The Circle at Zurich Airport is clad with inclined and curved closed cavity façades
17 Nov 2020
Ph.: © René Dürr, Architekturfotografie

For the first time, the drive system for sun protection louvres is integrated in the façade unit.


Gundelfingen, November 2020 - On 5 November 2020, after a construction period of over five years, The Circle was opened at Zurich Airport by the co-owners, Flughafen Zürich AG and Swiss Life, and presented to the media.


The Circle is a service centre of superlatives, with numerous new stores, restaurants & bars inviting visitors to shop and linger. The new University Hospital Airport offers a wide range of medical services. Congresses for up to 2,500 guests can be held in the new Convention Center, and two Hyatt hotels offer overnight accommodation. Other services such as coworking spaces, a fitness centre or a day care centre will round off the wide range of facilities from 2021.


The Circle at Zurich Airport is clad with inclined & curved closed cavity façades
The closed cavity façades of The Circle at Zurich Airport are both curved and inclined, harmoniously following the ring shape of the motorway and cantilevering up to 15 metres off the vertical drop line. The drives for the sun protection louvres, which were integrated in the closed double-skin façade units, are another unique feature of this architecturally striking complex. The energy-efficient and highly sound-insulating closed cavity façade, with more than 1,600 different façade units measuring up to 2.7 x 5.6 metres, covers a total area of 83,000 square metres. It has been manufactured by Josef Gartner GmbH in Gundelfingen, Bavaria, using narrow profiles and providing a flush view without corners and edges.

The mixed-use complex The Circle at Zurich Airport, which offers 180,000 square metres of usable floor space, is divided into individual buildings, 9 to 11 storeys high. Large-format buildings adjacent to the Butzenbühlring motorway merge into smaller buildings with partly covered lanes and squares towards the hill side. This structure also partitions the closed cavity façades (CCF) with their different unit sizes and design variants. The ring façade at the motorway covers 23,000 sqm, the hill façade 52,200 sqm, the courtyard façade 7,900 sqm and the pedestrian bridges 800 sqm. Parts of these façades meet high fire protection requirements according to E30 and EI30. CCF façades were tested for the first time in this context. Other parts of the façades serve as exhaust ducts, which are used by the fire brigade to open and keep the façade smoke-free. For this purpose, two chain motor-driven rotary wings were integrated into the façade units.


Closed cavity façades with a Ucw value of up to 0.77 and sound insulation of up to 47 dB
In order to meet the ambitious sustainability goals, the building owners had opted for a CCF, as this closed double-skin façade improves thermal insulation in summer and winter as well as sound insulation and allows for more daylight inside the building. The Circle ring façade achieves a U-value of 0.82 W/sqm K, the hill façade 0.77 - 1.08 W/sqm K and the courtyard façade 0.90 W/sqm K. The g-values for the ring façade without sun shading are 20 %, values for the hill and courtyard façades with closed sun shading are 8 % and with open sun shading 41 %. The highly transparent glasses, whose light transmission does not need to be restricted, except for the ring façade, by sun control coatings for thermal protection, achieve a light transmission of 63 % for the hill and courtyard façades with open sun shading.

A further criterion for the clients to opt for a CCF system was the high level of noise insulation in order to reduce traffic noise at the airport. The ring façade achieves 47 dB and the hill façade dB is between 41 and 44. As the façade cavity is protected from dirt, unlike with ventilated double-skin facades, there is no need for cleaning. This reduces maintenance and operating costs and increases the service life of the integrated sun shading devices.

The Circle façade was also the first CCF that was produced on a new assembly line with special washing system at Gartner’s main plant in Gundelfingen by the Danube (Germany). This system is very close to clean room production standards and prevents dust particles and other impurities to enter into the space between the inner and outer façade, which could impair the function. 


Inclined ring façades with cold-bent impact panes
Sizes of the standard units of the ring façade at the motorway are 2.7 x 3.7 m with a weight of 1,160 kg, with the largest unit measuring 2.7 x 5.5 m. The attic of this façade cantilevers up to 15 m above the base point and, with the cold-formed impact panes, forms a homogeneously curved outer skin along the ring road. This required 1,578 different unit size configurations with different angles of inclination between 10.5 and 18.4 degrees to the outside and cold deformation of the impact pane at one corner by up to 50 mm. For such a variety of intricate variants with loxogonal (oblique) glass panes, Gartner specialists engaged in an extensive 3D design process.

For cold bending, the impact panes were forced at one corner into the curved aluminium frame. This was done at the construction site itself. Lined up in a row, the CCF units thus follow the ring shape of the motorway, without corners nor edges. At the occasion of a visual mock-up meeting to discuss hot and cold bent glass, the building owners had decided against hot bending for visual reasons.

Both the inclination and the curvature of the CCF made it difficult to install sun protection systems inside the units of the ring façade. For this reason, the highly transparent impact panes, made of laminated safety glass, were coated with double sun protection and, unlike the other façades, have a darker appearance from the outside. The inner façade skin consists of highly transparent triple insulation glazing.


Hill and courtyard façades with integrated drive system for sun protection louvres and passerelles
The standard units (950 kg each) of the hill façade measure 2.7 x 3.6 m, the largest unit is 2.7 x 5.6 m. The courtyard façades consist of standard units with 510 kg and standard sizes of 1.35 x 3.6 m, with a maximum size of 2.7 x 5.6 m. For the passageways (“passerelles”), the standard units are 950 kg, with a standard size of 2.7 x 3.6 m and a maximum size of 2.7 x 4.1 m. The reinforced concrete structures of the three connecting bridges between buildings are fully clad with CCF, with a length of 18, 16 and 15 m, resp. These façades are glazed with highly transparent impact panes, made of laminated safety glass, and highly transparent triple insulating glazing. Their decorative exterior sheets featuring natural colour have a special radiant effect due to high-gloss.

For the hill and courtyard façades, the drive system for the 60 mm wide, white-coloured sun protection louvres was also integrated in the closed façade cavity for the first time. Therefore, the drive system is no longer visible and the ensuing noises can no longer be heard.

The terraced landscape has been particularly challenging in the area of the hill façade, with 44 differently-sized metal terraces. These open spaces are up to 392 sqm in size, featuring different geometric ground plans. The large number of sealing points required precise design solutions for the profiles, which were installed at different angles and heights, to ensure that the terraces in the areas of offices, clinic and hotel will be watertight.


Brands façades, smoke-pressure system doors and warm roofs
In addition to the approx. 83,000 sqm of CCF, Gartner also produced 6,900 sqm of branded façades for the shops in the hill area. This single-skin façade visually resembles the hill façade and was designed by the tenants themselves. 

The so-called Brands façades were executed with a newly developed 2,400 sqm of textile fabric with fire protection classification RF 1 (A1/A2). On the construction site, it was then stretched onto the metal frames measuring up to 2.7 x 5.5 m.

In addition, Gartner manufactured 200 external doors for smoke-pressure systems (RDA) with swing door drives, door control systems and exhaust ducts to keep staircases and other areas smoke-free. Special control modules had to be developed for these doors. Two warm roofs (243 sqm and 153 sqm) provide additional usable spaces on two floors in building no. 14.  


Start of production in November 2017, completion of façade installation in November 2019
In November 2017, the first Circle façade units had been produced in Gundelfingen. Before the start of installation, around 5,600 CCF units had to be temporarily stored in four covered outdoor storage facilities with an area of around 1.5 football pitches. The last façade units were manufactured in September 2019. Installation took place from August 2018 to November 2019 as only few façade units could be stored on site and up to 200 units were installed at different buildings per week, a 3,800 sqm hall was rented near Zurich serving as a “buffer”. From there, the façade units were delivered to the construction site virtually around the clock. On 5 November 2020, after a construction period of over five years, The Circle was opened at Zurich Airport by the co-owners, Flughafen Zürich AG and Swiss Life.

Ph.: © René Dürr
The CircleZurich | Switzerland
Latest News