A first dusting to start with the Notre-Dame interior rehabilitation

Notre-Dame interior rehabilitation was a delicate operation. After the fire, it is impossible to know the precise state of the vaults in the nave, choir and transept. No one is allowed to walk or work underneath them. Before any work is undertaken, rope access technicians secure the vaults by laying a temporary layer of plaster and wire from above. This temporarily prevents stones from coming loose and falling into the cathedral. Interior scaffolding can then be erected from the cathedral floor, providing access to all the upper parts of the cathedral. External scaffolding is used to support the wooden hangers that relieve the pressure of the flying buttresses on the vaults (See “Notre-Dame reconstruction after the fire, for the next centuries“).

More detailed information is available on our website:

• Notre Dame in fire – What happened ? Which consequences ?
• Securisation of Notre Dame after the fire of 2019
• Notre-Dame reconstruction of the buiding after the fire, for the next centuries
• Notre-Dame Reopening on December 8th, 2024 – An awaited moment
• 15 of the best hotels near Notre-Dame-de-Paris

The 4 stages of Notre-Dame’s refurbishment

You can find out more about the 3 stages that preceded this rehabilitation post by clicking on the following:

• Notre Dame in fire – What happened ? Which consequences ?
• Securisation of Notre Dame after the fire of 2019
• Notre-Dame reconstruction of the buiding after the fire, for the next centuries

Preparing for Notre-Dame interior rehabilitation

Cathedral reconstruction scaffolding

The scaffolding is made up of thousands of metal tubes, whose technical complexity enables them to harmoniously distribute the weight of the loads they will have to support. Each wooden half-arch installed under the vaults weighs from 1 to 6 tons. More than 1,200 tons of scaffolding are thus installed on the cathedral floor, rising to heights of 27 meters! At this height, the scaffolding is covered by a hermetically sealed floor, allowing the architects to inspect the condition of the vaults up close, and the carpenters to install the under-vault hangers that will secure them. The stone cathedral is now supported by a veritable cathedral of iron.

Damage to the interior of the building

The interior of the cathedral suffered indirectly from the fire, and mainly from the collapse of part of the nave and transept vaults. Through the breaches in the collapsed vaults, lead dust emanating from the combustion of the great roof and the building’s lead cladding has seeped in, and needs to be cleaned up. At the same time, the walls and interior decor of Notre-Dame de Paris, soiled by the centuries, are being restored. A veritable renaissance, the like of which the cathedral had not experienced since its origins.

To counteract this pressure, the architects decided to relieve the flying buttresses of their own weight by placing heavy framework structures underneath them. These were to remain in place until the cathedral’s vaults and great roof were rebuilt.

At the beginning of 2022, the interior of Notre-Dame underwent its first dust removal operation. Thousands of square meters were vacuumed using THE (Very High Efficiency) vacuum cleaners, equipped with filters that trap lead particles. This operation was made possible by the presence of scaffolding throughout the cathedral, including the upper sections, installed to secure the vaults and enable their restoration.

Restoration of interior walls, paintings and statues

The rehabilitation of Notre-Dame de Paris’ interiors and stained glass windows, undertaken between 2023 and 2024, was an essential step in the cathedral’s restoration following the fire of 2019. This phase required painstaking efforts and specialized techniques to respect the building’s original aesthetic and historical heritage. It also incorporated innovations to ensure the durability and safety of the works of art and stained glass.

• Paintings and furnishings
  Works of art and interior furnishings have been restored or reproduced to restore the cathedral to its pre-fire appearance.
• New safety equipment
  Protective devices and fire alarm systems were installed to prevent future accidents.

Thorough cleaning of stone and walls

The stone walls were thoroughly cleaned using gentle techniques such as laser and micro-abrasion, to remove soot and residues without damaging the original structure. This cleaning revealed the stone’s original colors and textures, restoring the cathedral’s interior to its former glory.

To remove the dust completely, the stonemasons applied a latex sprayed in vapour form to the facings of the interior elevations and to the unpainted sculpted decorations in the stone cathedral. The latex hardens until it forms a layer on the walls that catches the volatile particles. On sculpted parts, such as capitals and ribs, the application is carried out with surgical precision by sculpture restorers.

After a few days, the latex is removed like a second skin, taking the dust with it. After a final wipe with a damp sponge, the walls are restored to their former health, and appear in all the clarity of the blonde stone that has disappeared under decades of accumulated grime.

At the same time, certain gaps in the sculpted decorations need to be restored, as in the frieze beneath the cathedral’s north rose.

Cleaning wall paintings also part of the Notre-Dame interior rehabilitation

Unlike the facings of the nave and ambulatory, or the chapels in the nave, the chapels lining the choir have been entirely painted since the restoration undertaken by Viollet-le-Duc in the 19th century. The same applies to the choir enclosure, a vast wall adorned with historiated 14th-century bas-reliefs depicting the life of Christ. They are being restored one after the other, according to a protocol put in place during the security phase.

Once the scaffolding had been erected on 4 levels, the restorers began by re-fixing the support on which the painting rests, to halt its deterioration. Using a chemical preparation selected as part of the worksite tests, they cleaned the painted surface to remove the grime that had accumulated. Finally, they reintegrate color pigments where they are lacking, taking care to choose reversible products to differentiate between the original and restored parts.

Begun just before the summer of 2022, the restoration of the chapels of Sainte Marie-Madeleine, to the south, and Saint Marcel and Saint Germain, to the north, is rapidly nearing completion. Their legibility has been restored, revealing the splendor of their original hues.

The chapels of Saint Louis, Saint Marcel and Saint Jean l’Evangéliste/Sainte Agnès are following the cleaning operation, gradually revealing decorations that had completely disappeared under the grime accumulated over the years. The other chapels, such as the axial chapel and the Saint Georges chapel, were immediately equipped with scaffolding to enable mural restorers to work on their painted decorations.

Lastly, restoration work has begun on the choir enclosure, on both the north and south sides.

Notre-Dame interior rehabilitation : cleaning the stone statues

Each of the stone and marble sculptures remaining inside the cathedral during the fire, is being cleaned by specialist restorers.

Four mausoleums in the choir were completely cleaned by sculpture restorers from autumn 2022 onwards:

• The mausoleum of Jean Juvénal des Ursins and his wife Michelle de Vitry in the Chapelle Saint-Guillaume;
• The mausoleum of Cardinal Jean-Baptiste de Belloy in the Saint-Marcel chapel;
• The mausoleum of Monseigneur Dominique Auguste Sibour in the Sainte Marie-Madeleine chapel;
• The mausoleum of Monseigneur Hyacinthe-Louis de Quélen in the Saint Marcel chapel.
• The sculpture restorers then moved on to the mausoleum of Albert de Gondi in the axial chapel, Notre-Dame-des-Sept-Douleurs. The sculptures in the nave were treated in 2023.

Notre-Dame interior rehabilitation with restoring the railings

One of the distinctive architectural features of Notre-Dame de Paris is the presence of tribunes around the central nave. These are characteristic of the early Gothic style of the 12th century.
In the 19th century, they were fitted with neo-Gothic metal railings based on designs by Viollet-le-Duc.
All dismantled and transported to the workshop, the railings are being restored and re-gilded in 2022, before being returned to their original location.

In December 2022, cleaning of the interior of the south arm of the south transept was completed. Its scaffolding is dismantled, revealing what the final state of the entire monument will be when it reopens in 2024: thanks to the work of numerous tradesmen using a wide variety of techniques, Notre-Dame de Paris will be more beautiful than it has been for centuries.

Restoration of sculptures and works of art

Sculptures, frescoes and decorative elements were restored by teams of specialized conservators and restorers. Some pieces, weakened by the fire, required careful consolidation and retouching to ensure their long-term preservation.

Treatment of floors and furnishings

Stone floors and side chapels were renovated, and damaged furnishings were either restored or replaced by faithful replicas.

Important and difficult Notre-Dame interior rehabilitation: restoration of stained glass windows

The restoration of rosettes and stained glass windows, some of which date back to the 13th century, has been meticulously restored, particularly the famous rosettes.

Cleaning and consolidation

The cathedral’s stained glass windows, although partially spared by the fire, had accumulated toxic lead residues and soot deposits. The master glassmakers carried out a very delicate cleaning, using mild solvents to preserve the original colors and shapes of the glass.

Replacing damaged parts

Certain sections of the stained glass had to be reconstructed from original models, scrupulously respecting the techniques of the time. Pieces of mouth-blown glass were manufactured and integrated by specialized craftsmen to replace damaged elements.

Modern protection systems

To protect the stained glass windows from the elements and thermal variations, modern, discreet protection systems were installed on the outside. This protects the windows without altering the cathedral’s aesthetic appearance.

Improved lighting and sound also planned in the Notre-Dame interior rehabilitation

Installation of new lighting

Modern lighting has been installed to enhance the interior of Notre-Dame, highlighting the architecture and works of art, while remaining discreet and respectful of the spiritual atmosphere of the place.

New acoustics

The refurbishment also included an optimization of acoustics. The sound system was modernized to meet the needs of religious ceremonies and concerts, taking into account the acoustic requirements of such a large, reverberant building.

Preservation of new works and innovations

Enhanced safety systems

New fire safety and surveillance systems have been integrated to protect stained glass, sculptures and wooden elements.

Integration of climatic devices

Modern humidity and temperature control devices have been installed to protect works of art, paintings and stained glass, preventing deterioration due to climatic fluctuations.
Compliance with ecological and heritage standards

Use of environmentally-friendly materials

Use of environmentally-friendly materials

The restoration of interiors and stained glass incorporated the use of environmentally-friendly materials, such as environmentally-friendly paints and preservatives.

Respect for traditional techniques

Craftsmen employed methods and materials close to those used in the Middle Ages and Gothic period, in order to preserve the building’s coherent heritage.

Notre Dame: challenges and innovations during the Notre-Dame interior rehabilitation phase

The rehabilitation phase brought the interior of Notre-Dame and its emblematic stained glass windows back to life, while respecting its historical heritage and adapting to modern conservation requirements.

The challenge of cleaning and preserving historic materials

Cleaning up soot and toxic residues

Smoke and heat have left soot and lead deposits on stones, sculptures and stained glass. Cleaning these materials without damaging them presented an immense challenge.

Innovation used

Laser cleaning was used for the first time on such a large scale on the cathedral’s stone and artwork. This technique enables precision cleaning, removing soot particles without damaging the surface, thus preserving the historic appearance of the materials.

Notre-Dame interior rehabilitation and restoring stained glass with cutting-edge technology

The challenges of cleaning and conserving old stained glass

The stained glass windows, particularly the three large rosettes, were damaged by heat and smoke. Restoring them required expertise in glass conservation and advanced cleaning techniques.

Technological solutions

The stained glass windows were dismantled and cleaned in specialized workshops, where each piece was examined, restored or, if necessary, replaced with compatible period glass. Protective techniques, such as UV and weather protection films, were added to extend the durability of the stained glass without altering its transparency.

Incorporating modern security systems without altering the architecture

Ensuring safety while respecting the building’s authenticity

The fire of 2019 highlighted the importance of modern fire detection and suppression systems. Integrating these devices without distorting the architecture presented a particular challenge.

Innovations and discrete systems

Sprinkler systems, smoke detectors and thermal sensors were discreetly installed to preserve the visual integrity of the interior. These modern devices enable rapid detection of risks and protection against possible future incidents.

Logistical management and coordination of work with hundreds of craftsmen and experts

Coordinating an international team

The restoration of Notre-Dame involved hundreds of craftsmen, architects, carpenters, stonemasons, glassmakers and engineers from all over the world. The logistical and organizational coordination of these teams was a major challenge.

Collaborative management technology

Advanced project management software was used to track progress, ensure communication between teams and anticipate obstacles. These digital tools made it possible to meet the ambitious restoration deadlines.

Notre-Dame interior rehabilitation : public awareness and involvement

Public commitment and funding

The restoration of Notre-Dame drew public commitment and global funding, mobilizing donations and contributions from countries and institutions around the world. This support made it possible to finance the crucial stages of the restoration.

Innovation in communication

Digital devices and applications have been developed to show the public the progress of the work. Virtual tours and exhibitions have raised public awareness of the importance of heritage, creating a close link between the restoration and donors.

The restoration of Notre-Dame de Paris is a testament to the human ability to preserve and pass on heritage, combining traditional techniques and modern innovations to save a symbolic building. When the cathedral reopens its doors, it will bear the marks of this unique collaboration between historical heritage and cutting-edge technology, ready to stand the test of time and future generations.