Original subtitles

How do you build a museum

that hangs 7,000 feet in the air

half-hidden under the top of a mountain?

You feel like you're flying.

How do you build a station

over live railway tracks

while keeping the trains on time?

You have to deal with electrical power,

and that's very dangerous.

And how do you keep

a 586-foot-tall tower

standing, when you've cut huge bits out of its base?

You have these forces that want to twist and pull

the building apart under its own weight.

Welcome to a world

where anything is possible.

The space where innovation and creativity collide.

Part building, part transformer.

It's incredible.

Where the only limit

is human imagination.

Dr. Mabry: This is mind-blowing

when you think about it.

We're talking about actually living on another planet.

Unpacking the miracles

and mysteries of construction...

This was engineering

on a scale the world had never seen.

...to ask,

How Did They Build That?

Engineers love working on surfaces like this

because they're what is scientifically known

as nice and flat.

But when legendary climber

Reinhold Andreas Messner

recruited architects to design

his sixth and final museum,

he gave them a mountain to climb.

And after they climbed that mountain,

he asked them to stick a museum on top.

Born in Northern Italy in 1944,

Reinhold Messner began climbing as a boy

with his father and younger brother.

My dad had his alpine career before I was born.

He started with his brother, Gunther

to make really great and spectacular routes

in the Alps.

In 1980, Messner completes

the first solo ascent of Mount Everest

without supplementary oxygen.

Six years later, he's the first to conquer

all 14 of the world's highest peaks.

Then in 1995,

he begins a new project.

He decided to build six museums

about different themes

of mountaineering and about the mountains.

By 2011, with five museums dedicated

to mountain culture, sacred myths,

and glacial history built,

his sixth will explore the extreme limits

of the alpine climber.

But first, he needs somewhere to build it.

Messner wanted his final museum

to be extra special.

And he found an extraordinary location

in a perfect place for a climber:

on top of a mountain.

Called Mount Kronplatz

in the Italian Alps,

it's home to a ski resort

looking to attract visitors all year round,

so the museum is a perfect fit.

And it overlooks three mountains

with a deep personal connection

to Messner.

For him, it was really important

that the visitor see some special mountains,

which were really, really important

for the Alpine history.

So these are the Ortler,

the biggest mountain in South Tyrol,

then it's the Peitlerkofel,

which is the mountain where he grew up,

and the Heiligreuzkofel,

where he did the first difficult climbs.

World-class architect Zaha Hadid

is then brought in to bring his vision to life.

Hadid was known as the Queen of the Curve

and that's because she was so inspired by nature,

and it showed up a lot in her buildings.

Zaha Hadid had the idea then

to make three windows,

exactly on these mountains

that my dad, er, wanted to see.

Hadid sees the museum

as a curved, cave-like structure

buried beneath the 7.5-thousand-feet-high peak,

with three viewing windows

overlooking Messner's favourite mountains.

First, the team will need to figure out

how to excavate 140,000 square feet

of frozen soil and rock

and then lay a foundation

using concrete that will set

despite the freezing temperatures.

And all that's before constructing a balcony

out over the 7,000-foot drop.

Next, they'll need to make sure

the museum's walls and roof

are strong enough to carry the weight

of the mountain peak

when it's put back on top.

Then, they'll have to create the complex

and contoured interiors,

designed to look like a weathered rockface.

Finally, the whole thing needs to be buried

20 feet beneath hundreds of tons

of soil and rock,

and all of this is against the clock.

So, no small feat.

How do you build on such a steep slope

without the whole building going down the slope?

In Spring 2013,

the team is ready and waiting to start work

because when the snow thaws

there's only a brief window

to get stuff done.

You have to wait until May to begin.

So the time you can work,

there are only four or five months.

Three weeks after work finally begins,

they reach stable bedrock 33 feet down.

Now, to pour the concrete foundation slab,

which isn't going to be straightforward.

If you were looking

for the perfect construction site,

this is about as far away as you can get from that.

It's up high, it's cold,

it's inaccessible,

it's in the middle of three national parks,

two of which are UNESCO World Heritage Sites.

The only way up by truck, is via a single,

narrow winding gravel road.

It takes you, like, 40 minutes to go up there

and then it goes like, er, zigzagging,

er, because you can't go straight up there

in the mountain.

If the trucks are late

this would be a real problem

because concrete becomes hard in the truck.

Smaller trucks and lighter loads

help speed up the climb to the top

where the foundation's slab is being poured.

But that's only the half of it

because part of the pour

will also create a balcony

straight out over a 7,000-foot-drop.

It relies on a great piece of engineering

called a cantilever, used to dramatic effect

on buildings like New York's Jenga Tower.

A cantilever is a one of the engineers' best tricks

that allows you to fix elements

at one end while the rest floats in mid-air.

When gravity acts on a cantilever,

the top is stretched

while the bottom is compressed,

allowing the structure to resist bending.

So, to build the cantilever platform,

we used two beams on the side,

who was anchored in the walls,

and they are carrying the bottom

of the platform of the balcony.

Before any of this can be built,

the team needs to erect a scaffolding to support it.

Not that easy on a 36-degree slope

at the top of a mountain.

That's how you start. You build the scaffolding,

a working perform.

On top of that working platform,

you build, like, the moulds,

and then, er, put your steel in,

and then you pour your concrete.

And they need a lot of it.

Over 6,000 cubic feet to construct

the foundation and cantilevered balcony.

But in June 2013, it's done.

And work starts

on the two-and-a-half-foot thick walls and roof,

which need to be strong enough

to sit under the mountain peak.

The walls are quick thick

because they have to resist under pressure

of the rock and of the earth.

We did the calculation that we needed a thickness

of 80 centimetres.

The team makes good progress,

then winter arrives,

and temperatures plummet.

Dr. Mabry: You need the right temperature

for concrete pours.

Above 90 degrees

the concrete cures too fast and cracks.

But what's more of a problem here though,

is that below 41 degrees

the concrete freezes before curing.

So they have to create a special mix.

You can put add-ons in the concrete,

in the mixture,

to give them a special property,

like that it kind of, like, hardens

in minus temperature, for example.

The temperature is changing quite fast.

So to be sure

that we don't damage the concrete,

we covered them, for the night, with nylon.

Despite their best efforts,

by mid-November, the sub-zero winter temperatures

become too extreme.

The team has no option

but to down tools and shut the site

for another five months.

It would be spring 2014,

when they turn their attention

to architect Hadid's complicated museum interior.

The interior was also a bit shaped like a--like a cave

which was, like, washed out by water.

To do this kind of shape with in situ concrete

is super costly

because you have to build the mould first.

They enlist a specialist company in Germany,

that creates foam moulds

for shaping concrete panels.

Every panel was a bespoke,

unique panel.

And they need over 200 of them.

Every panel needed its own unique foam mould

cut with a computer-controlled machine,

and some of them were huge.

The largest panel was 26-foot long

and six-foot width,

round about like a two or three-storey,

er, building.

They also need to be super thin.

One of the bigger panels,

put it on a forklift and it--and it cracks.

The team building the Messner Mountain Museum

7,000 feet up in the Italian Alps

are facing a huge problem.

The building's interior should be clad

in hundreds of bespoke curved panels.

But the super thin concrete

has started to crack.

Then the team comes up with a clever idea

to stop them breaking.

The solution was to put a sheet

of aluminium honeycomb in the concrete.

By doing that, it allowed shrinkage and expansion,

but only within the honeycomb structure

and not throughout the entire concrete panel.

As one obstacle is overcome,

the team faces another.

Because there are 214 panels,

each of them unique,

and they have to fit together.

And by that, I mean fit together exactly.

If you work for Zaha,

you know one inch is one inch

and not more and not less.

Pulling it off calls

for a little ingenuity.

They have, er, developed special connectors

that give them the flexibility

to adjust the panels

and the gaps and the height

in a three-dimensional way.

There are no bolts.

No other connections, everything is, er,

completely embedded inside of the panels.

The super smooth curved finish

is then replicated in the floors

using cast-in-place concrete

which is machine-polished.

The building is a continuation

of the landscape.

Hard edges and soft curves,

this is what nature offers you

and we try to reflect it a bit.

Meanwhile, outside,

the team prepares to rebuild

the peak of the mountain,

with the museum buried underneath.

It should feel natural.

It should perceive as a-- as a kind of a cave,

which was there like since thousands of years

or millions of years.

That means carefully replacing

the 140,000 cubic feet of soil and rock

that they previously dug out of the mountain.

First, we did shaping by hand.

We used, er, small stones,

er, we use some green

we found around

so that finally the imagined

was the same as the landscape around.

To finish,

the visible parts of the exterior

are to be clad in perfectly curved

concrete panels, matching the interior.

The challenge for the installation team

is that while the panels are lightweight,

they're still made of concrete

and too heavy to move by hand,

which is why they had to use a crane up there

to lift them into place.

One wrong step,

it's 100 metres down minimum.

So you are dead.

It's a huge moment for the team,

when in August 2014,

the final panel is slotted into position.

At the end we reached exactly

this target we wanted.

The building has become part of the landscape.

On July 24th, 2015,

two years after construction began,

the Messner Mountain Museum Corones,

which means Crown,

is ready to welcome visitors.

When I came here the first time

and saw this entrance,

I thought, "Oh, my goodness,

this is extraordinary."

Accessible directly from the ski slopes,

visitors are drawn into cavern-like interiors

as if they're stepping inside the mountain itself.

The building could be in a James Bond movie

It's a masterpiece.

It's world-class.

Three panoramic viewpoints

frame Messner's favourite peaks,

while the audacious balcony

juts out over a sheer drop.

The terrace is an amazing space

because you feel like you're flying.

One of the last projects architect Zaha Hadid

saw to completion before her death in 2016,

the Messner Mountain Museum

is a triumph of ingenuity and design.

It's a great mixture of modern architecture,

and it's somehow hidden in the mountain.

It's like a cave.

I'm very proud of it,

and sometimes, we can't believe it

that we have realized it.

My father was really happy with this building.

The design is unique.

It's so spectacular.

His legacy is not forgotten.

Everyone has that one project

that matters more to them than any other.

For me, it was, of course, working with Tom Cruise

on Top Gun: Maverick.

What? Yeah. Okay. Yeah, sure.

Erm, for me,

it was working with you guys

on How Did They Build That?

For architect Santiago Calatrava,

it was the Gare de Mons in Belgium.

Santiago Calatrava has spent 50 years

creating ground-breaking structures

around the world.

From the Milwaukee Art Museum,

to the City of Arts & Sciences

in Valencia, Spain,

and the Sundial Bridge at Turtle Bay, California.

Dr. Mabry: Calatrava is more than just an architect.

He's an architect, he's a structural engineer,

he's a painter, he's a sculptor.

And all of his buildings

are the culmination of all this,

which is why they are so dramatic

and futuristic.

But when it comes to changing people's lives,

there are two structures Calatrava believes

make the biggest impact.

In my experience of almost 50 years of work,

there are two big generators of cities.

Ones are bridges,

and the others are railway stations.

In 2016, Calatrava created

what many consider to be one of the world's

most stunning stations,

called Oculus,

on the World Trade Centre site in New York City.

But turn the clock back to 2006,

some three and a half thousand miles away in Europe,

there's another city in need of a new station,

the city of Mons in Belgium.

The existing station that was there,

that was, er, very classical post-war design.

Er, but it was a station

that was on one side

of our tracks and our tracks,

railway tracks, were dividing the city.

As Mons expanded

beyond its historic centre

in the early 2000s, the old station

was no longer fit for purpose,

added to which, the railway tracks

now divided the city's new northern suburbs

from its historic heart.

So, it was sort of a barrier.

How can you cross so many railway tracks?

The only way was through, er, a tunnel,

which was dark, and small,

and not very comfortable.

So, when Mons decides to redefine itself

with a new railway station

that will also reconnect

the two halves of the city,

Calatrava has a radical idea.

You see the Americans, they have an expression

who say, "You was born on the wrong side of the tracks,

you are a poor guy."

And so we say we have to finish with that.

Calatrava's vision

is for a station that also acts as a bridge,

uniting both halves of the city

and regenerating the surrounding neighbourhood

in the process.

Centred around a 550-foot long

Cathedral-like gallery,

with no central columns holding it up,

the bridge-station will span seven railway tracks,

from the south side of Mons to the north side.

First, the engineers must figure out

how to build it without interrupting

hundreds of daily train journeys

and then somehow manoeuvre

the entire 5,700-ton structure

out over live railway tracks.

Next, they'll need to leave spans wide enough

for five covered platforms,

and work out how to bookend the bridge

with two massive staircases,

covered by gravity-defying glass and steel canopies.

Finally, it must not only serve

as one of the region's busiest transport hubs

and a bridge that reunites the two halves of Mons,

but also as a shopping and leisure destination.

Now, they've just got to build it.

Dr. Kwami: Building a bridge is hard enough.

But this is also a station, it's a street,

it's a roof, an entire concourse,

all floating over one of Mons' busiest railroads

which you simply can't switch off.

I saw this project, and I said, "Wow.

That's a big challenge."

Starting with working out what to do

about the 10,000 people

and 190 trains

that use the station every day.

Before they could prepare the site

for the new station,

they had to build a temporary one

out of old freight containers.

It's a very simple solution,

that means within weeks,

they've created a temporary station next door,

allowing the team to move on to the next stage.

Once it was operational,

er, we could, er, demolish

the old station.

But the real challenge

is going to be Calatrava's

incredible bridge structure

that will reconnect both sides of the city.

It's fraught with hurdles:

like how do you build

over seven live railway tracks?

You have to deal

with electrical power,

and that's very dangerous.

In the Belgian City of Mons,

the team is preparing to bring

Calatrava's extraordinary vision

of a bridge and station

that spans seven railway tracks to life.

The question is, how do you build it

when all seven railway lines are running and live?

You need to be able to operate cranes.

You need to be able to move concrete, steel.

And you cannot imagine on such a length

to stop the traffic and to create of it,

er, a building site.

If they can't build out

over the live railway tracks,

they'll need a radical solution,

which is exactly what they come up with.

The plan is to fabricate the component parts

of the bridge off-site,

and assemble them in sections

alongside the tracks.

Then they join them together

and float the whole thing

over to the city's south side.

That though, is a lot easier said than done.

Calatrava's architecture is very precise,

very fine architecture,

but it requires a lot of know-how

to produce those elements,

to assemble them correctly so that the end result

corresponds to what Calatrava has designed.

For the local team,

it's a whole new way of working.

This kind of operation,

for me it was the first time.

It takes around two weeks

for the first 160-foot-long, 1400-ton section

of the bridge to be assembled.

Now, the team will float it out over the tracks

using an engineering technique

called an incremental launch.

It's a system that's been used since the 19th century

to get bridges across tough terrain

like rivers or deep valleys.

You construct the bridge deck

in sections on one side,

pushing it out slowly,

and connecting the other sections

until you reach the other side.

What is less common is using it to build a station.

In June 2016,

the moment of truth arrives

as the team launches the first section.

We build the first portion.

We start to push it.

Gradually, it edges over the tracks

three feet at a time,

using a heavy-duty winch

called a strand jack.

The jacks are hydraulic jacks.

It looks like, er, kind of, a cylinder

through which the strands, er, pass

and connect it to an hydraulic pump.

The force is applied behind.

It's connected to the back of the structure.

So, I would say it's pushing by pulling.

It's maybe, er, a new Belgian compromise.

Nine hours later,

with the first section extended,

the next is added.

We pushed both of them together,

leaving the place free for the third one and so on.

Dr. Kwami: As it moves out over the railroad,

it's held up by temporary support towers

on each of the platforms,

topped with special hinges coated in Teflon,

which allow the enormous sections

to glide easily across the top of them.

Over two years,

the ever-expanding station bridge

inches out over the live railways tracks

in six carefully choreographed phases.

The total weight when all of the elements

were there was, er, 4,500, er, tons.

Completed without a hitch,

anyone would have thought they'd done it before.

No.

For everything, there is a first time,

and, er, even if it is the first time,

you have to do it well.

That though, isn't the end

because the next challenge

is building Calatrava's two statement entrances

at the north and south sides.

Each end is a big canopy

that gives us the feeling of a big space

and a big structure above us.

Weighing 500 tons each,

the canopies consist of an oval-steel frame

that appears to float in mid-air,

and each will require specially shaped steel beams.

So, the team turns to another industry for help.

This big challenge

was first to fabricate

these structures.

We have to use our shipyard.

They have the knowledge about bending

and doing these shapes, er, on the boat.

Even with the specialist ship-building team,

it is still too complicated

to fabricate Calatrava's design

with its unique and complex curves

in a single piece.

Instead, they break them down

into sections, each 13-feet long.

We have to make segments of four metres,

imagine, to make a piece of 12 or 13,

or 14 metres,

but they need to be welded.

To achieve the final position,

we need to do a pre-camber.

Pre-cambering is engineering wizardry.

You work out how much steel will bend

under the finished building

and then bend it the exact amount the other way

to allow for that.

People think steel is completely rigid,

but it will flex.

And so it will actually sag

under its own weight.

So, in Mons, they built in a curve

to compensate for the sag.

To build that pre-camber,

the steel sections are forced

into an exaggerated upward curve

and welded while resting on temporary supports.

When the steel settles down,

it's completely straight,

provided you've compensated the exact right amount.

If the team's calculations

are off by even a fraction,

the massive canopy could permanently warp.

That day, I was, er, quite a bit anxious

to say this will work well or not.

In the city of Mons in Belgium,

construction is underway on Santiago Calatrava's

ambitious new railway station and bridge,

designed to reconnect a city

that's divided by its railway.

After months of meticulous calculations,

the team is about to find out

if they've built enough curve

into the giant entrance canopies

to counteract the steel's natural sag.

We are speaking about 450 tons.

They'll only know when the temporary supports

are fully removed.

As it turns out,

their calculations are spot on.

It was a nice feeling in the end

when I saw that it was free of props

and say, "Yes. Perfect."

Over the next few months,

the glass is added,

and the canopies settle

into their final position,

just as Calatrava wanted.

If ever a designer was going to create

a sense of theatre, it was going be Calatrava.

Those entrances say, "Hello, you have arrived."

In January 2025,

Mons Station welcomes its first passengers.

A bridge, station concourse,

and mall all at the same time,

lifted above the tracks,

and reuniting both halves of the city.

It is a landmark in Belgium

and certainly in Mons.

It's a big challenge,

but when we had the moment

of official opening,

I think it was a great relief,

and, er, I was very happy that we finally did it.

It is, er, something to be proud of, certainly.

Immediately, it wins awards

and is named one of the most beautiful

train stations in the world.

It's marvellous.

The play of the lines,

er, is fantastic.

The big part of it was the light

and how it, like, er,

everything was also, like, symmetrical,

but at the same time very curvy.

There is a dynamic,

and I think it's very good for the city.

It's very beautiful.

More importantly, North and South Mons

are linked for good.

It's much easier for people from Mons.

The new design, er, of the station is for everyone.

This is what the engineering

has finally made possible.

Not just a landmark to admire,

not just a building to use,

but one that makes people feel good.

The station has a capacity to touching people,

not only offering them a service and a comfort,

but also offering them a little bit, er, beauty,

telling them you are an important guy,

offering a spark of dignity.

People, er, thought that Mons,

it's a city of the past.

Now, they think that it's a city of the future.

Vancouver's First Baptist Church

needed major repairs

and didn't have the money to make them.

So, they went looking for answers,

not just spiritual ones, structural ones.

And prayers were answered

in the form of a 57-storey tower

complete with an Olympic-length swimming pool.

It's 2012,

and in downtown Vancouver, Canada,

the First Baptist Church

has had a busy 100 years,

but it's feeling a little outdated.

It was built in 1911,

and it really limited our capacity

to serve our congregation.

It was also built in a seismically active area

at a time when planning legislation

was, how do I put it: limited.

In the early 1900s,

there were no design criteria

for how you design a building

to be resilient under, er, an earthquake.

We can be relatively sure that, you know,

severe damage or potential collapse

would have happened if an earthquake did hit.

Modernizing and protecting the church

are both possible, but neither is cheap.

It would have been around 30 million plus

to do the seismic upgrade.

So, they look to the heavens

for a solution.

In Vancouver, the air above a property

is known as the "air space" parcel,

and whoever owns the plot

legally owns the right to build upwards.

You can sell off the rights to build into that air space.

For the church, it's a blessing.

We were able to leverage the sale

of the air parcel above that

to be able to fund the seismic upgrade.

They sell it to developer, Westbank,

who bring in local architects, Revery,

to upgrade the church

and incorporate it into a new development

built around a butterfly-shaped tower.

From the beginning,

this idea of transformation

was the driver,

and the idea of the butterfly

was really interesting because, er,

the butterfly is about transformation.

Resembling a butterfly's wings,

the tower consists of four cylinders

joined around a single central core.

First, they'll have to dig down

to create a parking garage

and so they can reinforce the church

against seismic activity.

Then the team will have to work out

how the tower can sit alongside the church

without obstructing it.

But that will mean regular columns won't work,

so they'll need to find something

that will both support it

and stop it twisting.

Crosswinds are a problem with towers,

but here, there won't be a traditional damper,

meaning, they'll need something else instead.

Finally, they'll need to create

undulating white cladding

that's light enough to wrap around the exterior

before upgrading the church

and adding a three-storey community hub,

topped with a stunning Olympic-length swimming pool.

It's divinely inspired

and hugely ambitious.

This is the first time

I think something this complex

has been done in this city.

It's March 2018

when construction workers

finally get on site.

And it seems the only way is down,

nine-storeys down.

To fully excavate

and do the foundations of the--of the building,

it took about a year and a half.

Throughout that excavation,

the east shoring wall actually ended up

being right underneath the foundations of the church.

So, at one moment, you almost see

this old stone building just floating in mid-air.

And while they're down there,

they reinforce the church foundation

to make it earthquake-proof.

We carefully worked on the church

and began lowering the foundations of the church

by underpinning

and strategically working through that.

It's not until June 2021

when work finally begins at ground level.

And the team's first challenge

is working out how to scoop big chunks

out of the tower's lower levels

but still keep it standing

if it's hit by an earthquake.

We sculpted the bottom of the tower purposefully

because we want to set back a little bit,

to respect the historic church.

In a conventional tower,

the columns align top to bottom,

allowing the building's forces

to be channelled straight down

into the ground.

Here though, that isn't going to work.

You don't have to be an engineer

to know that if you cut the corners off

the bottom of a building,

it's going to destabilize it.

Where you do need to be an engineer

is working out what to do about it.

The solution for getting these columns that exist

above in the tower to the ground

was to start stepping to avoid it.

But stepping the columns

causes a problem.

These columns want to burst out of the building.

In Vancouver, Canada,

the team building the 57-storey Butterfly Tower

is figuring out how to cut corners

and still keep the building standing.

As the columns come down they change direction,

a change in direction results in an instability

where these columns want to burst out of the building.

To hold the splaying columns in place,

the team looks beneath their feet.

The solution in this instance was using

an extremely high-strength concrete mix

for the floors.

Unfortunately, that wasn't enough

because these loads were so high.

So, the team turns to something

called post-tensioning to reinforce

the super-strong concrete floors.

On these floors where these columns redirect

is embedded steel cables

that are cast within the floors,

and they're stressed to a tension

to oppose that force that's pulling out.

So, imagine this column is falling out.

We pulled a rope cast inside the slab

that's holding that back.

But even with the columns held firm

there's a new problem.

The stepping of these columns

happened radially around the tower.

So, not only do you have this force pushing outwards,

they corkscrew and they twist.

Stopping that happening

is going to take some serious strengthening inside.

Deeper within the building,

we created these, er, sort of, flank walls.

These would create more strength

and stability for the tower

and counteract that tendency

to want to, er, splay and twist.

That means structural steel beam sections

that are embedded in the core,

extra rebar that's threaded

and coupled between levels.

Around 200 tons of steel later,

the tower is stabilized.

And the team turns to the next hurdle,

glazing the huge curving cutouts.

But of course, these aren't any old ordinary curves.

The inside of the cutouts

is called a parabolic curve.

This means it curves in two directions.

From top to bottom

and from left to right.

Imagine the inside of a spoon

but a thousand times bigger.

That is a very difficult shape to glaze.

Curving the glass

to glaze these four massive cutouts

will be immensely complicated

and expensive to pull off.

So the team comes up with a way

of using flat panes of glass instead.

It's essentially, sort of, triangulated,

faceted panels that came in groups of four triangles

that's replicated around the perimeter.

The triangle shape is the only one way

to create this form and shape.

It slopes out, it's very dramatic,

and the slope increases as you go up.

By February 2022,

the building goes above the 12th floor

and the team faces its next obstacle.

Tall buildings are very dominated

by wind forces.

Especially on a coastal town like Vancouver,

you have prevailing westerly winds.

So going into the project,

we knew that we had a problem to solve, erm, with the wind.

Part of the Butterfly's solution

lies in its shape.

Round buildings kind of help us

solve that problem to begin with.

Rounded corners reduce vortexes of wind

moving around the building,

upwards of 20% reductions in, kind of, loads.

That, though, won't be enough.

In most skyscrapers,

engineers deal with the swaying movement

caused by the wind

with counterweights or pendulums.

These are called mass dampers.

They're usually located

in the upper floors of a tower,

where the structural sway is greatest.

But adding one to the Butterfly

would swallow up the luxury penthouse levels.

So, they come up with a surprising alternative.

What they did was split the core of the building in two

to create open breezeways

right through the building,

and this allows air to flow through.

Splitting the building's core in two

helps solve the problem

of where the wind goes,

but it creates another one.

We had two halves of a core,

which is inherently not as stiff

and not as robust as a single core would be.

Which is a big problem

when that building is in the middle

of an active earthquake zone.

So the solution for us was we put something

in the building that I think is unique

and hasn't been done to our knowledge.

In this case, it was a slab

linking the two halves of the core to make it one.

What that does is double the thickness

of the floor joining the two halves of the core.

Your tower slabs are 20 centimetres thick.

We had a slab in between the two halves of the core

that was 40 centimetres thick, so twice the depth.

And that, over the height of 57 levels,

linked the two halves of the core together

so that it behaved as one.

By 2023, Butterfly Tower

is getting close to completion,

and the team turns its attention

to a communal podium

that will interconnect the church

with its new neighbours.

Crowning this three-storey structure

will be an Olympic-length swimming pool,

sitting under an extraordinary roof.

The roof of the pool is one of my favourite structures

I've ever been involved in.

It's actually just one formwork piece

that's connected strategically

and opposed and mirrored

so that when it comes together,

it looks organic and unique,

but all in one singular form

of very simple geometry.

The ribs, though, aren't just a pretty addition.

Essentially, those structural ribs

are performing architectural functions,

they're performing structural functions,

and they're concealing all the services.

And by doing that, achieving that,

we get this purity of form.

We get this lightness, that kind of feeling

of being, you know, in the open air

just like a butterfly, just this sense of freedom.

In early 2025,

the Butterfly emerges.

And the first residents

of the 331 apartments move in.

Cool living and leisure spaces,

coupled with the open air breezeways,

giving a taste of the outside.

Butterfly Tower is one of a kind.

While next door, fully renovated,

reinforced, and restored,

the local community new and old,

is welcomed into a thoroughly modernized church.

Now it's a lot lighter and more airy,

and, er, it's been a beautiful change.

I was actually really shocked

and surprised how beautiful it is.

It feels like a home to me.

It just brings me a lot of joy.

And when you're up close to it,

I really like the celestial arch

which gleams like a jewel on a sunny day.

The Butterfly represents a transformation

for all those involved.

I think some of the things

that we've learned out of this project

has helped us, you know,

be better engineers and designers.

I feel proud to be involved

in this building.

This is a, er, iconic building,

and people will be talking about it

for a long time.

I think the main success

is to bring all these different, er,

programs together.

You feel like you've done something great.

In a world where imagination,

innovation, and creativity

define the spaces that surround us,

How Did They Build That? shows again and again

that humankind will overcome

the seemingly impossible.