How to rebuild a gothic cathedral: The future of Notre Dame

Written by Oscar Holland, CNN

As the ashes settle at Notre Dame, the laborious restoration process can begin. Rebuilding the cathedral will take years. Yet, for a structure that took decades to construct, and then stood for centuries more, this may simply mark the latest evolution of a building that has been reshaped many times during its 850-year history.

Those looking for hope amid tragedy will be heartened by president Emmanuel Macron's assurance that the French will "rebuild together," and immediate fundraising efforts leading to pledges of 50 million euros ($56 million) and 200 million euros ($226 million) from Paris' City Hall and the luxury goods and fashion house LVMH, respectively.

These early donations suggest that, perhaps, the most difficult part of any major restoration project -- funding -- may be taken care of. But, assuming the requisite backing transpires, how exactly will the process be carried out?

A 'war of attrition'

As with any fire-damaged building, safety will be the principal concern. The main structure (and two bell towers) may have been "saved and preserved," according to French authorities, but parts of the cathedral could still be at risk of localized collapses and falling debris.

Before distinguishing between the salvageable from the unrecoverable, immediate steps will need to be taken to prevent further damage, according to architectural historian and broadcaster, Jonathan Foyle.

"It's already a wet building because of the water that's been pumped on it, so they're going to need to provide some kind of cover from the elements," he said in a phone interview. "The roof's job was to discharge thousands of tons of water, so where's that going to go? Every time it rains it's going to cause damage at this point, so it's against a war of attrition now."

Firefighters spray water as they work to extinguish a fire at Notre Dame Cathedral in Paris early on April 16, 2019. Credit: Zakaria Abdelkafi/AFP/Getty Images

After protecting the building's remains, restoration teams will begin assessing the level of damage. The vault appears to be only partially damaged, but the stonework could be more compromised than it appears.

High temperatures can change the chemical nature of limestone, Foyle said, with the resulting calcification potentially weakening the structure. And pouring cold water onto hot stone -- as will have inevitably happened as firefighters tackled the blaze -- can caused thermal shocks that may have cracked parts of the cathedral's stonework.

An army of archaeologists

French authorities will then, ultimately, need to take a series of design decisions about how best to rebuild. To do so, they will need to better understand how the medieval cathedral was constructed.

"The stripped roof and upper masonry will reveal aspects of the building's history which probably haven't been understood," Foyle said. "Notre Dame has virtually no building records. We know (that construction) started in 1163 and was basically completed by about 1240, but there are no building accounts.

"Evidence for the evolution of that building is in the physical fabric, so you'll need an army of archaeologists all over it to better understand which parts they're repairing and what they belong to."

Another episode in 'creation, destruction and repair'

But the goal of restoration is not always to replicate the past. Modern tastes and technologies may influence how damaged structures are reimagined. Take, for instance, the recent restoration of the Cutty Sark, a 19th-century clipper ship renovated at a cost of £50 million ($65 million) following a devastating blaze. The vessel, which serves as a tourist attraction in Greenwich, London, now stands with a contemporary glass structure, housing modern facilities, at its base.

A worker inspects the hull section of The Cutty Sark on October 11, 2007. The original conservation project was interrupted because of the damage caused by a fire on March 21, 2007. Credit: Peter Macdiarmid/Getty Images Europe/Getty Images

The new Cutty Sark, London UK (part of "Maritime Greenwich", UNESCO world heritage site). Credit: Maria Swärd/Moment Open/Getty Images

Authorities may wish to stay faithful to earlier renditions of the state-owned cathedral. But it's also plausible that France takes a bold new direction with one of its most iconic national monuments.

Indeed, the spire that collapsed to gasps from stunned onlookers Monday evening, was itself a break from the past, having been built during a sweeping restoration from the 1840s. Its designer, the architect Eugène Viollet-le-Duc, made his spire taller and more elaborate than before.

That 19th-century restoration also saw other significant changes to the cathedral's facade and interiors.

"Notre Dame is not a building that has been fossilized in time, Foyle said. "It has not remained static since the early 13th century.

"It's not something that had been perfectly preserved which was totally destroyed last night. You might (instead) see this as a traumatic episode in the long history of cyclical creation, destruction and repair. It's lived through wars, it's lived through reformers, and this will, I think, prove to be another episode."

At this early stage, it remains difficult to predict the time and funding required to restore Notre Dame. But other large-scale fires hint at the expense involved. The Venice Opera House, which was gutted by a blaze in 1996, reportedly reopened eight years later at a cost of 60 million euros ($68 million). After Windsor Castle, one of the Britain's royal residences, was severely damaged in a fire in 1992, it reopened nearly five years later at a cost of £36.5 million ($47.8 million).

The cathedral of York Minster rising above the city. Credit: Terry Roberts Photography/Moment RF/Getty Images

Perhaps a more relevant precedent is the UK's York Minster, a gothic church partially destroyed in a 1984 fire. It was restored over four years a cost of just £2.25 million (about £7 million, or $9 million in today's money). And, in terms of structural damage, Notre Dame may be in better condition, as its vault was primarily made from stone, not wood.

"It seems as if the church beneath (the burned roof) has been protected from the intense fire," Foyle said. "That's the big difference between somewhere like Notre Dame and York Minster, which had oak vaults and therefore fell to the ground and burned upwards. And even so, York was salvaged."

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