South African carving – Zeitz Museum and the Silo Hotel, Cape Town

The transformation of a historic Cape Town grain silo into a contemporary art museum topped with a hotel involved carving out the inside to form an elliptical atrium, and covering the facade with glittering glass pillows. Stephen Cousins reports.

When architects Heatherwick Studio were approached to transform a historic grain silo building in Cape Town harbour into a spacious new museum for contemporary art, it was faced with an inflexible industrial concrete structure comprising a densely-packed network of 33 metre-high concrete tubes.

The 42 cylinders, formerly used for storing grain, each had a diameter of just 5.5 metres and were entirely unsuitable for use as functional gallery spaces, or indeed access by humans. The studio’s ingenious solution was to devise a form of architectural surgery, slicing into the structure to form a large elliptical central atrium, capped by a glass roof, and a network of 80 other gallery spaces.

The exterior of the building would remain largely intact, to pay tribute to the original industrial design, apart from a series of twinkling jewel-like faceted windows that light up at night like a lighthouse.

Stepan Martinovsky, project leader at Heatherwick Studio tells ADF: “Visitors entering the museum will understand in a single glance the cellular structure of the original building, the material it was made from, and get a view of it that no one has ever seen before. The architecture is like a 3D anatomy lesson exposing the different layers inside.”

An elephant in Cape Town

At 57 metres-tall, the Grain Silo building has dominated the harbour area of Cape Town since it was constructed in 1921, and for a while held the title of the tallest building in sub-Saharan Africa.

One of a network of silos built to process grain and ship it worldwide, the concrete-built block ceased commercial operation in 2001 and has remained empty ever since, despite several attempts to identify an alternative use.

“The Grain Silo was like the elephant in the room, it was so large everyone could see it, yet it was mostly ignored,” says Martinovsky. “When Heatherwick Studio became involved with the project, we recognised the need to do something cultural with it, such as a gallery or museum, which is the missing piece in the puzzle for the area.”

The lower 10 levels of the block are occupied by the £28m Zeitz Museum, the first museum of such a scale (9,500 m2) dedicated solely to displaying contemporary art from the African continent completed since 2000.

The top six floors of the complex, inside a former grain elevator adjacent to the main block, are occupied by the 28-bedroom Royal Portfolio Hotel. The hotel includes a rooftop bar and restaurant, on the 11th floor, with spectacular 360-degree views of the surroundings, including Table Mountain.

Liz Biden, the hotel’s owner and founder, was the brains behind the design for its interiors and furnishings, which comprise an eclectic mix of fabric, carpets, paintings and furniture, no two rooms are alike.

The rough industrial look of the building was exploited to create contrast, Biden tells ADF: “I tried to keep as much of the industrial feel of the building as possible, but added luxury comfort and colour to the look. We have some of the old machinery at our entrance and on our sixth floor. Each room has at least one new, one old and one customised piece of furniture in it.”

The design for the refurbished building had to both respect the listed status and create a recognisable landmark synonymous with the city – a key requirement of the client, Victoria & Alfred Waterfront, which owns 123 hectares of the former docklands.

Heatherwick Studio was wary of the modern trend, seen in many towns and cities, of creating iconic ‘trophy’ museums that are highly sculptural on the outside, such as the Guggenheim Museum Bilbao, designed by American architect Frank Gehry.

“Our building was already unique and present in terms of its significant monumentality, so we chose to exploit that,” says Martinovsky. “We wanted to preserve as much of its soulfulness, richness and uniqueness as possible.”

Excavating a void through the building’s innards would create a spectacle to draw in visitors to see the art, considered a challenge in a region that has no established museum-going culture.

Grain exploded

The atrium space is based on the elliptical shape of a single grain of maize that was 3D scanned and scaled up to 27 metres tall. “We liked the idea that all the grain is now gone, but one tiny piece of it is carved out of the building forever to remain there as a reminder,” says Martinovsky.

The void is intersected by glass lifts and a spiral staircase that rise up into the sawn-off cylinders. The floor below is also cut through to reveal the basement, where conveyor belts once shifted grain.

Carving out such a huge amount of concrete from the heart of the building was a tough construction challenge, made trickier by the fact the concrete cylinders were just 180 mm-thick with limited structural strength.

A new 250 mm sleeve of structural concrete had to be cast inside each of the tubes to boost integrity before they were cut into with jack hammers and circular saws. “The labyrinth of 5.5 metre-diameter tubes, only connected together via openings at the bottom, was a very tough space for the builders to work in,” says Martinovsky.

The method of construction made it difficult for the designers to see progress on site, as the final form was only revealed section by section, like a stone sculpture slowly chiselled away by an artist.

“The big reveal only came when a large portion of the atrium was cut out and we realised, thank god, this was actually working,” he adds.

Beyond the atrium space, interventions were made into the sides of other tubes to create space for footbridges that provide access to galleries.

A different approach was taken to create the galleries themselves, the museum’s director had specific vision for white rooms with no architectural detail to distract visitors from the art.

As a result, around two thirds of the existing silo tubes were removed, on either side of the atrium, to create space for a series of minimal white cubes that slot into the voids. As visitors walk through the building the cubes can be seen hovering above the ground floor, and they can be viewed from below and from the side.

Glittering pillows

The Silo Building is like an architectural pandora’s box, its flamboyant sculptural interior concealed behind a largely unadorned concrete facade.

A light-touch approach to the exterior involved simply stripping away a layer of magnolia-coloured waterproof paint, applied in the 80s, and washing the concrete to expose the aggregate.

“After revealing the aggregate, the wall came alive, making it possible to see the different strata, from the time the concrete was poured, and the mix of different sized blue, green and brown stones,” says project leader Martinovsky.

The top six floors of the building were stripped back to the base grid of concrete columns and beams, which define the layout of the new Royal Portfolio Hotel behind.

Each square opening in the facade is fitted with a curved, multi-faceted glazing panel that bulges outward by one metre, as if gently inflated.

The windows are based on designs for Venetian hand-blown lamps, created by blowing glass through chicken wire mesh to create miniature bubbles. Each acts as a form of structural dome comprising 56 triangular panes of structural glass, the largest opening is around 6 metres tall by 5 metres wide.

Heatherwick Studio worked hard to maximise the number of facets in each panel to create a form that looked as close to curved as possible, without blowing the budget.

The glass is fixed with structural silicon to T-section aluminium extrusions, which are attached to a frame of flat steel bars. A degree of opaqueness and reflectivity was required to reduce heat gain and glare in the searing heat of summer.

“We questioned whether to install a standard curtain wall facade, as this method is not very unique and associated with generic office buildings and towers. This building deserved something special that would be dignified enough for a cultural institution,” Martinovsky comments.

The windows glitter and pick up reflections during the day, and when lit at night, they draw public attention to the building. They now give it a special extra visual presence in the city, which despite its monumental size, it previously lacked.

PROJECT FACTFILE

Client: Victoria & Alfred Waterfront Holdings (Pty)
Location: Cape Town
Completion date: September 2017
Total area: 102,000 ft²
Exhibition space: 65,000 ft²
Designer: Heatherwick Studio
Project manager: Mace
Structural engineer: Arup / Sutherland
M&E / sustainability engineer: Arup / Solution Station