The new 21st-Century Engineering Building at King’s College London could probably lay claim to occupying one of the most awkward sites in UK higher education.
On KCL’s main campus, which slopes down on a thin strip of land from The Strand to the River Thames, it sits in a two-storey basement beneath the quadrangle, which is itself squeezed between the grade I-listed King’s Building and Somerset House to the west. There was only one way on to the site, via the notoriously traffic-choked Strand.
The existing basement didn’t give too much cause for hope either. Built in the 1950s, this was an unused, unlisted archive storage space built from concrete-encased steel with hollowpot slabs. It was long and narrow in shape, following the footprint of the quadrangle, and set back from the line of the historic buildings to allow strips of light in from above. Damaged finishes were peeling away from the structure, which indicated that the waterproofing on the deck above was failing. The deck itself was structurally fragile.
Fast-forward six years, however, and the KCL quadrangle offers an inspiring example not just of maximising constrained space, but also of using new-built elements intelligently to reanimate existing structures. A team led by design architect Hall McKnight and executive architect Rock Townsend has brought the two underground levels back to life as 3,000m2 of flexible teaching and workspace for research into sustainable engineering. The deck above has been waterproofed, thermally upgraded and re-covered to become a rejuvenated pedestrian square. Moreover, KCL has calculated that, by reusing existing elements, the structure achieves around 180kg/CO2e/m2 embodied carbon, one-third of a very high-performing new-build comparator.
As much of the original basement has been retained as possible. Structural engineer Elliott Wood carried out a series of investigations, including thermographic surveying, to assess the condition and capacity of the structure. “"While there were signs of corrosion to the frame and slab, even in the worst affected regions the structure still appeared robust and suitable for keeping. The roof waterproofing was wholly reinstated to provide protection against further corrosion,” says associate director Billy Squire. It was found that the central spine of the structure could be stripped back to historic brickwork vaults and columns that had been covered up by the postwar development. This area has been refitted as two long teaching rooms and a connecting space that links to the main King’s Building at basement level.
Inserted around the vaults are several new elements, for which in-situ concrete has been used as both structure and finish – a decision based on the brief’s specification of a robust workspace that would stand the test of time. “This is not a 25-year building that may be demolished soon,” says Richard Sharp, partner at executive architect Rock Townsend. “This is an investment in place and it's going to be there for a long, long time.”
With this in mind, considerable care and effort has gone into making the new spaces beautiful as well as functional. In particular, the stairwell that descends through the centre of the plan is a showpiece of cast-concrete construction. To produce this spiralling structure, Rock Townsend used Revit software to 3D model all of the reinforcement and cable routes as well as every day joint and shutter joint.
“There was a lot of back and forth between the different members of the team,” says Peter Phillipps, associate designer at Rock Townsend. “The actual pour itself was quite complex, with a lot of integrated MEP, reinforcement and conduits to piece together.” To help make sense of this multi-dimensional puzzle, the architects produced a set of colour-coded 3D pour sequence drawings for the stair contractor, who then used these to create shop drawings for the bespoke welded formwork. This was made from fair-faced ply in order to leave a matt finish.
Above the stairwell, the exposed soffit opens into a deep oculus, which draws light into the centre of the plan. Externally, this has been clad in precast-concrete panels with a pattern inspired by the DNA helix, the discovery of which was made possible by Rosalind Franklin’s work at King’s in the 1950s. The raised oculus can be used as seating and gives a focal point to the relaid quad.
The other significant new elements are the lightwells that extend within a metre of the King’s Building facade. The smaller volumes at the north and south contain toilets while the large areas in the middle of the plan are used as makerspaces. These are fair-faced concrete with deep beams beneath the rooflights that convey the ventilation ductwork and other cabling.
Working so close to the listed building, space was at a premium here, and a great deal of detailed design and thermal bridging analysis went into the wall build-ups to ensure that all insulation, waterproofing and structural demands were met without encroaching beyond the footprint. The concrete formwork posed another challenge as space for shuttering was extremely limited. The solution here was to use vertical panels of precast cladding, lowered in from above, as the outer skin – a detail only visible from the lower floors of the King’ Building.
As with the oculus, the lightwells resolve at surface level with precast concrete panelling, although here the irregular form changes from panel to panel. Again, this was extensively modelled in 3D, with profiles and geometries precisely defined for every single piece. The architects’ drawings also included approximate weights for each panel, which was essential as the quad’s fragile deck had a strict maximum load of 1 tonne. “You couldn’t drive anything of any weight onto the structure – when the panels came onto site, we had to use spider cranes to spread the load over the deck,” says Sharp.
This proved a problem for the in-situ concrete as well, as a mixer couldn’t be stationed on the quad itself, and the only obvious entrance was from the busy Strand. Eventually a route was found from the Embankment up through an existing lightwell, although this involved pumping concrete distances of up to 80m. “You couldn’t get the mixer any closer,” says Sharp. He adds that, for this reason, other structural solutions were considered at an earlier stage of design, but that “the client bought into the entire approach. They had the will and it was the right approach for this type of building.”
The result is a flagship research facility in what could easily still be an abandoned basement store. KCL expects post-occupancy monitoring to demonstrate a 70% reduction in energy demand compared to the original building, befitting a modern university estate. The college is now extending its retrofit strategy to the brutalist Strand Building, which stands guard at the front of the campus. Previously this was to be demolished to make way for a new block, but now will be refurbished and upgraded.