ADU Laws by State — 2026 Complete Guide
- Jun 12
- 5 min read
Accessory dwelling units are one of the fastest-growing housing categories in the US — but ADU laws by state (and by county) vary more than almost any other building type. What's allowed in Los Angeles may be prohibited or heavily restricted two counties over. This guide covers the key variables that differ across states so you know what to research before your project starts.
Why ADU Laws Vary So Much
Zoning authority in the US sits primarily at the local level. States can override local rules — California, Oregon, and Washington have done exactly that — but in most states, cities and counties set their own ADU standards independently.
That means two neighboring counties can have different maximum sizes, different setback rules, and different stances on whether you can rent the unit. Before drawing plans or pulling permits, verify requirements with your local building or planning department.
States With the Most Active ADU Legislation
California has passed more ADU legislation than any other state. SB 9 (2021) and a series of follow-on bills have removed most barriers: owner-occupancy requirements are largely gone for most property types, minimum lot sizes are restricted from being used as a ban, and fees for ADUs under 750 square feet must be waived. Maximum unit size is generally 1,200 square feet, but check your specific city — many set lower limits within the state framework.
Oregon adopted statewide ADU preemption in 2021 for cities over 2,500 residents. Cities can still set design standards and require permits, but they cannot prohibit ADUs outright on lots zoned for single-family use. Parking requirements are waived for ADUs within a half-mile of transit.
Washington passed HB 1337 in 2023, requiring most cities to allow at least two ADUs per single-family lot (one attached, one detached) without owner-occupancy requirements. Some cities are still updating local codes to comply.
Texas has no statewide ADU statute. Rules are entirely local — Austin, Houston, Dallas, and San Antonio each have their own ordinances. HOA restrictions apply independently of city rules and frequently override what the city would otherwise allow.
Florida leaves ADU regulation to counties and municipalities, with no statewide preemption. South Florida counties tend to be more restrictive; some rural counties have very few requirements. Impact fees can be significant in Florida — worth calculating early.
Colorado, Massachusetts, and Arizona have each passed bills in recent years easing ADU restrictions in specific ways, but implementation varies by municipality. Check your city's zoning code directly.
The Four Variables That Matter Most
Regardless of state, four factors drive most ADU permit outcomes:
Maximum size. States that have set floors typically cap ADUs at 800–1,200 square feet or a percentage of the primary dwelling (often 50%). Local codes may set lower limits within a state's framework.
Setbacks. Rear and side setbacks for ADUs are commonly 4–5 feet in permissive jurisdictions, but some cities require 10 feet or more. Your Assessor's Parcel Number (APN) lookup will tell you the lot dimensions you're working with.
Owner-occupancy. California eliminated most owner-occupancy requirements in 2020. Many other states and cities still require the primary owner to live on the property — either in the main house or the ADU. This affects financing and rental options.
Parking. Requirements range from zero (near transit in California, Oregon) to one off-street space per ADU bedroom. Check your city's current ordinance — many jurisdictions updated parking rules between 2022 and
.
What You Need Before Applying for a Permit
Most ADU permit applications require a site plan that shows:
Lot boundaries and dimensions (pulled from your Assessor's Parcel Number (APN))
Setbacks to all property lines
Location of the existing structure(s) and the proposed ADU footprint
Utility connections (sewer, water, gas)
Driveway and parking layout if applicable
InQI generates AI-powered site plans from an address and APN — scaled, data-backed drawings that reflect actual parcel dimensions. You can export to PDF, DXF for CAD, or SVG, and use the output as the basis for your permit application. Pair it with Codes.IQ to check local zoning requirements before you draw anything.
Coming Soon: ADU Concept Design Mode
Once you know your lot's setbacks and size limits, the next question is usually: what would actually fit here?
InQI is building an ADU Concept Design mode — generate a footprint, place it on your parcel, and see how it sits relative to setbacks and the existing structure, all from your address and Assessor's Parcel Number (APN). No drafting software, no back-and-forth with a designer to get to a first concept.
It's designed for exactly the moment between "I think I can build an ADU" and "I'm ready to submit permits." If you want early access, sign up for free and you'll be first to know when it launches.
FAQ
Are ADUs legal in every state?
ADUs are legal in all 50 states, but local zoning rules can significantly restrict them — including minimum lot sizes, setback requirements, and owner-occupancy rules. Several states have passed laws limiting how much local governments can restrict ADUs; most have not.
What is the maximum size for an ADU?
It depends on your county and state. California generally allows up to 1,200 square feet. Other states defer to local ordinances, which can range from 600 to 1,200 square feet or be expressed as a percentage of the primary dwelling's square footage.
Do I need a site plan to build an ADU?
Yes, in virtually all jurisdictions. Permit applications require a site plan showing lot dimensions, setbacks, existing structures, and the proposed ADU footprint. Your Assessor's Parcel Number (APN) is used to pull the parcel data the plan is built from.
Can I rent out an ADU?
In California, owner-occupancy requirements have largely been removed, so yes. In many other states and cities, renting is permitted but subject to local rules — and HOA rules may restrict rentals even where the city allows them.
Does my HOA have to allow an ADU?
In California, HOAs generally cannot prohibit ADUs (with limited exceptions). In most other states, HOA rules are a separate layer that can restrict ADUs even when the city and state allow them. Always review your CC&Rs.
How long does ADU permitting take?
Timelines vary widely by jurisdiction. California requires local governments to act on ADU applications within 60 days. Other states have no such requirement — permit processing can take 2–6 months in some counties. Submitting a complete application with a properly scaled site plan typically reduces back-and-forth.
Ready to check your lot? Run your address in InQI and get a scaled, data-backed site plan in minutes — export to PDF, DXF, or SVG and use it straight in your permit application. *Whether a generated site plan is accepted for a permit application depends on your local building department. Requirements vary by county — confirm with your jurisdiction before submission.
