Witold Rybczynski's recent post about the tragic fire at Notre-Dame de Paris provides an interesting summary of cathedral construction techniques over the years:

The Paris fire is also a reminder of what a weird hybrid structure Gothic cathedrals really are. The ancient Romans roofed their basilicas and baths with concrete vaults (the Pantheon with a dome), and the Byzantines used thin domes and vaults of brick. Over time, builders lost these skills and Romanesque cathedrals were roofed with exposed timber rafters like big barns. This made the buildings highly susceptible to fire, often caused by lightning strikes. The solution, pioneered at Durham Cathedral in the 11th century, was to build a lightweight ribbed stone vault over the nave. The timber roof remained, so the vault had no structural function (except to support itself) but it separated the interior from the flammable roof above. This was largely effective as the April 15 fire shows.

Below is an image from the WSJ depicting Notre-Dame's timber rafters and showing the extent of the area consumed by the fire. Fortunately, relatively little of the cathedral was actually destroyed.

Witold Rybczynski's recent post about the tragic fire at Notre-Dame de Paris provides an interesting summary of cathedral construction techniques over the years:

The Paris fire is also a reminder of what a weird hybrid structure Gothic cathedrals really are. The ancient Romans roofed their basilicas and baths with concrete vaults (the Pantheon with a dome), and the Byzantines used thin domes and vaults of brick. Over time, builders lost these skills and Romanesque cathedrals were roofed with exposed timber rafters like big barns. This made the buildings highly susceptible to fire, often caused by lightning strikes. The solution, pioneered at Durham Cathedral in the 11th century, was to build a lightweight ribbed stone vault over the nave. The timber roof remained, so the vault had no structural function (except to support itself) but it separated the interior from the flammable roof above. This was largely effective as the April 15 fire shows.

Below is an image from the WSJ depicting Notre-Dame's timber rafters and showing the extent of the area consumed by the fire. Fortunately, relatively little of the cathedral was actually destroyed.