Firefighting was helpless in Notre-Dame Cathedral

April 15 2019 is a day in which the world was shocked by the images of the iconic Notre Dame Cathedral in flames.

The internet got flooded by videos of firefighters trying to fight the flames that consumed one of the great monuments to the best of civilization. Unfortunately, this kind of firefight is helpless in this kind of buildings.

Gothic engineering buildings.

According to archaeologist Ted Henderson, a Gothic engineering technique used to waterproof the top of the cathedral involves placing a lead sheet roof over a wooden truss structure on top of the groin vault that serves as the ceiling of the cathedral’s nave. This results in 2 issues:

Even in modern structures, wooden truss are considered as flammable and extremely susceptible to fire. In the case of Notre Dame Cathedral, the truss was extremely flammable because the wood dried over hundreds of years.

The truss was sealed from the outside by the lead sheets. Thus, it was impervious to firefighter’s efforts.

Why Gothic Cathedrals are waterproof?

Gothic engineering uses lead sheet roof over a wooden truss with the objective to waterproof the building. Thus, when the firemen arrive on the scene and spray cathedral with water, the water is just running off the sides of the lead roof and can’t reach where the fire is actually spreading.

The combination of old dry wooden roofs (very flammable material) and the covering leads, result in buildings extremely susceptible to fire and to burn. A former NY city fire chief stated that “These cathedrals and houses of worship are built to burn”.

Another case of an iconic Gothic cathedral burned to near collapse is the Papal Basilica of St. Paul Outside the Walls, which burned in 1823.

Notre Dame on fire. Most Gothic churches are built so that they would burn (Image source: Axios)

How did the Notre Dame Cathedral fire spread?

The fire started in the cathedral’s attic, a space that is crisscrossed by giant, timber trusses. The fire began at about 6:30 p.m.

Orig of the fire (Image: NY Times)

According to The New York times, it took less than an hour for the fire to spread from the attic of the Notre Dame Cathedral in Paris across the wooden rooftop and topple its 300-foot spire.

As the fire grew hotter, the lead super-heated and melted, falling down onto the stone vault of the nave. This created an overload to vault and caused it to collapse inward, creating an imbalance of weight throughout the entire structure.

Probably, the most shocking moment was when the iconic 90 m spire collapsed. This tragedy should be an example to improve current fire protection and fire emergency procedures related to old monuments.