To many people, the image of a nuclear family in a stand-alone house with a green lawn and white picket fence still represents a fulfillment of the American dream.

However, this ideal is relatively new within a broader history of housing and development in the U.S. It’s also a goal that has become increasingly unattainable.

As professors of architecture, we explore how cities change over time, and how certain building trends become commonplace through cultural, political, technological and economic shifts.

Over the past century, the U.S. has lost a rich variety of living options because of the homogenization of zoning policies that prioritize single-family housing, as well as developers’ desire to have inexpensive and easily replicated building plans.

These development prescriptions are so pervasive that it is now illegal to build anything other than a single-family house on 75% of residential land in American cities. Single-family zoning restricts the supply of affordable housing, leading to higher costs, displacement and segregation.

Enter the ADU

Diverse patterns of living arrangements across families, communities and plots of land were far more common in the 19th and early 20th centuries.

To accommodate these living situations, a range of housing types emerged: multifamily apartment complexes, housing cooperatives, and duplexes and triplexes.

There were also accessory dwelling units, or ADUs, which are sometimes called “granny flats,” “backyard homes,” “in-law suites” or “backyard cottages.”

These terms all refer to essentially the same thing: an additional unit of housing on a single lot, typically smaller in square footage than the main residence. They include full amenities – a kitchen and a bathroom, along with a separate entry from the primary dwelling. ADUs can either be attached to or detached from an existing house and can either be built from the ground up or be converted from existing spaces, like garages, basements or attics.

You may have heard of minimalist living trends such as van life and tiny homes, but the ADU was the original compact housing.

While ADUs are not new, many Americans are unfamiliar with them. A recent Freddie Mac consumer survey found that 71% of homeowners were unfamiliar with the concept, though 32% expressed interest in having one on their property once they learned about it.

Addressing the ‘missing middle’

More diverse living arrangements are both desirable and necessary.