Nationwide Trends in ADU Regulations

In the last six months, municipalities from coast to coast have been rethinking how their zoning codes and planning processes can support more flexible housing options through accessory dwelling units (ADUs). Across 150 cities, local governments are updating regulations—not only to streamline development and increase housing supply but also to align with evolving state mandates and affordability goals. Below we break down the major themes emerging from these decisions. However, first we dive into some history on ADUs.

Historical Overview of ADU Regulation in the U.S.

Accessory Dwelling Units (ADUs) – often called granny flats, in-law suites, or backyard cottages – have evolved from niche housing to a mainstream development strategy amid housing shortages. Early ADU policies were largely restrictive. In the mid-20th century, single-family zoning dominated U.S. cities, effectively outlawing secondary units on residential lots. California was a notable early mover: in 1982 the state enacted a law preventing localities from outright banning ADUs on single-family lots. However, cities found workarounds, imposing onerous permits and design standards that kept ADU approvals low. A 2002 California law (AB 1866) tried to fix this by requiring ministerial (by-right) approval for ADUs, bypassing discretionary reviews. Still, many local governments layered on conditions that made ADU construction impractical in practice. The result was a few scattered “granny flats” rather than a scalable housing solution.

The modern ADU boom began in the mid-2010s, driven by state-level reforms. Facing housing affordability crises, several states passed landmark legislation to override local barriers. California’s Senate Bill 1069 (in 2016) was a watershed moment, requiring cities to permit at least one ADU per single-family lot and streamlining approvals.

State vs. City Regulation: Balancing Statewide Mandates and Local Control

State governments and cities have engaged in a dynamic interplay over ADU regulation. Traditionally, zoning was the domain of local governments, leading to a patchwork of ADU rules. In recent years, however, states have increasingly used preemption to override local zoning and ensure ADUs are broadly permitted.

In our analysis, we saw that:

• California Cities: From Santa Ana to Corona and San Diego, ordinances now reflect state mandates (such as SB 1211 and AB 2533) by eliminating restrictive parking requirements, expanding allowable ADU sizes, and legalizing previously unpermitted units. These updates aim to remove inconsistencies between local codes and state housing policies.
• Arizona Cities: Decisions in Phoenix, Tucson, Chandler, and Scottsdale illustrate efforts to update setback, density, and design provisions in line with HB 2720 and related state guidelines, thereby fostering more uniform housing policies.

A Wave of Zoning Code Revisions and Rezoning Actions

Municipalities are increasingly using zoning modifications to remove barriers for ADU construction. Cities such as Denver, Phoenix, Tempe, and Nashville have approved multiple spot rezonings and comprehensive code amendments that:

• Broaden Permissible Uses: Many jurisdictions now allow ADUs as a by‐right use in residential zones, often eliminating previous restrictions tied to legacy classifications.
• Simplify Permitting Processes: Updates include streamlined procedures and set timelines for reviewing ADU applications, reducing administrative hurdles.
• Modernize Outdated Regulations: Denver, for example, has removed obsolete zoning districts and clarified building standards—measures that support a uniform approach to ADU integration across neighborhoods.

Enhancing Housing Affordability and Flexibility

The renewed focus on ADUs is closely tied to affordable housing initiatives. Several cities are leveraging ADUs as a tool to:

• Increase Housing Options: Whether through rezoning (as seen in Nashville and Oklahoma City) or through special use permits (in Los Angeles and Richmond), many decisions directly support adding units in established neighborhoods.
• Facilitate Affordable Homeownership: Cities like Riverside and Anaheim are pairing ADU policies with financial assistance programs or grant applications. Such measures are intended to lower barriers for homeowners seeking to create additional rental income or multigenerational living solutions.
• Support Sustainable Urban Growth: By reducing parking requirements and streamlining design standards, municipalities are making it easier to integrate ADUs into existing urban fabrics without compromising neighborhood character or infrastructure capacity.

Notable Regional Highlights

Denver’s Cluster of Decisions: With multiple spot rezonings and map amendments, Denver is actively transforming long-standing residential zones. Efforts include both targeted rezonings—for instance, the update at 1920 South King Street to allow ADU additions—and citywide initiatives to simplify zoning maps.

Honolulu’s Forward-Looking Policies: Honolulu has not only amended its ADU regulations but also extended incentive programs until 2030, signaling a long-term commitment to expanding housing options in response to its chronic affordability challenges.

Innovative Variances and Special Permits: In cities like Richmond and Los Angeles, special use permits are being used to enable ADU development in areas where traditional zoning might otherwise inhibit additional housing.

Conclusion

Based on our analysis, it seems that municipalities nationwide are shifting toward making ADUs a cornerstone of their local housing strategies. We’ll keep tracking these decisions and periodically update this article to reflect the newest decisions related to ADUs.

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Bye now,
Daniel Heller
daniel@re-zone.ai