The new BBC Cymru Wales Headquarters is a striking new building in the heart of Cardiff, with precast concrete central to the design of architect Foster + Partners. Decomo, working with main contractor ISG, supplied 302 architectural precast sections, including the signature curved cladding on the corners and the columns of the three-storey high windows of the £80m development.
The new HQ comprises two five-storey office blocks which form an L-shape around a central media hub and will provide 25,600m² of flexible workspace for 1,200 BBC Wales staff. Internally, there is a full-height atrium linking the working spaces, including office, studio and production areas, plus a restaurant and roof garden. Located opposite Cardiff Central Station and built on the site of the Welsh capital’s former bus station, the building fronts on to a new public space for the city.
The 30m-high building is a hybrid structure, with a reinforced concrete frame at ground floor level and in the two-storey basement, three concrete cores and a steel-framed superstructure for the upper floors. Foster + Partners wanted to give “a permanence and timelessness to the building”, reminiscent of the Portland stone used to construct Cardiff’s historic civic ‘Bute’ buildings, so architectural precast, with a white, acid-etched finish, was specified for the Wood Street and Marland Street elevations.
“Precast can be cast in large single span units, which helped express the ‘verticality’ of the cores and the office façade,” explains Naji Chmayssani, technical director at Decomo. “Precast also gave the design team flexibility to create complex geometry in the cladding, such as curved panels with ribbed profiles on the ground floor level.”
The curved corners are one of the stand-out architectural features of the building, but were also among the most technically difficult for Decomo. “The manufacturing of these curved precast units was particularly challenging, as the design asked for an additional ribbed effect on ground floor level,” explains Chmayssani. “These were cast on large tilting beds to ensure an even, high-quality finish was achieved across each unit.”
Decomo manufactured 30 curved panels for the corners, each weighing 8.86t and measuring 3775mm by 7285mm, plus a further five curved ribbed panels for the ground floor, weighing some 10.89t.
The 27 flat ribbed panels at ground floor level were the heaviest on the project, weighing 14.27t tonnes. An additional challenge with these was the requirement for vertical vents, measuring 104mm by 3815mm, in some of the panels. "To create the vents, we had to design and manufacture slender, 100mm ‘fins’, which required a great deal of care and attention to ensure the performance of the panel matched the design criteria set out by the architect," says Chmayssani.
A further 141 flat precast panels, measuring up to 6195mm by 3775mm, were used across the Wood Street and Marland Street elevations. Along with the curved panels, there were fixed on to the floor slab and core walls of the reinforced concrete frame. The frames of the huge, three-storey high windows on these elevations were also constructed from architectural precast. Some 99 columns and beams were used, the largest single unit 6.495mm in length. “These are 'half oval' in profile and hollow on the inside, and fixed back to the steel structure,” explains Chmayssani.
The columns and beams Decomo supplied also included 10 thinner ribbed units, just 576mm thick, which were closing panels to clad the emergency exit door, with reinforcement made from resin-based composite mesh. The manufacturing on the project has been complex, says Chmayssani. “Apart from the flat panels, all the other units are bespoke, complicated moulds – flat ribbed panels, curved ribbed panels, oval shaped columns and the closing panels,” he says.
In addition to the precast elements, Decomo was responsible for the installation of approximately 230 sq m of glass-fibre reinforced concrete (GRC) in the soffits above walkways on the first floor and roof levels. “Installation of the GRC soffit panels over the walkways was a very delicate and intricate operation which involved rolling the panels into position on Titan beds and jacking them up in to their final position on to hooked connections,” explains Chmayssani.
The project has targeted a BREEAM ‘outstanding’ environmental accreditation. Precast will contribute to this, as the environmental strategy included identifying building materials that were robust, high quality, with a self-finish that would not only mature with age, but also have lower maintenance demands in operation. The precast units have also helped create an energy efficient envelope.
The new BBC Wales HQ was completed in early 2019.
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