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Side stepping the French issue..... & Brexit implications....
It is the green oak bit that interests me. I have crawled arond the interiors of a couple of cathedral roof spaces looking at the construction & joints. I would assume that during the lenthy build time the spire & roof were open to the elements, so from that guess the timber was not dry when it was pegged & jointed.
But was it 'green'? ...partially seasoned?
Quite large barns are made from Green timber & survive well...?
 
whereistheceilidh said:
Side stepping the French issue..... & Brexit implications....
It is the green oak bit that interests me. I have crawled arond the interiors of a couple of cathedral roof spaces looking at the construction & joints. I would assume that during the lenthy build time the spire & roof were open to the elements, so from that guess the timber was not dry when it was pegged & jointed.
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You're right. Kiln drying is a relatively modern innovation so anything made out of wood before about the late nineteenth century would have been either air dried or green. Big lumps of oak used for the construction of barns, cathedrals, churches, large houses, etc would have, at best, had some time to dry a bit stickered up in a draughty shed. All the same, any oak larger than about 100 mm square in section is going to take years to air dry to something like, at best, 20% MC here in the UK: lower moisture content may be achievable in drier parts of Europe. In reality, a large piece of oak, 150mm+ in section is most unlikely to ever air dry through to the centre to 20 - 25% MC.

The wood in Notre Dame cathedral's roof/spire parts, etc would have been pretty wet when those structures were made. I can't imagine the replacement roof, etc will be made with anything other than similarly wet oak, or at best a bit of air drying. The completed, thus sheltered roof structure will become drier and stronger over several years, perhaps taking as long as a decade or more. Those working on the repairs or replacement roof/spire parts will allow for this by overbuilding these replacements so that they will be at least 'adequate' when new knowing that as the wood dries the structure will become stronger. Slainte.
 
I do wonder whether use of green timber was a deliberate choice, or whether it was driven by logistics - no kiln drying, time taken to air dry, storage capacity, investment required to cut and transport oak before use etc.
  • if green oak is un or part seasoned, and air dried oak with a moisture content of (say) 15% in equilibrium with the surroundings, all oak eventually becomes air dried - it is just a matter of time which may depend on whether it is under cover or exposed.
  • unseasoned wood (oak in this case) distorts as it dries due to initial variations in moisture content and grain direction. Can craftsmen anticipate this or is it relatively random
  • green oak is (I think) much heavier than dried. This must have made a big difference to construction techniques and effort before mechanised handling.
  • in compensation for the extra weight, green oak is much easier to work than seasoned.
  • the stresses on that upon which oak beams etc were laid would need to cope with a greater weight initially than once the timber had dried. This may be a built in safety factor - if the building does not immediately collapse, over subsequent years the structure gets lighter
  • as wood shrinks as it dries be used by craftsmen who understand these things to make the structure stronger - tighten joints, lock pegs in position, etc.
 
Adam W. said:
It will most likely end up being much drier than 20% under a roof.

Let's also not forget that the carpenters working on this roof are Compagnons du Devoir or their apprentices and will certainly know what they are doing.
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Agreed. Wood in roof spaces tends to settle out at somewhere between 16% and 18% MC. That applies primarily to occupied buildings, e.g., houses and commercial buildings. At what MC the wood in the roof space of Notre Dame cathedral will be dependent upon how the building is used and what climate control measures are in place in the used space, but my guess is that the wood in the roof structure will eventually reach numbers reasonably close to the ones I mentioned above. Slainte.
 
Terry - Somerset said:
I do wonder whether use of green timber was a deliberate choice, or whether it was driven by logistics - no kiln drying, time taken to air dry, storage capacity, investment required to cut and transport oak before use etc.
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It will be a deliberate choice. The practicalities, time required and cost of kiln drying large baulks of oak for this type of job would be enormous, and a very large failure rate is highly likely, e.g., case-hardening, core collapse, honeycombing, shakes/checking, etc. Oak is a particularly refractory wood to dry, and kilning big lumps of the stuff is virtually unheard of. In reality, air drying a, say, 250 X 250 mm section beam of oak to an MC of 20% or below just isn't going to occur over even a number of years, certainly not in the climate prevailing here in the UK, and I'd guess throughout most of, if not all of France.

The repaired roof will be made out of green oak, or at most, oak that's had only a minimum of air drying. The craftspeople working on the replacement will know what they're doing, or had better know what they're doing, and will allow for all the factors you mentioned, and probably more that you didn't. Slainte.
 
Sgian Dubh said:
Agreed. Wood in roof spaces tends to settle out at somewhere between 16% and 18% MC. That applies primarily to occupied buildings, e.g., houses and commercial buildings. At what MC the wood in the roof space of Notre Dame cathedral will be dependent upon how the building is used and what climate control measures are in place in the used space, but my guess is that the wood in the roof structure will eventually reach numbers reasonably close to the ones I mentioned above. Slainte.
Click to expand...
Air dried to 18% is easily achieved outside in the UK and that will also occur in a roof space in Paris. Just because a timber has a large section, it doesn't mean that it will retain moisture indefinitely in a dry space.
 
Doug B said:
I wonder if the guy who worked on that went on to do cls production for B&Q ;)
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quality control at volkswagen mexico USA. Speaking from experience as an unintentional repeat owner. May have moved on to hyundai now (based on later experience).
 

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