SPIEGEL ONLINE: Mr. Zehetner, how well do you know Notre-Dame?

Wolfgang Zehetner: Pretty good. Last year, we were involved in a project from St. Stephen's Cathedral with Notre-Dame: We compared and analyzed our portals from an art historical perspective. By doing so, I know that there are very good, even three-dimensional plans of Notre-Dame before the fire, which can facilitate a reconstruction, at least on the computer screen.

SPIEGEL ONLINE: Do you think a reconstruction in five years, as President Macron has announced, for realistic? Colleagues have doubted you.

Zehetner: I think that's very ambitious. And not because I think the costs may be too high - with the current donation pledges that should work - but because I can not imagine that you can really fix all the damage that has occurred during this time. It will take more decades to do so - especially if you want to rebuild Notre-Dame true to the original.

SPIEGEL ONLINE: true to the original - what does that mean in concrete terms?

Zehetner: This means that even the delicate parts of the church have to be carved out of stone blocks again - by craftsmen. Some of these techniques are over 700 years old.

SPIEGEL ONLINE: Can not machines do that today?

Zehetner: Nowadays you can of course help with milling by computer. But the completion remains with the craftsman. That is also a charm of original Gothic buildings such as Notre-Dame: that in every detail a bit of the artist's handwriting drinsteckt. That requires know-how and tact. You can not even learn something like that in a crash course. And craftsmen who can do that, there are not many - maybe a few hundred across Europe.

In the video: So the fire was fought inside Notre-Dame

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REUTERS

SPIEGEL ONLINE: Does a true-to-original reconstruction reach its limits due to a shortage of skilled workers?

Zehetner: Yes, that's a major problem. We live in a time when people like to say, "Well, if the funding is up, the rest is already running." But it will not be that easy in the case.

SPIEGEL ONLINE: Suppose there are enough skilled craftsmen: Where do you get the material for such a true to the original reconstruction?

Zehetner: That's not easy. Normally one tries to take stone from the environment, which was already used in the original building. But I think that the quarries that have delivered this material are today exhausted or exploited or closed up: there may be skyscrapers in Greater Paris today. Therefore, in the case of Notre-Dame, I would consider it legitimate to procure the most suitable stone analyzed by geologists, say from India or Brazil.

SPIEGEL ONLINE: Not only the stone, but also the wood is currently an issue: A French expert said that the roof could not be built as before the fire. There are no trees in our regions the size of those felled in the 13th century.

Zehetner: I suppose so too. Tree trunks of the quality that should have such a roof, you will hardly be able to raise in Central Europe. One could of course take tropical or teak wood - and of course would say goodbye to the original.

SPIEGEL ONLINE: Would the faithful way from your point of view at all the right?

Zehetner: My personal wish would be to restore this medieval model for many cathedrals, this monument of gothic architecture, an icon as true to the original as possible - instead of putting down a plastic gargoyle from the 3D printer.

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Graphics: So the flames spread in Notre-Dame

SPIEGEL ONLINE: The wooden roof of St. Stephen's Cathedral burnt down completely in 1945, it was replaced by a steel structure. A role model for Notre Dame?

Zehetner: Yes, also because the steel roof has worked well with us. However, one has to say: This was done immediately after the war, so the engineers probably had more to say than the preservationists because it had to be done quickly. But that is technically a very good solution - and not as expensive as the original version.

SPIEGEL ONLINE: Technically very good, aesthetically and historically sufficient?

Zehetner: I would not express that quite strictly. It's like this: Notre-Dame forms a collective memory. The roof of the cathedral is lost. If such a component is now completely gone, it is legitimate in my view, as a substitute to choose a contemporary construction that brings the building in the long term benefits, such as lower weight and still higher stability.

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Reconstruction of Notre-Dame: "Please no plastic gargoyle"

SPIEGEL ONLINE: Would a steel construction also be safer?

Zehetner: Not necessarily. When it comes to firewood, it can be pretty well estimated how long it will take for this to burn away, and it can be used to deduce how much time you have to save people, for example. On the other hand, steel that is heated so much does not burn, but it can buckle in seconds, because it softens. So it's not like steel would protect you from all dangers.