Absolutely transparent

Case study: the refurbishment of a grade II-listed university building in Swansea, rounded off by AluK’s stunning facade

University of Wales Trinity Saint David has invested £8 million in the refurbishment, restoration and extension of the grade II-listed former Central Library building in Swansea to create the new Institute for Sustainable Design. Devised by Powell Dobson Architects, the development incorporates a twin-wall façade featuring AluK curtain walling systems, complementing and adding a new dimension to the original design.

The modern, double-skin façade extension provides an additional 657 sqm and incorporates a new reception entrance off Alexandra Road, workshops, teaching spaces and design studios. The original circular reading room has been restored and made available as a public venue.

Architect with Powell Dobson Yvonne Gibbs says: “Due to the context of the listed building, it was imperative that the new extension was as transparent as possible to express the original scale and features of the historic fabric behind. The university was also looking for a truly sustainable solution, to both reduce energy consumption and create an inspiring place to learn.”

As the main extension to the grade II-listed building, the twin-wall façade runs the full 38 metres of the Alexandra Road elevation. Designed by D2e, a multi-disciplinary engineering and management consultancy, the façade comprises an AluK SL60 curtain wall system forming the internal wall and a structurally bonded, glazed, toughened, laminated glass skin forming the outer wall, with an interstitial space between them.

“This arrangement provides the transparency that the listed building deserves, whilst introducing a number of opportunities for passive climatic control,” says Yvonne. “The facade is south-facing and therefore, through solar gain, the space between the two skins heats up naturally. This in turn acts as a thermal buffer, which keeps the building warm in winter months whilst promoting air movement and cross ventilation during warmer periods. It also facilitates the introduction of fresh air into the space, which is attenuated through a series of louvers at the base of the facade to temper noise pollution from the busy road outside.”

The gap between the internal and external wall makes it possible to control the flow of air and temperature within the building interior, using the air exhaust louver on top and the air inlet louver at the bottom to create a ‘chimney’. In winter, solar gain can be collected in the buffer zone, brought into the building and offset the heating costs, while in summer, when overheating can be an issue, windows can be closed and heat rejected using mechanical ventilation.

Banks of bespoke, top-hung, open-in AluK 58BW window systems located on the internal wall open and close automatically, depending on weather conditions, and are regulated by sensors located on the face of the curtain walling system. Manual operation is also possible to introduce further air.

With a visual sightline of 60mm and a mullion depth of 150mm, the SL60 ensures that the stringent aesthetic parameters set out by the architect were adhered to. The horizontal Vierendeel members, also designed to incorporate a 60mm face, ensured that the required visual transparency of the main facades was attained. With demanding structural requirements, the 150mm mullion was adequate to reach the project specification.

Internally, the SL60 system spans 12 metres between structural columns seemingly without support. The support comes from a bespoke design of the aluminium Vierendeel truss walkways, fixed at floor positions and supported by hanging stainless steel rods that are structurally retained in tension. These in turn act as a carrier for the glass Brise Soleil blades which run the full width of the building following the spectrum of the rainbow. “They are multi-functional,” says Yvonne Gibbs. “Environmentally, they protect the occupants and their computers from glare and they reduce over-heating. Their multi-coloured appearance, created in conjunction with a local glass artist from the application of a nano-technology coating, also signals the creativity and aspiration of the university within.”

Lee Jones, senior design engineer at System Glaze, the fabricator on the project, adds: “The SL60 curtain walling system and the external Vierendeel walkway act as a whole; this is the structural design intent, allowing the curtain wall to span over 12 meters – the full height of the lobby – unsupported. Implementation and erection of both elements at the same time proved to be difficult, and due to tight programme constraints, the required design could not be delivered. The SL60 needed to be installed and glazed prior to the walkway installation, allowing other trades to progress. A series of temporary restraints and connection brackets were specifically designed to ensure the curtain wall could handle the definitive wind loadings applied onto the fully glazed SL60 screen.’’

AluK SL52 curtain walling system, AluK bespoke 58BW window system, AluK single GT55 NI and double GT55 NI door systems were specified throughout the rest of the extension. Access from the interior into the twin-wall zone, for example, is via a set of the AluK double GT55 NI door system at each floor position, while the SL52 curtain walling system was specified for a 10m high external wall screen that runs the full building height to enclose one of the staircases and was also installed with a double GT55NI door system insert for a 4m x 7m wall screen shrouding the roller-shutter entrance door and providing ventilation via a run of fixed blade glazed-in louvers. The curtain walling system was also specified for an external 4m screen enclosing the second-floor lift lobby; a 17m slot screen situated directly below the main twin-wall screen to bring natural daylight into a basement workshop space; and two furthers screens overlooking reception from the ground and first floors, the largest of which runs unsupported for 5.5m and is internally lined with continuous mullion sleeve inserts with steel plates to provide the required structural properties.

In the main entrance, a 12m x 12m structurally glazed spider glass system runs the full height of the building and the full width of the entrance approach, adjoining the twin wall on one side and the existing grade II-listed building on the other. The glass has a low iron with light grey silicone finish to give the appearance of absolute transparency. The glass wall is structurally supported back to a series of internal 525mm deep, 19mm thick toughened low iron glass blades. The 12m span of the blades was achieved with one joint to minimise the amount of stainless steel bracket components. An over-clad entrance box with a double set of armour plate sliding doors provide a main point of ingress into the building, situated centrally within the spider glass wall. 



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