Less than five years after the fire that devastated the wooden framework of Notre-Dame de Paris, the cathedral is gradually recovering its "forest," as it was known. On January 12, following the rebuilding of the two arms of the transept and the spire, carpenters installed a bouquet at the top of the new choir frame, symbolizing the end of this stage of the project. The reconstruction of the nave is also expected to be completed shortly.

These milestones mark the end of a marathon to restore the cathedral's framework exactly as it was before the fire. To achieve this feat in record time, many trades were involved: carpenters, architects, foresters... and researchers from all disciplines.

After the fire, the architects were faced with several options. Should the structure be left as is to turn it into a commemorative site? Should a lighter, more modern structure be built in concrete rather than wood, like the Reims Cathedral? Or should it be rebuilt faithfully as it was before?

Rémi Fromont thought the answer was obvious. "Not restoring this framework identically would have damaged the cathedral's heritage value," explained the head architect of historical monuments, who is coordinating this titanic project. But there was no question of rebuilding the framework exactly as it was in the Middle Ages and ignoring the restoration work carried out in the 19^th century by the architect Eugène Viollet-le-Duc on the transept and especially on the spire. "Since its construction, the spire has been considered an absolute masterpiece. It is one of the most complex solid-wood frameworks of the 19^th century and the most remarkable for its design, the complexity of its assembly and layout, and its dimensions," Fromont said.

A fortuitous architectural survey

But was it even possible to rebuild the framework exactly as it was? What information was available on the wood and techniques that were used, the complex assemblies? And did France still have the wood, the know-how and the manpower needed to build this extraordinary structure? In the aftermath of the fire, these questions remained unanswered.

As a first step, a search had to be conducted for all the documents that could be used to determine the exact location of each beam and assembly that made up the structure that went up in smoke. Luckily, Fromont himself, with the help of his associate Cédric Trentesaux, had conducted an architectural survey of the structure in 2015.

This painstaking process had been conducted for a year by the two architects as part of their specialist training course. "It saved the framework of Notre-Dame de Paris," asserted Frédéric Epaud, director of research at the French National Centre for Scientific Research (CNRS). But this survey alone was not enough. "Let's just say it was a bit crude," joked the archaeologist, who is also a specialist in medieval wooden architecture. "We didn't know what dated from the 13^th, 16^th or 18^th century. And that's something we had to figure out," he said.

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