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Tim Ronalds Architects’ performing arts centre, Sevenoaks School, Kent

Tim Ronalds Architects’ performing arts centre for Sevenoaks School in Kent is a tough, unyielding and tactile development, with acoustic design that is totally integrated with the architecture, writes Felix Mara. Photography by Christian Richters

With the exception of the music teaching rooms, Tim Ronalds Architects’ performing arts centre for Sevenoaks School has no plastered or painted surfaces. Everything is self-finishing. It’s a highly tactile essay in brickwork, concrete and timber (all Douglas fir) in various guises, with the exception of the floors and the drama studio wall panels.

The client, an independent co-ed school, takes performing arts, especially music, very seriously and commissioned Tim Ronalds to design new facilities, including an auditorium large enough for symphony orchestras, a recital room, drama room and teaching spaces. There is also a world music room, used by the school’s gamelan (an Indonesian orchestra). Ronalds, initially appointed in 2005 to design the masterplan, positioned the three performance spaces on the same level, linked by a foyer which also connects directly to the Sackville Theatre, designed by theatre specialist Roderick Ham and completed in 1981. The hard-wearing finishes are complemented by a design philosophy notable for its intellectual toughness. Acoustic performance is regulated by geometry, architectural finishes and detail, rather than by applied acoustic treatments. Most of the accommodation, including the auditorium, has natural ventilation. All the habitable rooms have natural light and, where possible, views of Knole Park to the east. Groundwater boreholes provide cooling and there is solar heating for hot water. Downpipes and rainwater hoppers are exposed. It’s a hardcore piece of work.

The acoustic design is totally integrated with the architecture. Yet concert hall design is extremely complex. It depends entirely on the end user, but digitally modelled simulations of performances in the auditorium meant the client knew what to expect. Ronalds is an experienced designer of performance spaces, but there was no question of designing the acoustics from first principles. Some argue that reference to typologies pre-empts design and stifles invention, but as Ronalds explains, there are only two possible models for a concert hall intended for an audience of 450 and largely for the performers’ benefit. The first option is a rectangular box with a flat ceiling, as in Georgian theatres, and the second is a pitch-roofed, barn-like structure, similar to the Snape Maltings concert hall in Suffolk, built by Newson Garrett in the mid-19th century and more recently augmented by Haworth Tompkins (AJ 10.06.10). Arup acoustics consultant Matt Wilkinson says the acoustic performance of both models would have been similar.

Ronalds chose option two. Its height enables natural ventilation to work by the stack effect, without relying on negative wind pressure, and it offered more scope to create an intimate space. Also, having decided to articulate the building as a set of volumes - with the main axis of the auditorium, which burrows into the steep contours of the site, running east-west to minimise obstruction of the views towards Knole Park - Ronalds wanted the auditorium to be as high as the portico of the block that accommodates the dining hall to the west.

The auditorium is ventilated by a labyrinthine plenum that feeds outlets below its raked seating. Eighteen metres above floorlevel air passes through a series of acoustic baffles and then up to a long ridge cowl, with top-hung flaps on the down-wind side. This filters noise from aircraft and lawnmowers and limits the internal background noise level to NR 20. Supply air is cooled by water from boreholes. The classrooms and foyers also have natural ventilation, but the recital room has air-handling units and the drama studio has chilled beams. Heavily serviced raised floors allow concrete soffits to be exposed, regulating the temperature. Because the fabric is highly insulated, small radiators fed by gas-fired boilers are sufficient.

Daylight from rooflights and large windows animates the foyers, and a tripleheight space is carved out adjacent to the auditorium. Glare and solar gain from the east and west is regulated by internal blinds, solar control glass and, when opened, unglazed side-hung ventilators. The auditorium has rooflights with silver blinds in their cavities and a large window in the gable wall, providing views in and out. When daylight is screened out the quality of this space is totally transformed and it becomes more focused.

In contrast to the reductionist, universalizing architectural logic and the multivalent forms that this generates, the structure is a hybrid. The frame is typically in-situ concrete, but in the auditorium concrete columns support timber rafters. It has no ring beam because the wall thickness is minimised to enable the building to fit between the Sackville Theatre and the science building to the north, so there are trusses, braced by steel tie rods. There was a battle to control the sizes of timber members, given the roof ‘s height and the loading from two storeys of equipment and plant above.

The recital room has steel columns and a ring beam supporting rafters with steel flitch plates. Concrete columns, suspended from the roof, support the upper floors, providing column-free space below. So in contrast to the architectural philosophy, which seeks to express construction, there is more to the structure than meets the eye.

The interior is aggressively well-detailed and this reinforces the building’s performance. The teaching and practice rooms are acoustically isolated boxes within boxes, with floating slabs. The battens and rigid panels in the auditorium that, for acoustic reasons, has 13 layers of roof construction, balance its sound quality. Despite the tough fabric of the building a warm, glowing ambience is produced by the palette of materials.

The architectural philosophy makes few concessions or sacrifices and its external proportions would be easier on the eye if the architect had been more yielding. Having endured the post-modernism and neo-vernacular backlashes against modernism in the 1980s, I find the steep gable a bit hard to take. It looks awkward and bald with its square apex and large window. But the hipped east end of this roof doesn’t look right either. It appears to have been set down behind the parapet, with no relationship to the lower floors.

But although the massing and fenestration are a natural expression of the building’s logic and inner workings, its appearance and composition have been considered and consciously designed. Cardboard models at 1:25 scale were used as a design development tool. Theatre designers are accustomed to working at this scale.

The building is firmly grounded in architectural culture and the product of a critical design methodology. ‘One designs one building as a reaction to the way one designed before,’ explains Ronalds. Designed by a practice that specialises in arts and education projects, it has a serious-minded and contemporary approach to craftsmanship and urbanism.

There is also a resonance with the work of American architect Robert Venturi, for example the Vanna Venturi House in Philadelphia, completed in 1964, and also with Venturi’s mentor Louis Kahn. Ronalds’ performing arts centre belongs to a world where the work of these architects overlaps.

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