Which US States Have Passed ADU Laws?

If you’ve been looking into building an ADU, the first question is usually some version of “wait, am I even allowed to do this where I live?” The answer depends a lot on your state. Over the past few years, statewide ADU laws have spread fast, and they’ve quietly rewritten the rules in places that used to make a backyard cottage nearly impossible to permit.

As of 2026, eighteen states have passed laws that broadly legalize accessory dwelling units, and a nineteenth (Virginia) is on deck. Below is a plain-English rundown of every one, what the law actually does, and where to read the original text yourself. If you’d rather skip the research and get answers specific to your property, you can always book a call with Maxable. Curious what a unit like this runs? Start with our guide to how much an ADU costs (based on California rates).

(Pssst… the laws below change often. We update this page as new bills pass, but always confirm the current rules with your city before you spend money on plans.)

How Many States Have Passed ADU Laws?

Eighteen states have passed laws that broadly allow homeowners to build and rent out an ADU, according to the Mercatus Center’s 2025 tally of statewide ADU laws. Eleven of those states adopted their laws in just the past four years, which tells you how quickly this idea has caught on. Mercatus sorts them into ten “strong” laws and eight weaker ones, based on whether the state removed the three rules that tend to kill ADU projects: owner-occupancy requirements, off-street parking mandates, and discretionary (case-by-case) permit review.

Here’s the thing to remember as you read on. A statewide law is a floor, not a ceiling. It sets the minimum your city has to allow, and many cities choose to be more generous. So even the baseline rules below are often the worst-case version of what you can build. (If you’re still fuzzy on the size categories these laws keep referencing, our ADU sizes guide breaks them down.)

ADU Laws by State: Quick Comparison

Want the short version? This table covers the year each state’s main law passed, whether it counts as a strong reform, and the headline rule homeowners ask about most. State-by-state detail follows below.

Arizona ADU Laws

Arizona joined the club with House Bill 2720, signed in May 2024. It requires every city with more than 75,000 residents to allow ADUs in single-family neighborhoods, which covers Phoenix, Tucson, Mesa, Scottsdale, Chandler, Tempe, Gilbert, Glendale, and more.

• What’s required: Cities over 75,000 must allow at least one attached and one detached ADU on a single-family lot.
• By right: Qualifying ADUs are approved without a special hearing or discretionary review.
• Smaller cities: Towns under 75,000 can write their own ADU rules but aren’t required to meet the state minimum.

Mercatus ranks Arizona among the states that have removed the most barriers to building, putting it in the same tier as California and Washington.

Arkansas ADU Laws

Arkansas passed Act 313 in 2025, which took effect August 5, 2025 and made Arkansas one of the more homeowner-friendly states in the country. We’ve covered this one in depth in our Arkansas ADU regulations guide, so here’s the high-level version.

• By right: Every city and town must allow at least one ADU on a residential lot with a single-family home, without public hearings or special permits.
• All types allowed: Attached, detached, and internal ADUs all qualify.
• No owner-occupancy: You don’t have to live on site, so the unit can be rented for income.
• Fee cap: Application fees are capped at $250.

California ADU Laws

California has the most developed ADU market in the country, built on a decade of laws designed to make these units easier and cheaper to add. We could fill a whole blog about it (we have), so here are the must-know baseline rules. Remember, your city can be more generous than this.

• Owner occupancy: Not required and cannot be enforced by your city. The one exception is a JADU (junior accessory dwelling unit) without a dedicated bathroom.
• Sizes: Every homeowner can build at least an 800 sq ft ADU regardless of lot size or floor-area ratio. Larger sizes follow this pattern:
  • 850 sq ft for a 1-bedroom ADU
  • 1,000 sq ft for a 2+ bedroom ADU
  • Up to 50% of the main house for an attached ADU (unless that math comes in under 800 sq ft)
  • 1,200 sq ft max for detached ADUs in cities without their own ADU ordinance
  • No size cap on a garage conversion that stays within the existing footprint
• Setbacks: No more than 4 ft from the side and rear. Garage conversions within the existing footprint are exempt.
• Heights: 16 ft is allowed everywhere. 18 ft applies within half a mile of transit or on a lot with an existing two-story multifamily building. 25 ft applies to an ADU attached to the main house.
• Parking: No off-street parking required if the ADU is within half a mile of transit, inside a historic district, converted from existing space, within a block of a car-share vehicle, or in an area where on-street permits aren’t offered to ADU occupants.
• Permitting: Your city must issue a decision within 60 days, with all required revisions noted at once.

Two newer changes are worth knowing. SB 1211 now lets you build up to eight detached ADUs on a lot with existing multifamily housing (capped at the number of existing units). And AB 2533 expanded the path to legalize unpermitted ADUs and JADUs built before January 1, 2020 without impact fees, as long as they meet health and safety standards.

Colorado ADU Laws

Colorado’s House Bill 24-1152 passed in 2024 and took full effect June 30, 2025. It applies to “subject jurisdictions,” meaning cities with at least 1,000 residents that sit inside a metropolitan planning area. In plain terms, that’s every major metro: Denver, Boulder, Aurora, Lakewood, Colorado Springs, Fort Collins, and more. Small rural and mountain towns outside those areas are exempt.

• By-right zoning: Permits ADUs without extra discretionary approval.
• Flexible setbacks: Rear setbacks capped at 5 ft, or the same as the primary home.
• Lot-size parity: Cities can’t impose a higher minimum lot size for ADUs than they require for primary homes.
• Parking: Only one space can be required, and only where on-street parking is unavailable and a requirement was already on the books in January 2024.
• Owner occupancy: Can be required only at the time of permitting, not forever, which protects owners who later need to rent.

Connecticut ADU Laws

Connecticut passed Public Act 21-29 in 2021, and it works differently from every other state on this list: towns are allowed to opt out. Roughly two-thirds of Connecticut municipalities did exactly that, though most opt-out towns still allow ADUs under their own local rules. Where the state framework applies, it delivers:

• By right: Cities must allow attached and detached ADUs without special permits or public hearings. Units stay proportional to the main home.
• Fair housing: Zoning can’t discriminate based on income or personal characteristics, with narrow exceptions for age-restricted or disability-focused housing.
• Parking limits: The law curbs excessive parking mandates that block new housing.
• Zoning “character”: The term now refers to a site’s physical features, not subjective judgments about who belongs in a neighborhood.

Because of the opt-out, Connecticut is classified as a weaker reform. Check whether your specific town opted in or out before you plan.

Hawaii ADU Laws

Hawaii is fighting some of the worst housing costs in the nation, and Senate Bill 3202, signed in 2024, is its answer. Over half of Hawaii households spend more than 30% of their income on housing, and ADUs are seen as a fast way to add supply.

• Two ADUs per lot: All five counties must adopt zoning that allows at least two ADUs on residentially zoned lots by December 31, 2026.
• No blocking covenants: Private land-sale covenants can’t be used to prohibit ADUs.
• Adaptive reuse: The state is encouraging conversion of commercial space into housing to add inventory.

Iowa ADU Laws

Iowa’s Senate File 592 was signed in May 2025 and took effect July 1, 2025, making Iowa one of the more recent states to act.

• By right: Cities and counties must allow at least one ADU on a single-family lot.
• Sizes: Up to 1,000 sq ft or 50% of the primary home’s size, whichever is larger.
• No owner-occupancy: You can rent the unit for income.

Maine ADU Laws

Maine’s LD 2003 (2022) was written to ease a serious affordable-housing shortage by loosening zoning across the state.

• Unit limits: Up to two dwelling units on single-family-zoned lots, and up to four on undeveloped parcels.
• Location flexibility: ADUs can be inside the home (a basement or upper floor), attached, converted from a structure like a barn, or built as a standalone unit.
• Minimum size: Cities can set their own maximums, but the state requires that ADUs of at least 190 sq ft be allowed.
• Parking: No additional parking required.
• Local flexibility: Towns can adopt more permissive rules, including more than one ADU per lot.

Maryland ADU Laws

Maryland’s House Bill 1466, the Accessory Dwelling Units Act of 2025, took effect October 1, 2025. Rather than a single uniform code, it sets a statewide policy and tells local governments to build it into their own ordinances.

• No unreasonable restrictions: Local rules can’t effectively prohibit ADUs or pile on costs that make them infeasible.
• Density math: ADUs must be excluded from density calculations.
• HOA protections: Deed restrictions and covenants can’t unreasonably block ADUs.
• Local deadline: Counties and municipalities with zoning authority must adopt a local ADU law by October 1, 2026.

Massachusetts ADU Laws

Massachusetts legalized ADUs statewide through the Affordable Homes Act (Chapter 150 of the Acts of 2024). The by-right provision took effect February 2, 2025, and it applies to every city and town in the state.

• By right: Every community must allow at least one ADU on single-family lots without a special permit or public hearing.
• Sizes: Up to half the gross floor area of the main house, or 900 sq ft, whichever is less.
• Still required: You’ll still need a building permit, septic or sewer sign-off, and a certificate of occupancy. Towns can apply reasonable rules for setbacks, height, and parking.

Montana ADU Laws

Montana’s Senate Bill 528 passed in 2023 and took effect January 1, 2024. A court briefly paused it, but the Montana Supreme Court upheld the law in September 2024.

• By right: Cities must allow at least one ADU on any lot with a single-family home, with no special-use permit or public hearing.
• Sizes: Up to the lesser of 1,000 sq ft or the floor area of the primary home.
• Fee cap: Application fees are capped at $250 per ADU.

Nevada ADU Laws

Nevada’s Assembly Bill 396 (2025) directs larger municipalities to adopt ADU ordinances. The deadline is the lever here.

• Local deadline: Covered cities and counties must adopt an ADU ordinance by July 1, 2026.
• Backstop: If a covered government misses the deadline, ADUs become allowed on any residentially zoned parcel without local restriction.
• Parking: Local ordinances can’t require more than one additional parking space per ADU.
• Kitchens: Ordinances can’t prohibit a separate kitchen in an ADU.

Some Nevada jurisdictions also require solar on new detached units, but that’s handled at the city or county level, so check your local code.

New Hampshire ADU Laws

New Hampshire was an early mover, codifying ADU rights in RSA 674:71-73 back in 2017. The law stops cities from blocking reasonable ADUs.

• What cities can’t do: Require fewer than two bedrooms, cap the size below 750 sq ft, or require that a relative live in the unit.
• What cities can do: Set parking requirements, limit a property to one ADU, and require the design to fit the neighborhood.
• Owner occupancy: Towns are allowed to require the owner to live in one of the units, which is part of why New Hampshire counts as a weaker reform.

Oregon ADU Laws

Oregon was the first state to legalize ADUs broadly, starting with SB 1051 in 2017 and expanding through House Bill 2001 in 2019. As in California, the state rules are a baseline that cities can build on, and many (especially Portland) have gone further.

• Zoning: ADUs are allowed in all residential zones in cities over 2,500 people.
• Sizes: No fixed statewide maximum, but detached ADUs generally run up to 800–900 sq ft, and attached or interior units up to 75–85% of the main home.
• Height: No more than 20 ft, or the height of the primary home, whichever is lower.
• Parking: Not required for ADUs.
• Owner occupancy: Cannot be enforced.

Rhode Island ADU Laws

Rhode Island broadened its ADU rules in 2024 under General Laws §45-24-73. ADUs are allowed by right in three situations:

• On an owner-occupied property, as a reasonable accommodation for a family member with a disability
• On a residential lot of 20,000 sq ft or more
• Within the existing footprint of the home or an existing accessory structure, without expanding it

On size, cities can set maximums but must allow a studio or 1-bedroom ADU of at least 900 sq ft (or 60% of the main home, whichever is less) and a 2-bedroom ADU of at least 1,200 sq ft (or 60%, whichever is less). ADUs follow standard accessory-structure setbacks, and one off-street parking space per bedroom is required.

Utah ADU Laws

Utah’s House Bill 82 (2021) is narrower than most: it covers internal ADUs only, meaning a unit built inside the existing footprint of the main house. Still, it was a real step forward.

• Permitted use: An internal ADU is a permitted use as long as the owner lives on the property, and it can be rented out.
• Fewer barriers: Cities that previously buried internal ADUs in restrictions are required to roll those back.

Vermont ADU Laws

Vermont has allowed ADUs since 2005 and expanded that right through the HOME Act (Act 47) in 2023.

• By right: Every town must allow one attached or internal ADU for each owner-occupied single-family home, as long as it’s outside flood-hazard areas and the lot has enough wastewater capacity.
• Sizes: Up to 30% of the main home’s habitable floor area, or 900 sq ft, whichever is larger.
• Live in either unit: Owners can choose to live in the main home or the ADU.
• Detached units: Towns may still require discretionary review for detached ADUs, which is why Vermont lands in the weaker-reform group.

Washington ADU Laws

Washington’s House Bill 1337 (2023) required cities and counties planning under the Growth Management Act to overhaul their ADU rules. Compliance deadlines ran through 2025, so the law is now in effect statewide.

• Two ADUs per lot: Cities must allow two ADUs per lot inside urban growth areas, in addition to the main home.
• Sizes: Cities cannot cap ADU size below 1,000 sq ft, so you’re guaranteed room to build at least that large.
• Height: The ADU height limit can’t be less than 24 ft or the height of the main home.
• Owner occupancy: Cities cannot require the owner to live in either unit.
• Separate sale: ADUs can be sold separately as condos.
• Impact fees: Capped at 50% of the fees charged for the primary home.
• Parking and design: Parking rules are relaxed near major transit, and ADUs can’t face stricter design standards than the main home.

Coming Soon: Virginia

Virginia is the next state to watch. Governor Spanberger signed Senate Bill 531 in 2026, which will require localities to allow ADUs in single-family zoning districts. It caps ADU permit fees at $500, bars cities from imposing setbacks stricter than those for the main home, and removes any requirement that the ADU occupant be related to the owner. The catch: it doesn’t take effect until July 1, 2027, so Virginia homeowners have a wait before the new rights kick in.

What If My State Isn’t on the List?

No statewide law doesn’t mean no ADUs. It means your city or county has full control over the rules. Some places are genuinely ADU-friendly even without a state mandate, and others have made them nearly impossible. The only way to know is to check your local zoning code, or ask your planning department directly, before you spend a dollar on design.

Once you’ve confirmed you can build, the rest of the path looks the same in most places. Our step-by-step guide to building an ADU walks through feasibility, design, permitting, and construction.

If reading municipal code isn’t your idea of a good weekend, that’s exactly what we do. Maxable tracks ADU rules across the country and can tell you what’s actually buildable on your specific lot.

Frequently Asked Questions About State ADU Laws

How many states have ADU laws in 2026?

Eighteen states have passed laws that broadly legalize ADUs: Arizona, Arkansas, California, Colorado, Connecticut, Hawaii, Iowa, Maine, Maryland, Massachusetts, Montana, Nevada, New Hampshire, Oregon, Rhode Island, Utah, Vermont, and Washington. Virginia’s law passed in 2026 but takes effect in July 2027.

Which state has the best ADU laws?

California has the most developed ADU market and some of the most detailed protections, including a guaranteed 800 sq ft and no owner-occupancy requirement. Researchers also rank Arizona and Washington among the states that have removed the most barriers to building.

Was Oregon or California the first state to legalize ADUs?

California adopted an early, weak ADU law in 1982, but Oregon was the first state to broadly legalize ADUs with strong statewide rules, beginning in 2017 and expanding in 2019.

Do I have to live on the property to build an ADU?

It depends on your state. California, Oregon, Washington, Iowa, Montana, and Arkansas prohibit owner-occupancy requirements, so you can rent both units. Utah, New Hampshire, and some other states still allow cities to require the owner to live on site.

Can my city have different ADU rules than my state?

Yes. A statewide law sets the minimum a city must allow. Cities can be more generous than the state baseline, and in a few states, like Connecticut, they can even opt out. Always confirm the current rules with your local planning department.

Get the ADU Details With Maxable

State laws are only the starting line. What you can actually build comes down to your city’s code, your lot, and your budget, and those details are where most projects get stuck. That’s where we come in.

Download our free ADU starter kit to get up to speed, and when you’re ready to get serious, book a call with Maxable. Through our National ADU Builders Network, we’ll connect you with vetted, licensed designers, builders, and lenders who know the rules in your neighborhood, wherever you are.