ADU Laws by State: Which States Require Cities to Allow ADUs

ADU laws by state (new to the term? see what is an ADU) differ in one basic way: some states make local governments allow accessory dwelling units, and the rest leave it to each city. As of October 2026, at least a dozen states have a statewide rule, including California, Washington, Oregon, Montana, Utah, Arizona, Colorado, Florida, Hawaii, Massachusetts, Maine and New Hampshire, and laws passed in 2026 in North Carolina and Virginia take effect in 2027. Texas has no statewide mandate. Law current as of October 2026. The table below gives each law, who it covers and its size rule, with a link to our full guide where we have one.

We list only laws we have checked against the statute or the state's own text. Several other states, such as Vermont, Connecticut and Nevada, also have statewide ADU provisions that we have not yet covered.

ADU laws by state at a glance

What most state ADU laws have in common

The newer laws borrow from each other, so the same provisions keep appearing:

• By-right approval. No public hearing, variance or conditional use permit (Montana, Colorado, Florida, Massachusetts, New Hampshire; Utah for detached ADUs).
• No owner occupancy. Arizona, Montana, Washington, Massachusetts, Oregon and, since LD 1829, Maine bar it. Utah and New Hampshire still let cities require it.
• Parking limits. Arizona, Montana and Oregon bar any added parking; Maine allows nothing beyond what the house needs; New Hampshire caps it at one space; Washington and Massachusetts cap it and drop it near transit; Utah caps detached-ADU parking at one or two spaces by size; North Carolina's 2027 law bars parking minimums.
• Size as a floor, not a ceiling. Most laws say how small a city's cap may be (Washington 1,000 sq ft, New Hampshire 750 sq ft, California 850 or 1,000 sq ft). Montana and Massachusetts instead set a maximum for the protected unit.
• Building codes untouched. Every law leaves the residential code, fire code and septic rules in force.

Our state ADU guides

Each guide quotes the statute, explains what cities still control and walks through a plan you can open:

• Arizona ADU law (HB 2720): casitas in the big cities.
• California ADU size limits: the 850, 1,000 and 800 sq ft numbers, heights and setbacks.
• Colorado ADU law (HB24-1152): who is a subject jurisdiction and the 500 to 750 sq ft rule.
• Florida ADU rules: the 2026 by-right law and the December 1, 2026 deadline.
• Hawaii ADU rules: Act 39 and Honolulu's size tiers.
• Maine ADU law: LD 2003, LD 1829, sprinklers and deadlines.
• Massachusetts ADU law: 900 sq ft and how gross floor area is measured.
• Montana ADU law (SB 528): the 75% or 1,000 sq ft formula and the court case.
• North Carolina ADU rules: SB 445 from January 2027, and Raleigh, Durham and Charlotte rules today.
• Utah ADU law: internal ADUs and SB 284 detached ADUs.
• Washington ADU law (HB 1337): two ADUs per lot.
• Oregon middle housing: duplexes on every lot under HB 2001, alongside Oregon's ADU rule.

States without a statewide mandate

Where there is no state law, the city or county zoning code decides, and the answer varies street by street:

• Texas ADU rules: SB 673 passed the Senate in 2025 but not the House; Austin, Houston and San Antonio rules, and deed restrictions.
• New York City ADU rules: not a state law, but City of Yes allows ADUs up to 800 sq ft with one- and two-family homes.

North of the border, Ontario takes a similar approach through the Planning Act: see additional residential units in Ontario.

One plan, many state rules

To see how the size rules compare in practice, take FloorGen's 800 sq ft 2-bed ADU template: a detached cottage 40 × 20 ft to the outside of its walls (800.1 sq ft), 736.3 sq ft inside the exterior walls and 700.5 sq ft of net room area, with two bedrooms, a bath, laundry and an open kitchen, dining and living room.