It’s been more than two years since an unexplained fire wreaked havoc on the legendary Notre-Dame de Paris cathedral—the most famous Catholic church in Paris, and one of the oldest. Thankfully, no one was hurt, but the fire burned for around 15 hours and caused extensive damage to the iconic building.
A true gem of Gothic architecture, Notre-Dame de Paris (meaning “Our Lady of Paris” in French) is one of the most recognized and visited sites in Paris with over 3 million visitors a year. Construction originally began in 1163, making it more than 850 years old.
There have been reports of possible causes of the fire, which include a possible electrical shortage during a construction renovation, but no definitive cause has been confirmed.
Many parts of the cathedral were destroyed during the fire in 2019, including the flèche, or spire as it’s referred to in Gothic architecture, and most of the lead-covered wooden roof above the stone vaulted ceiling.
Following the fire, many proposals were made for work on renovating and modernizing the cathedral’s design.
Autodesk is one of the software providers that has agreed to assist with the cathedral’s renovation and future restoration, and in April announced an official patronage with the public establishment dedicated to the conservation and restoration of Notre-Dame de Paris cathedral. Through the patronage, Autodesk is contributing its design and construction solutions, including building information modeling (BIM) software such as Revit, Navisworks, ReCap Pro and access to the overall Autodesk AEC [architecture, engineering and construction] Collection, its BIM 360 Docs Collaboration platform, as well as providing a BIM model.
We talked to Emmanuel Di Giacomo, Autodesk BIM ecosystem development manager for Europe (EMEA), in a Zoom call from France, to learn more about Autodesk’s involvement in the project.
“We’ve been involved since the beginning, so just after the fire,” said Di Giacomo. “The entire world was emotional about what happened … and our CEO [Andrew Anagnost] was really sad about what happened as well, and we wanted to help as soon as possible.”
Autodesk started by contributing a cash donation and offered to help by providing the company’s software solutions, a BIM model and technical expertise for the renovation.
Di Giacomo said that after the fire, Autodesk began to work with EPRND, the French public establishment responsible for the conservation and restoration of Notre-Dame de Paris cathedral created by President Emmanuel Macron, and Army General Jean-Louis Georgelin, along with Georgelin’s team of experts, which oversees the reconstruction process.
“We are providing them with a collaboration platform with BIM 360 because you can imagine that on such a big reconstruction, we have many companies and trades involved—approximately 250 companies, so it’s important to have a BIM strategy to reconstruct faster, in a more efficient way,” said Di Giacomo. “If you can imagine between 10-15 people on-site in each company—it’s a lot. It’s a big number of workers on-site, so you have to be sure that they can all work safely and efficiently so that is where BIM can be really helpful in that domain.”
Di Giacomo has been on-site several times since the fire occurred, and he said extreme precautions had to be taken to protect those on-site from exposure to lead particles, including on-site showers and bungalows for construction teams to have meetings.
He said there was a lot of clean up of all the debris from the fire and all the stones that fell down. The spire was completely burnt as was the carpentry—known as “The Forest”—so the site had to be cleaned up while protecting the remainder of the cathedral. The structure of the cathedral had to be reinforced temporarily and the renovation teams had to come up with a strategy to remove the scaffolding that had been completely melted.
Specifically, Autodesk offered to create a precise BIM model of Notre-Dame, and fortunately had the opportunity to create a 3D BIM model of the cathedral before the fire using its reality capture and BIM technology. It has also used recent scans of the cathedral after the fire to update the 3D models for comparison.
Di Giacomo said that Autodesk has recently finalized the BIM models because the company had been asked to create some additional models of the presbytery, the crypt, and part of the cathedral’s surroundings like its gardens and trees, in order to understand the logistics of the construction site, such as where materials should be delivered, where cranes should be positioned, and so on.
Di Giacomo said the BIM model can primarily be used in three ways. First, it can be used for site logistics like where the cranes should be placed for optimal efficiency. Second, it can assist with construction logistics, like where and when the construction materials should be placed. And third, it can be used for collaboration with Autodesk’s BIM 360 Docs Collaboration platform to streamline exchanges, planning, construction and final commissioning between all stakeholders and, of course, the owners.
“BIM will be able to help the EPRND reconstruct faster, in a more efficient way and ensure that no errors will be made because if you imagine all the trades involved in the reconstruction of the cathedral, which is huge, the process will have to be perfectly coordinated, so it’s very important to plan and execute this correctly.”
Di Giacomo added that although it has not been decided yet, the BIM model may potentially also help with fire prevention in the structure’s future operation and maintenance phase by using a digital twin. “Using a BIM model could also help in the context of the integration of all the systems because as there were no official statements about the initial reasons of the fire, we can imagine that it could have been related to an electrical problem, so as everything has been burnt inside the cathedral, like the electrical wires … they have to completely redesign where all these elements will be positioned. And you know, the cathedral is a very complex structure, and it is huge.” To put things into perspective, Notre-Dame is 127 meters (1,367 square feet in length) by 48 meters (516 square feet in width), and the main nave is 43 meters high under the roof, and 69 meters (2,226 feet) tall. The nave is the largest unit of a Gothic cathedral, and the main area for the gathering of the congregation and for processions.
Di Giacomo said that BIM can also allow them to coordinate the different disciplines and ensure that electrical wiring of the cathedral will be hidden, will be protected, and will meet current standards of construction requirements to help with fire prevention down the road.
In addition, in July 2019, the French National Assembly enacted a law requiring that the restoration must preserve the cathedral’s historic, artistic and architectural interest, which is one requirement that everyone must consider.
We asked Di Giacomo what additional challenges the renovation might entail. For starters, he said the size of Notre-Dame will be one factor, and that modeling all the structure’s intricate details will not be easy. “So, first of all, you have to take into account the big size of the monument and the fact that every element is completely different, although they may look similar. You have to have software that is flexible and powerful enough to model differences between the elements; that applies to both vertical and horizontal elements as well, so that is one of the big challenges, as well as modeling complex traditional shapes and modenatures [moldings].”
Another challenge is the size of the Revit model, which is close to a gigabyte and consists of about 12,450 Revit families. For those of us who don’t use the software, a Revit family is a group of components used to build a model, such as walls, windows, stairs, doors, fixtures, columns, and so on, with a common set of properties, or parameters, and a related graphical representation.
“We were able to achieve this, obviously because Revit allows you to do that, but it has been a different paradigm if you compare it to modeling modern buildings.… So, you can make some complex modern shapes, but it was not designed to create, you know, buildings from, the 12th century, so we had to find a specific and smart approach to be able to model all these elements.”
As for the elements Di Giacomo referred to, this includes the moldings and décor on top of the cathedral that can also be quite difficult to model, he said.
The last challenge Di Giacomo mentioned was the fact that Autodesk is using a scan-to-BIM process, so point clouds must be cleaned up to extract the right information. He said even with a high-performing tool such as Revit, it can still be challenging to put the point clouds into the software because of their size, which can be up to 15 gigabytes. But Autodesk succeeded.
Although Autodesk ReCap Pro can be used to clean up and analyze the point clouds, the laser scanning process alone is still intensive, noted Di Giacomo, because the data collected consists at least of 46,000 images, made up of 20-60 million pixels for each image.
According to Di Giacomo, the BIM model consists of approximately 12,450 precise and complex objects that were created, with most of them being adaptive components, which are extremely specific Revit families that enabled them to create complex and flexible shapes. In terms of quantities of material with BIM, Autodesk was able to calculate something like 3,000 square meters of stone walls, which represents something like 323,218 square feet; and the roof, which is around 42,250 square feet. In addition, the team created over 186 unique vaults.
With all that in mind, which sounds tedious and time-consuming, it’s no wonder it has taken close to a year just to recreate a BIM model of the structural part of the model of the cathedral alone.
“It’s been a huge and long process, which took really lots of time—more than one year—but it’s exciting because I don’t know if you’ve seen the pictures, but the model is really amazing,” said Di Giacomo. He added, “So at this time, everything is still in the planning stage and construction has not begun yet. Not everything is clear, but what is clear is that they will use the model for two or three specific use cases, as I was mentioning.”
There’s still a long road ahead as Friends of Notre-Dame de Paris, the nonprofit public charity leading the international fundraising efforts to rebuild and restore Notre-Dame Cathedral reported in March of this year that the renovation is primarily still in the cleanup and safety phase, which is expected to be completed this summer.
The government of France had announced shortly after the fire that the target date for reconstruction was spring 2024, in time for the opening of the 2024 Summer Olympics. However, rebuilding the cathedral after the fire has been delayed due to several factors, including the COVID-19 pandemic, the time needed to secure the structure, and the cleanup process alone, including dealing with toxic lead dust in the area.
Last April in an article in Time magazine, Army General Georgelin (mentioned earlier) expressed his uncertainty with that time frame, saying, “Even today we do not know what the impact will be of the coronavirus.”
In addition, many officials have expressed their doubts about the cathedral reopening in 2024, contending that it could take up to 20 years to reconstruct the building.
Another factor to keep in mind is that construction of the cathedral was done over a period of 300 years, so it’s no small feat.
However, President Macron remains optimistic after visiting the cathedral this April, saying he believes the cathedral will be ready in three years, ahead of the 2024 Olympics in Paris.
Is this possible? Di Giacomo thinks so.
“I think it’s feasible, and I think that if we succeed in applying this BIM process, we will certainly save some time and gain some time and accelerate the process of reconstruction,” said Di Giacomo. “I’m totally confident in the teams that are involved on the construction side. So even though it will be a big challenge, we will make it, I'm sure.”
And based on various reports, it’s possible that the cathedral could likely open at least in some capacity by 2024, but only time will tell. We wish the project teams luck on this triumphant task and hope to visit the restored cathedral one day.
We also got word back from Jérémie Patrier-Leitus, head of communications, development and cultural programming of the public Institution responsible for the conservation and restoration of Notre-Dame de Paris for some input on the restoration. See our Q & A below.
How did your organization’s involvement in the restoration come about?
The public establishment responsible for the conservation and restoration of Notre-Dame de Paris cathedral, chaired by Army General Jean-Louis Georgelin, special representative of the President of the Republic, was created by decree on December 1, 2019, to ensure the project management of this exceptional site, which combines the peculiarities of a historic monument and the scale of a very large construction site. It is a complex task of leading the entire operation, defining a program, and securing its funding with the aim of returning the cathedral to worship in 2024.
What will be some of the challenges of restoring the Notre-Dame de Paris cathedral?
We obviously must deal with the ongoing global health crisis. To this is added the lead and the degree of danger, to which the site is still formally subject to. Despite this triple constraint, the work is progressing well. One of the essential keys to return the cathedral to worship in 2024, in accordance with the objective set by the President of the Republic, is precise planning and the work in unity of all those working on the site. In order to do this, we must in particular organize and coordinate all the players, including architects and companies.
What is the organization’s plan for the restoration?
The last big step in the securing phase will end as planned this summer. Restoration work will begin this winter, following calls for tenders, some of which are already underway. The examination by the public establishment of the diagnostic studies carried out by the chief architects of historic monuments and their teams is underway and will make it possible to finalize the work scheduling program, the precise timetable and the budget for the restoration.
What particular Autodesk solutions will be used and what is your experience with Autodesk products?
The use of digital technologies adapted to conduct and manage the restoration work of the cathedral is an important issue. Thanks to the patronage of Autodesk, the public institution benefits from a 3D digital model of the cathedral and the software and tools associated with BIM. This is a valuable contribution. In conjunction with the chief architects of historic monuments, we are studying the possible applications of BIM and more particularly in the context of the design and management of site facilities.
What other design technology will be used in addition to Autodesk products?
Since the day after the fire, CNRS [The National Center for Scientific Research] researchers have been working to build a digital ecosystem for the cathedral. This “digital double” of Notre-Dame brings together all past and future knowledge related to the building within a collaborative platform. It accompanies the scientific study and the restoration by gradually integrating all the information and knowledge from many actors: those who produce scientific knowledge on the current and previous states of the cathedral and those who are involved in its restoration.
How long will it take to restore?
The goal is to return the cathedral to worship and visitation in 2024. That doesn’t mean it’s all over. Since the laying of the first stone in 1163, the cathedral has been under permanent construction. At the time of the fire, it was also under construction.
What is the cost of repairing the cathedral?
The securing phase, which will be completed this summer, cost 165 million euros. For the restoration phase, which will begin this winter, it is still too early to give you a precise budget. However, 340,000 donors from 150 countries raised 833 million euros in donations. Taking into account the health assessment carried out on the cathedral in 2021, this sum will be necessary to carry out the work program planned for the reopening in 2024, and beyond 2024, the work required by the health assessment of the monument due to more pathologies. This is an extraordinary project, and an exemplary restoration of the cathedral must be carried out.