Everyone in the comments is raising the (valid) fire safety argument; however, I'd like to point out that this is a non-obvious trade-off.
How many house fires are there? How many of them are in tall buildings? How many of them would block just one stair, and not two?
Yes, there is a probability that an extra stair will save your life; however, this is a very tiny probability, against a certainty of extra living space, for everyone, every day.
How many house fires are there? How many of them are in tall buildings? How many of them would block just one stair, and not two?
Yes, there is a probability that an extra stair will save your life; however, this is a very tiny probability, against a certainty of extra living space, for everyone, every day.