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Right Royal restoration

The Royal Court Theatre in London's Sloane Square was kept alive by the architectural equivilent of open-heart surgery

On 8 May 1956 the Royal Court Theatre in Sloane Square, London, staged John Osborne's Look Back in Anger. The play was to change British drama forever, yet its showcase was an utterly conventional Victorian theatre in what was - and still is - a swanky shopping area. But all that has now changed; the theatre, lately refurbished and extended by the architect Haworth Tompkins, now reflects the radical and contemporary approach of the stage company under its roof.

In 1995, the theatre faced closure. The structure was unsound, and front-of-house and backstage conditions were damp and overcrowded. Haworth Tompkins was asked to double the floor area of the building, adding new facilities while respecting the theatre's history.

'It was a fantastically delicate operation' explains Steve Tompkins. 'Instead of a complete reconstruction behind the original facade, which was the easy option, we undertook a kind of open-heart surgery'.

The Victorian Sloane Square facade has been retained - it was listed - but is now more open and 'permeable', and the inviting entrance gives tantalising glimpses of a curved vermilion wall beyond. This, the original rear wall of the auditorium that rises through the building and is visible on all levels, was painted by artist Antoni Malinowski. The heart of the scheme is the original auditorium, which has been stripped down to its essentials. The frilly plasterwork - a post-war pastiche - has been removed to reveal the tough, bolted iron plates of the original structure which supports the upper circle.

The original theatre needed refurbishment, but it was also seriously short of ancillary space: backstage facilities were cramped, there was no access for scenery and the stage itself lacked any modern technological systems. But the site was restricted, flanked by Sloane Square underground station and the residue of the River Cranbourne, which is culverted in a sewage pipe at basement level. The only two directions to expand were along the side of the theatre and beneath Sloane Square.

New backstage and administration facilities are housed in a four-storey extension at the side of the theatre, while a cavernous new bar/restaurant was created by burrowing beneath the road and the square.Matching the stripped-down aesthetic of the refurbished interior and auditorium, the new spaces are clad with simple materials that will weather and age naturally. The bar is fitted with reclaimed timber and dark leather seating, and its walls are of polished cast in situ concrete.

The four-storey extension houses dressing rooms and offices on the upper floors.

These are clad with an open rainscreen of flat weathering steel (Cor-Ten) panels, perforated to allow actors and office workers to control any problems of overlooking, sound attenuation, solar glare or gain (the side extension runs alongside an alley which is only 3m wide in some places). Sliding doors and hinged screens of Cor-Ten are fixed in front of the oak-framed windows to give further control of view. They are operated by a pulley-and-wheel system. The ground floor is clad with solid profiled weathering steel Cor-Ten panels, painted to take additional wear and tear.

'Cor-Ten is a very attractive material, ' says Harry Montrésor, who acted as cladding consultant to the project, 'but the detailing is critical. All joints and profiles must be designed so that rainwater can run off - there must be no retention of water. And all contact with other materials - fixings, electrical conduit, lighting - must be avoided.'

In practice this meant that the Cor-Ten facade panels and their stainless-steel fixings had to be clearly separated (see Working Details, overleaf ) with nylon spacers, washers, bushes and sleeves. An additional problem is the rust-coloured rainwater run-off from the panels which occurs during the first few years after installation. A wide stainless steel gutter has been positioned at first floor level to collect this. Run-off from the painted Cor-Ten panels below is directed into a stainless-steel box gutter inset into the floor slab and covered with a perforated stainless-steel plate.

Cor-Ten was chosen as a cladding material for its inherent richness and durability.

Since it has been installed the cladding has weathered from light orange to a subtle dark purple-brown. Like the theatre, it should grow old gracefully.

CREDITS

Architect Haworth Tompkins

Structural engineer Price & Myers

Services engineer Max Fordham

Cladding consultant Montrésor Partnership

Fabricator Custom Metal Fabrications

Rainscreen of weathering steel panels

The new four-storey extension to the theatre, containing offices and dressing rooms, is clad with a rainscreen of solid and perforated weathering steel (Cor-Ten) panels. They are sized to reflect storey heights and spandrel areas and are fixed, except in front of window openings where they are formed into sliding and hinged screens.

The 150mm thick cast in situ concrete structure was waterproofed with a liquid bituminous membrane and fitted with a series of stainless steel support and restraint brackets, which were lined and levelled.Mineral-fibre insulation bats, 75mm thick, were then pinned to the structure; they are lined on the outside with black glass-fibre tissue to assist in shedding water and to give a neutral background to the perforated screens.

The oak windows were sealed to the waterproofing and a second series of stainless steel support and restraint brackets was fixed to the first, with a thermal resistor between them.

Each 5mm thick perforated Cor-Ten panel is fixed through the unperforated perimeter zone to a bracket with a stainless steel button-head socket screw. To ensure that the stainless steel and Cor-Ten are totally separate, the screw is sleeved in nylon spacers and washers; the spacer is thick enough to avoid rainwater bridging from Cor-Ten to stainless steel and vice versa by surface tension. Stainless steel captive nut clips were fitted over the top of each bracket to enable the button-head socket screws to be tightened from the outside.

Cor-Ten earthing connector tabs are used to achieve electrical continuity between panels.

At first-floor spandrel level, a stainless steel gutter is set below the rainscreen to collect the runoff. The ground floor is clad with red-painted solid profiled panels of Cor-Ten, fixed in the same way as the upper panels.

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