At Leeds University, ADP has used a ‘kit of parts’ of 1,750 structural components to create one of the UK’s most high-tech, and sustainable, labs
The Sir William Henry Bragg Building at the University of Leeds is both a sensitive extension to a grade II*-listed neo-classical building, and one of the most high-tech facilities in the UK. Designed by ADP, the vast 16,200m2 complex houses the schools of physics and astronomy, computing and robotics, and engineering, with a fortress-like reinforced concrete basement providing a vibration-free home for ultra-sensitive technology such as electron microscopes and high-resolution imaging equipment.
“The constraints of the site were massive,” says Joe Morgan, creative director at ADP. In addition to the heritage building in front, the broadly rectangular plot borders a busy A-road to the north and the listed wall of St George’s Field, a historic burial ground that is believed to contain the remains of about 120,000 bodies. The basement walls had to be cast within metres of both the listed cemetery wall (hardly an ideal spot for a massive excavation) and the road, which posed both logistical and vibration challenges. Many of the laboratories and clean rooms had to be VC-D-rated, which essentially meant that no vibrations at all could be transmitted from passing traffic or building plant, requiring the sort of heavy structure that could only be provided in a basement. To achieve this, a 6m-deep contiguous piled wall of 500mm-thick reinforced concrete rests on 750mm-deep, 2m-wide reinforced concrete strip footings that bear onto the limestone and mudstone below.
The 250mm-thick ground-bearing slab, between the strip footings and wall bases, is monolithic, with no separation joints. Active vibration isolation was included for equipment requiring greater than a VC-D rating, such as transmission electron microscopes. To reduce the embodied carbon of the substructure, a mix containing a proportion of fly ash was specified.
Above ground, the structure switches to precast concrete, and a “kit of parts” of over 1,750 structural components, including beams, columns, stairs, landings and twinwall cores. This was partly because there was limited access for heavy equipment, and partly because the architects wanted to be able to control the quality of finish, which is largely exposed throughout the interiors. The lab areas, at the north end of the building, needed a slightly less onerous VC-A vibration rating (which they nonetheless exceeded) and are based on a 6.6m x 7m structural grid, with 175mm prestressed precast planks and a 225mm in-situ structural topping. The office spaces on the south side have a 9m x 7m grid with a 225mm prestressed slab and 100mm in-situ structural topping.
The designers were anxious to keep the slabs as thin as possible, in order to make the most of the 4.5m floor-to-floor heights and restrict the overall building height. This thinking extended to the treatment of the soffits, which have been left exposed: “This was partly to moderate internal temperatures and to reduce unnecessary finishes. But it was also to increase airflow and volume – concealing the ductwork could have made these deep floor plates feel quite oppressive,” says Morgan.
The elements are all designed so that they can be demounted and reused at the end of the building’s life. To this end, none of the services have been cast into the slabs or columns and all relevant data about them is recorded in a BIM model (BIM level 2 was used throughout the project).
That said, nothing about the BREEAM Excellent building looks temporary. Its precast concrete cladding is intended to echo the Portland stone of the 1920s Old Mining Building it backs onto, and other buildings within the university conservation area. ADP previously designed the campus’ Laidlaw Library, completed in 2015, where it opted for a stone facade, including panels of “Roach bed” Portland stone with the ghostly trace of fossilised shells in its surface, in keeping with other buildings on the campus. On its secondary elevations, however, the library switches to precast cladding, and it was here that ADP discovered that the Roach-bed effect could also be cast in concrete, offering the possibility of creating much larger panels.
On the Bragg Building, 4m x 4.5m Roach-bed modules adorn both the south elevation and the prominent north gable elevation, facing the busy Woodhouse Lane. “We wanted it to feel as natural as possible,” says Morgan. “Not necessarily marrying entirely with the Old Mining Building, because there is obviously a slight separation, but still authentic. You'd be hard-pressed to tell the difference between the precast and the real thing.”
The fossil effect was created using rubber moulds that had been cast against natural stone samples, leaving a pattern with the illusion of randomness. “We used three or four templates, but found we could get enough variation just by rotating through 90 degrees each time,” says Morgan. The 150mm-thick modules are mechanically fixed to the building’s precast concrete frame in a horizontal arrangement, framed by lighter acid-etched panels. This lighter mix is reprised on the other elevations in the form of vertical fins, which lend definition to the facades of glass and anodised aluminium.
These fins also wrap round a one-storey extension on top of the Old Mining Building, mirroring the entrance portico below. The Bragg Building steps up towards the back, so this rooftop extension is one of the few visible parts of the new development. “We worked really hard with regards to the scale of the Old Mining Building,” says Morgan. “There’s an incredible amount of accommodation but it nestles really well into its context.”