Rise of the skyscraper: Why tall buildings must start scaling new heights

28/11/19

High-rise development is going through a turbulent period with big schemes on hold amid planning issues and a changing market.

When Sadiq Khan blocked Norman Foster’s proposed Tulip Tower in July, overturning the City of London’s approval, he made it clear that “the very highest quality of design” would be required to get a skyscraper through planning, even in this heavily built-up part of the Square Mile.

Weeks after the mayor’s landmark decision, the City of London Corporation weighed in on tall-tower design when it released 25 pages of wind-microclimate guidelines that set out a series of steps required to prove proposals would not unduly harm conditions at ground level.
This all came at an already turbulent time for high-rise construction, with combustible materials banned from towers above 18 m tall in the wake of the Grenfell Tower tragedy, and other elements of fire safety coming under intense scrutiny.

Sustainability is another key pressure on the skyline. Across the Atlantic, New York City mayor Bill De Blasio this spring pledged to pass laws banning the construction of heavily glazed glass and steel towers unless developers took stringent measures to reduce carbon emissions in other ways. Experts have called for cities in the UK to follow suit.

Political and economic factors have had an effect on developers’ plans to build high, too. Last year, work on what would be Western Europe’s tallest tower – Spire London in Canary Wharf – was put under review with its Chinese developer citing a residential market that had “changed significantly”.

So is the noose tightening around the long neck of the skyscraper?

Numbers on the rise
Construction Products Association senior economist Rebecca Larkin says the tall building sub-sector is the area of the industry “most exposed to uncertainty”.

“They’re typically either higher-end residential schemes or offices that require a large initial outlay to get started,” she says.
Ms Larkin says that a fall in demand or a rise in supply can hit residential schemes, while the increase in co-working spaces could dampen the appetite to invest in office towers.

"Any building over 100 m tall, we expect that various massing options would be put through a wind tunnel before an architect is even brought on board, to test which scenario is the most beneficial"
Gwyn Richards, City of London Corporation

However, if the future is bleak for skyscrapers, developers haven’t got the memo. According to research by New London Architecture (NLA), 76 buildings of more than 20 storeys are due for completion in the capital this year – up threefold on last year.

The same report found an astonishing pipeline of 541 proposed London towers.

Whatever the pressures are, they are not dissuading firms from trying to build upwards.

NLA chairman Peter Murray says the benefits of high-rise construction are manifold. “It makes better use of land, one of London’s finite resources, with the green belt restricting [development],” he says. “You can build at high density, creating the market for better shops, restaurants and other amenities. New York is buzzy because its density means it can deliver high-quality amenities. In Hong Kong, there are whole shopping concourses just serving the 50-storey blocks above.”

Mr Murray points out that many build-to-rent developers are even putting facilities such as gyms and cafes into the towers they propose, effectively self-generating demand.

Planning attitudes towards skyscrapers have gone full circle at least once since 55 Broadway opened up the sector in the 1920s. The 12-storey, 53m-tall headquarters for London Underground was built using a then-radical steel-frame system imported from the US, the like of which is now commonplace around the world.

With thick load-bearing concrete walls no longer required, super-tall buildings became viable.

“We built quite a few tall buildings in the 1960s and 70s, a lot of them not very nice and pretty unpopular,” Mr Murray says. “The reaction against them meant we hardly built any in London between Tower 42 completing in the City in 1980 and Canary Wharf starting in 1988.”

Back in fashion
The high-rise area in London’s Docklands sprung up as something of a surprise, according to Mr Murray, with light-touch planning rules and business incentives leading to a rush of tall towers amid the economic boom of the time.

“Canary Wharf really started to change attitudes,” he says.

Change was nonetheless slow in coming. Norman Foster proposed a 92-storey skyscraper for the site of the IRA-destroyed Baltic Exchange in the 1990s, but stiff opposition forced the plan to be dropped.

Then, as the new millennium dawned, deputy prime minister John Prescott gave the green light for the Swiss Re building on the same site, and everything changed. Although at 41 floors it measured about half the height of the earlier proposal, the Gherkin, as it is now known due to its tapered, cylindrical shape, has become an icon of the capital and the heart of the Eastern Cluster of skyscrapers that has sprung up around it to dominate the skyline.

Two years later, property tycoon Gerald Ronson won permission for the 42-storey Heron Tower at 110 Bishopsgate, before Irvine Sellar’s Shard was given consent south of the river.

“The Gherkin did more to reinstate the image of the tall building than anything else,” says Mr Murray. “People realised you could build tall, beautiful buildings. The Shard was also popular and the antipathy started to fade away.”

Until recently, perhaps. The horrific sight of the 24-storey residential Grenfell Tower ablaze in west London, in the early hours of 14 June 2017, certainly sobered up planners and developers alike.

The renewed focus on global warming has also caused many to think again about the pros and cons of building tall.

But, back in the City, we are perhaps coming full circle, with the rush of skyscrapers constructed in the past two decades leading to issues that have prompted caution around new developments.

Wind guidelines
In 2013, the controversial Walkie Talkie tower at 20 Fenchurch Street was given a sunshade after reports that reflected heat from its concave upper-floor windows had caused damage at ground level.

Two years later, talk of extreme gusts of wind at the base of the same tower made the news, prompting City of London Corporation chiefs to intervene. New wind-forecasting guidelines were published this year, with skyscrapers now expected to be planned around their impact on pedestrians and cyclists from an early stage.

Gwyn Richards, assistant director at the City of London’s Department of the Built Environment, says the corporation has a “very disciplined approach” to tall-building development.

“In the past, tall buildings were seen as progress – growth – and people accepted the by-products, such as wind and overshadowing, because we were a harder city full of bowler-hatted blokes,” he says.

“People can go to any architect or engineer, but they will get a building that isn’t fit for purpose. It won’t be economically feasible. It will go to planning – people will make money on the planning – but it won’t get built"
Kamran Moazami, WSP

“In the 1960s and 70s, people got out at the train station, went to the office, went to the pub and went home. There was no dwelling on the streets. Now, people are socialising [there], al fresco dining. We are a gentler, more humane city and we have to make sure developments don’t harm the character of the streets.”

As such, a very limited area is proposed for skyscrapers, and a series of requirements has been placed on developments.

“The area we have identified in our plan for tall buildings, you could walk through in 10 minutes,” Mr Richards says.

“Because it’s on a narrow Medieval street pattern, rather than a New York-style grid, some of the tall buildings are in very close proximity to each other. You need to be able to tease them apart aesthetically, give them their own identities, and [mitigate] a complex picture of microclimatic change at ground level.”

A key element of the new wind guidelines is that developers proposing a tower more than double the height of surrounding buildings must carry out both traditional wind-tunnel testing and a modern computational fluid dynamics assessment.

The City has been tough on developers that have failed to take its new guidelines seriously, refusing to progress applications that have not put wind mitigation at the forefront of design.

“Any building over 100 m tall, we expect that various massing options would be put through a wind tunnel before an architect is even brought on board, to test which scenario is the most beneficial,” Mr Richards says.

“We are still working with developers, architects and the wind industry to ensure that is done in that order. Some schemes are coming forward that are not doing that and we keep telling them to step back and start from a sound basis. It is a culture change – it will take time, but it is clearly set out in our guidelines.”

The corporation is trying to be holistic in its approach; research it is undertaking suggests there can be positive benefits to creating a breeze in the right places.

“Initial results suggest it has a cleansing effect,” Mr Richards says. “Where there are high pollution levels on Bishopsgate, wind dilutes or disperses it. Sometimes we need to generate air movement without making things uncomfortable.”

He adds that the City is working to come to a much greater understanding of microclimates.

“We are trying, for the first time internationally, to merge the datasets for wind and sun, creating something called thermal comfort, the real-feel of a public place.”

Guidelines could be produced early next year to bring this variable into the “planning toolkit”. “If there is a high level of thermal comfort [in an area], we have to make sure no development compromises that. If an area has low sunlight, we have to be even stricter on wind levels.”

Lifting the public realm
Rather than being dissuaded by the ever-changing rules of tall-tower construction, developers, as ever, are finding innovative ways of working within them. One recent trend to mitigate fears of a tall tower’s impact on street level is to move public space to the top of a building.

“There are about nine roof gardens [that have been] granted permission recently,” says Mr Richards. “On [architect] Eric Parry’s roof garden at 120 Fenchurch Street, you can have 200 people sitting in T-shirts while down below people are wrapped up to the hilt.”

Kamran Moazami, UK managing director of property and buildings at engineering consultancy WSP, underlines the inevitability of building higher.
“For major cities, you have to have tall buildings, there is no other way,” he says. “It’s stupid not to – land is limited and you need infrastructure.”

But he says that while it is hard to get skyscrapers through planning approval because they catch the attention, lower-rise structures get the go-ahead.

“There are hundreds of 10 to 12-storey buildings that are not good for the city, but they go through because they are not in the public eye,” he says.

Experience is critical in planning, designing and building successful tall towers, Mr Moazami says: “Designing tall buildings is very different to mid-rises. You need to ensure at concept stage that a scheme is economical, can be built quickly and minimises its impact on the environment.
“People can go to any architect or engineer, but they will get a building that isn’t fit for purpose. It won’t be economically feasible. It will go to planning – people will make money on the planning – but it won’t get built.”

Understanding the peculiarities of skyscraper construction is very important, he stresses: “Because a building is tall, you need more vertical transportation, people have to get in and out of it to build it. You need to have the maximum usable area.”

Mistakes magnified
The nature of building in high-density urban areas requires some hard thinking about the logistics of construction. And because of the scale of works, loose planning can be costly.

“Everything has to be optimised,” Mr Moazami says. “On a 10-storey building you do something 10 times then it’s finished. On a 50-storey building you are repeating the process 50 times so if you use a wrong material or sequence, then it really adds up. You magnify the mistake.”
He says his experience has taught him what is possible with tight planning and bespoke design: “Everyone said the Shard was the wrong side of the river, but we made sure everything worked properly. Every building has its own unique architecture, location and occupancy.

“We used a different type of construction for residential on the Shard than on the commercial and retail [parts].

“Timing was an issue on construction so, working with Mace, we came up with a core on a plunge column so we could build from the top as well as the bottom. We studied 20 different cores to come up with the right solution.”

Mr Moazami believes ingenious solutions can win approval regardless of the letter of planning rules. “I believe building officials are trying to protect themselves with rules to cover everything so people without experience don’t do the wrong thing,” he says.

“Our experience is that when you demonstrate your work and expertise – that you have covered everything – the regulation becomes a guideline.”

He encourages contractors to be open-minded and agile to the right way of working on a given site. “Engineer properly and cost will be lower,” he urges.

“Don’t be afraid. Don’t put risk on top of risk on top of risk,” he concludes.

Source: Construction News