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With the modernisation of the historic Chambre des Notaires in the heart of Paris, a landmark long embedded in the Haussmannian cityscape since the 19^th century has been reinterpreted. To give the historic building more openness, light and spatial depth, a crescent-shaped glass façade was created in the inner courtyard, making the dialogue between past and present visible. Eiffage Métal, one of the most internationally renowned façade contractors, realised this demanding façade construction, while Doering Berlin manufactured the curved insulating glass units. The project was supported by the flexible Super Spacer^® TriSeal™ Premium Plus spacer, which ensures the functional reliability of the edge seal across all storeys and thus makes a key contribution to the durability of the new façade.

 

 

 

"When the dear Lord is bored in heaven, he opens the window and looks at the boulevards of Paris," enthused the German poet Heinrich Heine, who died in 1856 and never lived to see the radical transformation of the medieval inner city. Under Prefect Georges Eugène Haussmann a comprehensive yet controversial modernisation began in 1853: thousands of old buildings were demolished, new ones erected, and broad boulevards, a modern sewer system and extensive green spaces created. To this day, the typically six-storey Haussmannian buildings define the face of Paris, with uniform façades of light ochre limestone, wrought-iron balconies and pitched mansard roofs.

The seat of the Paris Chamber of Notaries at 12 Avenue Victoria, also known as the Hôtel du Châtelet, inaugurated in 1855, is an icon of Haussmannian architecture. As the historic structure no longer met functional and technical requirements, the Chamber launched an architectural competition for the modernisation in 2019. The design was to open the building up, combine contemporary digital working methods with historic building fabric, and enhance the image of a profession often perceived as closed.

"The Hôtel du Châtelet embodies a subtle balance between heritage and modernity, much like the notarial profession itself: rooted in the 21^st century, yet faithful to its tradition and its public service mission," says Pierre Tarrade, President of the Chamber of Notaries.

The winning consortium Atelier Senzu + Lagneau Architectes succeeded in preserving the architectural heritage while creating greater transparency. Fixtures that had blocked light and spatial depth for decades were removed, allowing the ground floor to feel open and accessible again. At the heart of the redesign stands the semicircular glazed courtyard façade, which follows the geometry of the existing structure and extends from the ground floor to the 6th storey. It channels daylight into the interior and symbolises the transition from the historic fabric to the modern working areas at the rear of the building.

 

 

 

Wandrille Marchais, one of the founding partners of the architectural firm Senzu, described the technical realisation of the glass façade in essence as follows: “The glass panes are curved and self-supporting, and that is precisely where the magic of this glazing lies: it makes mullions and heavy structures superfluous and gives the open space and work areas a clear structure and direct access to intense daylight.”

The curved insulating glass units are supported on each floor by transoms made of coated, welded T section steel whose bending radius exactly matches that of the glazing. A curtain wall system based on RAICO THERM+ 56 is mounted on these transoms. The glazing rests on an EPDM profile that also serves to drain condensate and is secured by a pressure plate with an outer cover cap. Silicone setting blocks positioned locally compensate for tolerances resulting from the curved panes, and a final silicone joint completes the sealing. The butt joints between the panes are executed with a type B gasket profile. Integrated screw channels within the supporting structure made it possible to screw the bespoke aluminium cover caps directly into place without the need for welding on the façade.

The 77 insulating glass units, each 35.52 millimetres thick, are designed as cylindrically curved, concave panes with fully finely ground edges. The outer pane consists of laminated glass comprising 6-millimetre float glass and 6-millimetre SG COOL-LITE® SKN 176 II, bonded by a 1.52-millimetre PVB interlayer, a 16-millimetre Super Spacer^® TriSeal™ Premium Plus spacer, and 6-millimetre float glass on the inside. A continuous 12.5-millimetre-high stepped edge is formed around the perimeter. The arc length is 1,305 millimetres, the inner radius 1,000 millimetres and the unit height approximately 1,287 millimetres.

The glazing is fixed at the head and at the base, while the vertical edges are free. The evenly distributed load transfer is provided by three setting blocks per unit. As the façade also must provide protection against falls, it was statically designed in accordance with balustrade requirements. A soft-body impact test with a 50 kg impactor confirmed the resistance of the construction.

 

 

The semicircular geometry of the seven-storey courtyard façade created a strong interdependence of all components. The permissible tolerance deviations of the curved insulating glass units were up to five millimetres for the radius and up to seven millimetres for the height. Even minor deviations in the insulating glass units or in the elevation of the steel transoms would have added up over the full height of the façade. “A deviation of one millimetre per floor would already have resulted in a noticeable offset over seven storeys and could have led to fit issues, uneven clamping forces and varying silicone joint widths,” explains Benjamin Jourdanne, Director of operations deputy at DO Bâtiment / Eiffage Métal.

Structural requirements further increased this sensitivity. The curved glass panes provide fall protection and are supported only at the head and base. As a result, they react sensitively to deformations of the supporting structure, since glass can hardly accommodate structural movements. Thermal length changes of the steel transoms or minimal settlements are transmitted directly into the glass and could lead to local stress peaks.

“A flexible spacer such as Super Spacer helps to reliably accommodate the permitted tolerances in radius and height. Thanks to its ability to adapt to the individual glass geometry, local deviations at the edge are compensated and additional stress peaks avoided. This ensures the functional reliability of the edge seal over the full height of the façade,” says Carsten Kunert, site manager of Doering Berlin GmbH.

Installation also posed stringent demands. Installing the curved panes in a radial geometry required a precisely coordinated sequence across all storeys. Each transom and each pane was a unique element that could only be installed in a defined order and at a defined elevation. Even small deviations in the position or angle of a transom had a direct impact on the fit of the next unit. Errors in sequence, elevation or alignment could have resulted in clashes, varying joint widths or insufficient clamping. The installation therefore required a highly precise, continuously monitored assembly process in which each level determined the dimensional accuracy of the next.

 

 

With a thermal transmittance of 1.0 W/m²K, the glass façade provides efficient thermal insulation in winter. In summer, the solar control coating limits overheating by means of a maximum total solar energy transmittance of 38%, while a light transmission of at least 45% ensures sufficient daylight with minimal glare. The Super Spacer® spacer from Edgetech/Quanex also contributes to the energy performance.

“We use Super Spacer spacers exclusively for the manufacture of our curved glazing for several reasons. One of them is the ability of the foam-based, metal-free system to avoid thermal bridges at the glass edge, as more customers specify glazing with demanding energy performance values,” Kunert explains.

In addition, curved insulating glass units place particularly high demands on the edge seal. Due to their increased bending stiffness, they react more sensitively to climatic pressure fluctuations and temperature-related length changes. The resulting pumping movements act directly on the sealant layer.

The silicone-based structural foam spacer Super Spacer^® TriSeal™ Premium Plus combines low thermal conductivity with high elasticity and reliable shape memory. It compensates shear stresses caused by one-sided heating and climate-related volume changes, relieves the PIB primary seal and distributes forces across the bonding surfaces and the lateral acrylic adhesive layer. Particularly in climatic zones with extreme or strongly fluctuating temperatures, this contributes to the long-term stability and functional reliability of the insulating glass units and reliably reduces gas diffusion and condensation in the cavity.

“In large-format, curved façade glazing, flexible spacer systems are structurally the only way to accommodate movements in a controlled manner,” confirms Mike Moran, Vice President Sales at Edgetech/Quanex. “Super Spacer TriSeal Premium is perfectly designed for manual application, as is standard for curved insulating glass units, since the polyisobutylene primary seal is already factory-applied.”

 

Edgetech Europe GmbH, located in Heinsberg, Germany, is a fully owned subsidiary of Quanex Building Products Corporation, (NYSE: NX) a global, publicly traded manufacturing company primarily serving OEMs in the fenestration, cabinetry, solar, refrigeration and outdoor products markets. Edgetech Europe GmbH services markets in continental Europe with a total of 490 employees and 17 extruders. We are “A Part of Something Bigger” by improving the performance and aesthetics of end products through continuous innovation, helping customers achieve greater production efficiencies, and giving back to communities where we operate. Visit quanex.com for more information.

Quanex is a global manufacturer with core competences and a wide range of applications in various end markets. The company works with leading OEMs to provide innovative solutions in the areas of windows, doors, plastic fencing, solar panels, refrigerators and cabinets. In the future, Quanex plans to leverage its material science and process engineering expertise to expand into adjacent markets.