Council on Tall Buildings and Urban Habitat
 

 Heron Tower Technical Tour
Conference Technical Tour
June 13, 2013
Simon Lay, AECOM

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LONDON - Heron Tower is a world-class office building at the heart of London’s financial district. Stretching 230 meters into the London skyline, the 46-story building, which was completed in 2011, is the tallest in the City of London. It provides 36 stories of exceptional office space, with bars and restaurants on the ground and uppermost floors.

It's hard not to be impressed by Heron Tower. The £3.5M fish tank features lavish attention to detail, from the imported brilliant white stone and the careful selection of precisely the right thickness and patterned stainless steel cladding. The building stands as a testament to the business environment in 2004, when the scheme was amended to make it taller and more impressive than even the original planning permission the site had achieved.

But in a post-2008 era, does the exquisite building stack up? Will Heron rue the decision to spend money beefing up the structure to add 3 floors of lettable space, rather than making it possible to infill the atria that define the North facade?

Photo of Heron Tower
“The ‘village effect’ will really come to life when you have lettings that span floors,” explains Paul Simovic, director responsible for the project at KPF. However, even without that physical connectivity, the light penetration into the open span office spaces is remarkable, creating a sense of perimeter and tradition that was found in early sky-scrapers in the US, which articulated their facades to bring in light and fresh air.

Sadly, to date, tenants at the tower are not opting to take up the option of fresh air via the mixed-mode design that was incorporated in the scheme. Undeniably, offering tenants the option of a fully-sealed box against natural ventilation in a mixed-mode design was essential in a city where operable windows are far from the norm. However, one can't help feel that in operation, the tower is not fulfilling its maximum sustainable potential.

Like the Leadenhall "Cheesegrater," the Heron tower adopts a side-loaded core design, and it may perhaps initially seem wrong that the core is on the side of the tower that arguably has the best views. But as Simovic explains, views into the high rise cluster are fleeting, and both the Pinnacle and 100 Bishopsgate projects will impact on sight-lines to the south. More important to the scheme was the idea of using the core to shade the southern elevation. This single decision contributed to more than half of the energy savings achieved in the design.

The asymmetrical core introduced specific construction challenges, explained Jonathan Inman of Skanska. Lateral movement during construction as building mass is added plays a significant role in a side-loaded core design, and a 40-story "pre-camber" had to be calculated and incorporated into the construction.

Resolving the construction challenges of a tight, historic site, whilst seeking to shave months off the build schedule helped Skanska win this project, explained Inman. A complex and highly ambitious top-down approach used 3m-wide caissons to enable the piles to be driven through the ground, before the excavation of the soil around the access shafts to create the basement box commenced. This was, quite rightly, recognized with plaudits and awards.

Delegates tour Heron Tower with views of The Gherkin

Overlapping construction elements of the project, which are normally separated, took over 6 months off the schedule. Constructing the superstructure whilst the basement was being dug out, and enabling archaeological investigations whilst demolitions took place were critical to the accelerated schedle. Further time and cost savings came from the adoption of digital design methods and BIM, rationalizing the structural connections so as to reduce their number by a third.

It's questionable whether a building of the same quality as Heron Tower will be built in the foreseeable future in London. The push for smaller floor plates and shareholder revolts at opulent HQ locations will surely shape the next tranche of towers.  It's also not clear whether the construction improvements achieved by Skanska on this scheme will be repeated, as many of the pioneering advances they executed on this scheme have become the new norms.

Perhaps the great leaps forward have been made, and future improvements will be more incremental, unless of course the tenant demand really shifts towards the more utilitarian, clearing the way for the the fully modularized, off site approach emerging from China to find a place in London.

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