Nova (1974–…): Season 47, Episode 16 - Saving Notre Dame - full transcript
Engineers race to rebuild the roof of the Notre Dame cathedral and secure the medieval structure within five years.
Notre Dame de Paris...
A treasured icon
of Gothic architecture
and medieval engineering,
built from glass,
stone,
and timber over the course
of two centuries.
For 850 years,
this 226-foot-tall cathedral
has been an enduring symbol
at the heart
of French culture, and more...
Notre Dame is one of
humanity's greatest
artistic and architectural
achievements.
Notre Dame is not just Paris.
It's France.
And beyond France,
it's the world.
But on April 15, 2019,
a disaster that threatens
to destroy it all strikes.
A massive fire
raging out of control...
Oh, my God!
Leaves the cathedral in ruins.
Now, an elite team of engineers,
scientists,
and master craftspeople,
battle to save
this fragile structure
from a catastrophic collapse.
Out of tragedy,
an opportunity is born...
Oh!
This is a dating fossil.
To solve archaeological
mysteries
and understand the very fabric
of this medieval megastructure
like never before.
We can identify
each chemical element.
Can clues from the past
help save and rebuild
this landmark?
And can pioneering technology
prevent another disaster?
What we are producing today
will be the information usable
for the next generations.
"Saving Notre Dame"...
right now, on "NOVA."
Major funding for "NOVA"
is provided by the following:
The Cathedral
of Notre Dame de Paris...
an 850-year-old Gothic wonder.
It's the heart of France.
The distance from Paris
to all other places
is traditionally measured
from this iconic structure.
There is a continuation,
a historical continuation,
from the Middle Ages
to nowadays.
And it's very important
to build a kind of identity.
Notre Dame is one of
the monuments
which achieved this identity.
For Christians, it's a place
of worship, right?
And, and for those of us
with different beliefs,
it's one of just this incredibleartistic
and historic landmark.
You've had coronations there,
you've had the crowning of
Napoleon and King Henry.
There's just so much attached
to the cathedral.
But Notre Dame is much more
than that.
It's also a pinnacle
of medieval engineering.
The cathedral can hold
9,000 worshippers,
and its 100-foot tall walls
contain more than 32,000
square feet of stained glass.
The ceiling is a series
of domed Gothic vaults
that hold up the cathedral
from the inside.
A complex 550-ton web of timber
forms a cross-shaped roof,
topped with 1,300 lead tiles
and a 300-foot tall
central spire.
Wrapped around the church
are 28 flying buttresses,
limestone arches that brace
the walls from the outside.
And at the front,
two mighty towers,
with ten massive bronze bells
inside,
soar over 226 feet into the sky
over Paris.
The construction
took many generations.
Architecture was not learned
at the university,
so the architects and
allworkers learned mostly on site.
Along the way,
there were many setbacks.
In 1789, at the height
of the French Revolution,
anti-Catholic forces
destroy parts of the Cathedral.
A newly secular France
leaves Notre Dame
in a state of neglect.
But when Victor Hugo writes
"The Hunchback of Notre Dame"
in 1831, it sparks a $60 million
restoration,
that tops out the cathedral
with a new roof
and a 750-ton
timber and lead spire.
Periodic renovations continue
to this day.
On April 15, 2019,
Notre Dame is wrapped
in 550 tons of scaffolding,
as workers begin
a $6 million operation
toshore up the cathedral's spire.
Notre Dame's rector,
Father Patrick Chauvet,
has finished evening worship.
His world is about to be
turned upside down.
I stopped here because
I really like Mado.
She offered me a drink, and
when she came back she said,
"Father, there's smoke above
the spire of the cathedral."
So I left my drink and went back
to check there was nobody
in the cathedral.
At 6:18 p.m.,
a sensor detects smoke
in the medieval roof timbers.
The system sends a coded fire
alert to the security team.
Instead of heading
straight for the roof,
a guard is dispatched to the
sacristy building nearby,
to check for a fire.
But he finds nothing.
He climbs up into
the church attic.
But by the time he gets there,
he's too late.
The fire has been burning
for almost 30 minutes
and has spread across the roof.
And there was this horrifyingly
huge plume of smoke billowing up
out of it.
It was surreal.
I'd never seen anything
like that before.
You saw the fire trucks come up
alongside the cathedral
and ladders went up,
and the hoses came out,
you could see that the ladders
were just too small
for a building of this size
and the hoses were not nearly
big enough
for this kind of blaze.
It was tragic; the resources
that were available
were not going to be
what was needed to bring
this thing under control.
A lot of us realized
that this fire was just going
to ravage the cathedral.
We saw what was happening,
but we were powerless,
we could do nothing.
It really looked like
the end of the world.
It was so chaotic.
A delay in responding
to a fire of this nature
is absolutely critical.
A small fire burning locally
is a very different thing
than ten minutes laterwhen
all of the timber elements
are involved.
So in a situation like this,
five, ten, 30 minutes can make
all the difference.
This delay will have huge
repercussions.
As firefighters arrive on scene,
so does one of France's
chief architects
of historic monuments,
Rémi Fromont.
I managed to pass
the police checkpoint
and I joined the firefighters.
As the inferno rages
at the top of the cathedral,
Rémi risks his life
to venture inside
with the firefighters.
We did a tour of the cathedral
several times.
We checked the nave.
I saw the flames
and saw the blaze.
I gave them all the advice
that I could.
Within minutes, the firefighters
are pumping tons of water
into the roof space,
but to no avail.
To the horror
of the growing crowd,
the fire engulfs
the iconic spire.
The world watches helplessly
as the 750 ton oak and lead
masterpiece gives way.
Oh, my God!
Oh, my God...
That is awful.
When the spire
fell into the roof,
additional ventilation
will have caused
more oxygen-rich air
to be sucked in at the bottom
of the compartment.
That influx of oxygen
could have caused an increase
in the severity of the fire
within Notre Dame.
All of a sudden, there was
a huge, huge ball of fire
rising out of the cathedral.
It was spitting ash and
debriseverywhere, so we took shelter.
It was just devastating
to watch.
We were suddenly really aware
that of, of how easily this
whole thing could come down.
90 minutes after the fire
begins,
the entire roof of the cathedral
is ablaze.
Inside, it's become even more
dangerous for Rémi
and the firefighters.
Getting this fire under control
looks impossible.
The fire on the ground,
smoke everywhere,
a hole in the ceiling.
We were trying to understand
what was going on,
where the problems where,
check what had collapsed
and if there were other risks.
A southeasterly wind picks up
and pushes the blaze towards
the famous bell towers.
If the bell towers catch fire,
and the bells fall,
then they will smash through
everything below.
Inside the ingeniously
engineered
13th century north tower
a scaffold of wooden beams
holds eight bells.
The biggest weighing more than
four tons.
If the beams burn through,
they'll spark a fatal
chain reaction,
causing the bells to fall
like wrecking balls,
destroying the tower's
wooden backbone.
If the tower falls, it could
trigger a deadly domino effect
that brings down
the entire cathedral.
To avert this
catastrophic collapse,
the firefighters have no option
but to venture deeper inside.
"No doubt,
we must send
the firefighters in.
The cathedral must be saved."
We headed to the North tower
just when the flames
had reached the belfry.
The firefighters also knew it
well.
We were guiding each other.
To douse the fire on the roof,
firefighters pump water
from the River Seine
and feed it to fire trucks
around the cathedral.
But to stop the towerscollapsing
they must send a team
into the burning structure.
Drop hoses in between the towers
and fight the fire spreading
from the roof.
But the steady wind
doesn't let up.
And despite their efforts, the
timber frame holding the bells
has caught fire and could
trigger the destruction
of the cathedral at any moment.
So the team must drag their
hoses to the top of the tower
and soak the timber frame
to prevent the unthinkable.
Throughout the night,
the fate of Notre Dame
hangs in the balance.
Eventually the firefighters
get the upper hand.
The flames have been beaten back
and only glowing embers
light up the night sky.
Nobody knows
how the fire started.
An investigation begins.
But for now,
the urgent question:
how damaged is the structure
and can it ever be rebuilt?
President Macron pledges
to restore the cathedral
in five years.
Tonight, I tell you
very solemnly,
we will rebuild this cathedral
together.
Meanwhile, the world keeps vigil
for Notre Dame.
Daylight reveals the full extent
of the terrible destruction
wrought by the fire.
The oak roof and spire
are completely destroyed.
Tons of toxic lead
that covered the roof
have been sprayed into the air,
contaminating the site.
Burned roof timbers
cover the vaulting.
Three gaping holes
in the stone vaults
weaken the entire structure.
And the 550 ton scorched carcass
of scaffolding
could collapse at any moment,
something unthinkableto
those tasked with preserving
France's rich cultural heritage.
I'm in front of my cathedral,
which is in this state.
I need to work.
Phillipe Villeneuve is in charge
of historic monuments in France.
This is the cathedral
that inspired him
to become an architect.
I must have been five
or six years old.
My parents brought me here
one day,
like every child from Paris.
I was fascinated
by the architecture.
It stayed with me since.
Since 2013,
Phillipe has been responsible
for conserving Notre Dame.
It was the culmination
of a dream.
A dream come true.
Today that dream has turned into
a nightmare.
The stricken cathedral
is a giant house of cards.
If the stone vaulting collapses
the weight of the buttresseswill
push in the 100-foot walls.
And Notre Dame will be no more.
So Phillipe heads up
a rapid response team...
dozens of engineers,
architects, and scientists.
Their task is to prevent a total
collapse of the cathedral.
From the bottom of my heart,
I want to thank you all for your
dedication, your approach,
your passion.
You are doing a very difficult
job, which is essential
for the cathedral.
It's not only a difficult job,
it's also hazardous.
The crumbling stone vaults
and twisted scaffolding
make any visit
inside to investigate the
stability of the structure
extremely dangerous.
On the vaults we have
the problem of the impact
of the fire, but we will
alsohave to evaluate
the impact of the water used
to put out the fire.
And we can see from here
the inside of...
Go out.
The scaffolding is moving.
Scaffolding!
Motion sensors are installed
in the melted jumble
of scaffolding overhead.
These can be triggered
by gusts of wind...
a warning before a possible
full-scale collapse.
It's the alarm, because the
scaffolding has moved.
We must leave.
There are evacuations like this
each week; necessary,
but an impediment
to the urgent work
of stabilizing the structure.
It's very difficult to juggle
all these issues.
The problem is that we have to
take action very quickly.
But we need to consider
the reality of this building.
It's still in danger
of collapse.
We are still in the
stabilization phase
of the cathedral.
To avert a catastrophic
collapse,
engineers could builda
steel skeleton inside the nave
to brace the walls.
Then, even if the vaulting
caves in,
the walls of Notre Dame
would stay standing.
But it's far too dangerous
for workers to erect steelwork
beneath the compromised
structure.
We cannot go under the vaults
because we don't know
whether they'll fall or not.
So, instead of bracing the walls
from the inside,
the team will build timber
frames
under the buttresses outside.
Now, if the vaulting does fall
in, the buttresses can't push
on the walls, and they won't
come tumbling down.
They are very difficult because
no flying buttress is identical
to another.
They are made to measure.
Workers at this factory race
to cut
and assemble around 250 tons
of timber
to create the massive supports
Philippe's team needs
to prop up the vaults.
It's critical each support fits
perfectly
beneath each flying buttress
to hold its weight.
Working around and inside
this space
is a logistical nightmare.
210 tons of lead cladding
covered the cathedral roof.
This was mostly melted during
the fire,
and now toxic lead dust covers
every surface.
The worksite is highly
contaminated.
Until the site is cleaned,
team members must wear full
protective clothing
to pass into
the contaminated zone.
When leaving site,
they undress,
discard all clothing,
carefully wash equipment,
then shower themselves.
Only then can they go back
to the clean area
even for a lunch break.
It's very difficult to endure
for the workers
who have had to deal with these
procedures for months.
These regulations
are not normal.
But this whole site
is not normal.
But, finally, five months later,
all 28 flying buttresses
are locked in place
and the walls are safe.
Now they can turn
to the next challenge...
secure the melted mass of
scaffolding
that hangs precariously
over the cathedral.
The scaffold weighs more
than a jumbo jet,
and only rests on
four spindly legs.
The team plans to wrap three
massive steel lattice beams
around it to tie the fragile
upper parts together.
Then they'll build more
scaffolding either side
and lay steel beams across it.
That way workers can get inside
the stricken scaffolding
to help cut off its
50,000 steel poles,
a truly Herculean task.
Only then can the team put up
a temporary roof
to protect them from the
elements
while they rebuild Notre Dame.
It's going to be an extremely
dangerous operation.
The spire has disappeared,
but the scaffolding is still
there.
It moves a bit,
but it's still there.
While engineers gear up
to remove the scaffolding,
architect Rémi Fromont
and Livio De Luca
begin a groundbreaking project
that will combine
the investigative work
with new scientific analysis.
Their ambition is to create
adata-rich model of Notre Dame...
a digital twin.
The digital twin will embed not
only the geometric structure,
or the visual appearance
of the cathedral,
but also all the scientific data
coming from the studies.
For example, you can click
on a stone in the vault
and access to all
the information
about its physical properties
such as the provenance,
but also the mechanical behavior
within the entire structure.
Luckily for Livio,
a series of highly detailed
laser scans of the cathedralhave
been conducted since 2006.
These are brought together in
this priceless 3D dynamic map
to show every stone, timber,
and iron nail in the structure,
across time, from the12th
century to the present day.
This is an unprecedented
project.
The ambition is to collect all
the information from the past,
to pass it to the future.
There's very little first-hand
information
about the construction
of Notre Dame,
or the craftspeople
who built it.
In the wake of the fire,
new studies of the cathedral's
materials
could unlock these secrets.
This new data, once included in
the digital twin,
will provide a blueprint for
the restoration and rebuild.
Inside Notre Dame,
scientists begin to gather data
and investigate the damage
to treasured statues,
murals,
and windows.
The cathedral's most fragile
wonder, its stained glass,
dates back to the 13th century.
36 windows circled the
lower level,
42 around the middle level,
and 43 around the upper level.
The three famous Rose windows
span up to 42 feet in diameter
and are made up of over
1,100 panels
of beautiful stained glass.
Miraculously,
they survive the fire intact.
But the intense heat that melted
the cathedral's
lead-covered roof
means that much of the glasswork
is now covered in a layer
of toxic lead powder.
Removing it could damage
the delicate glass
and be harmful to restorers.
It was really painful to see
the catastrophe on the TV.
I was looking to see what's
happen around the windows
and it was, of course,
totally difficult
to have a good idea
of what's happened.
There is a before and after
15 April,
for historical monuments,
that's for sure.
Glass scientist Claudine Loisel
uses a handheld digital
microscope
to investigate the levels
of lead powder
on the stained glass.
She must then formulate
a strategy
to clean every single panel;a
vast decontamination program.
This window is in the back
of the cathedral,
in the lower level,
furthest from the inferno.
But it's still badly
contaminated.
Fortunately, these windows
havenot been cleaned for 100 years,
so the lead has settled on top
of a dust layer,
not on the glass itself.
The first thick layer of deposit
was, we can say
has a small protection
in one way.
So we have just to remove all
the deposit,
to clean these windows
from the 19th century.
Claudine examines deposits from
windows around the cathedral.
The samples reveal vital clues
about the spread of the
lead contamination.
After the spire fell,
the cloud of dust, lead,
and different particle,
push in the other direction,
so we are a little bit more
protected in this area.
The windows of the upper level,
in the path of the lead cloud,
have been most contaminated.
The team takes out and
transports these panels
to this special laboratory
where they experiment with ways
to remove the lead.
First, Claudine uses a precision
vacuum cleaner
to remove the hundred years
of dust
and most of the lead powder
along with it.
So this is a good way to protect
the conservator.
You can control the action,
the pressure on the glass
and also on the painting.
Then she uses water
and cotton balls
to remove the last of the lead.
Of course,
you need scientific evidence
that it's working.
Claudine uses x-ray spectroscopy
to determine exactly how many
wipes it takes
to bring the lead down
to normal levels.
So we can identify each
chemicalelement we have in the material.
Too few wipes
and the lead will remain.
Too many wipes and restorationwill
take longer than necessary.
Okay,
now the analysis is finished.
After five wipes,
Claudine checks to see
if the glass is decontaminated.
Okay, we have different chemical
element... calcium, iron,
and if we want to see
the lead...
there is no lead!
After nine months we can see
a good solution, a good way
to clean and to preserve
the stained glass windows
from Notre Dame.
The upper level windows
were not only in the path
of the lead cloud,
but also closest to the inferno.
Claudine hunts
for hairline cracks
caused by thermal shock,
the rapid heating and cooling
of the glass.
These cracks is due to the fire.
This is a recent cracks
and this is typical
thermal shock.
It looks like the upper level
stained glass
will need to be painstakingly
glued back together.
But inside Notre Dame,
the lower level stained glass
appears
to have survived unscathed.
And here we can see we have
a good stability,
adherence of the painting,
so there is absolutely no
thermal shock,
that's good news for us.
On site,
the teams of scientists
meet the engineers and
architects
to share their findings.
Once Claudine's team
hasrestored Notre Dame's glasswork
to its former glory,
they may use
a radical new preservation
technique
to safeguard it for future
generations.
It's being used on a huge scale
here, in northern England.
This is York Minster,
an 800-year-old Gothic
masterpiece
and home to the largest expanse
of medieval stained glass
in the U.K.,
the Great East Window.
It is one of the largest windows
ever made
anywhere in the medieval world.
We've got glass from the
12th right through
to the 18th century in quite
significant quantities.
And it is really our nationaltreasure
house of stained glass.
Engineers here are completing
a $12 million project
to protect York Minster's
stained glass
from harmful UV rays and the
corrosive effects of moisture.
In modern stained-glass
conservation,
we're really doing as much as we
can to keep
both surfaces of the historic
stained glass dry and stable,
and that's where our ventilated,
environmental protective
glazing comes into play.
You can see that I'm almost in.
I think it's just
this last bit here.
Matt Nickels is installing
this new conservation system.
He slots a protective clear
glass exterior frame
into the window opening.
This goes into the original
glazing groove,
where the medieval glass would
have been.
This protective
glazingprevents corrosive condensation
from forming on the 800-year-old
stained glass
that will sit behind it.
The gap created means that
there's air circulation running
through.
And when you've got air
circulation,
it's regulating the temperature,
which means that there's less
moisture on the glass.
Each frame is custom made
and takes great skill to fit.
You don't want to make it
too small
because it's going to obviously
slide through.
No two windows
are gonna be the same.
With the outer panel installed,
they can reinstate the layer
of medieval glass.
They're actually in fairly good
condition
considering that they're early
13th century.
There's always the worry
whenever
you're handling glass like this,
but you just got to make sure
that you're really,
really careful.
There's nothing quite like
seeing it with sunlight
behind it.
When you put it up like this,
it's quite magical, isn't it?
Techniques like this
offer a glimpse of how
scientists like Claudine
may eventually preserve
Notre Dame's glass.
This is the best way to protect
stained glass windows,
so it will be for sure an option
to protect the windows for
Notre Dame.
Had the vaulting collapsed
next to the windows,
the glass could have been
badly damaged.
But luckily, the stone vaulting,
which sits just under the timber
and lead roof,
protected the windows
from the inferno above.
When the architects of the
Middle Ages
constructed this vaulting,
they used it to separate the
timber frame of the roof
from the rest of the cathedral.
So the vaulting took the shock
of the falling timber
and the fire
and the firefighters' water.
The magnificent vaulting was
built to be resilient,
thanks to precise medieval
craftsmanship,
using over a thousand cubic
yards of limestone.
The arches work together
to support the roof
and stabilize the outer walls.
But the intense heat
from the fire
and the collapsing spire
took out 15% of
the stone vaulting.
Today, three 40-foot-wide holes
and several smaller gaps
mean the vaults could collapse
at any moment.
The team collects, storesand
catalogues the fallen stone
in this tent, located
alongside the cathedral.
They may be able to use
some of this stone
to reconstruct the vaults.
But it's clear they'll also need
to source new stone.
Notre Dame is made up of many
different types of limestone.
Medieval masons chose hard
limestone for the towers,
pillars, and outer walls
tobuild tall and hold up the roof.
For the sculptures, they chose
dense, fine-grained limestone,
that can be carved with
great detail.
And for the vaults they selected
softer, more porous limestone
that's light but strong.
If the team rebuilding
the vaults
pick a limestone
that is too heavy,
the new vaults may not last as
long as they should.
Geologist Lise Leroux
investigates what quarry this
stone came from.
We have some blocks coming from
the collapse of the vault
for study.
This detective work will help
the team source
replacement stone that
sharesidentical mechanical properties.
We have to verify.
The fallen vaulting stone
contains a rare micro-fossil
called orbitolites complanatus,
a kind of plankton.
Fossils like this are found in
just one layer of rock.
This will make sourcing
new stone
of the same type even trickier.
Can they use this geological
fingerprint
to discover the original source
of the vaulting stone?
To find out, Lise and fellow
Notre Dame scientist
Claudine Loisel venture deep
beneath Paris.
Hidden under the city streets is
a rich source of limestone,
a vast labyrinth of
quarry tunnels.
Lise and Claudine
enter this maze
two miles south of Notre Dame in
the famous Catacombs.
Oh!
In the late 18th century,
the quarries were given a
different purpose
and they housed bones from
old cemeteries,
which were inside the towns.
Cemeteries which were closed at
the end of the 18th century
for sanitary reasons.
Among the bones,
Lise and Claudine find traces
left by the medieval miners.
Here, the block's been removed
and we're left with this trace.
They then square off the sides,
and use it to build Notre Dame.
And the strata height here,
itdictates the height of the block
that can be extracted.
The blocks we see at Notre Dame
have this height.
So the quarry itself puts
a constraint
on the construction
of Notre Dame.
We have life and we have death.
Well, yes.
The upper level of the quarry
holds hard limestone with
large, well-preserved fossils.
These fossils are
more characteristic of
the limestones
used for the pillars,
the arch in Notre Dame.
But not for the vault.
Lise and Claudine hope to find
a match for
the soft vaulting stone
in the lower level
of the quarry.
Now to look if we can find
the specific micro-fossils.
I'm not sure, because
the surface is very rough
and it's not so clear because
ofall of the state of the surface.
The limestone here is softer,
but Lise cannot see a match
for the rare micro-fossil
found in the Notre Dame
vaulting sample.
So, back in the lab,
she takes a closer look
at a sample of limestone
from the lower level
of the quarry.
These little fossils...
this one, this one,
this one...
are, in fact
some planktonic fossils,
which are called foraminifera.
It's not the fossil signature
she's looking for.
But then...
Oh!
This one here
is orbitolites complanatus.
This little planktonic fossil
is a dating fossil,
which match with the stone
coming from the vault.
It's a stratigraphic indicator,
characteristic from
the Middle Lutetian,
which is a geological
age of deposit.
Lise confirms the origin of
the Notre Dame vaulting stone.
It's quarried
from the deepest seams
of limestone beneath Paris.
Conclusive.
But what about the harder
limestone,
used by medieval masons to build
Notre Dame'sload-bearing
pillars and arches?
Another micro fossil signature
confirms the origin
of this type as well.
The arches are built
with a hard stone...
with a resistant stone,
to support the vault.
And the vault itself
is logically constructed
with a lighter,
more porous stone.
And in the quarry located
in Paris,
we have this two kind of stone.
Medieval masons knew exactly
how to exploit
the varying
mechanical properties
of the limestone for Notre Dame;
knowledge passed down
through the generations.
Sourcing more of the
correct stone won't be easy...
the old quarries
are no longer active.
But engineers now know
what limestone to look for...
this will help them find a match
in quarries outside Paris.
Stone is not
the only raw material
that will need to be replaced
as engineers reconstruct
Notre Dame.
The timber roof
was also a medieval wonder.
It was constructed from
25,000 cubic feet of timber,
cut from 52 acres of oak...
that's approximately
1,300 trees.
For this reason,
it was known as "the forest."
Every single oak
in Notre Dame's forest
was handpicked for
the physical properties needed
in the roof structure...
from dense straight oak
for pillars,
to curved oak
for support arches.
But the fire burned
every beam in the forest.
Today, this intricate 550-ton
timber jigsaw lies in ruins.
We thought this sublime roof
would be here forever.
It was a big puzzle with beams
from different periods,
all the way back
to the 13th century.
And to see it suddenly
all burned, all mixed up...
Oh, it's very emotional.
It's very difficult.
Almost 60 tons of the
precious roof timber
still lie precariously
on top of the vaults.
Despite the destruction,
every single beam holds
the history of Notre Dame.
It has deep
archaeological value.
It's vital that workers
forensically record
the position
where each beam fell,
before they remove them.
This helps them determine
where it originally sat in
the roof structure.
Now, these highly trained
rope access technicians
gear up to catalogue and clear
the charred timber
on the vaults.
It's not possible
to walk on the vaults,
because the structure
is very precarious.
They needed to
create a way
to access with ropes.
We need to wear a special mask
because of the lead dust
that we might inhale.
We label the timbers
and we mark them with a code
that the architects will
be able to identify.
The team has their work
cut out...
there are thousands
of separate pieces
of timber to catalog.
We are working day and night.
We have a lot of work to do.
They've already extracted
around 4,000 pieces.
Timber scientist
Catherine Lavier
begins painstaking
detective work to reveal
how Notre Dame's vast forest
was originally assembled
and could be rebuilt today.
Some pieces were
very well-preserved
because as you see here,
with different faces
and another piece of wood is
coming here,
with a wooden joint
here to assemble them.
And it's rather typical
from the medieval period.
And here,
you have a mark,
of carpenters.
So they are sure that this piece
with this piece are together.
It's very important
for carpenters.
They prepare
the wood on the ground
and after that,
they go to the roof
and reassemble again.
Every carpenter
has his own way to mark,
but in general it's based on
the Roman numbers,
but we can find some differences
between teams of carpenters.
We were very surprised
to find that
because I thought
everything will be destroyed.
And, finally, not.
The tree rings of the timbers
conceal further clues.
Each ring represents
one year of growth;
a time capsule of information
about the life of
the tree in that year.
Catherine analyzes core
samplesfrom Notre Dame's roof trusses.
She measures each ring
to reveal the secret story
of some of
the original oak trees
the structure was made from.
This screen shows the size
of each ring I measured.
At the start of its life,
you see it has
very, very large rings,
which correspond
to very rapid growth.
Next, it looks like it
experienced
some more dramatic events,
some difficult years,
here, when the rings
are very thin,
This could be because of
too much rain,
not enough sun,
and not enough nutrients.
And then,
the life of the tree continues
until it's cut down,
around its 96th year.
Catherine is gaining new insight
into the types of trees
best suited to rebuild
the complex forest
of Notre Dame.
This extraordinary challenge
will require
around 1,300 oak trees,
craftspeople versed
in the lost art
of medieval carpentry practices,
and a blueprint for possibly
the most geometrically complex
timber structures in Europe.
The one person who can unlock
the lost forest's
geometrical secrets
is architect Rémi Fromont.
In 2014,
Rémi spent the entire year
mapping every inch
of the timber.
It was a magical place
to go in there;
there was a smell.
There was a very special
atmosphere of light.
We still had the traces of tools
also on the woods.
It sometimes seemed like
they only left yesterday.
We are collecting photographs,
3D point clouds,
and the physical
and chemical characterization
of all the materials.
The fire at Notre Dame
triggers a race across France
to 3D scan historical monuments,
inside and out.
These represent
a digital insurance policy
to preserve French heritage.
The laser bounces off
each contour in the room.
The machine then measures
the time it takes
for the laser to return.
Millions of measurements
form a cloud of data
called a "point cloud."
In 2016, researchers used
this same technology
to create a full point cloud
of Notre Dame's
lost timber roof structure.
This remarkable 3D scan
willcombine with Rémi's 2014 survey,
in Livio's digital twin
for Notre Dame.
What we are producing today
will be probably
the information useful
for the next generations.
The team now has
the data they need
to rebuild the timber roof
with the exact same geometry.
The new oak needed
could come from
forests like this.
Almost a third of France
is covered with forest.
Oak is a vital
strategic resource
throughout theMiddle
Ages and the Renaissance.
Vast forests are needed
tobuild cities and expand navies.
This is the Château de
Beaumesnil in Normandy.
It's a
National Historic Monument,
built on the site of
an 1,100-year-old castle.
It was built in seven years.
It's something extraordinary
for just seven years' work.
The château has seen
better days.
The curved beams
that hold up the roof
are close to collapse
and must be replaced.
The wood grain has been
cut through.
This weakens the support beam.
And then you see that the beam
is completely eaten away.
The wood is degraded,
eaten by the fungus.
The restoration work here
requires much of
the same skill and knowledge
it will take to rebuild
Notre Dame's lost forest.
The timber has been chosen
so the curve of the grain
perfectly matches
the curve of the new beam.
If you get a straight tree,
which has a straight grain,
and...
if you cut a curved piece,
piece of wood inside of this,
so here is the fiber,
so it can break, right there.
But if you take
the tree that's curved,
the fiber is like this.
So it cannot break.
You keep all of thestructural
strength of the tree.
The carpenters use
an original beam as a template
to mark out the new beam
on the oak.
The carpenters who built
Notre Dame
would be familiar with
the tools this team uses
to hew the raw timber.
So after you split
most of the wood,
you use a broad-axe.
They have a single bevel,
long cutting edge,
and the handle is offset.
So...
if you're working,
as you go down, your hand here,
you see I'm not
hitting this sharp edge.
For skilled carpenters,
cutting Notre Dame's
roof timbers with axes,
compared to a modern sawmill,
will take roughly
twice the time;
possibly too long.
This curved oak will be
one of ten the team
needs to install
as part of
the château roof restoration.
It sits alongside this
400-year-old original beam.
This one was cut
probably 1635, '37,
and then this one 2020.
I hope our ancestors are
happy with this.
Just like the Notre Dame beams,
the Château's
original beam holds
messages from
the old carpenters.
It's extraordinary to find
all these marks.
It's very old
and at the same time,
it looks like
it was done yesterday.
French craftspeople
have the oak,
they have the skills, and
they have the plans required
to reconstruct Notre Dame's
vast forest of roof timbers.
It's over a year since the fire
ravaged Notre Dame cathedral,
and the investigators
have not pinpointed
the cause of the blaze.
Immense challenges and
uncertainties still lie ahead.
The building
is not yet out of danger.
Over the next 12 months,
engineers must remove
the melted scaffolding
and seal the cathedral roof
to make it watertight,
then stabilize
the weakened vaulting.
It's a monumental task.
And rebuilding
the entire cathedral
could take much longer than
the five years decreed by
President Macron.
Faced with such a drama,
thankfully there's hope.
We need faith for this project.
It's this building itself
that generates this faith...
even for atheists...
And that's something magical.
Architects around the world
have unleashed
their imaginations
to submit grand plans for what
the new spire above Notre Dame
could look like...
from mirrored roofs
with kaleidoscopic pinnacles,
and vast solar panels
powering nearby buildings,
to stained glass edifices
thatwill light up the Paris skyline.
However Notre Dame is rebuilt,
the unique collaboration
of architects and scientists
is rewriting how we understand
the very fabric of
this magnificent cathedral.
I think the fire in some ways
helped remind a lot of people
what an important part
of our sort of shared history
and shared culture this is.
Soon, a complete digital twin
of Notre Dame
should allow future generations
of craftspeople
to maintain, protect, and
faithfully rebuild Notre Dame,
preserving this world treasure
for all time.
I have only one obsession...
save the cathedral,
resurrect it,
and reopen it to the public.
To order this program on DVD,
visit ShopPBS
or call 1-800-PLAY-PBS.
Episodes of "NOVA" are available
with Passport.
"NOVA" is also available
on Amazon Prime Video.
A treasured icon
of Gothic architecture
and medieval engineering,
built from glass,
stone,
and timber over the course
of two centuries.
For 850 years,
this 226-foot-tall cathedral
has been an enduring symbol
at the heart
of French culture, and more...
Notre Dame is one of
humanity's greatest
artistic and architectural
achievements.
Notre Dame is not just Paris.
It's France.
And beyond France,
it's the world.
But on April 15, 2019,
a disaster that threatens
to destroy it all strikes.
A massive fire
raging out of control...
Oh, my God!
Leaves the cathedral in ruins.
Now, an elite team of engineers,
scientists,
and master craftspeople,
battle to save
this fragile structure
from a catastrophic collapse.
Out of tragedy,
an opportunity is born...
Oh!
This is a dating fossil.
To solve archaeological
mysteries
and understand the very fabric
of this medieval megastructure
like never before.
We can identify
each chemical element.
Can clues from the past
help save and rebuild
this landmark?
And can pioneering technology
prevent another disaster?
What we are producing today
will be the information usable
for the next generations.
"Saving Notre Dame"...
right now, on "NOVA."
Major funding for "NOVA"
is provided by the following:
The Cathedral
of Notre Dame de Paris...
an 850-year-old Gothic wonder.
It's the heart of France.
The distance from Paris
to all other places
is traditionally measured
from this iconic structure.
There is a continuation,
a historical continuation,
from the Middle Ages
to nowadays.
And it's very important
to build a kind of identity.
Notre Dame is one of
the monuments
which achieved this identity.
For Christians, it's a place
of worship, right?
And, and for those of us
with different beliefs,
it's one of just this incredibleartistic
and historic landmark.
You've had coronations there,
you've had the crowning of
Napoleon and King Henry.
There's just so much attached
to the cathedral.
But Notre Dame is much more
than that.
It's also a pinnacle
of medieval engineering.
The cathedral can hold
9,000 worshippers,
and its 100-foot tall walls
contain more than 32,000
square feet of stained glass.
The ceiling is a series
of domed Gothic vaults
that hold up the cathedral
from the inside.
A complex 550-ton web of timber
forms a cross-shaped roof,
topped with 1,300 lead tiles
and a 300-foot tall
central spire.
Wrapped around the church
are 28 flying buttresses,
limestone arches that brace
the walls from the outside.
And at the front,
two mighty towers,
with ten massive bronze bells
inside,
soar over 226 feet into the sky
over Paris.
The construction
took many generations.
Architecture was not learned
at the university,
so the architects and
allworkers learned mostly on site.
Along the way,
there were many setbacks.
In 1789, at the height
of the French Revolution,
anti-Catholic forces
destroy parts of the Cathedral.
A newly secular France
leaves Notre Dame
in a state of neglect.
But when Victor Hugo writes
"The Hunchback of Notre Dame"
in 1831, it sparks a $60 million
restoration,
that tops out the cathedral
with a new roof
and a 750-ton
timber and lead spire.
Periodic renovations continue
to this day.
On April 15, 2019,
Notre Dame is wrapped
in 550 tons of scaffolding,
as workers begin
a $6 million operation
toshore up the cathedral's spire.
Notre Dame's rector,
Father Patrick Chauvet,
has finished evening worship.
His world is about to be
turned upside down.
I stopped here because
I really like Mado.
She offered me a drink, and
when she came back she said,
"Father, there's smoke above
the spire of the cathedral."
So I left my drink and went back
to check there was nobody
in the cathedral.
At 6:18 p.m.,
a sensor detects smoke
in the medieval roof timbers.
The system sends a coded fire
alert to the security team.
Instead of heading
straight for the roof,
a guard is dispatched to the
sacristy building nearby,
to check for a fire.
But he finds nothing.
He climbs up into
the church attic.
But by the time he gets there,
he's too late.
The fire has been burning
for almost 30 minutes
and has spread across the roof.
And there was this horrifyingly
huge plume of smoke billowing up
out of it.
It was surreal.
I'd never seen anything
like that before.
You saw the fire trucks come up
alongside the cathedral
and ladders went up,
and the hoses came out,
you could see that the ladders
were just too small
for a building of this size
and the hoses were not nearly
big enough
for this kind of blaze.
It was tragic; the resources
that were available
were not going to be
what was needed to bring
this thing under control.
A lot of us realized
that this fire was just going
to ravage the cathedral.
We saw what was happening,
but we were powerless,
we could do nothing.
It really looked like
the end of the world.
It was so chaotic.
A delay in responding
to a fire of this nature
is absolutely critical.
A small fire burning locally
is a very different thing
than ten minutes laterwhen
all of the timber elements
are involved.
So in a situation like this,
five, ten, 30 minutes can make
all the difference.
This delay will have huge
repercussions.
As firefighters arrive on scene,
so does one of France's
chief architects
of historic monuments,
Rémi Fromont.
I managed to pass
the police checkpoint
and I joined the firefighters.
As the inferno rages
at the top of the cathedral,
Rémi risks his life
to venture inside
with the firefighters.
We did a tour of the cathedral
several times.
We checked the nave.
I saw the flames
and saw the blaze.
I gave them all the advice
that I could.
Within minutes, the firefighters
are pumping tons of water
into the roof space,
but to no avail.
To the horror
of the growing crowd,
the fire engulfs
the iconic spire.
The world watches helplessly
as the 750 ton oak and lead
masterpiece gives way.
Oh, my God!
Oh, my God...
That is awful.
When the spire
fell into the roof,
additional ventilation
will have caused
more oxygen-rich air
to be sucked in at the bottom
of the compartment.
That influx of oxygen
could have caused an increase
in the severity of the fire
within Notre Dame.
All of a sudden, there was
a huge, huge ball of fire
rising out of the cathedral.
It was spitting ash and
debriseverywhere, so we took shelter.
It was just devastating
to watch.
We were suddenly really aware
that of, of how easily this
whole thing could come down.
90 minutes after the fire
begins,
the entire roof of the cathedral
is ablaze.
Inside, it's become even more
dangerous for Rémi
and the firefighters.
Getting this fire under control
looks impossible.
The fire on the ground,
smoke everywhere,
a hole in the ceiling.
We were trying to understand
what was going on,
where the problems where,
check what had collapsed
and if there were other risks.
A southeasterly wind picks up
and pushes the blaze towards
the famous bell towers.
If the bell towers catch fire,
and the bells fall,
then they will smash through
everything below.
Inside the ingeniously
engineered
13th century north tower
a scaffold of wooden beams
holds eight bells.
The biggest weighing more than
four tons.
If the beams burn through,
they'll spark a fatal
chain reaction,
causing the bells to fall
like wrecking balls,
destroying the tower's
wooden backbone.
If the tower falls, it could
trigger a deadly domino effect
that brings down
the entire cathedral.
To avert this
catastrophic collapse,
the firefighters have no option
but to venture deeper inside.
"No doubt,
we must send
the firefighters in.
The cathedral must be saved."
We headed to the North tower
just when the flames
had reached the belfry.
The firefighters also knew it
well.
We were guiding each other.
To douse the fire on the roof,
firefighters pump water
from the River Seine
and feed it to fire trucks
around the cathedral.
But to stop the towerscollapsing
they must send a team
into the burning structure.
Drop hoses in between the towers
and fight the fire spreading
from the roof.
But the steady wind
doesn't let up.
And despite their efforts, the
timber frame holding the bells
has caught fire and could
trigger the destruction
of the cathedral at any moment.
So the team must drag their
hoses to the top of the tower
and soak the timber frame
to prevent the unthinkable.
Throughout the night,
the fate of Notre Dame
hangs in the balance.
Eventually the firefighters
get the upper hand.
The flames have been beaten back
and only glowing embers
light up the night sky.
Nobody knows
how the fire started.
An investigation begins.
But for now,
the urgent question:
how damaged is the structure
and can it ever be rebuilt?
President Macron pledges
to restore the cathedral
in five years.
Tonight, I tell you
very solemnly,
we will rebuild this cathedral
together.
Meanwhile, the world keeps vigil
for Notre Dame.
Daylight reveals the full extent
of the terrible destruction
wrought by the fire.
The oak roof and spire
are completely destroyed.
Tons of toxic lead
that covered the roof
have been sprayed into the air,
contaminating the site.
Burned roof timbers
cover the vaulting.
Three gaping holes
in the stone vaults
weaken the entire structure.
And the 550 ton scorched carcass
of scaffolding
could collapse at any moment,
something unthinkableto
those tasked with preserving
France's rich cultural heritage.
I'm in front of my cathedral,
which is in this state.
I need to work.
Phillipe Villeneuve is in charge
of historic monuments in France.
This is the cathedral
that inspired him
to become an architect.
I must have been five
or six years old.
My parents brought me here
one day,
like every child from Paris.
I was fascinated
by the architecture.
It stayed with me since.
Since 2013,
Phillipe has been responsible
for conserving Notre Dame.
It was the culmination
of a dream.
A dream come true.
Today that dream has turned into
a nightmare.
The stricken cathedral
is a giant house of cards.
If the stone vaulting collapses
the weight of the buttresseswill
push in the 100-foot walls.
And Notre Dame will be no more.
So Phillipe heads up
a rapid response team...
dozens of engineers,
architects, and scientists.
Their task is to prevent a total
collapse of the cathedral.
From the bottom of my heart,
I want to thank you all for your
dedication, your approach,
your passion.
You are doing a very difficult
job, which is essential
for the cathedral.
It's not only a difficult job,
it's also hazardous.
The crumbling stone vaults
and twisted scaffolding
make any visit
inside to investigate the
stability of the structure
extremely dangerous.
On the vaults we have
the problem of the impact
of the fire, but we will
alsohave to evaluate
the impact of the water used
to put out the fire.
And we can see from here
the inside of...
Go out.
The scaffolding is moving.
Scaffolding!
Motion sensors are installed
in the melted jumble
of scaffolding overhead.
These can be triggered
by gusts of wind...
a warning before a possible
full-scale collapse.
It's the alarm, because the
scaffolding has moved.
We must leave.
There are evacuations like this
each week; necessary,
but an impediment
to the urgent work
of stabilizing the structure.
It's very difficult to juggle
all these issues.
The problem is that we have to
take action very quickly.
But we need to consider
the reality of this building.
It's still in danger
of collapse.
We are still in the
stabilization phase
of the cathedral.
To avert a catastrophic
collapse,
engineers could builda
steel skeleton inside the nave
to brace the walls.
Then, even if the vaulting
caves in,
the walls of Notre Dame
would stay standing.
But it's far too dangerous
for workers to erect steelwork
beneath the compromised
structure.
We cannot go under the vaults
because we don't know
whether they'll fall or not.
So, instead of bracing the walls
from the inside,
the team will build timber
frames
under the buttresses outside.
Now, if the vaulting does fall
in, the buttresses can't push
on the walls, and they won't
come tumbling down.
They are very difficult because
no flying buttress is identical
to another.
They are made to measure.
Workers at this factory race
to cut
and assemble around 250 tons
of timber
to create the massive supports
Philippe's team needs
to prop up the vaults.
It's critical each support fits
perfectly
beneath each flying buttress
to hold its weight.
Working around and inside
this space
is a logistical nightmare.
210 tons of lead cladding
covered the cathedral roof.
This was mostly melted during
the fire,
and now toxic lead dust covers
every surface.
The worksite is highly
contaminated.
Until the site is cleaned,
team members must wear full
protective clothing
to pass into
the contaminated zone.
When leaving site,
they undress,
discard all clothing,
carefully wash equipment,
then shower themselves.
Only then can they go back
to the clean area
even for a lunch break.
It's very difficult to endure
for the workers
who have had to deal with these
procedures for months.
These regulations
are not normal.
But this whole site
is not normal.
But, finally, five months later,
all 28 flying buttresses
are locked in place
and the walls are safe.
Now they can turn
to the next challenge...
secure the melted mass of
scaffolding
that hangs precariously
over the cathedral.
The scaffold weighs more
than a jumbo jet,
and only rests on
four spindly legs.
The team plans to wrap three
massive steel lattice beams
around it to tie the fragile
upper parts together.
Then they'll build more
scaffolding either side
and lay steel beams across it.
That way workers can get inside
the stricken scaffolding
to help cut off its
50,000 steel poles,
a truly Herculean task.
Only then can the team put up
a temporary roof
to protect them from the
elements
while they rebuild Notre Dame.
It's going to be an extremely
dangerous operation.
The spire has disappeared,
but the scaffolding is still
there.
It moves a bit,
but it's still there.
While engineers gear up
to remove the scaffolding,
architect Rémi Fromont
and Livio De Luca
begin a groundbreaking project
that will combine
the investigative work
with new scientific analysis.
Their ambition is to create
adata-rich model of Notre Dame...
a digital twin.
The digital twin will embed not
only the geometric structure,
or the visual appearance
of the cathedral,
but also all the scientific data
coming from the studies.
For example, you can click
on a stone in the vault
and access to all
the information
about its physical properties
such as the provenance,
but also the mechanical behavior
within the entire structure.
Luckily for Livio,
a series of highly detailed
laser scans of the cathedralhave
been conducted since 2006.
These are brought together in
this priceless 3D dynamic map
to show every stone, timber,
and iron nail in the structure,
across time, from the12th
century to the present day.
This is an unprecedented
project.
The ambition is to collect all
the information from the past,
to pass it to the future.
There's very little first-hand
information
about the construction
of Notre Dame,
or the craftspeople
who built it.
In the wake of the fire,
new studies of the cathedral's
materials
could unlock these secrets.
This new data, once included in
the digital twin,
will provide a blueprint for
the restoration and rebuild.
Inside Notre Dame,
scientists begin to gather data
and investigate the damage
to treasured statues,
murals,
and windows.
The cathedral's most fragile
wonder, its stained glass,
dates back to the 13th century.
36 windows circled the
lower level,
42 around the middle level,
and 43 around the upper level.
The three famous Rose windows
span up to 42 feet in diameter
and are made up of over
1,100 panels
of beautiful stained glass.
Miraculously,
they survive the fire intact.
But the intense heat that melted
the cathedral's
lead-covered roof
means that much of the glasswork
is now covered in a layer
of toxic lead powder.
Removing it could damage
the delicate glass
and be harmful to restorers.
It was really painful to see
the catastrophe on the TV.
I was looking to see what's
happen around the windows
and it was, of course,
totally difficult
to have a good idea
of what's happened.
There is a before and after
15 April,
for historical monuments,
that's for sure.
Glass scientist Claudine Loisel
uses a handheld digital
microscope
to investigate the levels
of lead powder
on the stained glass.
She must then formulate
a strategy
to clean every single panel;a
vast decontamination program.
This window is in the back
of the cathedral,
in the lower level,
furthest from the inferno.
But it's still badly
contaminated.
Fortunately, these windows
havenot been cleaned for 100 years,
so the lead has settled on top
of a dust layer,
not on the glass itself.
The first thick layer of deposit
was, we can say
has a small protection
in one way.
So we have just to remove all
the deposit,
to clean these windows
from the 19th century.
Claudine examines deposits from
windows around the cathedral.
The samples reveal vital clues
about the spread of the
lead contamination.
After the spire fell,
the cloud of dust, lead,
and different particle,
push in the other direction,
so we are a little bit more
protected in this area.
The windows of the upper level,
in the path of the lead cloud,
have been most contaminated.
The team takes out and
transports these panels
to this special laboratory
where they experiment with ways
to remove the lead.
First, Claudine uses a precision
vacuum cleaner
to remove the hundred years
of dust
and most of the lead powder
along with it.
So this is a good way to protect
the conservator.
You can control the action,
the pressure on the glass
and also on the painting.
Then she uses water
and cotton balls
to remove the last of the lead.
Of course,
you need scientific evidence
that it's working.
Claudine uses x-ray spectroscopy
to determine exactly how many
wipes it takes
to bring the lead down
to normal levels.
So we can identify each
chemicalelement we have in the material.
Too few wipes
and the lead will remain.
Too many wipes and restorationwill
take longer than necessary.
Okay,
now the analysis is finished.
After five wipes,
Claudine checks to see
if the glass is decontaminated.
Okay, we have different chemical
element... calcium, iron,
and if we want to see
the lead...
there is no lead!
After nine months we can see
a good solution, a good way
to clean and to preserve
the stained glass windows
from Notre Dame.
The upper level windows
were not only in the path
of the lead cloud,
but also closest to the inferno.
Claudine hunts
for hairline cracks
caused by thermal shock,
the rapid heating and cooling
of the glass.
These cracks is due to the fire.
This is a recent cracks
and this is typical
thermal shock.
It looks like the upper level
stained glass
will need to be painstakingly
glued back together.
But inside Notre Dame,
the lower level stained glass
appears
to have survived unscathed.
And here we can see we have
a good stability,
adherence of the painting,
so there is absolutely no
thermal shock,
that's good news for us.
On site,
the teams of scientists
meet the engineers and
architects
to share their findings.
Once Claudine's team
hasrestored Notre Dame's glasswork
to its former glory,
they may use
a radical new preservation
technique
to safeguard it for future
generations.
It's being used on a huge scale
here, in northern England.
This is York Minster,
an 800-year-old Gothic
masterpiece
and home to the largest expanse
of medieval stained glass
in the U.K.,
the Great East Window.
It is one of the largest windows
ever made
anywhere in the medieval world.
We've got glass from the
12th right through
to the 18th century in quite
significant quantities.
And it is really our nationaltreasure
house of stained glass.
Engineers here are completing
a $12 million project
to protect York Minster's
stained glass
from harmful UV rays and the
corrosive effects of moisture.
In modern stained-glass
conservation,
we're really doing as much as we
can to keep
both surfaces of the historic
stained glass dry and stable,
and that's where our ventilated,
environmental protective
glazing comes into play.
You can see that I'm almost in.
I think it's just
this last bit here.
Matt Nickels is installing
this new conservation system.
He slots a protective clear
glass exterior frame
into the window opening.
This goes into the original
glazing groove,
where the medieval glass would
have been.
This protective
glazingprevents corrosive condensation
from forming on the 800-year-old
stained glass
that will sit behind it.
The gap created means that
there's air circulation running
through.
And when you've got air
circulation,
it's regulating the temperature,
which means that there's less
moisture on the glass.
Each frame is custom made
and takes great skill to fit.
You don't want to make it
too small
because it's going to obviously
slide through.
No two windows
are gonna be the same.
With the outer panel installed,
they can reinstate the layer
of medieval glass.
They're actually in fairly good
condition
considering that they're early
13th century.
There's always the worry
whenever
you're handling glass like this,
but you just got to make sure
that you're really,
really careful.
There's nothing quite like
seeing it with sunlight
behind it.
When you put it up like this,
it's quite magical, isn't it?
Techniques like this
offer a glimpse of how
scientists like Claudine
may eventually preserve
Notre Dame's glass.
This is the best way to protect
stained glass windows,
so it will be for sure an option
to protect the windows for
Notre Dame.
Had the vaulting collapsed
next to the windows,
the glass could have been
badly damaged.
But luckily, the stone vaulting,
which sits just under the timber
and lead roof,
protected the windows
from the inferno above.
When the architects of the
Middle Ages
constructed this vaulting,
they used it to separate the
timber frame of the roof
from the rest of the cathedral.
So the vaulting took the shock
of the falling timber
and the fire
and the firefighters' water.
The magnificent vaulting was
built to be resilient,
thanks to precise medieval
craftsmanship,
using over a thousand cubic
yards of limestone.
The arches work together
to support the roof
and stabilize the outer walls.
But the intense heat
from the fire
and the collapsing spire
took out 15% of
the stone vaulting.
Today, three 40-foot-wide holes
and several smaller gaps
mean the vaults could collapse
at any moment.
The team collects, storesand
catalogues the fallen stone
in this tent, located
alongside the cathedral.
They may be able to use
some of this stone
to reconstruct the vaults.
But it's clear they'll also need
to source new stone.
Notre Dame is made up of many
different types of limestone.
Medieval masons chose hard
limestone for the towers,
pillars, and outer walls
tobuild tall and hold up the roof.
For the sculptures, they chose
dense, fine-grained limestone,
that can be carved with
great detail.
And for the vaults they selected
softer, more porous limestone
that's light but strong.
If the team rebuilding
the vaults
pick a limestone
that is too heavy,
the new vaults may not last as
long as they should.
Geologist Lise Leroux
investigates what quarry this
stone came from.
We have some blocks coming from
the collapse of the vault
for study.
This detective work will help
the team source
replacement stone that
sharesidentical mechanical properties.
We have to verify.
The fallen vaulting stone
contains a rare micro-fossil
called orbitolites complanatus,
a kind of plankton.
Fossils like this are found in
just one layer of rock.
This will make sourcing
new stone
of the same type even trickier.
Can they use this geological
fingerprint
to discover the original source
of the vaulting stone?
To find out, Lise and fellow
Notre Dame scientist
Claudine Loisel venture deep
beneath Paris.
Hidden under the city streets is
a rich source of limestone,
a vast labyrinth of
quarry tunnels.
Lise and Claudine
enter this maze
two miles south of Notre Dame in
the famous Catacombs.
Oh!
In the late 18th century,
the quarries were given a
different purpose
and they housed bones from
old cemeteries,
which were inside the towns.
Cemeteries which were closed at
the end of the 18th century
for sanitary reasons.
Among the bones,
Lise and Claudine find traces
left by the medieval miners.
Here, the block's been removed
and we're left with this trace.
They then square off the sides,
and use it to build Notre Dame.
And the strata height here,
itdictates the height of the block
that can be extracted.
The blocks we see at Notre Dame
have this height.
So the quarry itself puts
a constraint
on the construction
of Notre Dame.
We have life and we have death.
Well, yes.
The upper level of the quarry
holds hard limestone with
large, well-preserved fossils.
These fossils are
more characteristic of
the limestones
used for the pillars,
the arch in Notre Dame.
But not for the vault.
Lise and Claudine hope to find
a match for
the soft vaulting stone
in the lower level
of the quarry.
Now to look if we can find
the specific micro-fossils.
I'm not sure, because
the surface is very rough
and it's not so clear because
ofall of the state of the surface.
The limestone here is softer,
but Lise cannot see a match
for the rare micro-fossil
found in the Notre Dame
vaulting sample.
So, back in the lab,
she takes a closer look
at a sample of limestone
from the lower level
of the quarry.
These little fossils...
this one, this one,
this one...
are, in fact
some planktonic fossils,
which are called foraminifera.
It's not the fossil signature
she's looking for.
But then...
Oh!
This one here
is orbitolites complanatus.
This little planktonic fossil
is a dating fossil,
which match with the stone
coming from the vault.
It's a stratigraphic indicator,
characteristic from
the Middle Lutetian,
which is a geological
age of deposit.
Lise confirms the origin of
the Notre Dame vaulting stone.
It's quarried
from the deepest seams
of limestone beneath Paris.
Conclusive.
But what about the harder
limestone,
used by medieval masons to build
Notre Dame'sload-bearing
pillars and arches?
Another micro fossil signature
confirms the origin
of this type as well.
The arches are built
with a hard stone...
with a resistant stone,
to support the vault.
And the vault itself
is logically constructed
with a lighter,
more porous stone.
And in the quarry located
in Paris,
we have this two kind of stone.
Medieval masons knew exactly
how to exploit
the varying
mechanical properties
of the limestone for Notre Dame;
knowledge passed down
through the generations.
Sourcing more of the
correct stone won't be easy...
the old quarries
are no longer active.
But engineers now know
what limestone to look for...
this will help them find a match
in quarries outside Paris.
Stone is not
the only raw material
that will need to be replaced
as engineers reconstruct
Notre Dame.
The timber roof
was also a medieval wonder.
It was constructed from
25,000 cubic feet of timber,
cut from 52 acres of oak...
that's approximately
1,300 trees.
For this reason,
it was known as "the forest."
Every single oak
in Notre Dame's forest
was handpicked for
the physical properties needed
in the roof structure...
from dense straight oak
for pillars,
to curved oak
for support arches.
But the fire burned
every beam in the forest.
Today, this intricate 550-ton
timber jigsaw lies in ruins.
We thought this sublime roof
would be here forever.
It was a big puzzle with beams
from different periods,
all the way back
to the 13th century.
And to see it suddenly
all burned, all mixed up...
Oh, it's very emotional.
It's very difficult.
Almost 60 tons of the
precious roof timber
still lie precariously
on top of the vaults.
Despite the destruction,
every single beam holds
the history of Notre Dame.
It has deep
archaeological value.
It's vital that workers
forensically record
the position
where each beam fell,
before they remove them.
This helps them determine
where it originally sat in
the roof structure.
Now, these highly trained
rope access technicians
gear up to catalogue and clear
the charred timber
on the vaults.
It's not possible
to walk on the vaults,
because the structure
is very precarious.
They needed to
create a way
to access with ropes.
We need to wear a special mask
because of the lead dust
that we might inhale.
We label the timbers
and we mark them with a code
that the architects will
be able to identify.
The team has their work
cut out...
there are thousands
of separate pieces
of timber to catalog.
We are working day and night.
We have a lot of work to do.
They've already extracted
around 4,000 pieces.
Timber scientist
Catherine Lavier
begins painstaking
detective work to reveal
how Notre Dame's vast forest
was originally assembled
and could be rebuilt today.
Some pieces were
very well-preserved
because as you see here,
with different faces
and another piece of wood is
coming here,
with a wooden joint
here to assemble them.
And it's rather typical
from the medieval period.
And here,
you have a mark,
of carpenters.
So they are sure that this piece
with this piece are together.
It's very important
for carpenters.
They prepare
the wood on the ground
and after that,
they go to the roof
and reassemble again.
Every carpenter
has his own way to mark,
but in general it's based on
the Roman numbers,
but we can find some differences
between teams of carpenters.
We were very surprised
to find that
because I thought
everything will be destroyed.
And, finally, not.
The tree rings of the timbers
conceal further clues.
Each ring represents
one year of growth;
a time capsule of information
about the life of
the tree in that year.
Catherine analyzes core
samplesfrom Notre Dame's roof trusses.
She measures each ring
to reveal the secret story
of some of
the original oak trees
the structure was made from.
This screen shows the size
of each ring I measured.
At the start of its life,
you see it has
very, very large rings,
which correspond
to very rapid growth.
Next, it looks like it
experienced
some more dramatic events,
some difficult years,
here, when the rings
are very thin,
This could be because of
too much rain,
not enough sun,
and not enough nutrients.
And then,
the life of the tree continues
until it's cut down,
around its 96th year.
Catherine is gaining new insight
into the types of trees
best suited to rebuild
the complex forest
of Notre Dame.
This extraordinary challenge
will require
around 1,300 oak trees,
craftspeople versed
in the lost art
of medieval carpentry practices,
and a blueprint for possibly
the most geometrically complex
timber structures in Europe.
The one person who can unlock
the lost forest's
geometrical secrets
is architect Rémi Fromont.
In 2014,
Rémi spent the entire year
mapping every inch
of the timber.
It was a magical place
to go in there;
there was a smell.
There was a very special
atmosphere of light.
We still had the traces of tools
also on the woods.
It sometimes seemed like
they only left yesterday.
We are collecting photographs,
3D point clouds,
and the physical
and chemical characterization
of all the materials.
The fire at Notre Dame
triggers a race across France
to 3D scan historical monuments,
inside and out.
These represent
a digital insurance policy
to preserve French heritage.
The laser bounces off
each contour in the room.
The machine then measures
the time it takes
for the laser to return.
Millions of measurements
form a cloud of data
called a "point cloud."
In 2016, researchers used
this same technology
to create a full point cloud
of Notre Dame's
lost timber roof structure.
This remarkable 3D scan
willcombine with Rémi's 2014 survey,
in Livio's digital twin
for Notre Dame.
What we are producing today
will be probably
the information useful
for the next generations.
The team now has
the data they need
to rebuild the timber roof
with the exact same geometry.
The new oak needed
could come from
forests like this.
Almost a third of France
is covered with forest.
Oak is a vital
strategic resource
throughout theMiddle
Ages and the Renaissance.
Vast forests are needed
tobuild cities and expand navies.
This is the Château de
Beaumesnil in Normandy.
It's a
National Historic Monument,
built on the site of
an 1,100-year-old castle.
It was built in seven years.
It's something extraordinary
for just seven years' work.
The château has seen
better days.
The curved beams
that hold up the roof
are close to collapse
and must be replaced.
The wood grain has been
cut through.
This weakens the support beam.
And then you see that the beam
is completely eaten away.
The wood is degraded,
eaten by the fungus.
The restoration work here
requires much of
the same skill and knowledge
it will take to rebuild
Notre Dame's lost forest.
The timber has been chosen
so the curve of the grain
perfectly matches
the curve of the new beam.
If you get a straight tree,
which has a straight grain,
and...
if you cut a curved piece,
piece of wood inside of this,
so here is the fiber,
so it can break, right there.
But if you take
the tree that's curved,
the fiber is like this.
So it cannot break.
You keep all of thestructural
strength of the tree.
The carpenters use
an original beam as a template
to mark out the new beam
on the oak.
The carpenters who built
Notre Dame
would be familiar with
the tools this team uses
to hew the raw timber.
So after you split
most of the wood,
you use a broad-axe.
They have a single bevel,
long cutting edge,
and the handle is offset.
So...
if you're working,
as you go down, your hand here,
you see I'm not
hitting this sharp edge.
For skilled carpenters,
cutting Notre Dame's
roof timbers with axes,
compared to a modern sawmill,
will take roughly
twice the time;
possibly too long.
This curved oak will be
one of ten the team
needs to install
as part of
the château roof restoration.
It sits alongside this
400-year-old original beam.
This one was cut
probably 1635, '37,
and then this one 2020.
I hope our ancestors are
happy with this.
Just like the Notre Dame beams,
the Château's
original beam holds
messages from
the old carpenters.
It's extraordinary to find
all these marks.
It's very old
and at the same time,
it looks like
it was done yesterday.
French craftspeople
have the oak,
they have the skills, and
they have the plans required
to reconstruct Notre Dame's
vast forest of roof timbers.
It's over a year since the fire
ravaged Notre Dame cathedral,
and the investigators
have not pinpointed
the cause of the blaze.
Immense challenges and
uncertainties still lie ahead.
The building
is not yet out of danger.
Over the next 12 months,
engineers must remove
the melted scaffolding
and seal the cathedral roof
to make it watertight,
then stabilize
the weakened vaulting.
It's a monumental task.
And rebuilding
the entire cathedral
could take much longer than
the five years decreed by
President Macron.
Faced with such a drama,
thankfully there's hope.
We need faith for this project.
It's this building itself
that generates this faith...
even for atheists...
And that's something magical.
Architects around the world
have unleashed
their imaginations
to submit grand plans for what
the new spire above Notre Dame
could look like...
from mirrored roofs
with kaleidoscopic pinnacles,
and vast solar panels
powering nearby buildings,
to stained glass edifices
thatwill light up the Paris skyline.
However Notre Dame is rebuilt,
the unique collaboration
of architects and scientists
is rewriting how we understand
the very fabric of
this magnificent cathedral.
I think the fire in some ways
helped remind a lot of people
what an important part
of our sort of shared history
and shared culture this is.
Soon, a complete digital twin
of Notre Dame
should allow future generations
of craftspeople
to maintain, protect, and
faithfully rebuild Notre Dame,
preserving this world treasure
for all time.
I have only one obsession...
save the cathedral,
resurrect it,
and reopen it to the public.
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