The Resurgence of the Backyard Cottage: A Chronological History of ADU Permitting in America
Accessory Dwelling Units (ADUs)—also known as granny flats, backyard cottages, or in-law suites—have emerged as one of the most promising solutions to America's housing shortage. Yet, these small, independent living spaces are not a modern invention. They are a revival of a centuries-old American housing tradition that was nearly regulated out of existence before making a dramatic comeback. This article traces the chronological history of ADU permitting across the United States, culminating in the recent wave of zoning reforms in the Twin Cities market.
The Early Years: An American Tradition
Before the mid-20th century, building secondary units on a single-family lot was a common and largely unregulated practice. Early settlers often built small homes to live in while constructing their primary residences. Wealthy landowners built carriage houses for horse-drawn carriages and stable hands, many of which were later converted into rental apartments. In the early 1900s, garage apartments and alleyway homes provided flexible, workforce housing
However, the post-World War II suburban boom fundamentally changed the American housing landscape. Fueled by federal policies and the rise of the automobile, municipalities rapidly adopted single-family zoning ordinances. These strict land-use regulations mandated that only one home could be built per lot, effectively banning the legal construction of ADUs in most American suburbs. For decades, ADUs practically ceased to be built legally, though many homeowners continued to construct them "under the radar" without permits.
The 1980s and 1990s: The "Granny Flat" Experiment
The first signs of a regulatory thaw appeared in the 1980s. As housing costs began to rise and the population aged, some municipalities recognized the need for alternative housing options. In 1982, California became one of the first states to enact legislation encouraging local governments to adopt "second unit ordinances." During this period, communities in Long Island, New York, and other areas also began experimenting with ADU policies, primarily framing them as "granny flats" that allowed elderly parents to age in place near their families. Despite these early efforts, ADU construction remained sluggish. Local governments often imposed severe restrictions, such as requiring the property owner to live on-site (owner-occupancy requirements), mandating off-street parking, and setting strict size and aesthetic standards. These discretionary review processes meant that getting an ADU permitted was expensive, time-consuming, and highly uncertain.
The 2000s: Laying the Groundwork for Reform
Recognizing the potential of ADUs to serve older adults, the AARP and the American Planning Association (APA) partnered in 2000 to publish a highly influential "Model State Act and Local Ordinance" for ADUs. This document provided a blueprint for state and local legislators to ease restrictions and legalize ADUs. Throughout the 2000s, the concept of "gentle density" gained traction among urban planners. However, local opposition—often rooted in fears of increased traffic, altered neighborhood character, and declining property values—kept most municipal ADU ordinances highly restrictive. By the late 2010s, it became clear that piecemeal local reforms were insufficient to spur meaningful ADU development.
The 2010s: The State Preemption Rebellion
The true turning point in ADU permitting occurred in the late 2010s, driven by a severe statewide housing crisis in California. Frustrated by local governments blocking ADU construction, the California state legislature passed a series of aggressive preemption laws starting in 2016.
Key California legislation included:
SB 1069 (2016): Mandated that cities approve ADUs ministerially (without discretionary hearings) and capped parking requirements.
SB 13 and AB 68 (2019): Eliminated exorbitant impact fees for smaller ADUs, shortened approval timelines, and allowed for both an ADU and a Junior ADU (JADU) on a single-family lot.
The results were staggering. Prior to 2017, Los Angeles permitted only a few hundred ADUs per year. By 2018, that number had leaped to thousands, and today, California permits tens of thousands of ADUs annually. Following California's lead, other states facing housing shortages enacted their own statewide ADU reforms. In 2019, Oregon passed HB 2001, a landmark bill that not only legalized ADUs but essentially banned exclusive single-family zoning in large cities by allowing "middle housing" like duplexes and triplexes. Washington, Maine, and several other states soon followed suit, stripping local municipalities of the power to ban ADUs or impose prohibitive parking and owner-occupancy rules.
The 2020s: The Twin Cities Embrace Gentle Density
While the West Coast was leading the state-level ADU revolution, the Midwest—particularly the Twin Cities of Minneapolis and St. Paul—was pioneering its own approach to zoning reform.
Minneapolis: The 2040 Plan
Minneapolis made national headlines when it adopted the Minneapolis 2040 Comprehensive Plan, which took effect in 2020. The city became the first major U.S. municipality to eliminate exclusive single-family zoning citywide, allowing duplexes and triplexes on lots previously reserved for one home. Minneapolis had actually legalized ADUs citywide back in 2014, but the initial rules were restrictive. In 2021, the city took a crucial step by eliminating the owner-occupancy requirement, which had severely limited the financial viability of ADUs for investors and homeowners alike. Today, Minneapolis allows attached, internal, and detached ADUs, with detached units permitted up to 1,300 square feet (subject to lot coverage limits)
St. Paul: Ordinance 23-43
St. Paul initially allowed ADUs in 2016 along the Green Line transit route before expanding them citywide in 2018. However, like Minneapolis, strict regulations stifled development. Between 2016 and 2022, St. Paul saw fewer than 30 ADUs built. Recognizing the bottleneck, the St. Paul City Council passed Ordinance 23-43 in late 2023, representing one of the most progressive ADU policies in the Midwest. The key changes included:
• Eliminating Owner-Occupancy: Property owners are no longer required to live in the main house or the ADU
• Doubling Density: Single-family lots can now host up to two ADUs (e.g., one internal and one detached)
• Removing Lot Size Minimums: Smaller parcels are no longer excluded from ADU development
• Height and Size Allowances: Detached ADUs can be built up to 25 feet tall (allowing for units above garages) and up to 800 square feet.
The Suburban Shift
The momentum has spilled over into the Twin Cities suburbs. In 2024, cities like Edina and Bloomington updated their municipal codes to embrace ADUs. Bloomington, for example, initiated code amendments to allow detached ADUs, recognizing that attached-only rules were a barrier for homeowners wanting to utilize backyard space or build above detached garages. Furthermore, the Minnesota State Legislature has taken an active interest in housing reform. In 2024 and 2025, lawmakers debated statewide housing omnibus bills aimed at streamlining environmental permitting and further reducing local zoning barriers, signaling that the state may soon adopt the preemption models seen on the West Coast
Conclusion
The history of the Accessory Dwelling Unit is a testament to the evolving nature of American urban planning. Once a traditional housing staple, ADUs were regulated out of existence during the era of suburban sprawl. Today, driven by an acute need for affordable, flexible housing, they are making a triumphant return. The recent regulatory overhauls in the Twin Cities demonstrate a critical lesson learned from decades of policy experiments: simply legalizing ADUs is not enough. To truly unlock their potential, cities must dismantle the financial and bureaucratic barriers—such as owner-occupancy rules and parking mandates—that prevent homeowners from breaking ground. As Minneapolis and St. Paul continue to refine their zoning codes, the Twin Cities market stands poised to become a leading example of how "gentle density" can help solve the modern housing crisis.
References
[1] AARP. "ADUs Are an American Tradition."
[2] Harvard Joint Center for Housing Studies. "Single-family Zoning: Can History be Reversed?"
[4] Metropolitics. "The Second Coming of the Accessory Dwelling Unit."
[6] AARP. "ADU Model State Act and Local Ordinance."
[7] Creation G, Inc. "The History of ADUs in California (and Why 2025 Feels Different )."
[8] Shovels.ai. "America's ADU Boom: What 2.8 Million Permits Reveal About the Housing Solution."
[10] Local Housing Solutions. "Minneapolis 2040 Plan."
[11] Strong Towns. "ADUs Are Working Great—Just Not for the Twin Cities."
[13] Steadily. "ADU housing laws and regulations in Minnesota."
[14] City of Bloomington, MN. "Accessory Dwelling Unit (ADU ) Code Amendments."
