> I’ve lived in Australia and France and I’ve always attributed the taller size of Australians to the excellent state of their ventilation in buildings. Vents (and rooms themselves) are systematically bigger than in France

The average male height in France is 178.60 cm, while in Australia it is 178.77 cm:

* https://worldpopulationreview.com/country-rankings/average-h...

Some sources even have France being higher than Australia:

* https://ourworldindata.org/human-height

> it makes no secret to me that they grew bigger

That sounds like something you made up to justify your beliefs…

So how does any of that relate to height? From what data I could quickly find, both countries are essentially equal in average height.

France is indeed ridiculously bad at ventilation (not to mention air conditioning). Restaurants, offices, even gyms - most have bad to non-existing ventilation. Coming from the States this is just insanity.