The vaulted stone ceiling largely contained the burning roof as it collapsed, preventing extensive damage to the interior.

Its walls and interior vaulted ceiling are of stone; its roof and flèche (spire) were of wood (much of it 13th-century oak),[13][14] sheathed in lead[15] to exclude water.

[16][17] The cathedral's stonework had been severely eroded by years of weather and pollution,[18] and the spire had extensively rotted because fissures in its lead sheathing were admitting water.

About fifteen minutes later the error was discovered, but by the time guards had climbed the three hundred steps to the cathedral attic the fire was well advanced.

[35] The fire was primarily fought from inside the structure, which was more dangerous for personnel but reduced potential damage to the cathedral; applying water from outside risked deflecting flames and hot gases (at temperatures up to 800 °C or 1500 °F) inwards.

[25] Aerial firefighting was not used because water dropped from heights could have caused structural damage, and heated stone can crack if suddenly cooled.

[26] Shortly before the spire fell, the fire had spread to the wooden framework inside the north tower, which supported eight very large bells.

Fourth Arrondissement Mayor Ariel Weil stated "At that point, it was clear that some firefighters were going to go into the cathedral without knowing if they would come back out."

[26] Adjacent apartment buildings were evacuated owing to concern about possible collapse,[25] but on 19 April the fire brigade ruled out that risk.

[30] The remnants of the roof and spire fell atop the stone vault underneath, which forms the ceiling of the cathedral's interior.

[45] The cathedral contained a large number of artworks, religious relics, and other irreplaceable treasures,[46] including a crown of thorns said to be the one Jesus wore at his crucifixion, a purported piece of the cross on which Jesus was crucified, the Tunic of Saint Louis,[47][48] a much-rebuilt pipe organ by Aristide Cavaillé-Coll, and the 14th-century Virgin of Paris statue.

[needs update][52][53][54] Several pews were destroyed, and the vaulted arches were blackened by smoke, though the church's main cross and altar survived, along with the statues surrounding it.

[13] Airparif, an air quality monitoring organization, said winds rapidly dispersed the smoke, carrying it away aloft along the Seine corridor.

[113] The following Sunday at Saint-Eustache Church, the Archbishop of Paris, Michel Aupetit, honoured the firefighters with the presentation of a book of scriptures saved from the fire.

[115] Renovation presents a fire risk from sparks, short circuits, and heat from welding (roof repairs involved cutting and soldering lead sheets resting on timber[20]).

[121] The security employee monitoring the alarm system was new on the job, and was working a second eight-hour shift that day because his relief had not arrived.

[127][130] European art insurers stated the cost would be similar to ongoing renovations of the Palace of Westminster in London, which was estimated to be around €7 billion.

[131] While Macron hoped the cathedral could be restored in time for the 2024 Summer Olympics in Paris, experts expect the work could take from 10 to 40 years.

[136] French prime minister Édouard Philippe announced an architectural design competition for a new spire "adapted to the techniques and the challenges of our era.

"[138][139] The spire replacement project gathered a variety of designs and some controversy, particularly its legal exemption from environmental and heritage rules.

[144] In 2020, Jean-Louis Georgelin, a retired high-ranking French general, was appointed to oversee the cathedral's reconstruction; he died on 18 August 2023.

[145][146] On 15 April 2020, Germany offered to restore "some of the large clerestory windows located far above eye level" with three expert tradesmen who specialize in rebuilding cathedrals.

[148] Macron toured the site where works are being carried out to restore the iconic landmark and spoke to those undertaking the project about their progress so far.

In the spring of 2022, eight workshops of master glassmakers and locksmiths, selected across France, began the process of cleaning and restoration of the cathedral's stained glass windows.

[149] Macron led a video unveiling of the reconstructed building on 29 November 2024, a week ahead of the planned reopening on 7 December 2024.

[164][165] A proposal by former minister Jean-Jacques Aillagon that corporate donations for Notre-Dame should get a 90% tax deduction (rather than the standard 60%) was retracted after public outcry.

[168][169] The minister in charge of national museums and monuments, Franck Riester, predicted that further donations would materialise as reconstruction work progressed,[169] though it was reported that some who made pledges have renounced them because fundraising has been so successful.