Early on, housing lots in San Francisco were subdivided into plots as little as 25 feet wide -- just enough room for a parlor and a staircase.

Reported by Sarah Craig. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Paul Lancour, Ryan Levi and Suzie Racho. Additional support from Julie Caine, Ethan Lindsey, Katie McMurran and David Weir. Theme music by Pat Mesiti-Miller. Ask us a question or sign up for our newsletter at BayCurious.org. Follow Olivia Allen-Price on Twitter @oallenprice.

Why Are San Francisco Houses So Close Together?

Bay Curious is a show about your questions – and the adventures you find when you go looking for the answers. Join host Olivia Allen-Price to explore all aspects of the San Francisco Bay Area – from the debate over "Frisco", to the dinosaurs that once roamed California, to the causes of homelessness. Whether you lived here your whole life, or just arrived, Bay Curious will deepen your understanding of this place you call home.