You know the building: Two stories, an apartment unit on each floor, usually with bay windows and a facade of brick or greystone.

But how did the two-flat become so popular, and who was it originally built to serve?

In our last episode, we looked at the types of places Chicago’s single women lived in at the turn of the 20th century.

In today’s episode, we explore the Bohemian origins of the humble Chicago two-flat. As it turns out, the advent of the two-flat mirrors the development of the city’s middle class.

“Our design No. 144 is a two-family flat designed for a money making proposition,” begins a 1915 ad enticing homebuyers to build a two-flat. “Anyone wanting a comfortable home and at the same time a good income on the investment will do well to consider this proposition.”

Plus, we answer another housing-related listener question: why are Chicago fire escapes distinctively wooden (read: flammable) and are they actually effective during fires?

This episode was reported by Chris Bentley and was originally published in 2014.