Engineering tools designed for modern buildings helped bring the storied cathedral back to life—and could help preserve other cultural landmarks.
On December 8, 2024, the Notre-Dame de Paris cathedral officially reopened to the public, a little over five years after a fire ravaged the iconic structure. When the church’s spire collapsed and the lead-lined wood roof melted away, the world, and especially the French people, responded. French President Emmanuel Macron vowed that Notre-Dame would be restored, and fast.
Over the five years since the fire, hundreds of millions of euros have been spent and around 250 companies and hundreds of experts have worked to bring the Paris icon back to life. Although many of those that lent their expertise to the restoration were experts in traditional craftsmanship—carpenters, roofers, art restorers and so on—engineers and digital technology served a critical role as well.
One company that has lent their software, workforce and skills to the restoration is Autodesk. Back in 2021 Engineering.com spoke with Autodesk about how they planned to create a building information modeling (BIM) model of the cathedral with Autodesk Revit. That model ended up being used in more ways than anticipated, and even resulted in changes to Revit itself.
Creating the BIM model of Notre-Dame
Putting together a BIM model of a structure with the complexity of Notre-Dame was only possible because 3D scans of the cathedral had been made prior to the fire.
“It was crucial for rebuilding,” Nicolas Mangon, VP of AEC industry strategy at Autodesk, told Engineering.com. “They decided to rebuild as it was before. So if there was no scan, there were no drawings, there was nothing.”
The France-born Mangon led the restoration project for Autodesk. Working with contractors and a core team of around 15 Autodesk employees, the team focused on using their BIM technology to meet the ambitious deadlines that had been set out for restoration.
It was not easy to develop a complex BIM model like that for Notre-Dame, but the Autodesk team had a window of time to do so. When Mangon visited the cathedral in 2022, the level of lead was still 10 times higher than what humans can be exposed to (all workers and visitors had to wear extensive protection equipment). The process of removing gave Autodesk the time they needed to build the model.
“We hired a company that had 10 to 12 people full time just creating the model for over a year,” Mangon said.
When the restoration teams were ready for the next stage, the BIM model was ready too.
“We saved them a lot of time,” Mangon said. “And they could use BIM and the value of it and instantly they had ROI.”
Adapting modern software to the 1200s
Built primarily in the 1100s and 1200s, Notre-Dame’s design and construction is much different than modern buildings created with the help of 3D design software. But that also means modern BIM tools find older buildings to be a bit of a challenge.
Revit has built-in intelligence and rules that help with making walls straight and aligning elements like columns, beams and the floor. These are typical features that usually make the user’s life easier, but they didn’t quite work for Notre-Dame.
“In Notre-Dame, nothing was straight. It was impossible to do anything,” Mangon said. “So we had to add capabilities to remove some of the logic in Revit to be able to support these kinds of projects in the future. Now we think that this type of technology could be used for a broader scope than just buildings from the last 50 years.”
How the Notre-Dame BIM model was used
Once the restoration team had the BIM model, it was time to put it to use. Here are 4 ways it was used in the restoration:
Scaffolding
Notre-Dame’s repairs required extensive use of scaffolding inside and outside of the building. The cathedral is also covered in complex geometry that can be difficult to perfectly match with scaffold. The BIM model was an important resource for planning the temporary structure.
“They spent a lot of time using the model to design the scaffolding digitally. Every single bar, every location of the scaffolding was predefined months before it was installed,” Mangon said.
Planning construction
The crane at a construction site is one of the most critical pieces of equipment. The BIM model was used to ensure that the crane could be fully used on the job site and reach all deliveries, no matter if they arrived via boat on the Seine River or via truck on nearby roads.
“They used the model to know exactly on which day, which materials were arriving and where the truck needed to park,” Mangon said. “They simulated every minute of the construction process digitally.”
Planning with the BIM model extended to creating instructions for individual workers as well. Many of the processes used to originally craft Notre-Dame are not in use any more, requiring extensive planning with the tradespeople. The BIM model was a key tool at every phase of planning out their work.
Lighting
As a tourist hotspot, the original Notre-Dame had few chances to close and make changes. That meant that the historically dark building remained fairly dim. The restoration provided the opportunity to renovate the building, and specifically, its lighting.
To understand what kind of lights needed to be put inside and where they would be located, engineers again turned to the BIM model.
“It’s very easy in the BIM model to add a direct light or diffuse light, and put it on top, at the bottom, on the side, or wherever. You can really simulate the way it’s going to look. So that was a byproduct of also using BIM for the project,” Mangon said.
Restoration of surroundings
The restoration and reopening was also a chance to improve Notre-Dame’s surroundings. Autodesk’s team scanned the surroundings of the cathedral, creating a model that included the utilities and buildings in the area.
“[The city of Paris] used this digital twin for the architectural contest. So four different companies actually bid on the renovation of the surroundings, including a new museum, new parking, new areas, and they used the digital twin that we created,” Mangon said.
The future of Notre-Dame
Although Notre-Dame reopened this weekend, restoration work continues. The cathedral’s website reports that the restoration of the chevet and sacristy will happen in 2025 and installation of stained glass windows will occur in 2026.
The cathedral’s small stairs and tough-to-navigate spaces mean the BIM model will continue to be used for these projects and for future maintenance and restoration. To enable this, the massive digital asset will be given to the church in Autodesk Construction Cloud.
As the project nears its end, Mangon’s biggest takeaway from the restoration is that none of the work his team has done would have been possible without the initial scans of Notre-Dame.
“I think it’s important to scan historical landmarks,” Mangon said. “If a disaster happens… at least we have something to start with.”
He pointed to the importance of the movement to help preserve Ukraine’s cultural heritage by 3D scanning monuments. The war in Ukraine has destroyed numerous structures, but with these scans, they are not gone forever.
“In the future, technology could help bring to life some of these destroyed structures,” Mangon said.
