He said the cathedral is still at risk of collapse after a fire struck the cathedral in April, destroying the roof and spire and damaging the windows and vaults. He said alternative materials to wood might have resulted in further damage to the cathedral.
"The cathedral has been there for 800 years. Had it been built in concrete or steel it would not still be there," he further added.
"Even with all the (chemical) protection treatments, given the intensity of the blaze... the steel would have held for half an hour and then it would have twisted, pulling on the walls and everything would have collapsed."
He said that even if metal or concrete roofs were lightweight, the building's structure is built for a heavy roof, and that such Gothic cathedrals "stand up structurally because there is a large mass on the vaulted ceiling … they only work because the roof is heavy."
"We are lucky to have all the information we need to rebuild an identical roof."
The comments came after Jean-Louis Georgelin, army general in charge of the restoration, said the call for an oak roof is just "lobbying" by wood industries. He said all options will be analyzed before anything is put in place.