By 2050, the world's population is expected to soar to almost 10 billion people...
...and two-thirds of us will live in cities
Space will be at a premium
High-rise offers a solution
But concrete and steel, the materials we currently use to build high...
...have a large carbon footprint
An answer might lie in a natural material we've used for millennia
Our view is that all buildings should be made of timber
We think that we should be looking at concrete and steel...
...like we look at petrol and diesel
I think it's very realistic to think that someone will build a wooden skyscraper...
...in the coming years, there's a lot of potential that's unrealised...
...for using timber at a very large scale
Throughout history, buildings have been made of wood
But it has one major drawback, it acts as kindling
Fire has destroyed large swathes of some of the world's great cities
But by the early twentieth century, the era of modern steelmaking had arrived
Steel was strong, could be moulded into any shape and used to reinforce concrete
It allowed architects to build higher than ever before
So why, after more than a century of concrete and steel...
...are some architects proposing a return to wood?
If concrete were to arrive as a new material on Dragon's Den...
...if you were to pitch it and say, "I've got this brand-new material...
...it's liquid, and you can pour it into any shape and it'll solidify"
That sounds great
But when you say, "We need a whole new fleet of trucks to move it around
And actually, when it solidifies, it's not strong enough
We have to stick this other stuff in it called steel"
I don't think it would be a compelling case
Concrete and steel are costly to produce and heavy to transport
Wood, however, can be grown sustainably and it's lighter than concrete
And crucially, as trees grow...
...they absorb carbon dioxide from the air, locking it into the timber
One study showed that using wood to construct a 125-metre skyscraper...
...could reduce the building's carbon footprint by up to 75%
Regular timber isn't malleable like steel or concrete...
...and isn't strong enough to build high
But engineers have come up with a solution
It's called cross-laminated timber, or CLT for short
It's basically a new material, even though the underlying material...
...is something we've used for millennia
It's cross-laminated so the layers of wood are glued at 90 degrees to each other
That makes for a very, very stable material
CLT is light and it's comparable in strength to concrete and steel
But how does it cope when burnt with a high heat source?
Charred wood is extremely insulating
That's the tree's natural protection against a forest fire
It chars, it loses some of its structural mass, but when you remove the source of flame...
...it extinguishes itself
When steel gets hot, it gets a bit softer
We've actually seen some steel roofs collapse in fires...
...where wooden roofs have not
London architects Waugh Thistleton...
...are already designing buildings with this new kind of timber
There's a CLT building behind, where the timber building sits behind timber clad
And then there's a really simple galvanised steel walkway
Cross laminated timber is a material we work with a lot
Once these panels arrive on site...
...we're building a floor a week, at least
So this is incredibly fast, maybe twice as fast as concrete
Because when you a concrete building - what we call concrete buildings...
...are actually floor slabs and columns
When we build a cross laminated timber building, it's building floor slabs...
...all the external walls, all the internal walls, the lift cores...
...the stairs, the stair cores, everything is made of timber
So these are like honeycomb structures
Andrew and his colleagues designed...
...Britain's first high-rise wooden apartment block...
...and have recently completed the world's largest timber-based building
Behind these bricks is a timber core...
...made from more than 2000 trees, sourced from sustainable forests
And this London practice is not alone in advocating the use of CLT
Ambitious wooden high-rise buildings are also being constructed in Scandinavia...
...central Europe and North America
As yet, nobody has used CLT to build beyond 55 metres
But Michael Ramage's research centre in Cambridge...
...working with another London practice...
...has proposed a concept design of a 300-metre tower, to be built on top...
...of one of London's most iconic concrete structures - the Barbican
The way we've engineered the Oakwood Tower is to look at the global structure
Is it stable, and would it stand up?
We believe the answer is yes
The columns at the base of the Oakwood Tower would be about 2.5 metres square...
...so that's solid timber, made of small elements glued together
I think we'll probably see incremental increases from the current height...
...of about 50 metres, and at some point...
...someone will make a step change, probably to up about 100 metres
Making that jump in height will be a difficult sell
The cost of building wooden skyscrapers is largely unknown...
...but those costs could be reduced...
...by prefabricating large sections of buildings in factories
And city-dwellers will need to be persuaded...
...that CLT does not burn like ordinary wood
As an attractive, natural material, wood is already popular for use in low buildings
If planners approve, it could rise to new heights