Additional dwelling units, also known as ADUs, granny flats or mother-in-law suites, are now being found in backyards across the Golden State. These units share a lot with an already built home, allowing a homeowner to generate a new source of income or more affordable housing space for their family. Since 2016 there have been 60,000 ADUs permitted. As more states start to legalize these units we are able to help alleviate the affordable housing crisis we have today.

Although ADUs are newly heard to be the solution to the housing shortage we are facing nationwide, their idea was here before zoning laws took place. In areas such as Brooklyn, some buildings had extra units built out of their basements that landlords could rent out. This allowed for someone to be able to have a home in a city they might have otherwise not been able to afford to live in the first place.

Over the last century, single-family zoning districts were cemented as the norm in California and across the US, helping to create the homogeneous and segregated suburban landscape we know today. The origin of this trend dates back to 1916 when Berkeley became home to the first single-family zoning district, intended solely for segregation purposes. This was followed by a Supreme Court ruling in 1926 which legitimized apartments as ‘mere parasites’. Such zoning prohibitions have had severe consequences for California’s housing crisis; according to one estimate, nearly 1 million units are currently missing from the state. Until recently, it has been illegal to build apartments in 75 – 90 percent of residential neighborhood zoning districts in California.
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The growth of ADUs has been particularly pronounced in Los Angeles, a city with high home prices and ideal lot sizes for developing ADUs. The number of ADU permits issued within the city increased from 80 in 2016 to an extraordinary 5,064 this year, with one in every four new homes built being an ADU. Suburban areas that have not traditionally seen much apartment development over the past four decades have also joined this growing trend; of nine sampled jurisdictions characterized by high median household incomes and home prices in the Bay Area, five had not authorized any ADU permits in 2016 but have recently seen exponential growth such that ADUs constitute most of the housing being built within them.

In 2019, California lawmakers removed barriers to legalizing ADUs throughout the state, and cities had to comply. Since then, a survey conducted by researchers at the Terner Center for Housing Innovation at UC Berkeley revealed a revolution in affordable housing — ADUs were overwhelmingly used for housing instead of short-term rentals and data collected by the state housing authority showed that most new ADUs built in exclusive suburban areas qualified as being affordable to households earning 80 percent or less of the area’s median income. This massive change in house availability came without any cost impacts to taxpayers.