What states allow ADUs? Statewide ADU laws compared

What states allow ADUs by law

A city can allow ADUs through its own zoning. A statewide ADU law is different: it forces cities, and sometimes counties, to allow them and limits the conditions they can impose. These are the states whose laws we read in the statute or enacted bill.

Other states have passed or debated ADU bills too. We left out any we couldn't confirm in the official text, so treat this as a floor, not a full count.

ADU laws by state compared

Most of these laws follow a similar pattern: a guaranteed ADU, no owner-occupancy rule, little or no extra parking. The details are where they split.

California's owner-occupancy ban is in section 66315 and its parking exemptions in section 66322; our guide to California ADU laws covers the rest. Arizona, Colorado, Vermont and Maryland are left out of this table because the text we read didn't settle all three points.

Western states

Washington

Washington's law is the closest to California's. In zones that allow single-family homes inside urban growth areas, cities and counties must allow at least two ADUs per lot: two attached, two detached, or one of each. They can't require owner occupancy, can't set a size cap under 1,000 square feet or a roof height under 24 feet, and can't charge ADU impact fees above 50% of the main home's. It applies to jurisdictions planning under the Growth Management Act; RCW 36.70A.680 makes the rules take effect at each one's next comprehensive plan update, and preempts local rules where a jurisdiction hasn't complied.

Oregon

ORS 197A.425 requires cities of more than 2,500 people and counties of more than 15,000 to allow at least one interior, attached or detached ADU for each detached house, inside the urban growth boundary. “Reasonable” siting and design rules can't include owner occupancy or extra off-street parking. Local governments can still regulate vacation rentals.

Montana and Arizona

Montana covers every city and town that zones. It allows at least one ADU by right, bars impact fees and owner-occupancy rules, and caps the ADU application fee at $250. Arizona's law applies to cities over 75,000 people and requires one attached and one detached ADU on lots where a single-family home is allowed, plus a third on lots of an acre or more if one unit is restricted-affordable. Side and rear setbacks can't exceed 5 feet, and the city can't require extra parking.

Utah and Colorado

Utah's law is narrower. It makes an internal ADU, one inside the main home, a permitted use in primarily residential zones. A city may still require one parking space, bar ADUs on lots of 6,000 square feet or less, and prohibit renting an ADU where the owner doesn't live in the house.

Colorado's HB24-1152, signed May 13, 2024, requires “subject jurisdictions” to allow one ADU wherever detached single-unit homes are allowed, with administrative approval, from June 30, 2025. It covers cities of 1,000 or more in a metropolitan planning organization area, and county areas within census-designated places of 40,000 or more in one.

New England

Every New England state has an ADU law, though their strength varies.

• Vermont. Local bylaws can't exclude one ADU within or attached to a single-family home as a permitted use. The house with an ADU gets the same review as one without, and converting an existing detached building can't face stricter criteria.
• New Hampshire. RSA 674:72 allows one attached or detached ADU as a matter of right in every district that permits single-family homes. The default cap is 950 square feet, and a town can't go below 750. A town may require the owner to live in one of the units, but not which one.
• Maine. Maine's law requires municipalities to allow an ADU on a lot with a single-family home or a 2- or 3-unit building, wherever residential uses are permitted. The owner doesn't have to live on the lot, and no additional parking can be required.
• Connecticut. As amended by Public Act 26-7, effective October 1, 2026, section 8-2o requires at least one ADU as of right on each lot with a single-family home, attached, inside or detached. Towns must decide within 65 days. Towns could opt out only before January 1, 2023; those that did aren't bound, except for long-time owners in transit-oriented districts.
• Rhode Island. Rhode Island grants one ADU by right in three cases: on a lot of 20,000 square feet or more, inside the existing footprint of a house or accessory building, or on an owner-occupied property to house a family member with a disability.
• Massachusetts. The Zoning Act bars a special permit for a single ADU in a single-family zoning district, bans owner-occupancy rules and limits extra parking to one space. Under the law's definition, the ADU can be no larger than half the main home or 900 square feet, whichever is smaller. A second ADU needs a special permit.

The newest state ADU laws

Three of the newest laws passed in 2025.

• Iowa. Senate File 592 requires both cities and counties to allow at least one ADU on the same lot as a single-family home, approved without discretionary review. They can't require the owner to live there, require extra parking, or apply a different impact fee structure than for the house.
• Arkansas. Act 313, approved March 18, 2025, requires municipalities to allow at least one ADU by right. It bans owner-occupancy and extra-parking rules and caps both impact fees and application fees at $250 per ADU. Conflicting local rules in effect on or after January 1, 2026 are invalid.
• Maryland. The Accessory Dwelling Units Act (Chapter 197 of 2025) makes ADUs state policy and requires certain counties and cities to adopt a local law allowing ADUs on lots with a single-family detached home by October 1, 2026. Check your county's new ordinance for the details.

How California compares

California goes furthest. State law requires every city to approve a conversion ADU, a new detached ADU of up to 800 square feet and a junior ADU on one single-family lot, and multiple ADUs on apartment lots. Owner occupancy can't be required for an ADU, and parking can't be required within half a mile of public transit, among other cases.

The results show. HCD's ADU handbook reports that ADUs permitted each year grew from 1,336 in 2016 to 30,354 in 2024, and made up more than 26.6% of all homes permitted statewide in 2024.

California also lets you split a single-family lot or build a second primary home under a separate law; see SB 9 vs ADU. For the changes arriving January 1, 2027, see California ADU laws for 2027, and for apartment lots, our multifamily ADU guide.

States without a statewide ADU law

If your state isn't on the list, ADUs aren't banned; they're up to your city or county. Many cities allow them by ordinance. To find out:

• Search your city's zoning code for “accessory dwelling unit” and also older terms like “accessory apartment”, “secondary suite” or “guest house”.
• Check where it's allowed. Look for which zones permit an ADU, whether it's by right or needs a hearing, and any owner-occupancy, parking or size rules.
• Check private rules. Deed restrictions and HOA rules can limit ADUs in states without a protective law. California limits them; see ADU HOA rules.
• Watch for new laws. State ADU laws now pass every year, and a city ordinance that conflicts with a new state law usually loses.

Building in California? Start with what an ADU is, then what an ADU costs in San Diego and how to hire an ADU contractor. Our verified ADU builders in San Diego are each matched to an active state license.

Common questions