Professor Paolo Vannucci, a mechanical engineering specialist at the University of Versailles has warned that the structure is now extremely fragile, according to a report in French newspaper Le Figaro.
He said that a storm with winds of 90km/h could result in the partial collapse of the building.
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Large parts of the roof were totally destroyed in the blaze. Photo: AFP
After the devastating blaze that ripped through it on the night of May 15th, the gothic cathedral has lost its spire and a large part of its roof.
The elaborate stonework of the vaulted roof also partially collapsed, and it is this area that the professor, who produced a fire risk report for Notre-Dame in 2016, speculated was now the most fragile.
He said: “A 60 percent decrease in wind resistance was measured.
“The structure has changed. Part of this structure no longer exists, the roof has disappeared, as well as part of the vault.
“This collapse of part of the vault caused the most significant damage.”
The professor, who added that he was working from models and had not had the chance to examine the cathedral; said that the structure could previously have withstood winds up to 137mph, but now the wind resistance had decreased to around 55mph.
On Tuesday climbers were brought in to hastily erect covers over the damaged roof as rain swept Paris.
“The biggest priority is to protect the cathedral from the coming rain,” the cathedral's chief architect Philippe Villeneuve told France's BFMTV, saying he wanted to “speed up” efforts to erect the tarpaulin before the heavens opened.
Christophe Villemain, a specialist in restoring historic buildings, told the channel that the rain could potentially cause further sections of the roof to collapse.
“The rain risks falling on the vaulted ceiling and filling up what we call its haunches, or hollow sections, and that would put the arches at risk of collapse,” he explained.
Flames swept across the roof of the gothic cathedral and engulfed the spire on the night of April 15. Photo: AFP
The covering would only be temporary, with plans to replace it with a more sturdy protective “umbrella” that would remain in place throughout the work to restore Notre-Dame, which took 200 years to build.
President Emmanuel Macron wants it rebuilt within five years.
Before the umbrella can be set up however, scaffolding that was erected to do renovation work before the fire must first be removed, in an operation which is likely to take up to a month, Villemain said.
Images of the ancient cathedral going up in flames sparked shock and dismay across the globe and in France, where it is considered one of the nation's most beloved landmarks.
Since then, firefighters and engineering experts have been working to erect scaffolding and other wooden supports to stop any of the structure's stonework collapsing.
Notre-Dame survived the devastation of two global conflicts in the 20th century and famously rang its bells on August 24th, 1944, the day of the Liberation of Paris from German occupation at the end of the World War II.
Engineer – ingénieur
Wind resistance – résistance au vent
Scaffolding – échafaudage
Sacred – sacré