After a devastating Notre-Dame Cathedral fire on April 15, heritage experts warned that the five-year restoration deadline is impossible and it can be more complex and could take a decade or more, despite President Emmanuel Macron’s statement to "rebuild the cathedral even more beautifully" within five years.

While many analyzes and discoveries on the building still continue, art historians, cultural heritage experts and researchers warn: the completion of the restoration work of the structure can take ten years or more, reported The Art Newspaper. 

The article reveals many opinions from art historians, conservationists and heritage experts to reveal the correct analytical framework of the structure.

A view of the debris inside Notre-Dame de Paris in the aftermath. Image © Christophe Petit Tesson/Pool via Reuters

"Any decision to deviate from the original material would be viewed as a betrayal"

Rémi Desalbres, the president of France’s association of heritage architects, said in the article: "The weight has its importance", adding that any decision to deviate from the original material would be viewed as a “betrayal”. 

Especially, one of the key discussions is replicating the cathedral’s “forest”—roof timbers made of 1,300 oak trees that were as much as 400 years old when they were felled in the 12th and 13th centuries— which has sharply divided opinion in France, reported the article. 

The entire works for cathedral’s treasure of religious objects and most of its works of art was safely evacuated and transferred to the Louvre Museum for treatment. 

Desalbres also said that France lacks the old-growth wood to restore the roof as it was - by mentioning about “generous donors”, such as the insurance firm Groupama, which has pledged 1,300 oak trees from the forests it owns in Normandy.

Image courtesy of Dan Kitwood/Getty Images

Cathedral's stone vaults raise concerns about their stability

However, some concerns still continue on the stability of the cathedral’s stone vaults, which were exposed to searing heat for hours as an inferno raged through the lattice of oak roof beams in the attic above, known as “the forest", according to the article.

The fire majorly damaged the wooden central spire and three-quarters of the roof, leaving three gaping holes in the vaulted ceiling. Now engineers and scientists will test whether the stones were permanently weakened by the heat of the blaze or with the shock of the cold water used by firefighters.

"Limestone can lose about 75% of its strength when it’s exposed to heat over 600ºC,” said George Wheeler, a leading expert in stone conservation. "And that fire certainly exceeded 600ºC in many locations."

Experts will clear the debris inside for forensic analysis, and specialists may be able to mount a scaffolding to conduct systematic ultrasonic pulse velocity tests, “pinging” the stones and listening to the reverberations to detect potential areas of weakness, reports The Art Newspaper. 

"Ground-penetrating radar can also be used to identify voids and cavities." 

Notre Dame's north rose window dates back to around 1250. Image courtesy of Wikipedia

Notre Dame’s three 13th-century stained-glass rose windows may be under risk

Conservators also said that the cathedral's three 13th-century stained-glass rose windows may be under the risk since they were exposed to extreme heat. 

"A high risk for the glass but also for the cames, the connecting lead frame," said Hannelore Roemich, a conservation scientist at New York University. "I don’t feel optimistic until someone is up there with a magnifying glass."

The combination of heat and rapid cooling can cause micro-cracks on the glass, emphasized Sarah Brown, the director of the York Glaziers Trust.

Brown added: the process is “very time-consuming and potentially very costly” although there are fortunately "very good historical records of the windows" in the Corpus Vitrearum stained-glass archive. Soot can be removed in a careful workshop cleaning, Roemich added.

The spire was added in the 1850s by Eugène Viollet-le-Duc. The architect replaced the original 13th-century spire with the new one. Image © Clem/Wikimedia Commons

Finding a consensus between the “ancients and moderns” can be extremely difficult for the new spire design

Designing a new spire can also stir a controversy for the cathedral and it will be extremely difficult to make a consensus between the “ancients and moderns”, says art historians. 

Art historian Jean-Michel Leniaud said: "finding a consensus between the “ancients and moderns”, Christians and secularists “will be extremely difficult”, although the practicalities are “simplified” by Macron’s political commitment and the international outpouring of donations, which raised €1bn days after the disaster. 

Soon after the fire, Prime Minister Edouard Philippe announced that the government will launch an international competition to design a new spire for the cathedral - "a new spire that is adapted to the techniques and the challenges of our era".

However, the architectural historian Alexandre Gady warned that Macron is “bypassing” the usual procedures that govern major restorations in his rush to reopen the monument for the Paris Olympic Games in 2024.

Gady added: the restoration will be “very long and delicate, and we absolutely can’t say it will take four, five or ten years." "The president should have said we will do it as well as we can, not as fast. It is the monument that commands—we must obey."

Following the fire at Notre-Dame cathedral on Monday 15 April, the French President has taken several decisions. The President appointed his own special representative responsible for the reconstruction of Notre-Dame cathedral: General Jean-Louis Georgelin, who will begin work immediately. 

Top image © Thibault Camus/Associated Press

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