I live in Edinburgh, and 100 year old buildings are the newest ones in the city. A good chunk of the city is what we call a “conservation area” - so you can’t modify the aesthetic of the building (windows included), but the vast vast vast majority of people outside that space have double glazed windows I’d wager.

Windows have a lifetime of only 15-30 years, though. If you have to replace them anyway, you might as well get double-pane (even if the rest of the house isn't well insulated).

I think this is the stated lifetime of insulated windows. But obviously single glazed windows were never insulated in the first place so there is no practical lifetime on them...

In my house and on my road a lot of the glass is 150+ years old.

Haha. Made of what? Come on, around here there are plenty of wooden doors and windows 70-100 yo and this is a humid climate.

What does 'lifetime' mean? Mine are nearly all original.

Windows last hundreds of years because glass lasts hundreds of years.

Modern windows don't last very long, because the seals leak, and the argon gas or whatever leaks out. The glass is still good, but the insulative quality is gone.

The parent poster didn't realize that if you don't have double pane windows, you have single pane windows, which have no gas to leak.

Even if it's mostly air it insulates quite a bit better than single pane windows. Of course worse than with the original gas filling, as the windows are optimized for maximum distance between the glass panes without having the inner gas start to "circulate" - which starts to happen at a smaller distance for air than for the noble gasses.

Yes, for sure. My house is 65 years old, and all the windows have leaked.

But my point was that windows, the glass part, lasts centuries, if not longer. Not the mere decades cited upstream.

I live in the UK and nobody is replacing windows every 15 years. 30 _maybe_

That is the stated lifetime - but they typically last much longer.