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Airport terminal building in Carlsbad with a Kalzip aluminium envelope

An unusual airport terminal has been constructed in the spa town of Carlsbad in the Czech Republic. This stunning building sets new standards in terms of design and materials. In the construction of this ingenious piece of architecture, which is known as the “intermediate aircraft” and is open to many different interpretations, Architect Petr Parolek, chose to use Kalzip aluminium profiled sheets for the entire building envelope.

Carlsbad (Karlovy Vary) is the most famous spa town in the West Bohemian Spa Triangle and is situated above the River Tepl at its junction with the River Ohře. The hot springs were used as far back in time as the Middle Ages. This sophisticated town has been famous since the 18th Century when it became the meeting-place for emperors, kings and tsars, politicians, statesmen, Russian grand princes, Indian maharajahs and the wealthy international aristocracy.

Carlsbad subsequently developed into an architectural gem. The new airport which serves this spa town also embraces this architectural tradition. It features an unusual terminal hall designed by architect Petr Parolek. According to the architect himself, this building resembles a flying submarine and has been completely clad in Kalzip aluminium profiled sheets.

“My idea for the new terminal building was to create a design with different symbolic meanings”, explains Petr Parolek. “It could be a flying projectile, a spaceship or a submarine – simply a means of transport which hovers over Carlsbad.” The unusual shape of the building is formed by the geometry of three regular tubbing segments which were cut in a way which creates a uniform construction principle. Petr Parolek: “It is of course no coincidence, but rather my intention, to utilise the virtually unlimited potential of the Kalzip system to its full advantage to enable implementation of the precise aerodynamic geometry of this building, which has now been achieved.”

Architect Petr Parolek

At the beginning of the 1920’s a basic airport was opened in the vicinity of Carlsbad. Due to the requirements of the cosmopolitan visitors, the demands on the airport grew rapidly. Following a varied history, which includes the threatened closure of the airport on politically motivated grounds, the decision was taken to reuse the complex following the “Velvet Revolution” in 1989. The status of “international” airport was granted and Carlsbad soon reinstated its former standards of quality. In 2004, ownership of the airport was handed over to the “Region Karlsbad”. It quickly introduced an extensive modernisation programme and an extension to capacity. Work began with the modernisation of those areas which were necessary for
flight operations such as runways, guidance systems and air traffic control.

In order to meet the travel requirements of the “Schengen Zone”, it was also important to modernise the arrival and departure hall which still dated back to the 1930’s. The young, but nevertheless experienced architect, Petr Pavolek, from Brno, was appointed as the designer. It very soon became clear to those involved in the project that, alone in terms of space, the existing buildings simply could not cope with the demands placed on them. For this reason, architect Petr Parolek therefore proposed an extension towards the South in the direction of the pick up/drop off zone and car park.

The primary objective of the extension was to increase capacity, which since its opening in May 2009 has reached a level of 800 passengers per hour. This is the approximate equivalent to checking-in the passengers for four medium-sized aircraft per hour and, with an annual capacity of around half a million passengers, opens up new reserves for future developments.

Curved trussed girders in longitudinal direction

The existing buildings were renovated and any subsequent extensions were removed. The development axis remained unaltered. The new structure is positioned at right angles to it and connects to its former main entrance. Petr Parolek: “This configuration resembles an H in plan view and opens up two perspectives for observing the airport: on arrival at Carlsbad, passengers mainly observe the functional and historical component of the building, which also leads them into the corresponding world of the spa town. On departure, they observe the “intermediate aircraft” an organic technoid shape which creates an intermediate link to the world of flight. This so-called “Zwischenflieger” is a masterpiece in sophisticated, organic architecture:
its external shape has drawn inspiration from the world of aircraft design. The detailing used and the choice of materials underline this impression as the building envelope is constructed entirely from aluminium. The slightly elliptical body is structured in the longitudinal direction through the arrangement and alignment of profiled sheets in three segments, in order to increase the arch of the 70-metre long hall and to create a connecting passageway to the main entrance which has been cut away in a similarly elliptical manner. These dynamics support the symmetrically angled narrow sides and the light slots to the uppermost segment. “Here it was an important criterion for us to define all geometric surfaces and radii in a way which would allow the desired metal skin to be optimised both in technical and economical terms,” says Petr Parolek.

Different radii also present in the interior

The inside of the hall is characterised by the visible, supporting skeleton structure. An unusual solution, in terms of both structure and design, is the arrangement of both curved trussed girders, contrary to conventional logic, in a longitudinal direction in the hall. In this way, starting from the same base point, they sweep upwards and away from each other in a V-shape. Via these trussed girders, a logical system of compression and tension bars and formers are tensioned. The external metal skin takes on this form in a recognizable manner.

The architects chose radii which would allow the entrance area and the light slots to develop organically out of the shape of the building. The vertical structuring of the individual sheet panels gives the “intermediate aircraft” its plasticity and creates a shortened optical appearance in the longitudinal direction. The two-storey hall is surprisingly open and light, which is due to the light slots already mentioned, which have been cut horizontally into the roof skin. In this way, they appear to be much larger inside the building than one would expect from the outside.

The “Zwischenflieger” has a foyer which fulfils all functional requirements, featuring a small catering unit, the check-in desks, as well as two rentable business and office units. On the second floor there are sanitary facilities and additional offices which open out onto a gallery. The gallery can be accessed via four staircases and lift.

Roll-forming technology enables complex and organic shapes to be created

The unusual shape of the terminal called for a special solution in terms of the outer building envelope; one which would fulfil both functional and optical requirements in equal measure. The architects chose to cover this organic structure with aluminium in the form of Kalzip profiled sheets from Kalzip GmbH. Aluminium is a material which is not only highly durable and visually appealing, but also extremely flexible.

The sophisticated and complex geometry of the building is not only curved in the cross and longitudinal sections, but also in terms of the ground plan. For this reason, to create the building envelope’s construction elements, an exlusive roll-forming technology provided the only solution to producing freely-formed profiled sheets. This enables the production of free-form profiled sheets (Kalzip XT). This meant that each profiled sheet was individually adapted, practically tailor-made, to suit the existing geometry.

The overall area to be covered consisted of a multitude of individual components. This required very close coordination with the installation company and the preparation of a precise installation plan. The actual building envelope was divided into three sections. This therefore creates a fluent transition from roof to facade.

Kalzip determines the form

The roof consists of pre-curved profiled sheets with a radius of 15.8 m and a construction width of 300 mm up to 320 mm. They are arranged in a manner which accentuates the contours of the skylight. The profiled sheets which blend into the facade adjoin directly underneath. They were manufactured in one piece in the factory and with a radius of 5m. They run right down to the floor at both ends of the building. To emphasise the dynamics of the building structure,
the profiled sheets end in a visible separation, which is continued in the entrance area.

Here the adjoining profiled sheets which go right down to the floor on the right and left of the entrance, have a construction width of 510 mm up to 520 mm. The large, shaped components which frame the entrance oval, conceal the drainage system located beneath in an aesthetically pleasing manner. The structural design of the building envelope required a non-ventilated roof structure. Steel trapezoidal profiles were mounted on the supporting structure. The vapour barrier was installed on top of these.

A specially designed multi-part and height-adjustable substructure was then fixed to the upper flanges of the steel trapezoidal profiles. The Kalzip system fasteners, the so-called clips, were then installed on this.

Compressible thermal insulation was then laid. The uppermost final outer layer is formed by the Kalzip profiled sheets which are installed in a non-penetrative manner.

In the Kalzip system, the profiled sheets with the small seam are clicked onto the fixed system fasteners, covered with the big seam of the next element and zipped together to create a friction-locked connection.

“We decided to use Kalzip because the profiled sheets manufactured using the new XT free-form technology
were the only ones able to fulfill the precise material requirements, which were necessary to create the organically technology supporting system of the new entrance hall with its large span width,” explains Petr Parolek.