I live in a classic tenement apartment, meaning the tub's in the kitchen & the toilet was once in the hall. When I moved in, in 1977, I was shown several empty apartments, one where the toilet was still in the hall. Even though I'd moved to New York only two months before from a cabin in Maine with an outhouse & without running water, I couldn't see dressing every time I needed to pee.
I also often explain that I live in a two-room studio. I've been reading John Berryman's biography of Stephen Crane, & he describes in some detail various buildings of artists where Crane lived or crashed. It got me interested in studios.
According to Charlotte Beach in Hunker, "studios were originally occupied by rich artists from wealthy families in the late 1800s. They were dubbed 'studios' because their creative inhabitants not only lived in them, but they also made their art on site, much like in an art studio." The Tenth Street Studio Building in New York City, built in 1857, is accepted as the first-ever studio apartment building.
However, Beach adds, "The studio apartment's fall from grace came through a sneaky tactic from the real estate field," when it began to use the term for one-room apartments (like mine) that were nothing like the original light-filled, high-ceilinged studios. Before that, it would have been called (if not a tenement, an "efficiency" & I probably wouldn't be nearly so chipper about it. An efficiency sounds like it's for career girls before they get married. A studio is for ARTISTS.
Now "studio" is the accepted designation for any small apartment & those olden-days studios pretty much don't exist. The Tenth Street Studio Building was torn down in 1955, & the last residents of the 170 studios above Carnegie Hall left (were forced out) by 2010.