Garsington Opera pavilion by Snell Asscociates
Sliding fabric screens were chosen to clad this temporary venue for the Garsington Opera Company in Buckinghamshire.
Wormsley Park, Buckinghamshire
Designing a temporary pavilion for opera performance presented Snell Associates with an acoustic challenge. Fabric was an obvious choice for the building envelope because of its light weight and demountability. The issue was how to use this to enhance not only the visual appearance of the pavilion but the sound performance as well.
It was a task welcomed by Robin Snell, who was project architect on the Glyndebourne opera house when he worked at Michael Hopkins & Partners and has since built up a track record in working with lightweight and transportable structures.
The Garsington Opera brief was for a pavilion that could be put up each summer for a month, and then demounted quickly and stored until the next opera season.
The site – a new venue for the Garsington Opera Company – is the Wormsley Park country estate, whose picturesque nature Snell was keen to make the most of through the use of a transparent material for the pavilion walls that allows views of the surrounding 1,000ha parkland during the opera performance.
The 600-seat structure is positioned to make use of a 2.1m deep ha-ha – originally a boundary for the deer park – for the orchestra pit. The design is conceived visually as two horizontal planes – the roof and the floor – floating in the landscape. The walls and roof will be constructed from PVC fabric, configured to provide a high degree of reverberance that will assist the unamplified outdoor acoustics. This 1kg/sq m weight fabric is supported on a galvanised steel frame arranged in 4.8m modules.
There are just two solid vertical elements – the back of the stage and the back of the auditorium – which are clad in feather-edged timber board. Sliding panels along the side of the pavilion can be positioned to shield performers and the audience from direct sunlight.
The £3 million pavilion will be constructed in time for the 2011 summer season. The contractor, Unusual Rigging, reckons it will take less than two weeks to put up and take down. The pavilion is designed to last for the duration of the opera company’s 15-year lease but Snell reckons it could have a lifespan of at least 25 years.
“There’s a huge industry that puts up temporary buildings for rock concerts. We’re doing an architectural version of one of them for opera,” says Snell.
Sliding shoji screens, as found in traditional Japanese architecture such as the Katsura Imperial Villa in Kyoto, informed the incorporation of screens into the pavilion design. Five 8m x 4m high screens on each side of the pavilion are hung from the roof on tracks and positioned manually as required for solar control. The Soltis fabric, manufactured in France by Ferrari, is perforated to maintain some views out and is stretched onto a steel frame.
Roof contractor Architen Landrell set up a testing rig and worked with acoustician Sound Space Design to help the architect arrive at the best roof configuration to withstand rainy and windy conditions.
The architect needed a roof envelope that would not just keep the rain out but do so with the minimum of noise. They decided to use two layers of PVC fabric by Heywinkel – the upper mesh acting like an attenuator to gradually let the rain through to the lower layer, where it can be drained off via spouts – one per bay – so reducing rain noise.
Another issue was how to separate the two layers and avoid them flapping together in high winds. The test rig used a sheet of perforated plastic to simulate rain falling onto fabric with the two layers at various distances to see how spacing affected sound performance. This showed a 100mm gap on the main truss line halved the noise of the rain by 14dB. Any larger gap made little difference.
The architects decided on a gap of 100mm and separated the two layers with a 250mm diameter airbeam – a tube filled with air – fixed to the underside of the mesh top layer in the middle of each of the 10 4.8m-wide bays. This puts the two layers into tension while allowing for some movement, but not enough to cause the two layers to meet. They are held together by extruded aluminium components.
The fabric for each module is threaded through and pulled across the roof span by hand with the help of a cherry picker. The fabric measures 30m across the width of the pavilion, including a 4.5m overhang on either side above the veranda.
The silver/grey upper mesh is combined with black PVC over the stage, where light reflection must be minimised, and grey PVC over the audience.
A single-layer of stressed PVC forms the walls, configured into curved ’sail’ like forms to give the optimum sound performance.
Robin Snell’s team worked with acoustician Sound Space Design to ensure the angles of the sails gave the right acoustic results. They came up with five panels that are curved differently according to their position in the auditorium to ensure an equal sound coverage.
Each is twisted to provide lateral reflections which bounce the sound back into the room. These are arranged on an inclined line to allow the sound to reflect downwards on to the audience. This is enhanced by the convex roof, which reflects sound back to the audience, stage and orchestra pit.
The PVC, which was supplied by Kayospruce, is fixed on spars and ribs like a yacht sail. The walls are opaque facing the car park and entrance, and clear on the garden side to give views over the park.
According to Snell, who is a great admirer of Norfolk Wherry sail aesthetic, the effect will be “like a mainsail in full sail”.
Architect Snell Associates, Client Garsington Opera, Acoustician Sound Space Design, Structural engineer Momentum, Services engineer Buro Happold, Cost adviser Gardiner & Theobald, Project safety Gardiner & Theobald Project Safety, Main contractor Unusual Rigging, Fabric roof specialist Landrell, Fabric roof contractor Architen Landrell, Steelwork specialist Sheetfabs (Nottingham)