Which US States Require ADUs By Right —
Is Yours on the List?

States With an Effective Statewide ADU Law (19)

These 19 states (plus Washington, DC) have a statewide law in force today that requires municipalities to allow ADUs on single-family lots — some universally, some gated by city/county population size. Local governments can still regulate design, setbacks, and size within state parameters, but cannot outright prohibit ADUs where the law applies.

These states have passed a statewide law, but counties/cities are still in the process of updating their local codes to comply.

States Without a Statewide ADU Law — Local Control (28)

These states leave ADU regulation entirely to city and county governments — allowance and rules vary by municipality. A few have specific local quirks worth noting; most simply have no statewide framework at all.

Why the Reform Wave Happened — and What's Next

The drivers of the reform wave

The 2019–2026 ADU reform wave has three primary drivers. First, a worsening housing affordability crisis in virtually every US metropolitan area — ADUs offer a politically viable way to increase housing supply without the controversy of high-density rezoning. Second, bipartisan political support — effective statewide ADU laws are now on the books in both deep-blue states (California, Massachusetts, Rhode Island) and deep-red states (Montana, Utah, Arizona, Idaho). Third, the California template — California's experience showing that ADU reform dramatically increases housing production without significant adverse effects gave other state legislatures a proven model to follow.

What's likely next

Housing-policy researchers broadly expect more states to consider statewide ADU preemption in coming legislative sessions, following the pattern of the past several years. We don't speculate here about which specific states will pass legislation next or when — bills get introduced, amended, stalled, and re-referred constantly (North Carolina's HB 627/S 495 is a recent example: it passed two House committees, was calendared for a floor vote, then withdrawn the same day). We track actual enacted outcomes on each state's own page and in the table above rather than forecasting votes.

What an effective statewide law does NOT mean

Even in the 19 states with an effective statewide framework, ADUs are not unrestricted. Municipalities generally retain authority to regulate setbacks (within state minimums), maximum size (up to state maximums), height, design compatibility, and historic district standards. What these laws eliminate is the ability to simply prohibit ADUs entirely — or, in most of these states, to impose owner-occupancy requirements. Several of these laws are also population- or jurisdiction-gated rather than universal (Colorado, Nevada, Arizona, Idaho, and Utah's new detached-ADU coverage all work this way) — always check your specific municipality's current standards alongside state law.