Chris Rogers writer on architecture and visual culture

The Leadenhall building

Settled comfortably around a black conference table – the only item of furniture in an office space still lacking its carpet tiles – on the 40th floor of the new Leadenhall Building as part of a small group of journalists and writers invited to its press view last week, I had a rare and valuable opportunity to discuss with lead designer Graham Stirk and his partner, practice co-founder Richard Rogers, the forces that had shaped their new building and how they came to be working in the City of London once again.

Rogers Stirk Harbour + Partners have of course a rich presence in the Square Mile, one that goes far beyond the landmark Lloyd’s of London, completed more than 25 years ago and standing directly opposite the Leadenhall Building. With Lloyd’s Register of Shipping, the discreet conversion of Billingsgate and 88 Wood Street also to their credit, the firm has specialised in assured, sometimes assertive insertions within the City’s fine and historic urban grain. Even their unbuilt projects attract, notably the aborted scheme for Daiwa on the Wood Street site.

Our interest, then, was tangible, leaving aside the sheer bravura of the 52-storey, 225 metre skyscraper just handed over for a nine-month fit-out to commence, with its sloping glass façade to the south (giving it the popular nickname of the Cheesegrater), a north face filled with colourful lifts and toilet pods, and – scooped out of its base – a great, five-storey public space extending right underneath the building and out the other side.

Ignoring, for the moment, the widescreen view available from that 40th floor, one that encompasses those earlier works by the firm and many by its rivals, including former colleague Norman Foster’s 30 St Mary Axe and Willis Building, former collaborator Renzo Piano’s Shard and Raphael Vinoly’s almost-complete 20 Fenchurch Street, the first question that arose was a simple one – how did the building come about?

Developer British Land held a limited competition to replace the admired but outdated former P&O tower at 122 Leadenhall Street with a new building containing office space designed to contemporary standards and one likely to attract the insurance businesses that have made this very specific area of the City their preferred location (“All the negotiations are done at ground level, the signing on the upper floors,” quips Stirk) Without a pre-let, occupiable area was everything and so RSHP’s winning scheme, though promising, was ultimately rejected as underperforming in that regard. Both height and servicing were clearly the key to unlocking the maximum potential of the site, and from a fresh look at applicable height rules and further exploration of form with planners, the current profile emerged.

Explained as biasing services to the north to leave clear-span office floors to the south where are found the best views, and then inclining that façade back to satisfy a protected view of St Paul’s from Fleet Street further west, it was, says Stirk, about discovering “how we could swing all of the mass away from the southern site boundary” while still attaining a distinctive yet visually coherent shape for the new building, something absent in earlier iterations.

This asymmetry – a building “defined by section, not in plan,” explains Stirk – then needed an engineering solution that would make it possible.

Work with Arup generated the concept of the megaframe, cage-like modules formed by a perimeter of steel beams up to 28 metres long that are placed one on top of the other to create the final structure. Megaframe elements are joined by immense, bespoke steel ‘nodes’, weighing 30 tonnes each. Further steel pieces in the shape of a letter K are stacked horizontally to form the ladder frames visible at the two northern corners. These provide extra stiffness by tying-in to the megaframes.

The north core, structurally separate from the megaframes but firmly connected, houses the lifts, toilets, risers and local plant, this last also contributing to freer office floors. Stirk describes it as “a bookend”, placed as it is on that part of the site where there are more development constraints. Each level was constructed from three ‘tables’ spanning the width of the building; pre-assembled and even pre-wired, they were craned into place swiftly.

Innovative ‘active alignment’ was employed during construction to correct the slight lean that a building with all its weight to one side of its footprint developed, tightening joints incrementally to bring it back into true.

Six of the seven-storey megaframe modules contain the office floors. The strength of the megaframes permitted the openness required by occupiers, those on the lowest levels needing just six additional columns over an area of more than 2,000 square metres . Every floor in the building is of constant width but, as the building rises, diminishing depth (by 750mm each time). It is a progression which climaxes for the office levels at the 45th floor, just 550 square metres but, with its double height and powerful metal 'trees' (a pleasant accident, more or less, due to the need to balance internal and external column forces), particularly dramatic and the highest workspace in London.

The floors above, comprising the seventh megaframe module, house plant – generators, cooling towers, boilers and the building maintenance units used for cleaning the façade glazing, which are neatly retracted below the roofline when not in use.

The lowest megaframe generates that remarkable public space at street level, defining it by the points where the raking beams touch the ground in front and to the sides of the building.

The need to pull the top of the building so much higher, says Stirk, made British Land amenable to moving the usual functions of a tower’s ground floor – lobby, security, lifts – up higher as well, to a point where they are suspended from the fifth floor level, the first office storey. This audacious move allowed a ground floor that is in fact a continuation of Leadenhall Street and one which is landscaped as part of the street rather than part of the building, with an area of grass and trees, an open portion, seating and glazed screens to ameliorate downdraft. A pair of escalators, offset from each other in height and plan, suggest double-deck lifts but in fact one services a dedicated reception for principal tenant Aon, who – in a sign of quick acceptance – is moving its world headquarters here from Chicago. That isn’t to say the lift arrangement lacks interest; there are three groups or flights serving the lower, middle and upper floors, and they can be programmed with considerable flexibility within that.

Stirk is keen to point out that the connectivity between here and the adjacent St Helen’s Square (the sunken plaza made with the P&O building and its sister, the taller former Commercial Union tower) is not yet complete, but that “a sense of the space” that will eventually appear can still be had. The north-south route between Leadenhall Street and Undershaft is an addition to the original plan and provides even greater permeability.

“Rather than create a podium, we’ve created a cut,” says Stirk of this space. Required by planners to respect the cornice line of the neighbouring Lutyens facade, something achieved by a projecting canopy at that level that also mitigates downdraft, Stirk was also personally concerned to give something back to the street scene. He therefore sought to bring “a level of depth and complexity” to this part of the building, “a texture rather than an expanse of 200mm glazing wrapped around it.”

Defining a street by a negative, as Stirk puts it, may seem counter-intuitive but it has an obvious and highly successful precedent in the Seagram Building in New York, and the plaza it gifted to that city. Stirk was also emulating buildings in the City of London where voids around their perimeter are as vital as solids, such as Wren’s cathedral, Leadenhall market nearby and of course Lloyd’s of London, fortuitously – and magnificently – framed when ascending or descending the Leadenhall Building’s escalators.

Unsurprisingly, Lloyd’s was also prominent in our discussion about the search for an appropriate overall expression for the new building.

At the heart of that quest, said Stirk, was the difference between a commissioned building like Lloyd’s and a speculative one like the Leadenhall Building. The latter has no ‘branding’ during its life, and must appeal to many possible occupiers over that timespan. Richard Rogers summarised this as Lloyd’s wanting privacy and history, but British Land a public and open face, and volume.

Over 30 to 40 years, what is possible and what is permissible changes. “The technology makes a number of means of expression possible,” begins Stirk. Exposed structural steel, without the need for the stainless steel overcladding necessary at Lloyd’s (necessary, but also welcomed; the budget profile was “completely different” too, adds Stirk) is now perfectly acceptable from a fire safety point of view.

There is, too, “a certain heroic quality” in the newer London buildings to aspire to; a richness, as Rogers puts it, considering that expansive view out of the window. “Out there, there is a pyramid [the Shard], a curved roof [20 Fenchurch Street], a razor [the Strata tower, nicknamed the electric razor].” Engaging with these other towers that have appeared over the intervening years was also crucial; “it was about “trying to relate to those buildings,” says Stirk; “Height, height, height,” asides Rogers.

Inevitably, the question of context – perhaps the most misused and misunderstood term in architectural theory – arose at this point. Stirk described Lloyd’s – very poetically – as “a beautiful, simple diagram of a box that just crumbles down” toward and in deference to its then-neighbours, but in immediately pointing out that the latter have changed, alights on what he sees as the inherent problem; “the context you design for disappears.”

Taking all of these considerations into account, the Leadenhall Building therefore became “an externalised expression of a neutral area.” The coloured toilets (blue for men, red for women) inserted into areas of the north core not occupied by lifts constituted “an architectural language of supergraphics” for that façade, given further expression by the orange and green frames of the glass lift cars and the yellow of their shafts (all three colours, according to Stirk and project architect Andy Young, originating from their love of 1970s Italian sportscars). The diagrid structure of the megaframes and ladder frames – plain to see yet meticulously designed – has its own cadence and feel, and operates above the supergraphics for a layered effect.

Notwithstanding their differences, both Lloyd’s and the Leadenhall Building are part of the same lineage, maintains Stirk. “There is a relationship, just in a different way. It’s a form of thinking, not an aesthetic. That might result in a particular look, but it’s driven by each job.”

The physical process of achieving this was well documented in the recent television documentary Superskycrapers. Around 85% of the building was prefabricated, partly a pragmatic response to a constricted site but primarily, it is clear, a direct result of the evolution of construction technology. No wet trade work was involved above the foundations, all 52 floors erected using only steel and pre-cast reinforced concrete plates. As Stirk said, in response to my question about the extent of pure research at RSHP, much technical

...contd

Leaden 1s

View of The Leadenhall Building from the East along Leadenhall Street
(Richard Bryant, 2014 Courtesy of British Land/Oxford Properties)

Leaden 2s

Detail of K-Bracing at the top of the Leadenhall Building (Richard Bryant, 2014 Courtesy of British Land/Oxford Properties)

Leaden 3s

The northern support core of the Leadenhall Building (Richard Bryant, 2014 Courtesy of British Land/Oxford Properties

Leaden 4 DSC_8138

The eastern portion of the ground floor 'lobby' of the Leadenhall Building, as seen from the second floor reception area. The connection with St Helen's Square has yet to be made. Note the V shapes formed by the columns of the megaframes (Chris Rogers)

Leaden 5 DSC_8064

Lloyd's of London seen from the escalators, with the fifth floor wind canopy of the Leadenhall Building and its megaframes (Chris Rogers)

Leaden 6 DSC_8129

View of and through lift shafts in the Leadenhall Building (Chris Rogers)

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