On the Zürichberg, between rows of villas, stands an oddity: the House with a missing Column by Christian Kerez made of steel and glass.

The villas are lined up high on the Zürichberg – mostly hidden behind high hedges. From here, you can look out over the rooftops of the city, the lake and – on a clear day – the mountains. But there is an oddity in between: instead of plaster and scrollwork, it features steel beams, large windows and concrete ceilings. It is the so-called “House with a missing Column” by Christian Kerez.

Previously, an old building with a view of the lake stood here, which did not fill the maximum permitted building mass. The owners therefore decided to demolish the building in favor of a new building that would house three apartments. In their search for a suitable architect, they came across Christian Kerez by chance. On a walk through Zürichberg, they passed a house that Kerez had built for his mother – the apartment building in Forsterstrasse. Impressed by the raw power of the building, they knew that this architect of a monolithic-looking concrete structure should also build their home.

However, Kerez chose other dominant materials for this building: steel and glass. He wanted to open up the view of Lake Zurich and extend the interior to the outside. This is made possible on the one hand by the floor-to-ceiling windows with their fine frames, and on the other by the column-free rooms. The result is an unobstructed view of the lake. Sliding glass doors that run between the steel beams face the terraces. The balustrades of the terraces are also made of glass panels so as not to obstruct the view.

Missing support

The construction of the building allows for column-free spaces. It consists of three pairs of gallows-shaped bar structures, which are positioned on the three sides that do not face the lake. There, the gallows supports enclose the uses that Kerez has placed on the outside: the elevator to the north, the building services shaft to the west and the staircase to the east, which only serves as an escape route. Each of the three gallows consists of a column that is three storeys high. A 12.50-metre-high cantilever is clamped onto each storey, which makes the column-free living areas possible.

There is no support on the lake side, which one would actually expect to find there. This is not only due to the view of the lake, but also to the building law, as the development plan stipulated that no pillars were allowed at this point on the property. In place of the missing support, tension rods stabilize the construction in the horizontal direction. Almost invisibly, they enable the floating cantilevers.

A large glass surface

The support of the gallows is clamped into a reinforced concrete base on the first floor. The horizontally prestressed reinforced concrete ceilings additionally reinforce the steel gallows. The steel girders alternate with the windows between them. This turns the entire façade into a single large expanse of glass, allowing views of the surrounding landscape and insights into the raw appearance of the building. Despite the solid construction, the building appears transparent and blends into its surroundings. In Kerez’s words, the building has “a Californian charm with Swiss insulation specifications”. In order to create this subtropical atmosphere despite Central European temperatures, insulating blocks made of glass fiber reinforced plastic thermally separate the steel construction in the façade area.

All pictures by Georg Aerni

A cloud of fog is supposed to cool the urban space above Turbinenplatz in Zurich. The first impression: it does little. “Alto Zürrus” is an immediate measure, read here how the square is to be cooled in the medium term and how the pilot project works and is received.

A cloud called “Alto Zürrus”

Zurich’s Turbinenplatz in the west of the city is regularly up to 6 degrees hotter than the surrounding area. To regulate the effect of the urban heat island, the city has now launched a pilot project: An artificial cloud of fog behind the Schiffbau building switches on at 30 degrees and is intended to have a cooling effect. Up to 10 degrees less should be possible thanks to the evaporating water particles, which extract heat from the surrounding air.

Anyone standing directly below or in the direction of the wind next to this artificial cloud will feel a slight cooling effect. Cooling water sprays from 180 nozzles over the heads of passers-by. To achieve this, the sensors of the ring-shaped installation must detect an air temperature of at least 30 degrees. There are also humidity sensors. If these detect impending rainfall, the cloud called “Alto Zürrus” does not become active.

The artificially generated fog cloud comes from an aluminum ring with fog nozzles that hangs from four wooden poles about five meters above the turbine site. The water is atomized so finely that the air around the cloud cools down. This should allow people in the vicinity to enjoy the cooler air without getting wet. It is expected that “Alto Zürrus” will operate on up to 44 dry, hot days per year.

Criticism of the cloud

Zurich’s new cloud has already attracted many interested parties. However, it quickly became apparent that the hoped-for effect is only minimal. People standing directly under the aluminum ring report a slight cooling effect. However, this is barely noticeable in the surrounding area and in other corners of the Turbine Square. The cooling spray mist does not reach the ground and the ambient air does not have a noticeably lower temperature.

The water consumption of “Alto Zürrus” is also a point of criticism – especially in view of the droughts in Europe. This is because it consumes drinking water and energy. Up to 100,000 liters of drinking water are sprayed each year. This equates to 7.5 liters per minute with the energy consumption of a vacuum cleaner.

The pilot project started in July 2022 and is scheduled to run until fall 2024. It is part of the specialist planning for heat reduction. The aim is to cool down the city in hot summer months. The funding comes from a Smart City innovation loan.

An employee of Grün Stadt Zürich came up with the idea for “Alto Zürrus”. He came out on top in an internal city competition. According to Grün Stadt Zürich, the project costs CHF 140,000. This also includes the costs for the scientific monitoring of the effect. This is because the effect is to be precisely measured and documented.

Comparison with “Le Nuage” in Yverdon 2002

Observers such as the Neue Züricher Zeitung (NZZ) compared the artificial cloud on Turbinenplatz with “Le Nuage”. This walk-in cloud at Expo 2002 in Yverdon was significantly larger. It is a steel construction in Lake Neuchâtel with a height of 20 meters and 31,400 stainless steel nozzles.

The NZZ wrote at the time: “Anyone strolling through the earth mounds of the Arteplage in Yverdon-les-Bains is reminded of prehistoric tumuli and dolmens. If you approach the lake from this direction in wet weather, you can see a small island rising out of the mist in front of you. From this perspective, the cloud looks like the mystical Avalon. Two fiberglass footbridges lead into it.”

In the “Alto Zürrus” cloud, it is not possible to walk through a cloud like in the mystical Avalon. However, the pilot project on Turbinenplatz is not art, but a means to an end.

The urban heat island Turbinenplatz

The city of Zurich planted additional trees on Turbinenplatz in the Escher-Wyss-Areal back in 2021. This is one of the largest squares in the city. As it is mainly covered in concrete, it gets oppressively hot here in midsummer. However, these trees need time to grow. The site conditions at Turbinenplatz are also not ideal: the trees will not be able to spread significantly or develop a large crown. At the same time, trees are the most effective means of combating the heat due to their cooling effect through evaporation and shade.

According to Zurich city councillor and head of civil engineering Simone Brander, we must assume that cities will become increasingly overheated as a result of climate change. The number of hot days could double to 44 per year by 2040. According to Brander, cities like Zurich have the potential to support heat reduction at a local level. According to the city councillor, the cloud is an immediate measure, while trees and surface sealing have a medium-term effect. Overall, a combination of different measures is needed.

Other cities, such as Vienna, are also experimenting with heat reduction measures in the form of artificial clouds. The effectiveness of “Alto Zürrus” will become clear from 2024 when the data is evaluated.

Read more about the city heat hotspot and measures for climate-conscious urban planning here.