Notre Dame fire: How do you restore an architectural masterpiece?

“It’s okay to cry,” said Jorge Otero-Pailos.

As news spread of the tragic fire that consumed the roof of Notre Dame cathedral, a national, spiritual, and architectural symbol with few parallels, Otero-Pailos, director of the preservation program at Columbia University, was still taking in the enormity of what had been lost. But with hundreds of millions of dollars already pledged to the rebuilding effort, Otero-Pailos was also wrestling with questions of what comes next.

“It’s of course technically feasible, but you won’t have the same fabrics, the same craftsmanship,” he told Curbed. “You won’t have the continuity. A lot of what heritage objects and buildings allow us to do is connect with the past. We’ll lose the fabric and the continuity will be broken.”

Notre Dame seems poised to rise again. But the complexity of that task, and the technology and technical skill involved, will only become clear in the coming days and weeks, as investigators take stock of the remaining shell of the Gothic cathedral. Curbed spoke to three experts to get a sense of what comes next for the building, where the reconstruction effort may be one of the longest of the modern era. Otero-Pailos and other experts predict it will take decades.

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Assessing the damage to the cathedral’s frame

Initial reports the morning after the blaze suggest that while the roof and spire have burned, the main structure and the stone walls remain standing. The most important task now—once a membrane is erected to prevent further water damage to the exposed interior—is figuring out the condition of the stone shell. Daniel Allen, Principal at CTA Architects, a New York-based architecture firm that specializes in historic reconstruction of churches, said that while it’s assumed the masonry is fireproof, bad things can happen when a structure such as Notre Dame is hit by heat shock (sudden heat followed by rapid cooling).

When exposed to such heat, the limestone walls and mortar can calcine due to the high temperatures. Between the rapid heat of the fire, which was extinguished Tuesday morning at 10 a.m. local time, and the rapid cooling from the firefighters extinguishing the blaze, it’s possible that the centuries-old stone could crumble. Investigators the morning after have already found weaknesses in the vault and gable of the structure’s northern transept (one of the “arms” in the cross-shaped cathedral layout).

That would be a substantial problem for a building with simple, straightforward construction. Notre Dame, a Gothic cathedral completed in 1260, raises the complexity level exponentially.

“This isn’t a simple building, it’s an aspirational building,” says Allen. “The people building this were pushing the envelope of what these materials could do. It was intended to be a soaring structure, so it’s fragile to begin with.”

According to Allen, yesterday’s fire might be the most significant damage done to Notre Dame—a church that has seen centuries of damage, reconstruction, and repair.

An assessment of authenticity

The damage assessment is only the beginning. Once it is finished, architects, designers, and preservationists need to decide if they want to save the original, damaged stonework or whether it’s better to replace it.

“Do you take down the part that’s charred and original, or do you not take it down in order to preserve what’s original?” asks Otero-Pailos. “You may have to take down parts that are technically standing, that aren’t structurally sound.”

He compared it to the debate over restoring the Rennie Mackintosh Library at the Glasgow School of Art, a 1910 Art Nouveau library that burned down in a fire and will be reconstructed in its original form.

Caroline Bruzelius, a Duke professor of art, art history, and visual studies who had previously worked on a clean-up effort at the cathedral in the ’70s, says the intricate craftsmanship of the original stone masons will make repairs extra tricky.

“Each piece of stone is locked into one another, they’re all part of a system that supports the building, and are integral to the structure’s overall integrity,” she told Curbed. “For instance, the flying buttresses and vaults are basically interconnected. You lose one, you may lose the other.”

Craftsmanship of the past meets the technology of the present

Once the true nature of the damage to the stone walls is understood, and a plan of reconstruction and preservation is devised, the actual reconstruction becomes a question of talent. Master stone masons are few and far between. Luckily, some recent efforts to reconstruct cathedrals have preserved a core group of skilled experts. A 75-year effort required a team of masons to restore Nidaros Cathedral in Trondheim, and similar efforts were required for the York Minster Cathedral in York, England, after a 1984 lightning strike sparked a fire. Many new masons will need to be trained and upskilled to be able to contribute to the reconstruction effort at Notre Dame.

Luckily, modern technology can play an important role. Today’s preservationists benefit from high-tech solutions like laser scanning to provide a digital record that helps preservationists maintain fidelity to the original designs. In 2010 the late Vassar professor Andrew Tallon took laser scans of the cathedral’s interior, providing a high-tech blueprint for those now looking to recreate Notre Dame.

“This reconstruction effort will be a great testament to the importance of new technologies in the restoration of such buildings,” says Duke’s Bruzelius.

A number of additional, high-tech touches will help craftspeople and construction workers build a stronger, more resilient, structure, says CTA’s Allen. When replacing the wooden roof and other wooden elements, workers could consider using more modern materials, treated to prevent rotting. Computerized routing machines can duplicate intricate details in ways that weren’t possible decades ago. Concealed structural members in the roof can strengthen the bones of Notre Dame. And new ways of waterproofing can offer additional layers of protection.

Allen says it’s humbling, as an architect, to consider this kind of reconstruction work. Even with access to amazing equipment and technology, it’s still a monumental task. It makes the thought of 13th-century craftspeople piling scaffolding to reach the soaring heights of the cathedral vaults that much more amazing.

As architects fret over what may be lost, they also know that no building is ever frozen in time. As Bruzelius pointed out, Notre Dame itself has been through many changes, most notably the 19th-century restoration project led by Eugène Viollet-le-Duc, a “profound intervention that reinterpreted the building” over roughly two decades.

“While it is made of stone, it’s a frame that’s constantly changed over time,” says Bruzelius.