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Structures Restructured | Reusing and modifying structures

Finsbury tower proposed crop

Modern buildings could last 1,000 years. Understanding how to renew and reinvent them will stretch the skills of engineers, starting now.

If you are looking for an example of long term reuse and renewal, then arguably the Tower of London is an interesting one. Since the White Tower was erected for William the Conquer in 1078, the structure has been expanded and adapted. Over more than a millennium it has been used as a fortress, a palace, a prison, a zoo, a mint, a public records office, a tourist attraction and a concert venue.

In the modern era many of the tall towers in the capital could potentially have as long a life as the Tower itself. Our descendants, barring disaster, could in the year 3018 still be using the Shard, the Gherkin or any of the high rise structures appearing on the skyline not only in London but around the UK and indeed the world.

“In the history of the world there have only been four buildings taller than 150m that have been demolished on purpose,” says consultant WSP director Bill Price.  

The new Tate Modern image (copyright Hayes Davidson and Herzog & de Meuron)

The new Tate Modern image (copyright Hayes Davidson and Herzog & de Meuron)

Tate Modern: Converted power station, now an art museum

“Tall buildings are so strong, so robust and so expensive to bring down, that they are potentially here for 500 or 1,000 years.”

The key to their survival will be adaptability, enabled by engineering skills that allow these structures to be continually reborn to meet the standards and economic needs of many future generations. Why destroy something if it still has value and still has a use?

That approach to building refurbishment has always happened – the Tate Modern art gallery was Bankside Power Station, the Musée d’Orsay art museum in Paris was a railway station. But now it is not structures primarily with historic merit that are being preserved, expanded and given a new use. Everything is worth considering.

“It’s only in the last 40 or 50 years that our first thought has been to pull down redundant or out of date buildings,” says Simon Allford, director of architect Allford Hall Monaghan Morris. “The Georgians hid old Tudor buildings behind new façades for instance. There has always been reuse.

Transforming the essence of a building

“But what we want to do now is reinvention, find the essence of the original, draw it out and transform it so it is better than it was before. And when we look at a new site, we always start with looking at what is there already and what can be achieved with that. If there is a decent frame we are unlikely to want to break it down and release all that embodied energy.”

Price agrees. “The first part of the conversation we have with many clients is:  ‘can you really not keep this building?’” Price says. “There are many blocks from the 1960s to 1980s that are just really poor and there is no viable case for retaining them. But when the structure is good, often reuse and renew can be the best solution in terms of programme, price and planning as well as environmental or carbon issues.”

A062134 site images 160216 n2 screenpresentation[1]

A062134 site images 160216 n2 screenpresentation[1]

South Bank Tower: Extra storeys added

He points to the decision to add 11 new storeys to the South Bank Tower in Central London, rather than demolish and rebuild. This meant the development was ready for the peak of the property cycle.

The idea of adding two storeys to existing structures to get more capacity out of existing building stock is widely accepted politically and within the bounds of what most structures can accept.

Adding extra storeys

“It is often possible to justify the addition of a couple of floors to many office buildings especially from the 1970s and 1980s,” Price says.

“At that time, office-imposed floor loadings tended to be over specified. The issue when weighing up the options for a conversion is whether there are primary structural elements ‘in the way’ – how the building is put together and what are the critical factors that keep it standing up.

“Usually engineers are good at understanding the value equation and helping to achieve cost effective,  sustainable solutions.”

Foundation capacity is critical.

“For an existing building in good condition that has already undergone initial settlement deformation, a 10% increase in foundation loading is usually a reasonable starting point,” says Expedition engineering director Julia Ratcliffe.

Getting more from a structure

“If you have original piling records or can confirm the dimensions of bearing foundations, there is sometimes the opportunity to get a bit more through detailed ground analysis. Also you can take load out of a building by stripping out heavy finishes, partitions or cladding and replacing them with light weight options.”

Most important, she says, is for engineers to be involved in the early discussions for a development, when the commercial decisions are being made.

“Too often we are brought in too late and opportunities are missed. I like getting involved when things are marginal and when people don’t realise the additional capacity and floor area that could be generated through infills or vertical extensions. Clients can be reluctant to invest in design when they are planning, but it can yield a good return.”

Clifton external completed

Clifton external completed

Expedition has added extra storey to this building on London’s Euston Road

Expedition has recently added three floors of grade A office space to an existing seven storey structure built as a warehouse in 1936 on London’s Euston Road.

IStructE transformation

And Ratcliffe herself has turned a rather unprepossessing 1960s building into the striking new headquarters of the Institution of Structural Engineers (IStructE) including a library, lecture theatre and feature glass staircase.

The reinvention of the old 1960s building has not only reinvigorated the structure but has had a positive effect on the client’s membership. “Opting for a full refurbishment for our new HQ has created a  real connection with our membership,” says IStructE chief executive Martin Powell.

“Members can see the engineering in the form of a bridge, feature concrete wall, and the staircase and they can identify with the creativity that has gone into it. It has helped people feel really confident about their profession.”

Good engineering workout

Reviving tired structures can be a good workout for engineering creativity, offering engineers the chance to make a satisfying difference.

“You need to do forensic work to establish the potential of a structure,” Ratcliffe explains. “That allows you to highlight which factors are critical and to look at how they might be developed.

“It’s really interesting and you learn from how historic buildings are constructed. Work in this field demands a different kind of creativity and sometimes a very inventive response is often demanded by the constraints of capacity, dimension and condition.”

Case study 22 Bishopsgate

Ext from bg street 6k option 3

22 Bishopsgate

A building’s fabric is not the only thing that can be reinvigorated

For 22 Bishopsgate in the City of London consultant WSP has used 100% of the foundations and 50% of the basement built for the previous tower on the site – the Pinnacle, construction of which was halted during the banking crisis before it got out of the ground.

This new landmark 22 Bishopsgate tower will be the second tallest in London (278m) after the Shard. It will accommodate around 12,000 people working for up to 100 companies.

The developer’s ambition is to create London’s first “vertical village”, providing a wide range of facilities throughout the building including retail, restaurants, fitness centres, an auditorium and spaces for a variety of leisure and learning activities.

The reuse potential of commercial and public buildings is one strand to the reinvention debate.


Reinventing 28M homes

Another is renewal of Britain’s housing stock, which over the next few years will increasingly need engineering input above the norm to improve energy efficiency.

“Every scenario says that to hit the requirements of the Climate Change Act of an 80% reduction in greenhouse gas emissions by 2050, we have to halve the UK’s energy consumption.

Around 30% of all energy consumed is in people’s homes. And over 80% of the UK housing stock of 28M homes will still be standing in 2050.

“We have 30 years to fix our housing stock and cut its energy use by 50%,” says Arup’s global buildings retrofit leader Chris Jofeh.

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Reinventing homes

Insulating existing homes in the UK is key to meeting energy efficiency targets

To achieve the target “whole house retrofits” will be needed, which will include a blend of a number  of possible measures including:

  • Installing external or internal wall insulation
  • Improving loft  insulation
  • New glazing and draught-proofing
  • Installing new energy-efficient appliances
  • Installing smart energy controls
  • Installing renewable energy technologies, with energy storage

“In the short term, homeowners simply having their boilers serviced every year can reduce their energy consumption. If thermostatic radiator valves are installed and set correctly, more energy can be saved.

“In planning for the large-scale retrofit of homes, the UK should look to Germany, where accredited engineers are required to sign off plans for home upgrades as a prerequisite for very low interest loans from KfW, a government-owned development bank,” says Jofeh.

It all sounds expensive, so how can homeowners be persuaded to pay up? In its report “Towards the delivery of a national residential energy efficiency programme” Arup has recommended that the government funds the upgrades of homes in fuel poverty for reasons of social justice and for more pragmatic ones.

“The UK has about 4M homes in fuel poverty; if they were upgraded over 10 years not only would we end the scandal of people living in freezing conditions during the winter but we would also create the demand at scale that would give industry the confidence to invest, innovate and drive down costs,” Jofeh says.

“The general public would, I hope, see the benefits and choose to invest in low energy retrofits for their own homes.”

“It’s a huge target, but needs to be taken seriously.”

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