After 1945, they invested the drywall + synthetic insulation . Windows nowadays have a 25-year warranty vs. 100+

Drywall is great if you need to knock out a wall.

The busiest bus route in DC is 16th St. I lived steps from the bus stop, and we couldn't hear the buses stopping and going every 2-3 mins. A few times with total silence, I heard "the fare is one dollar and...".

The stone walls were so thick on the facade and great windows, so heating and cooling was easier.

In some cities even 1960-1970 ok but most old developments in DC is pre-1920