Engineers back plans to encourage vertical extensions

Hanif Kara, design director at structural engineers AKT II, backed proposals in the Upward Extensions in London consultation.

He told New Civil Engineer that there were clear reasons to build extra storeys from a development and infrastructure point of view. But he cautioned that increasing the density of communities may raise some cultural issues in forcing people to live closer to each other than they were used to.

“From an engineer’s perspective or from the community of London this is the obvious answer,” said Kara. “And that starts from wanting to make denser populations. The trigger for that is usually infrastructure and infrastructure for existing properties is already there so it’s the easy answer rather than waiting for Crossrail or HS2 before you densify.”

However, he said that developing upwards could help to save time, delivering projects much earlier than if new planning proposals had to be submitted, buildings had to be demolished and construction work was to start from scratch.

Technically, most structural challenges involved with extending buildings in this way can be overcome, said Kara.

Heavy dead loads such as the cladding can be removed and replaced with lighter alternatives; foundations can be usually be strengthened or new ones threaded around the existing structure; and buildings can be adapted to carry any additional sideways wind loads incurred.

However he said that cost and affordability both had large parts to play in the decision to extend upwards.

“Technically most things are possible, but you have to deal with cost,” said Kara. “The barrier seems to be how do you value these kind of things? How do you bring this model into affordability?”

AKT II are currently working on an upward extension of 11 storeys on an existing 26 storey building on the Southbank near Blackfriars bridge in London. Kara said this required a new level of engineering, but that it is now possible to push boundaries that were not possible before.

“We are finding tools and methods that are allowing us to push load paths in slightly different directions,” he said. “We are trying to use old stability systems and combine them with new ones, because the tools to do that are available. You find a lot more capacity than before by reanalysing stuff.”

The project was also delivered four years earlier than getting planning permission to build a new tower, according to Kara. He said that there was a feeling in the UK that contractors were not capable of building high rise buildings - but that this was not true.

“There is a perception that UK builders can’t build towers, but actually projects like this and the shard, it’s unbeatable and something that should be exported,” he said.