My parisian building is timber framed (as many are in the city) and was built around 1860. We replaced the damaged wood this year, and it should be good for another 150 or 200 years.

It all depends how you build.

You're aware Europe has the oldest timber framed buildings and the us took their building lead from old Europe.

You act like Europe decided stone was the better solution when that's just not true, Europe by in large deforested itself into leaving stone as the only affordable solution left and only then switched off timber framed homes.

Source for 30 year rating? I'm not aware of such in either Europe or North America. I found a few sites reporting that number but couldn't find an actual authority giving that rating.

Also, there's a difference between a wood (or stick) frame and a timber frame, at least if you're including North America in context. In our terminology, a timber frame has large timber beams and columns supporting the load, and dividing walls are put in between. A stick frame house uses smaller lumber studs, and most of the internal and external walls are supporting the floors or roof above.

American houses are stick frame, and with proper maintenance a stick frame house can last easily over 100 years. Wood doesn't rot if treated and maintained properly. Settling of the foundation is a bigger problem, and simply subject to ground conditions which would impact even a steel frame house.

Timber frame is becoming more popular again for large buildings though, since ~12"/30cm timber columns have pretty good fire ratings, can support 3-4 stories, and are good carbon sinks for more environmentally friendly construction versus concrete or steel. My city is putting up some 3 story timber apartment buildings that look pretty awesome.

Long story short, wood is a great, renewable construction material if you're smart about how you build with it and how you treat it.

I do kind of wonder whether it would have been cheaper to, back then, go through and seal all of this stuff against moisture, if that is possible. It sounds like what kills it is exposure to moisture.

If they're already starting to collapse and inspections are finding a lot of instances of degraded concrete, though, I assume that it's too late for that.

EDIT: It also sounds like the stuff has been widely used in mainland Europe, not just the UK. I don't know whether the UK being particularly rainy might be a factor, but if the UK is seeing serious problems now, then it might be worth taking a look at usage in mainland Europe as well.

https://en.wikipedia.org/wiki/Reinforced_autoclaved_aerated_concrete

RAAC was used in roof, floor and wall construction due to its lighter weight and lower cost compared to regular concrete,[1] and has good fire resistance properties; it does not require plastering to achieve good fire resistance and fire does not cause spalls.[2] RAAC was used predominantly in public-sector construction in Europe, in buildings constructed since the mid-1950s.[3][4] RAAC elements have also been used in Japan as walling units owing to their good behaviour in seismic conditions.[5]

Reading some other articles, it sounds like we in the US and the Canucks do have some as well, but not much, mostly because apparently wood is cheaply available and dominates as a material, and the American construction industry isn't very familiar with use of AAC. There is only one small (13 person) US factory that produces the stuff, in Haines City, Florida.

https://www.resilientdesign.org/aac-an-ideal-material-for-resilient-buildings/

It’s no secret that autoclaved aerated concrete (AAC) has struggled to gain a foothold in North America. AAC is in widespread use in Europe, Mexico, and much of the world, but it has had trouble competing against wood-frame building here in the United States and Canada.

I couldn't find reference to specifically the reinforced form (RAAC) in the US, but looking at the factory's webpage, they list reinforced AAC roof panels as one variant that they can provide, so I assume that they must have sold some.