperature, luminosity and CO2 sensors. As it is built above a vehicular road, Trinity enables a double use of the site, one of many ways in which high-rise density is a factor of sustainability.
A local French stone was used to cover the ground of the public areas. 50 non-allergenic trees (a range of species encouraging biodiversity planted in a permeable soil collecting rainwater) contribute to wind reduction for pedestrian comfort. The trees on the ground are echoed vertically up the tower, with about 20 planted terraces. By means of soil beneath timber decking, these areas are home to around 40 different plant species, whose varieties were inspired by mountain vegetation.
Many specific technical solutions were developed in 27 response to the site constraints. The framing design enabled the team to keep the road in service at all times. The roadway-covering structure was made of concrete sidewalls founded on piles (850 micropiles of 250-milimeter diameter) to adhere to a very limited foundation area. The composite floor system of the high-rise was designed in order to minimize the total weight to be supported by foundations with limited bearing capacity: the tower core and columns were made of reinforced concrete while the peripheral slabs around the core were made by castellated steel girders, in order to let ducts and cables pass through, and to provide the maximum free height in office areas. Atop these were placed concrete-filled corrugated steel floors.
The common design of the infrastructure and the building superstructure, usually built separately, was an asset to the overall project, as it enabled significant optimization: a 50 percent reduction of the concrete used for the tunnel construction and 7 percent for the high-rise. These savings equated to a reduction in CO2 emissions (100 kilograms of C02 equivalent per square meter) and a gain of three floors of office area for the owner.
Both the façades and the volume of Trinity were 29 determined by its context. The tower presents two specific typologies of façade, each adapted to its orientation and corresponding to the dual challenge of being both bioclimatic and architectural. The north and east façades, comprised of a simple skin, form an angle that is also marked by a succession of terraces, and by a large urban window at mid height highlighting the location of the sky lobby. The south façade consists of a double skin to reduce solar gain, which are most important here. Thanks to a “bright” layer, a continuous reflection across the entire upper section highlights the tower’s slender aspect of by visually erasing the floor of each story. The west façade is undoubtedly Tour Trinity’s most characteristic one. Its sheets of glass, silk-screen printed on a gradient and lightly creating the effect of a net fabric, unify the volumes on either side of the vertical open core, and from the plaza, blur the horizontal reading of the floors. Thanks to their incline, these glass sheets also play an environmental role by acting as a mask to protect from the sun.
Architecturally speaking, these narrow glass sheets on the façade enhance the interaction between the building and its environment because they also make it kinetic, a feature perceptible from the viewpoint of pedestrians as they cross the plaza. The notion of interaction is also visible in the openable windows, present on each block of the façade. This vertical pantographic element, which allows the “air and the hum” of the city to penetrate, places users in direct contact with the exterior. With its great height of more than 8 meters, its triple orientation, and the treatment of the facade in «ultra clear» glass, the lobby welcomes users into an urban oasis bathed in natural light.