A category of policy that didn’t exist five years ago

Until roughly 2019, state-level preemption of local zoning was a fringe idea in US housing policy. Local control over land use had been treated as untouchable for nearly a century, with state legislatures historically deferring to municipalities on what could be built where.

That changed. Oregon’s HB 2001 in 2019 became the first significant state law overriding local single-family-only zoning at scale. California followed with SB 9 in 2021. Washington passed HB 1110 in 2023. Massachusetts has implemented the MBTA Communities Act since 2021. Montana, Vermont, Maine, and several other states have advanced their own versions. Each is different in design; together they represent the most consequential housing-policy development at the state level in a generation.

What these laws actually do

The laws share a common structural move: state governments establish a floor on what local jurisdictions must allow, particularly with respect to multifamily housing.

Oregon HB 2001 (2019) legalized duplexes in cities of 10,000+ and triplexes/fourplexes in cities of 25,000+, on lots zoned for single-family homes. Implementation was phased through 2022.

California SB 9 (2021) allowed lot-splits and duplexes by-right on most single-family lots — effectively allowing four units on what had been a single-family lot. Implementation has been mixed, with some local governments adopting compliant ordinances quickly and others creating procedural barriers.

California’s broader package includes SB 10 (allowing local governments to opt into denser zoning near transit), AB 2011 (enabling 100% affordable housing on commercial sites), and ongoing Housing Element reform that conditions state grants on local affordable-housing planning.

Washington HB 1110 (2023) is the most ambitious state-level reform to date — requiring duplexes on most single-family lots statewide, fourplexes in cities of 25,000+, and sixplexes near transit. Implementation began in 2024.

Massachusetts MBTA Communities Act (2021) requires the 177 cities and towns served by MBTA transit to allow at least one zoning district where multifamily housing is permitted by-right at 15+ units per acre. Implementation has been contested; several towns have refused to comply, with state enforcement actions following.

Montana SB 528 / HB 819 (2023) legalized duplexes in cities of 5,000+, with some additional reforms.

Vermont Act 47 (2023) requires towns to allow duplexes in residential zones served by water and sewer.

What’s working

The laws are too new for full empirical assessment, but early indicators are encouraging:

Permit data. Cities with state-mandated zoning reform are issuing more multifamily permits than they were before, in measurable proportions. The effect is uneven by city, but in compliant cities it’s real.

Production pipeline. Multi-unit projects are advancing in jurisdictions where they would have been illegal three years ago. Conversion of existing single-family homes into duplexes (and small multi-unit projects) is occurring.

Political durability. No state that has enacted significant zoning preemption has reversed it through subsequent legislation, despite local pushback in many cases. The political coalitions supporting these reforms have, on the whole, held.

Federal interest. HUD’s YIMBY initiatives, federal-grant conditions tied to local zoning practices, and federal guidance on exclusionary zoning have all advanced in parallel with the state-level work.

What’s been harder

Compliance is uneven. Local jurisdictions that opposed state-level reform have often slow-walked implementation, added procedural barriers (additional design review, fees, parking requirements that effectively block compliant projects), or refused outright.

The MBTA Communities Act in Massachusetts is the highest-profile compliance fight. The state attorney general has sued towns that refused to adopt compliant zoning. Litigation is ongoing.

In California, SB 9 implementation has been substantially less productive than initial projections suggested. Many lot-splits and duplexes that would be allowed by-right require local approvals that local jurisdictions have made costly or slow. Subsequent legislation (SB 423 streamlining, AB 2011 commercial-conversion rules) has tried to address this.

Tenant-protection coupling has been weaker than housing advocates would prefer. Most state preemption laws focus on supply expansion without coupling tenant protections (just-cause eviction, rent stabilization). The Oregon framework includes some tenant protections; most others don’t.

What’s next

Expanding the laws that work. Several states with enacted reforms are considering deeper preemption — moving from duplexes to fourplexes by-right, expanding ADU rules, addressing parking minimums, allowing missing-middle housing.

Closing implementation gaps. Subsequent legislation in California (SB 423, AB 2011, ongoing) addresses the friction points where SB 9 has underperformed. Oregon and Washington have implementation-monitoring infrastructure.

Bringing more states in. Active reform efforts in Connecticut, New York, New Jersey, Colorado, Maryland, Illinois, Minnesota, and others are at various stages.

Federal action. Federal grant conditions for transportation, housing, and economic-development funding could meaningfully reward states and cities that allow housing supply. The Biden administration began moving on this; continued movement depends on the next administration.

Coupling supply with tenant protection. The next generation of preemption laws would, ideally, include both — supply expansion to address shortage, tenant protections to ensure existing residents aren’t displaced as new construction arrives.

What to watch

• Compliance enforcement in Massachusetts, California, Washington — the empirical test of whether state preemption produces real change or stops at the statutory threshold.
• Reform proposals in CT, NY, NJ, CO, MD and other states.
• Federal grant conditions for housing, transportation, and economic development funding.
• Tenant-protection coupling. Whether the next wave of reforms includes both sides of the equation.
• Ballot initiatives. Several states are considering ballot measures to either codify or roll back zoning preemption.

Bottom line

State zoning preemption is the most consequential housing-policy development in a generation. The laws are too new for full assessment, but the early evidence is encouraging: permit data is up, projects are advancing, political durability has held. Closing implementation gaps and coupling supply expansion with tenant protections are the priorities of the next phase. The path from here is unromantic, technical, and slow — and is producing the most concrete progress US housing policy has seen in decades.