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Wednesday30 July 2014

Concrete proves crucial to Mather’s Ashmolean redevelopment

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Rick Mather Architects has doubled the display area at Oxford’s Ashmolean Museum of Art & Archaeology with a 10,000sq m extension tucked behind the existing 1845 building

Architect Rick Mather Architects
Location Beaumont Street, Oxford

Climb the steps to the main entrance of Oxford’s Ashmolean Museum of Art & Archaeology and the eyes of actor Ben Kingsley, artist Maggie Hambling, historian Bettany Hughes and architect Rick Mather meet your gaze.

These arresting portraits by fine-art photographer Theo Chalmers are just a handful of more than 30 photographs on show in the museum’s forecourt, part of an exhibition to celebrate the personal connection many people have made with the Ashmolean.

Some of the portraits are also touring Oxford on the city’s buses, spreading word of the museum’s enhanced facilities and galleries in the lead-up to its official opening in November.

In spite of its size — the £61 million redevelopment will double the Ashmolean’s display space — the 10,000sq m extension by Rick Mather Architects is a subtle affair, discreetly tucked behind the neo-classical Charles Cockerell building, opened in 1845.

You almost wouldn’t know it were there. Nor would you know that the primary structure of this complex new development was made from reinforced concrete, or that its concrete and steel-framed interior walls — or fat walls — contain all the building’s services.


Rick Mather Architects’ appointment in 2003 to redevelop and reconfigure the world’s most important museum of art and archaeology couldn’t have come soon enough.

As Mather himself points out, the existing facilities were woefully inadequate. Only one room’s temperature was environmentally controlled. An Assyrian relief stone carving — which he describes as “one of the greatest objects in the world” — had been placed next to a fire escape due to space constraints. And in the gallery for the reserve Greek collection of ancient vases, the number of visitors had been restricted to minimise floor vibrations.

The proposal for the landlocked site, which is contiguous with seven other buildings, is described by Mather as “the most complex scheme we’ve ever done”.

The challenges began when work started on site in early 2006 with the demolition of listed Victorian buildings behind the Cockerell building. These had been built piecemeal and originally intended as temporary structures.

Planning for this involved protracted discussions with English Heritage. The architect had to prepare a detailed conservation plan demonstrating the far greater value of the Cockerell building compared with the later additions.

Three extra floors have been formed in the new building, bringing the total to six, together with 39 galleries, an education centre and schools entrance off St Giles, conservation studios and Oxford’s first rooftop restaurant.

Mather believes that his practice’s design “will do justice to the Cockerell building” and will ensure a seamless connection between the old and new.

The refurbishment will also involve the conversion of the vaulted, crypt-like basement from a toilet area into the shop. To create a smooth transition from old to new, and to aid access, the ground floor has been levelled, which has called for the removal of three steps.

This presented a considerable technical challenge because the raised area of the columned tribune, which replaced the museum’s apse in 1894, had to be removed but its columns retained.

Rick Mather Architects is no stranger to specifying concrete structures for its public buildings. It has used the material for the Towner Art Gallery in Eastbourne, the Sloane Robinson accommodation and teaching building at Keble College, Oxford, and, in the US, the Virginia Museum of Fine Arts, which is due for completion next May.

Project architect Stuart Cade says the practice hadn’t always intended the Ashmolean to have a concrete structure. Steel was originally proposed but a combination of cost, mass, the ability to create thinner floors with concrete, and the inability to achieve clear spans in steel eventually led to the decision to use concrete.

It seems to have been the right one. Concrete achieves a solidity that may not have been possible with steel. And, given the intricacy of the project, concrete has enabled the project team to vastly increase the display space in a dense, compact site, while still making the galleries appear generous and well proportioned.

Perhaps, most importantly, the new building respects the original Cockerell building by being subservient to it.

The key to this has been in the integration of services into the fat walls so that there are no false ceilings hiding pipework and cabling. That would not have been possible if steel alone had been used.

Fat Walls

To create tall-ceilinged galleries and maximise space in the new building, it was not possible to include false ceilings for the services in the design.

That meant the team had to come up with an alternative place to locate much-needed services, such as air-conditioning and other environmental controls.

The proposal for the landlocked site is described by Mather as ‘the most complex scheme we’ve ever done’

 

The solution came in the form of “fat walls” more than a metre wide.

A fat wall being constructed

Credit: Andy Matthews

A fat wall being constructed

The walls work hard and have no dead space. They are structural, they hide the services, but Rick Mather has also used them to house recessed display cases.

When the redevelopment is completed, about 80% of the fat walls will feature integrated display cases. The recess will vary from 300mm deep to 1m, with some cases running right through the wall.

Glass and steel display cases are being made in Belgium. Their simple design will allow the valuable objects within them to stand out.

Patrick Berning, architectural assistant at Rick Mather Architects, has spent at least a year integrating the exhibition design into the fat wall.

He describes the structure as a tripartite section broken into three parts. A plenum runs the full length of the gallery at the base of the wall, supplying cool air that warms and rises. At the top of the wall is another plenum extracting the warm air. And in the central section of the wall are the services.

To construct the fat wall, a reinforced concrete slab is poured. Posts are fixed into this vertical steel, running every 2.4m centres and averaging 2.5m in height.

The posts stretch between the slab and the concrete downstand beam above.

Spanning between these posts at two levels is a continuous horizontal steel rail — a 70mm x 70mm square hollow section.

The space between the display cases is filled with 70mm Metsec steel studs. Steelwork provides a supporting framework for the plenums and cases.

Plywood is screwed to the framework, and plasterboard to the gallery face, which is then plastered and painted.

Full-height oak doors separating each gallery will also be folded within the depth of the fat walls.

First Staircase

A sculptural architectural feature within the new building is the reinforced concrete first staircase rising from the lower ground floor to the top floor.

The staircase, which has five gently curving flights, changes direction from one flight to another. This provides dramatic views into a “grand stairwell”, naturally daylit by rooflights, which Rick Mather dubs “the connection to heaven”.

The staircase, treads for which will be covered in Portland stone, are recessed further at the top of each flight, so that the grand stairwell is wider at the top than it is at the bottom.

The staircase under construction

Credit: Rick Mather Architects

The staircase under construction

The staircase is bounded on its open side by a polished plaster wall that tapers from ground level at the bottom of each flight to 1.1m at the top. Above it is a mirror image of its shape in glass, tapering in from the bottom.

A stainless-steel handrail is clamped into the glass and a continuous cold cathode light is integrated into the inside face of the balustrade.

Project architect Stuart Cade describes it as a “cascading staircase”, explaining: “The appearance of the stair will be solid but there will be this ribbon of glass for the balustrade that will act like an orange peel of glass”.

The subcontractors would have preferred to build the staircase in steel but the design called for reinforced concrete poured into a ply formwork.

It was intricate work and the tolerances were tight. The formwork had to be made to curves carefully aligned from flight to flight.

Original print headline - Ashmolean Museum redevelopment

PROJECT TEAM

Architect Rick Mather Architects, Structural engineer Dewhurst MacFarlane & Partners, M&E engineer Atelier Ten, Quantity surveyor Gardiner & Theobald, Main contractor BAM, Concrete sub-contractor Thames Formwork

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