When you think of a tiny house, you likely think of something like Walden—living amongst nature in spartan accommodations. But there's plenty of room for tiny homes in cities around the world, if you count their rooftops. These often-underused spaces represent as much as 30%of additional developable real estate in some cities. Building additional housing on rooftops isn't simple or inexpensive, but as real estate prices and rents skyrocket, many building owners are already converting rooftops into living spaces.

But what if there was a prefab home that you could simply build atop a building, adding enough space for a studio apartment, for less than the price of a car? A project called the Parasitic House is just that. Designed by El Sindicato Arquitectura, it's a 39-square-foot, A-frame house for urban rooftops.

"We were not hired for this project," says Nico Viteri, the firm's founder. "We developed it as a prototype of what we think is small and replicable solution to city and worldwide problems such as gentrification, unwanted urban sprawl, global warming, and more."