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Heron Tower, London, by Kohn Pedersen Fox Associates

Time capsule: Kohn Pedersen Fox Associates’ Heron Tower provides lessons from the past that are relevant to the future, writes Felix Mara. Photography by Hufton + Crow

The Gherkin, the Shard, the Cheese Grater - many of London’s recent skyscraper projects have compact, natty little names which reflect a market for ‘icons’ and ‘brands’.

But not Heron Tower. This spec office building, topped and tailed by restaurant, bar and retail accommodation, belongs to a different era. It was finally completed in March, after complications with the planning system, existing tenancies and funding, but its conceptual design hasn’t changed significantly since 1998.

Meanwhile, a lot of other things have changed. Millennium fever, icon fixation, eco-hysteria and easy access to credit are no longer with us and the partners in US architect KPF’s London office, which designed Heron Tower, have left to set up a new practice, PLP Architecture (AJ 21.07.2009), so you could almost describe it as a posthumous work.

‘The design of Heron Tower wasn’t just about shape-making,’ says PLP partner Fred Pilbrow, who, as a principal at KPF, had a central role in its design. It is a straightforward late Modern building that seeks to reconcile multiple design objectives in its planning, environmental performance, urban design, construction logic and expression. Heron Tower is not a one-liner.

According to KPF partner Paul Simovic, many aspects of its design were intended to be timeless. Its designers looked backwards to tall buildings of the recent past, such as Foster + Partners’ Century Tower in Tokyo and further, to exemplars such as Mies van der Rohe’s Seagram Building, completed in 1958.

‘It was extremely important to me that this building should be as close as possible to perfection in terms of design, finish and sustainability,’ says Heron International chief executive Gerald Ronson. ‘But, above all, it had to be commercial.’ And commercial it is, with a stack of 13 three-storey ‘villages’, which are the optimum size for letting. The large, oblong office floor plates are served by cores that extend to the irregular south boundary of the site and there are few internal columns.

Pilbrow proposed diagonal bracing on the north facade to minimise the three-storey atrias’ perimeter structures and he wanted this bracing to be outside the cladding line. To provide further flexibility, the volume of each village is small enough to form a single fire compartment, so there is more freedom to sub-divide into tenancies of various sizes. Each village has its own plant and can be naturally or artificially ventilated.

This commercial logic gives Heron Tower its raison d’être and it uses architectural quality to increase yield. The atria and low-iron external glazing increase daylight penetration to the deep floor plates. Because there is no central core, it has been possible to provide a grand entrance lobby and you walk towards daylight as you approach the lifts. Despite the building’s long gestation period, its environmental performance is far from anachronistic.

‘The primary energy profile is about cooling,’ says Pilbrow. The extensive floor-to-ceiling glazing, which reduces lighting costs, is either north-facing or part of the ventilated cavity systems on the east and west elevations (see AJ Specification 03.2010). The core on the south side, which reduces solar gain and acts as a thermal shield, has a facade incorporating one of Europe’s largest integrated photovoltaic arrays, although, it has to be said, the square proportions of its cells are rather tedious.

As a late Modern building, Heron Tower has a subtle and mature urban design logic that is integrated with its performance, so it is impossible to say whether it was designed from the inside out or vice versa. ‘Its language aims to express what’s going on’, says Simovic.

Currently the tallest building in City of London, it was subjected to intense scrutiny by the Corporation of London, the GLA, CABE, English Heritage and, because it appears alongside St Paul’s Cathedral when viewed from Westminster Bridge, Wesminster City Council.

One positive outcome of this scrutiny is its public realm space. It is set back from the site boundary, with an arcaded elevation facing Bishopsgate, which has pedestrian flows of 5,000-6,000 people an hour. Traffic in Houndsditch, to the north, has been diverted to Camomile Street to the south, creating pedestrian space where its ground-floor restaurant can spill out. Two glazed lifts provide public access to a rooftop bar, restaurant and terrace.

Despite its size, Heron Tower benefits from a townscape approach to its massing and elevation design. Elevations are inflected and tailored to their context and the diagonal bracing, which follows the three-storey modules, creates visual interest.

‘Towers with central cores are all a bit samey and lend themselves to shape-making design, which is only interesting up to a certain point,’ says Pilbrow. ‘A centre core building would have been higher, because it would try to balance its form.’

Heron Tower’s context was asymmetrical and the plot, surrounding road network, buildings and views, and the sun’s path encouraged KPF to develop an asymmetrical design. But, whereas Pilbrow wanted both the core and the offices to step up to the west, Corporation of London city planning officer Peter Rees urged him to reverse the steps in the offices. This set up a spiral massing at roof level and created more visual interest in the view from Westminster to the west, with Heron Tower stepping upwards towards the peak of the citadel-like cluster of towers to the south. Unfortunately, this arrangement appears less satisfactory when viewed from the east.

There have been compromises. The height of the mast at the top of the slender tower, which marks the intersection of Bishopsgate and the Roman wall, was reduced from 42 to 30 metres to save costs, significantly undermining its sense of acceleration. The diagonal bracing members, a formidable technical problem, are so thick they read as a stainless steel wall that has had holes punched into it. They would look better if they tapered more and were more detached from the facade.

But, considering its cocktail of objectives, the number of people who were involved in the design and consultation process and its protracted timescale, Heron Tower is remarkably consistent. Perhaps as a building designed in a past era, it is easier to understand, because we have the benefit of hindsight.

But it can also be seen as a time capsule, which reminds us where late Modernism was circa 1998, or as a baton to be picked up by architects willing to take up its cause.

Credits

Start on site October 2007
Completion March 2011
Gross internal floor area 66,260m²
Form of contract JCT major works two-stage tender
Total cost n/a
Client Heron International
Architect Kohn Pedersen Fox
Structural engineer Arup
M&E consultant Foreman Roberts
Quantity surveyor Davis Langdon
Planning consultant DP9
Landscape architect Charles Funke
Facade engineer Emmer Pfenninger
Lighting consultant Illuminating Concepts
Transportation consultant Arup
Fire consultant Arup
Project manager Mace
Main contractor Skanska
CDM co-ordinator Arup
Approx. annual CO2 emissions 34.11kg/m
Average U-value for glazing 1.1W/mK
Average U-value for roof 0.25W/mK
Average U-value for basement floor and walls 0.25W/mK
Airtightness @50Pa Better than 10m3/h.m²

Design team credits

‘170 people worked on Heron Tower’, says KPF director Paul Simovic. ‘19 left their mark.’

Core architectural team
Gene Kohn, Chairman
Paul Simovic, Project director
Dennis Hill, Project architect

Laura Piccardi, Claudia Maggi, Leif Lomo, Marcos Blanes, Elzbieta Dabkowska, Ivan Equihua, Takatomo Kashiwabara, Puneet Khanna, Hannah Ko, Raita Nakajjima, Ross Page, Fred Pilbrow, Millie Plinston, Lee Polisano

Additional
Kei-Lu Dinsdale, Keb Garavito, Turgay Hakverdi, Greg Hughes, Matty Jackson, Iaia Loppi, Robert Peebles, Rosa Rius, Marcus Springer, Danielle Tinero, Ian Walker, Dean Weeden

Other
Mustafa Chehabbedine, Yanko Apostolov, Albert Chan, Robert Callahan, Katie Carley, Chris Challoner, Samantha Cooke, Robert Dunbar, Roman Falcon, Mark French, Cristina Garcia, John Gordon, Lars Hesslegren, Nilesh Jadhav, Jim Keen, Paul Knight, Luigi Laria, Pierre Lemaire, Cindy Liu, Josh Ma, Anja Meerhoff, Alan Marten, Neil Merryweather, Ted Neilan, Graham,Newell, Jacovos Pittas, Phillip Richards, Jorge Seabrook, Shibboleth Shecter, Kai Stellar, Simon Stubbs, Eva Tiedemann, Andrew Watts, Richard Woolsgrove, Cass Weaver

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