Finished basements.
The house in 1950 had a unfinished basement and was listed at 1200 sq ft. They finished the basement and later sold it as 2400. The difference is a couple pallets of drywall.
The house in 1950 had a unfinished basement and was listed at 1200 sq ft. They finished the basement and later sold it as 2400. The difference is a couple pallets of drywall.
These also don’t exist in the south since there’s no need to get below a frost line.
If the frost line is lower, then a basement is very little extra cost since you are digging deeper and laying more concrete anyway.
If you are building on a hill, then making a 3 story house is also very little extra cost.
Anecdotally, finished basements are practically required if there is any sort of hill, which fairly common in the west, whereas they're likely to be absent for houses built on the floodplain.