New headquarters of the regional bank Caisse d’Epargne by GRAAM

Project description by GRAAM

The design brief
As a regional bank, Caisse d’Epargne, a member of the BPCE group, should be part of the French territorial reform adopted by President Hollande in 2015.

It had two regional headquarters: one in Besançon and one in Dijon, the latter being located in two adjacent but not adjoining buildings.

It is in this context, as part of its business project aimed at accelerating its transformation, the Caisse d’Epargne BFC wanted a new head office in Dijon which aims to be exemplary.

Owner of forests in the Morvan, a low mountain massif a few kilometers from Dijon, the Caisse d’Epargne wanted to be a new head office demonstrating local resources but not ostentatious for its members, testifying to its environmental commitment.

Concepts
The main idea was for a wooden demonstrator building inscribed on a sloping ground. Like an open book on the great landscape, the book of the history of wood construction in France. This square facing the large landscape that wants to show and explain in an educational way what wood construction is. The building is then part of a structuralist reflection: show the structure, show the formal dissociation between structural elements, according to their role and their structural behavior: “dynamic” for the bracing exoskeleton, but “static” for the postbeam of the facades with timber frame filling.

Highlight
The client was first convinced by the use of local forest wood as part of their investment, this point particularly responded to their local economic roots. They were also hit by the form : a two level base, stable and anchored to its land, and a 4 level upper part. Fun fact, this form was for them the expression of a bank “seat” which is the French translation of a headquarters.


Caisse d’Epargne by GRAAM. Photograph by Sergio Grazzia.

Location and position of the building
Located in ZAC Valmy, a new business district in the northern outskirts of Dijon, the headquarters of the Caisse d’épargne of Bourgogne Franche-Comté is served by a circular boulevard (RN 274) and line 2 of tramway, “Pôle Santé” station. The plot’s eastern and western slopes (8300 m²) welcome parking for visitors. Employees park their vehicles in the concrete base as well as in the parking silo built in wooden structure, at the site’s north. Not only does the natural slope of the ground allow a single storey access to the base’s parking, but it also installs a slightly overhanging ground floor level, so that users benefit from a clear view on the environment.

Outline details of local vernacular building
The design of this building, draped in its exo wooden structure, echoes the half-timbered houses of the historic center of Dijon. The half-timbering is the set of beams forming the framework of a wall, this wooden frame is made up of wooden sections whose beams delimit the filling compartments. In the history of French construction, half-timbered houses have been present for many centuries. This constructive method of small wooden elements highlights the use of local resources, available in reasonable quantities.

It was with the First World War, the loss of many carpenters and their know-how in the trenches as well as the arrival of reinforced concrete that stopped the evolution of this construction method.

This large-scale building wishes to highlight the pursuit of French know-how of traditional carpentry and the reasoned use of materials.


Caisse d’Epargne by GRAAM. Photograph by Sergio Grazzia.

Ground floor : a crossing North-South axis
The main entrance is located on Françoise Giroud avenue, facing the tramway, where the architects designed a large covered parvis (ground made with Bourgogne stones), lengthened by a succession of interior and exterior crossing spaces: patio, lobby, atrium, secondary entrance hall, from which one joins the parking silo. Fully glazed, this spatial structure of the ground floor’s central part generates two wings with distinct functions. The first one, at the east, shelters the sports hall and rooms for logistics (mail treatment for instance). The second one, at the west, presents a public vocation, with training and reception rooms.

Level 1 to 6 : first day lightening at every workstation
Every office (mainly 300 m² platters) and meeting rooms (placed between the atrium and the patio) benefit from a natural direct lightening. Refuting tertiary real estate standards, its doubling of corridors and its built thickness between 18 and 21 meters, GRAAM devoted themselves to diversify user’s experience of the Caisse d’épargne, and their relation to exterior.

Complementary Levels
The last four levels’ thickness, comparable to the one of housing buildings, is only 13.5 meters. This modest dimension in terms of rentability is compensated by the important superficy of the first two levels (40.50 x 62 m), whose center is lightened by the atrium as well as by the patio. Goal: create an interiorized environment, complementary to the extrovert universes of peripheral spaces and superior levels, which offer aerial panoramas on Dijon and its countrysides.

The subtle combination of wood, concrete, steel and glass
The building is set on a slope, facing a landscape where, in good weather, the peak of Mont Blanc rises in the distance. Its glazed skin, placed lightly on the timber exostructure, allows the wooden mesh to appear or to reflect the great landscape, making the building disappear, depending on the weather. The formal dissociation of the structural elements, according to their role and behavior allowed the realization of a bioclimatic ventilated double skin. Made of simple extra-clear glass, the external wall of the latter is suspended from the upper beams of the wooden exoskeleton. The combination of concrete, timber, steel and glass makes this building unique.


Caisse d’Epargne by GRAAM. Photograph by Sergio Grazzia.

A building with the least possible impact
The forceful idea of GRAAM: investing on the territory and projecting into the future! In other words: realizing a demonstrative building on wooden structure, by local firms, recalling that the Bourgogne Franche-Comté region has wide forests, which has the least possible impact on its environment.

The building is built 100% dry process (and offsite) and has 2579 m³ of wood, that is 2579 T of stored CO2. Built to a high thermal standard (passive building), it consumes only 15 kW/h per m² annually. The implementation of the smart building certification (R2S) allows an open and communicating building.

Constructive systems in a few words
The head office of the Caisse d’épargne Bourgogne-Franche- Comté consists of a concrete infrastructure (basement, ground floor) and six wooden floors:

• Structural cores made of glulam solid wood panels
• Main Structure made of glulam column-and-beam system
• Solid wood panel structural boards and non-structural precast concrete floors
• Wood Frame Wall Facade Fillings
• Glulam bracing exostructure
• Double bioclimatic glass and galvanized steel skin, attached to the exostructure

Caisse d’Epargne by GRAAM. Photograph by Sergio Grazzia.

Material optimization
Faithful to their requirement in matters of material optimization (the right material in the right place), GRAAM has drawn a supporting structure made of glulam posts (a row on the facade, and a double row in the central circulation), on which stand LVL longitudinal beams in and glulam transversal beams. Cross Laminated Timber is only used in two cases, when they are strictly necessary for bracing : core walls and center circulation floors , in which transit wind loads are transmitted by the triangled exoskeleton.

A green energy building
Wood, a living material, allows a natural regulation of the ambient hygrometry. The materials used in the office spaces, all classified A+ in terms of VOC emissions, combined with a ventilation system that allows for air renewal above the norm, ensures high indoor air quality. Cooling is achieved by an adiabatic system of cooling the water network passing through the technical ceilings. The building is connected to district heating: a city network heated by biomass, 100% renewable energy.

Heating and cooling is made by radiation from the ceiling.

Safety and security of occupants
The building is divided into 300 m² platforms intersected by fireproof walls for 1 hour. The three vertical circulations are also partitioned, fireproof for 1 hour and their interior lining is incombustible.

Dry risers located in the staircase may be used, provided that they open less than 40 m from a fire hydrant.

On the largest facade (North West facade) each level is accessible by a firefighter access materialized on the facade by a red dot.

The bioclimatic double skin is cut against fire every two levels, and the large ventilation grids allow the smoke, if necessary, to evacuate quickly.