The new Sadler’s Wells East by O’Donnell + Tuomey might just be the hardest working building in showbusiness. The building – the latest addition to the East Bank cultural development on the former Olympic Park – houses a 550-seat auditorium, six large dance studios, a hip-hop school, and a public foyer with café, bar and community performance space.
Britannia Morton, executive director and co-chief executive of Sadler’s Wells, describes it as “a new kind of cultural destination: a purpose-built theatre specifically for dance and an inviting space for seeing, creating and participating in dance … It will fill a much-needed gap in the UK dance ecology.”
The structure of the BREEAM Excellent building has been designed so that the facilities can all be used at the same time, requiring high levels of acoustic isolation. It also has to cope with a challenge perhaps unique to this type of building: the vibrations arising from large groups of people moving in step, sometimes to different rhythms in different parts of the building all at once.
“It’s quite different to normal footfall,” says Jonathan Jackson, associate director at structural engineer Buro Happold. “We needed to think about the typical weight of the dancer, the typical number of dancers moving in unison, and the frequency at which they could excite the floor.” They also needed to think about noise: “The building has quite a small footprint, so we’ve had to stack a lot of dance studios on top of each other. There’s also a train line that runs behind the site. All of that drove quite an onerous acoustic design.”
In order to contain all of this music and motion, the team specified a concrete frame for the auditorium, fly tower, public areas and most of the dance studios. The studios are all 15m x 15m, and this became the basic organising principle of the building design. “The 15m spans were part of the brief from Sadler’s Wells,” says Jackson. “They know what makes a great studio, and 15 is the magic number.”
The main studio sits above the auditorium and has a lightweight structure entirely isolated from the space below. The other five studios are in the main L-shaped volume of the building above the public areas. Each is supported on post-tensioned beams, 15m long, 1.2m deep, and spaced 4.5m apart. By placing the concrete under compression, post-tensioning adds stiffness to control the vibration.
A 250mm-deep flat slab sits above the beams and this in turn supports a 100mm-thick concrete sprung floating floor in each studio. These floors were cast on a plastic sheet on top of a 1m x 1m matrix of helical springs. Once cured, they were raised using adjustable jacks to create an air gap, allowing the spring to absorb any vibrations.
Some of this structural fleet-footedness can be enjoyed from the double-height foyer below. This has an industrial aesthetic of exposed brick and concrete walls and beams – the thermal mass of which also plays a key part in the natural ventilation strategy of the public areas. The post-tensioned beams step rhythmically across the soffits, before a quickening of tempo to 9m-long spans with 200mm-wide ribs spaced 1m apart. The move to shorter-span ribbed slabs reflects a change of activity on the floor above, with the less dynamic world of office work replacing dance workouts.
Much thought has been given to the exposed concrete elements. “O’Donnell + Tuomey treated it as a really tectonic material,” says Jackson. The stair core – usually quite an insular space – has been punched open with sculpted, tapered windows that frame views across the foyer and into the park. The foyer walls, meanwhile, are more muted, and are intended to act as a background for large-scale artworks. A 30% GGBS mix cast against ply shuttering has left a lightened tone and a smooth finish. Board joints are largely aligned, but purposefully offset in places to make the layout feel less contrived. Bolt holes have been infilled flush in “background” areas where artworks are likely to hang, but hand-grouted with a slight dome elsewhere.
The main auditorium occupies almost half the volume of the building, and is a flexible space with fully retractable seating. The dimensions of the stage are identical to the main Sadler’s Wells theatre in Islington, to enable productions to transfer seamlessly from one venue to another. Above the audience, 15m-long precast planks form a lid over the hall: “It’s a more functionally driven space, so the concrete isn’t architecturally expressed,” says Jackson, adding that the height of the theatre and fly tower made in-situ slabs less viable. An acoustic void completely separates the lid of the auditorium from the slab of the studio above, so performances and rehearsals can take place simultaneously.
With so many different demands on the structure, it was important to specify the concrete precisely, according to the needs of each location. Where strength was less of a requirement, cement content was optimised to reduce embodied carbon. “We strategically tuned our concrete grades to the application. So in the fly tower walls, where the requirements were more acoustic than stress driven, we used a C30/37. In the higher stress areas, we used a C40/50. We also used lower grade mixes in the architectural walls to control early age shrinkage and reduce the reinforcement required to control cracking.”
Externally, the building is characterised by facades of handlaid Venetian red bricks beneath a sawtooth roofline, which draws daylight into the studios. Like the interior, however, some of the more public spaces are denoted by areas of exposed concrete. Along the front of the building, facing the river, a sculpted canopy shades seats and planted areas. Propped formwork had to stay in place for 56 days to give this dramatic element, which cantilevers 4.5m from the facade, the required strength and stiffness.
On the other side of the building, a concrete wall has been left as another canvas, perhaps for a muralist or graffiti artist. Some of this external concrete was precast for constructability reasons, says Jackson, but it was precast on site with the same mix that was used throughout the building, “so we could achieve a consistency of concrete expression”.
The art wall frames one side of the foyer café. On the other side of its glazed frontage, the café has a concrete flourish of its own – a terrazzo-like espresso counter that runs the length of the window. Here, the top of the concrete has been ground and polished, while the edges have been left as struck. “The idea is that the windows will open in the summer and this will be an inside-outside space.” As visitors sit down with their coffee, the rhythm of the city will merge with the many different beats of Sadler’s Wells’ new base.