It's also pretty well solved in old construction. There are just a lot of post-war apartments built as cheap housing with crappy thin walls— those are where you hear your neighbors through the walls.

We've been in our current flat in Edinburgh for 9 years - we've never heard a single sound from neighbours and I know there have been families with young kids and teens living directly next to us.

It's not a really old property - ~200 year old townhouse converted to flats about 120 years ago.

Walls are roughly 1m thick sandstone.

That sounds amazing. I was just in Edinburgh and the build quality of all the stuff downtown seemed extremely high. "Not really old" is different here in SF, and the quality is terrible. Half the town was built as cheap housing for migrant/temp workers a century ago and the new stuff isn't much better.

I live in one of the older apartment buildings in SF, built in 1907. (Not much exists older than that, for... reasons) I can tell whether my upstairs neighbor drops a quarter or a dime, and I am regularly woken up by the next door neighbor's iPhone alarm clock. The whole building shakes slightly whenever a Bart train (which is pretty far underground) goes by.

Walls are roughly 1cm thick plywood, apparently. And yet it still costs a fortune!

'200 years old' is ancient in the US.

I live in a 100 year old brick tenement in Brooklyn, though, and hear very little of our neighbors myself— occasional creaking floorboards, and some sounds from the staircase near the front doors, but that's about it.

I also live in an apartment in downtown Seattle and I've never heard anyone through my walls. Maybe we live in the same building. ;-)

Three makes company?

I'm in an older (~1930) building in Belltown and have only heard my neighbor above me one time (I think a chair fell over or something). Honestly, the biggest source of noise for me is outside in the summer months when I leave the windows open.