Outstanding natural beauty built in Oxford

Attention to detail and a marriage of traditional skills and modern construction techniques will deliver a striking addition to Oxford’s heritage. Stephen Cousins reports. Photographs by Morley von Sternberg.

Nestled in the corner of a Grade II*-listed park and gardens, alongside a cricket pitch and close to some of Oxford’s most treasured historic buildings, it is hard to imagine a more bucolic site than the one occupied by the Sultan Nazrin Shah Centre.

The 846 sq m auditorium and conference centre is being built for £8.8m by regional contractor Beard Ltd for Worcester College in the University of Oxford. It is designed to merge into the protected setting by exploiting a palette of natural materials, primarily limestone and timber, assembled using a combination of traditional craftsmanship and state-of-the-art construction techniques.

The rectilinear facade, with its expansive vertical windows, incorporates more than 500 tonnes of masonry-grade Clipsham limestone, precision cut using CNC machines, then laid painstakingly by hand. Equally complex was the timber joinery, a structural oak lattice ceiling in the foyer, and a geometrically complicated fan-shaped ceiling, made of glass reinforced gypsum (GRG), in the focal auditorium.

The biggest challenges arose where traditional and modern materials intersected, explains Richie Carter, contracts manager at Beard: “The intricacy of the building is such that you can’t consider one element without considering all the others, and how one trade will affect the next. For example, if the blockwork wall is not built to the tightest of tolerances, the oak ceiling will not line up with the stonework on the face of the blocks. There is the constant concern that something is going to be out of line, creating a knock-on effect.”

The Sultan Nazrin Shah Centre is located in the northern grounds of Worcester College and is spread across a single storey. Due for completion in December, the facility will feature a 160-seat theatre, two seminar rooms, a studio for teaching and performance, and an e-hub social learning space, all linked together by a large foyer and bar area.

The rectilinear facade incorporates 500 tonnes of Clipsham limestone

It will be used by students for lectures and activities, including drama and music sessions, for conferences and as a meeting space for local community groups.

The building forms two sides of a three-sided quad (the third side is a neighbouring block of student housing) that mimics the existing three-sided Front Quad at Worcester College, with its Grade I-listed row of medieval buildings, known as “the cottages”, and two Grade I-listed neo-classical style buildings, built in the 18th century.

An existing natural lake near the historic college quad will be extended to run from the base of the east-facing studio elevation, with its large bay window. Water will be pumped from under the facade to appear as if the building is the source of the water, matching a similar detail used at the other end of the lake.

Níall McLaughlin Architects’ design aims to “nestle” the building into the historic landscape and maximise views out from inside. It incorporates design ideas and materials employed in the Stirling Prize-nominated Bishop Edward King Chapel at nearby Ripon Theological College, also designed by Níall McLaughlin Architects and constructed by Beard in 2012.

Both buildings have limestone facades, intricate timber roof/ceiling structures, and a curved halo-like clerestory, on the upper level, divided by a row of tapered stone mullions.

The Sultan Nazrin Shah Centre places greater emphasis on the stone mullions. Larger mullions on the main elevation create a regular rhythm and formal frontage onto the cricket pitch, and those in the curved clerestory drop down into the building to form the rear of the auditorium space.

Carter says: “I came away from Ripon college fully aware of the architects’ exacting standards and ready to promote the same standards into my team. Everything here is on a much grander scale, the clerestory windows are 4m tall, compared to 2.5m tall on the chapel, the mullions are 850mm-deep, compared to just 300mm.”

The auditorium ceiling is ribbed and features a double pitch

The facades incorporate more than 500 tonnes of Clipsham limestone, supplied from quarries run by Stamford Stone, north of Peterborough, and installed by stonemason Szerelmey. Clipsham has a rough surface and wide tonal variation, picking up various pinks and blues. It has been used widely around Oxford, and in prominent UK buildings such as King’s College Chapel, in Cambridge, York Minster and Windsor Castle.

The masonry is laid in a regular 300mm-deep course across the elevations, switching to a 150mm course from the ground floor to the base of the structure to create a subtly differentiated base to the building.

The building is in a flood zone and the ground floor slab is raised up on a number of concealed plinths. A chequer pattern of holes in the base of the limestone walls allow water to flow underneath.

Carter comments: “Uniquely, we spent seven to eight months on site before we even got the ground floor slab on. A key challenge was deciding which services to include in the floor void above the flood zone (principally large ductwork and ventilation). Other services are either run through screed, or through very tight ceiling voids.”

The limestone appears to be self-supporting, but is in fact fixed back to the building’s primary steel frame using a variety of bracketry, ties and dowels, most extensively in the lintels over window openings. The use of a primary steel frame, over concrete, reduced the overall weight of the structure and made it simpler to attach the stone.

There was only one alignment issue in all 35 windows

Alastair Crockett, project architect at Níall McLaughlin Architects, comments: “It has been a challenge to get the stonework into its current state to make it appear as effortless as possible, a lot of hidden elements have been included that are not necessarily visible to the eye.”

The Sultan Nazrin Shah Centre is defined by its tight lines of geometry, but Clipsham stone is relatively soft, for example, compared to Portland Stone. Design development between NMLA and Szerelmey allowed the sharp profiles of the stonework to be maintained whilst robust detailing ensured that fractures and accelerated weathering would be avoided.

“The limestone involved a real mix of modern and traditional techniques,” says Crockett. “The stonework was CNC cut from raw blocks by Meister Masonry in Cheltenham to achieve the correct profiles, but on site it was a case of three guys lifting large blocks of stone and fixing them in place.” The specific profiles were designed by Szerelmey in accordance with the detailed design provided by the architect.

The project programme was put in jeopardy when the glazing installer went into liquidation and the stonework had to be installed out of sequence, before the windows. This threatened issues with tolerances, particularly around large 600kg sliding windows in the front elevation that allowed for just +/-0.5mm of variation.

The ceiling comprises a primary oak structure, a secondary structure offset at 90 degrees, and a third supporting layer above.

“Thanks to some good setting out and a little bit of flexibility to pack and move the stone, there has only been one slight alignment issue in all 35 windows,” says Carter.

That was not the project’s only setback. Unforeseen circumstances led to a nine-week delay associated with the replacement of the main sewer running through the site.

The dialogue between high-tech and traditional construction played out during construction of the focal auditorium space, where a geometrically complex ceiling, resembling a folded paper fan, was built using GRG.

The ceiling is ribbed and V-shaped in section, with a double pitch that kicks back up over the stage. It also curves in plan, on the rear edge of the stage, and on the front edge that extends out to meet the mullions at the top of the clerestory windows.

“The fan shape behaves well acoustically, the idea of a compressed stage and an open auditorium was a nod to one of Níall McLaughlin Architects’ previous projects, a bandstand at Bexhill on the south coast,” says Crockett.

Sultan Nazrin Shah Centre cross section

Concern for light has always been central to Níall McLaughlin Architects’ work. Light from the clerestory streams across the surface of the GRG, so to avoid any unsightly blemishes a precise framework mould for each section of the ceiling was first modelled in 3D, then CNC cut. The process of casting the moulds then reverted to a more traditional plaster process.

The critical moment came when setting out the ceiling to a pattern of radial lines. Each fold in the GRG had to line up precisely with the centre of each of the stone mullions in the clerestory, a central radius point around the edge of the stage and a third point at the rear of the stage. Because of the level of complexity the GRG contractor, Fine Art Mouldings, employed its own designer to ensure that the moulds were cast to the highest degree of accuracy to meet the tight tolerances.

“The finished article looks fantastic, just how it was supposed to,” says Carter. “It seemed a long way off when we were at the start of the job and sitting in a design team meeting scratching our heads wondering how to achieve it.”

Timber structure and timber joinery are used to impressive effect in the Sultan Nazrin Shah Centre. The floors and ceilings of the seminar rooms are built in exposed oak and the ceiling structure in the foyer area features a multi-layered lattice of oak beams supported on slender oak glulam columns, installed by Inwood Developments. The timber theme is continued in the studio where oak floors will sit below an exposed, softwood glulam roof structure.

“The lattice is designed to tie together the surrounding rooms, but also to feel directionless, light streaming into the space will make it feel like being outside,” says Crockett. The ceiling comprises a primary oak structure that runs north-to-south on 3m-wide grid lines, a secondary structure offset at 90 degrees, and a third supporting layer above. The ceiling will look hand crafted, but is in fact a panelised system, installed in 3m by 2m modules.

Beard has constructed the building under a two-stage design & build contract, with Níall McLaughlin Architects novated to oversee the design. According to Carter, the architect has been committed to producing a high quality building, but also flexible to alternative options when issues with budget, buildability, or maintenance were highlighted.

As a result, the stone floors proposed for the auditorium and foyer have been replaced with maintenance-free porcelain tile alternatives and a pre-stressed concrete plank roof to the studio has been replaced with a softwood glulam structure which could achieve the required span members more suited to the restrictive nature of the site access. In addition, the GRG was preferred to curved, stress skin plywood for the auditorium ceiling on the basis of the flexibility and quality control which could be achieved with the product.

Níall McLaughlin Architects is very happy with the building so far, says Crockett: “You can see the plan and the elevations and views produced in the early competition stages coming through now on site, thanks primarily to the skill of all trades involved.”

Will it be another Stirling Prize winner to rival Bishop Edward King Chapel? Watch this space.