Last reviewed April 1, 2026

6 sources cited

ADU Laws by State: Where You Can Build an ADU in 2026

Q: Can my city override state ADU law?

In strong statewide framework states (CA, OR, WA, CO, ME, AR, IA), no — your city cannot reimpose the barriers that state law removes. In partial states, your city may retain control over certain regulations. In city-by-city states, your city has full control.

By The Dwelling Index Editorial Team · Last verified: April 2026 · Sources: State statutes, Mercatus Center ADU Taxonomy (August 2025), California HCD, AARP, state housing agencies

More than 20 states have now enacted statewide ADU legislation — and the number keeps climbing. We mapped ADU laws for all 50 states, and the picture is more promising than most guides make it sound. At least seven states have removed every major regulatory barrier that used to kill ADU projects before they started. If you live in California, Oregon, Washington, or four other states, your city cannot require you to live on-site, cannot demand extra parking, and cannot force you through a public hearing just to add a backyard cottage or garage apartment to your own property.

But here is what most guides leave out: even in the most permissive states, state law sets the floor — not the finish line. Your city's zoning code, your lot shape, your HOA, and your utility access still determine whether a specific ADU is feasible on your property. We built this page to give you both layers: the state-level baseline and a clear path to checking what your city still controls.

Use the tracker below to find where your state stands. Then check what you can actually build at your specific address.

Reader-supported: The Dwelling Index may earn a commission when you use our links to explore financing or request pricing, at no extra cost to you. Our editorial recommendations are based on independent research and are never influenced by compensation. Read our full disclosure →

Last verified: April 2026 · Sources: State statutes, Mercatus Center ADU Taxonomy (August 2025), California HCD, AARP, state housing agencies · See full methodology →

Cedar-sided detached ADU backyard cottage with standing seam metal roof and warm interior lighting, next to a craftsman main house with mature landscaping and stone pathway — a permitted legal ADU in a strong statewide framework state

In states with strong statewide frameworks, a detached backyard ADU like this must be approved by right — no public hearing, no neighbor vote, no discretionary review.

The 50-State ADU Comparison

Every state below is classified into one of four tiers based on how easy it is for a typical homeowner to actually get an ADU built. Our classification draws on the framework developed by housing researchers Emily Hamilton and Kol Peterson at the Mercatus Center, who identified three “poison pill” regulations that stop ADU construction even where it is technically legal: owner-occupancy requirements, parking mandates, and discretionary approval processes. States that eliminate all three earn our highest tier.

Tier	What It Means	States
🟢 Strong Statewide	State law removes all three poison pills. By-right approval, no owner-occupancy mandate, no parking mandate, both attached and detached allowed. Cities cannot add these barriers back.	CA, OR, WA, CO, ME, AR, IA
🟡 Partial Statewide	State law exists but leaves one or more barriers in local hands, or the framework is newer with implementation still rolling out.	VT, CT, MA, MT, MN, AZ, HI, NH, RI, MD, NV, UT, NY
🟠 City-by-City	No broad statewide ADU mandate. Whether you can build depends on your local zoning code. Major metros often allow ADUs even without state preemption.	TX, FL, NC, GA, IL, VA, NJ, NM, OH, PA, MI, TN, MO, WI, NE, OK, SD, ND, LA, SC, AK, DE, KS, WY, DC
🔴 Restricted	No statewide law, and most local governments severely restrict or functionally ban ADUs.	AL, IN, KY, MS, WV, ID

A note on accuracy: ADU legislation is moving faster than at any point in U.S. housing history. We verify every state entry against official statutes, but laws change — confirm with your local planning department before making financial commitments. Each state entry below includes the specific statute or agency source so you can verify independently.

Already know your state allows ADUs? The real question is whether your specific lot qualifies.

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Detailed reports available in CA, UT, TX, CO, and NY.

Infographic: State Law Sets the Floor, Your Property Determines What's Possible — showing 6 property-level factors that still control ADU feasibility even in permissive states: city zoning, setbacks, lot size and shape, utilities and septic, HOA/CC&Rs, and overlays and special zones

State law sets a legal floor — but city zoning, your lot shape, utilities, and your HOA still determine what is actually buildable. Always check the address, not just the state.

Which States Are Actually ADU-Friendly?

Not all “ADU-legal” states are equal, and the difference matters more than most guides let on. A state with a “strong statewide” framework means your city legally cannot impose the three biggest project-killers. A state with “partial” preemption may still let your city demand that you live on-site, or require extra conditions that add months and fees. And in a “city-by-city” state, your neighbor one town over might be building freely while your municipality says no.

🟢 Strong Statewide Frameworks

These states have done the most to clear the path. If you live here, the state has your back — though you still need to check lot-specific rules like setbacks, utility access, and overlay districts.

California

California is the undisputed national leader. Detached ADUs can be up to 1,200 square feet. Cities must approve or deny complete applications within 60 days (with a 15-day completeness review window under SB 543). Owner-occupancy is banned. Parking is not required near transit. HOAs cannot block ADUs. Under AB 1033, some cities allow ADUs to be sold as separate condominiums. In 2025, the legislature passed SB 543 (tighter permitting timelines and impact fee protections — no fees on ADUs of 750 sq ft or less), AB 1154 (JADU owner-occupancy only applies if the unit shares a bathroom with the primary dwelling), and AB 462 (certificate-of-occupancy and coastal-permit timing changes for ADUs in disaster and coastal areas). These took effect January 1, 2026.

Source: Cal. Gov. Code §§ 66310–66342; California HCD ADU Handbook with 2026 addendum. Verified April 2026.

Oregon

Oregon was the first state to eliminate single-family-only zoning in cities over 25,000 residents. HB 2001 allows duplexes, triplexes, and ADUs by right. No owner-occupancy requirement, no parking mandates. Portland has become a national model — including “3-pack” developments with a primary dwelling, attached ADU, and detached ADU all owned as condos.

Source: ORS 197.312; HB 2001 (2019). Verified April 2026.

Washington

Washington goes further than most: HB 1337 requires urban municipalities to allow at least two ADUs per residential lot. One can be attached, one detached — or any combination. No owner-occupancy requirement. ADUs can be sold separately from the primary residence under certain conditions. Cities cannot set maximum floor areas below 1,000 square feet.

Source: RCW 36.70A.680–696; Washington Dept. of Commerce ADU Guidance. Verified April 2026.

Full Washington ADU laws guide →

Colorado

Colorado is one of the most significant newcomers. HB24-1152, which took effect June 30, 2025, requires subject jurisdictions (cities in metropolitan planning areas with 1,000+ population) to allow ADUs of 500–750 square feet by right. HOA restrictions on ADUs are overridden. Colorado also offers ADU financing programs through the Colorado Housing and Finance Authority (CHFA) and local lenders.

Source: C.R.S. 29-35-402–405; Colorado DOLA ADU Compliance Framework. Verified April 2026.

Maine

Maine targets its affordable housing shortage head-on. LD 2003 allows ADUs and duplexes on almost all residential lots. Cities cannot require extra parking beyond what the primary dwelling needs. Minimum ADU size is just 190 square feet, making small conversions viable. Shoreland zones have special requirements but cannot prohibit ADUs outright.

Source: 30-A M.R.S. § 4364-B. Verified April 2026.

Arkansas New — effective Jan. 1, 2026

Arkansas surprised the housing world in 2025. Act 313 (HB 1503), signed in March 2025 and effective January 1, 2026, requires every municipality to allow at least one ADU by right on any lot with a single-family home. Attached, detached, and internal ADUs are all permitted. No extra parking or owner-occupancy requirements. Maximum size is 1,000 square feet or 75% of the primary dwelling, whichever is smaller. Application fees capped at $250. Any conflicting local ordinance is automatically invalid.

Source: Arkansas Act 313 (2025); A.C.A. § 14-17-209. Verified April 2026.

Iowa New — effective July 1, 2025

Iowa joined the strong tier in mid-2025. SF 592, signed by Governor Reynolds on May 1, 2025, requires every city and county to allow at least one attached or detached ADU on any single-family lot. Maximum size is 1,000 square feet or 50% of the primary residence, whichever is larger. No owner-occupancy requirements. No additional parking mandates. ADU permit applications must be approved without discretionary review or hearing. ADUs can be used as rental properties. HOA rules cannot be more restrictive than state law.

Source: Iowa SF 592 (Chapter 38, Acts of the 91st General Assembly). Verified April 2026.

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🟡 Partial Statewide Frameworks

These states have passed ADU legislation, but the laws leave one or more critical barriers in local hands — or the framework is newer with implementation still rolling out.

🟡 Vermont

Requires by-right ADU approval statewide under Act 47 (2023), and cities must act within 30 days. However, the statutory baseline ties the ADU right to an owner-occupied lot. Vermont also offers ADU funding through the Vermont Housing Improvement Program (VHIP 2.0), structured as 0% interest forgivable loans — one of the most generous state programs in the country.

Source: 24 V.S.A. § 4412(1)(E); Vermont Housing Finance Agency. Verified April 2026.

🟡 Connecticut

Public Act 21-29 (2021) sets statewide standards, but municipalities can vote to opt out. About 67% of towns opted in. Where the law applies, both attached and detached ADUs are allowed by right. The opt-out mechanism means statewide coverage is not guaranteed.

Source: Conn. Gen. Stat. § 8-2(a); PA 21-29. Verified April 2026.

🟡 Massachusetts

The Affordable Homes Act allows by-right ADUs in single-family zones. Max 900 sq ft or 50% of the primary dwelling. ADUs remain subject to otherwise applicable dimensional and parking requirements, and municipalities may impose additional restrictions. MassHousing ADU Loan Program now available.

Source: M.G.L. c.40A § 1A, § 3; MassHousing. Verified April 2026.

🟡 Montana

Requires ADUs to be allowed as rental housing. Max 1,000 sq ft or 75% of the primary dwelling's floor area, whichever is less.

Source: MCA 76-2-345 (municipal); MCA 76-2-215 (county zoning). Verified April 2026.

🟡 Minnesota

Statewide ADU provisions enacted. Max 800 sq ft. ADUs must include a kitchen, bathroom, and lockable entrance. Cities retain some local design authority.

Source: Minn. Stat. § 462.3571. Verified April 2026.

🟡 Arizona

Requires covered municipalities (pop. 75,000+) to allow at least one attached and one detached ADU as a permitted use, and limits parking and design restrictions cities can impose. Phoenix and Tucson have active ADU programs; suburban cities vary.

Source: A.R.S. § 9-461.18 (municipal); A.R.S. § 11-810.01 (county). Verified April 2026.

🟡 Hawaii

Counties have required ADUs since 1981. Act 39 (2024) expanded the framework: all urban residential-zoned lots must permit at least two ADUs by end of 2026, and CC&Rs cannot block ADU development.

Source: HRS § 46-4; Act 39 (2024). Verified April 2026.

🟡 New Hampshire

Municipalities must allow both attached and detached ADUs where single-family homes are permitted. The 2025 revised law sets a minimum ADU size floor of 750 sq ft that cities cannot restrict below. However, municipalities can still require owner-occupancy of one of the units.

Source: NH RSA 674:71-73; HB 577 (2025). Verified April 2026.

🟡 Rhode Island

Updated 2024 law allows one ADU by right on residential lots of 20,000 sq ft or more within an existing footprint. Sets uniform statewide standards, voids conflicting HOA and deed restrictions, and bans tourist/transient ADU use.

Source: R.I. Gen. Laws § 45-24-73. Verified April 2026.

🟡 Maryland

The Accessory Dwelling Units Act of 2025 (HB 1466), effective October 1, 2025, establishes state policy promoting ADUs and requires all charter counties and Baltimore City to adopt local ADU laws by October 1, 2026. ADUs cannot exceed 75% of the primary dwelling's size. HOA restrictions cannot unreasonably limit ADU development.

Source: Md. Code, Land Use § 1-501 et seq.; HB 1466 (Chapter 197, 2025). Verified April 2026.

🟡 Nevada

AB 396 (2025) requires the most populous counties (100,000+) and cities (60,000+) to adopt ADU ordinances by July 1, 2026. If a qualifying jurisdiction does not comply, ADUs are authorized on any residential parcel without restriction. Reno adopted its ADU ordinance in October 2025.

Source: NRS 278 (as amended by AB 396, Chapter 365, 2025). Verified April 2026.

🟡 Utah

State law allows internal (attached) ADUs by right on single-family lots. Detached ADUs remain under local control. Salt Lake City, Ogden, and other Wasatch Front cities have their own ADU ordinances.

Source: Utah Code § 10-9a-530; OPRO Guidance. Verified April 2026.

🟡 New York

No comprehensive statewide zoning preemption for ADUs, but the Plus One ADU Program offers grants up to $125,000 — one of the most generous programs nationally. Administered through participating municipalities and nonprofit partners. Local zoning still determines what is structurally allowed.

Source: NY Homes and Community Renewal. Verified April 2026.

Found your state? The real question is whether your specific property qualifies.

Our free report checks your specific property against local zoning, size limits, and setbacks — takes about 60 seconds.

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Detailed reports currently available in CA, UT, TX, CO, and NY.

Infographic: 5 Rules That Shape ADU Feasibility — illustrated columns showing Approval Path (by-right vs discretionary), Owner-Occupancy requirements, Parking mandates, ADU Type (attached vs detached), and Size plus Fees

These five rules decide how easy or hard an ADU is to build — and which states have eliminated each barrier.

The Five Rules That Determine Whether Your ADU Gets Built

Before you dive into the full state directory, understand the five regulations that matter most. These are the make-or-break levers that separate a straightforward project from one strangled in red tape.

By-Right vs. Discretionary Approval

"By-right" means your city must approve your ADU through a standard building permit — no public hearing, no neighbor vote, no conditional-use permit. "Discretionary" means a planning commission can deny you, often after a months-long process costing thousands. Research consistently shows that discretionary review is one of the biggest barriers to ADU construction.

Owner-Occupancy Requirements

An owner-occupancy mandate means you must live on-site, either in the main house or the ADU. This kills investment flexibility: if you ever move, you cannot rent both units. It also shrinks your buyer pool. The Federal Housing Administration now allows mortgage borrowers to qualify partly based on ADU rental income — but only if the ADU can be rented without restriction.

Parking Requirements

If your city requires extra off-street parking for an ADU, your backyard may not have room for both the parking and the unit. This is especially fatal for garage conversions — you lose the garage but must somehow replace the parking. Strong states ban parking replacement requirements for garage conversions.

Attached and Detached ADU Types

Some states only allow attached ADUs but not detached backyard cottages. This dramatically limits what you can build — and often makes the ADU less valuable as a rental because it shares walls with the main home. All seven strong statewide states require cities to allow both types.

Size Limits and Impact Fees

Size limits that are too restrictive (under 500 square feet) can make an ADU financially unviable. Impact fees can add significant costs to a project. Strong states cap or eliminate impact fees for smaller ADUs — California, for example, exempts ADUs of 750 square feet or less from impact fees entirely.

ADU Laws in Every State: The A–Z Directory

Check locally: Whether your jurisdiction is a "subject jurisdiction" (metropolitan planning area, 1,000+ population).

Source: C.R.S. 29-35-402–405; Colorado DOLA ADU Compliance Framework.

Verified: April 2026

Full Colorado ADU laws guide →

Iowa

🟢 Strong Statewide

SF 592 (2025), effective July 1, 2025. Every city and county must allow at least one ADU. Max 1,000 sq ft or 50% of primary residence (whichever is larger). No owner-occupancy. No extra parking. No discretionary review. ADUs can be rented. HOA rules cannot be more restrictive than state law.

Check locally: Deed restrictions, HOA/common-interest community rules.

Source: Iowa SF 592; Iowa Code §§ 331.301(27), 364.3.

Verified: April 2026

Maine

🟢 Strong Statewide

LD 2003 allows ADUs and duplexes on most residential lots. Cities cannot require extra parking beyond what the primary dwelling needs. Minimum ADU size is just 190 sq ft, making small conversions viable. Shoreland zones have special requirements but cannot prohibit ADUs outright.

Check locally: Shoreland zone rules, septic capacity.

Source: 30-A M.R.S. § 4364-B.

Verified: April 2026

Oregon

🟢 Strong Statewide

HB 2001 eliminated single-family-only zoning in cities over 25,000 residents. ADUs allowed by right — attached, detached, and interior. No owner-occupancy requirement. No parking mandates. Portland has become a national model, including 3-pack developments with a primary dwelling, attached ADU, and detached ADU all owned as condos.

Check locally: City-specific design and setback standards, historic district review.

Source: ORS 197.312; HB 2001 (2019).

Verified: April 2026

Washington

🟢 Strong Statewide

HB 1337 requires urban municipalities to allow at least two ADUs per residential lot. One can be attached, one detached — or any combination. No owner-occupancy requirement. ADUs can be sold separately from the primary residence under certain conditions. Cities cannot set maximum floor areas below 1,000 sq ft.

Check locally: Whether your town requires owner-occupancy, local conditions.

Source: NH RSA 674:71-73; HB 577 (2025).

Verified: April 2026

New York

🟡 Partial Statewide

No comprehensive statewide zoning preemption for ADUs. However, the Plus One ADU Program offers grants up to $125,000 — one of the most generous programs nationally. Administered through participating municipalities and nonprofit partners. Local zoning still determines what is structurally allowed.

Check locally: Local zoning code, Plus One program eligibility.

Source: NY Homes and Community Renewal.

Verified: April 2026

Rhode Island

🟡 Partial Statewide

Check locally: Whether your lot meets the 20,000 sq ft minimum, local implementation.

Source: R.I. Gen. Laws § 45-24-73.

Verified: April 2026

Utah

🟡 Partial Statewide

Check locally: Whether your city allows detached ADUs, local setback rules.

Source: Utah Code § 10-9a-530; OPRO Guidance.

Verified: April 2026

Vermont

🟡 Partial Statewide

🟠 City-by-City

No statewide mandate. Nashville allows ADUs in some zones.

Check locally: Metropolitan zoning code.

Source: Local ordinances.

Verified: April 2026

Texas

🟠 City-by-City

No statewide ADU law. Austin is one of the most ADU-friendly cities in the country. Houston's minimal zoning effectively allows ADUs in many areas. But most Texas cities set their own rules, and many restrict ADUs.

Check locally: City zoning code, lot-size requirements, deed restrictions.

Source: Local ordinances.

Verified: April 2026

Full Texas ADU laws guide →

Virginia

🟠 City-by-City

No statewide mandate. Arlington, Alexandria, Fairfax County, and Charlottesville allow ADUs.

Check locally: County or city zoning code.

Source: Local ordinances.

Verified: April 2026

Wisconsin

🟠 City-by-City

No statewide mandate. Madison, Milwaukee, and some cities allow ADUs.

Check locally: Municipal zoning code.

Source: Local ordinances.

Verified: April 2026

Wyoming

🟠 City-by-City

🔴 Restricted

No broad statewide ADU mandate. Most municipalities restrict ADU development.

Check locally: Municipal zoning.

Source: Local ordinances.

Verified: April 2026

Found your state? Now the real question is whether your specific property qualifies. State law sets the floor — your city, lot, and site conditions set the ceiling.

Your next step is simple:

State law confirmed — now check what your specific address can support.

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What State Law Still Does Not Tell You

This is where most ADU guides stop — and where most homeowners get blindsided. Even in the strongest ADU states, state law does not override everything. Here is what your state tracker cannot answer:

City zoning and overlay districts

Your city may have historic preservation overlays, coastal zones, wildfire hazard areas, floodplain designations, or other special districts that add requirements even when state law broadly allows ADUs.

Setbacks and lot coverage

State law may guarantee your right to build an ADU, but it does not determine where on your lot it can go. Setback requirements, lot coverage maximums, and floor-area ratios are typically set locally.

Utilities and septic

In suburban and rural areas, utility capacity — especially sewer, water, and electrical — can make or break a project. If your home is on septic, adding a second dwelling may require a Title 5 inspection (Massachusetts), a septic upgrade, or a new drain field.

HOA and deed restrictions

California, Colorado, and Arkansas have banned HOA interference with ADU construction. Iowa prohibits HOA rules from being more restrictive than state law. Maryland prohibits unreasonable restrictions. Most other states have not addressed HOAs. Always check your CC&Rs.

Corner lots, flag lots, and irregular parcels

Unusual lot shapes can create setback conflicts, access issues, or fire-code complications that standard rectangular lots would not face.

Short-term rental rules

Even if your state and city allow the ADU, they may prohibit short-term rentals (Airbnb, VRBO). California JADUs cannot be used as short-term rentals. Rhode Island's updated law bans tourist/transient ADU use. Many cities have separate short-term rental ordinances.

One honest reality: ADU permitting is not instant, even in the friendliest states. Plan review typically takes weeks, not days, and construction costs are higher than they were a few years ago. But here is the bigger picture: more states have passed ADU legislation in the last four years than in the previous four decades combined. The systemic barriers that used to make ADUs nearly impossible — discretionary approvals, parking mandates, owner-occupancy rules — are falling fast. Homeowners who navigate the process are adding real property value and creating housing that generates real monthly income.

Side-by-side comparison of three ADU types: Detached ADU showing a standalone two-story unit in a backyard, Attached ADU showing a brick addition with shared wall and separate entrance, and Garage Conversion showing an existing garage transformed into living space

All seven strong statewide framework states require municipalities to allow both attached and detached ADUs — not just one type.

How to Check If You Can Build an ADU — In About 10 Minutes

Here is the fastest path from “I wonder” to “I know.”

Step-by-step infographic: How to Check ADU Feasibility Fast — 7 steps: Step 1 Check State Law, Step 2 Find Local Zoning, Step 3 Confirm Lot Size and Setbacks, Step 4 Check Overlays, Step 5 Verify Utilities and Septic, Step 6 Review HOA and CC&Rs, Step 7 Contact Planning. Bottom line: Start broad. Verify local. Confirm the lot.

Start broad, verify local, confirm the lot. These 7 steps take about 10 minutes and prevent costly surprises.

Check your state's baseline

Use the directory above. If your state has a strong or partial statewide framework, you have a legal floor that your city cannot easily take away.

Find your city's zoning map

Search "[your city] zoning map" or "[your city] GIS parcel viewer." Find your property and note your zoning classification. Then search "[your city] ADU ordinance."

Confirm lot size, setbacks, and existing structures

Your city's zoning code will specify minimum lot sizes, setback requirements, and maximum lot coverage. These numbers determine where on your lot the ADU can physically go.

Check for overlay districts and special zones

Look for historic districts, floodplain designations, fire hazard zones, or coastal zones. These can add requirements even in states with strong statewide frameworks.

Verify utility and septic capacity

If you are on municipal sewer and water, check whether your city charges utility connection fees for ADUs. If you are on septic, contact your county health department. Septic capacity is a common deal-breaker in suburban and rural areas.

Check HOA and deed restrictions

In California, Colorado, Arkansas, and Iowa, HOAs cannot block ADUs or impose more restrictive rules than state law. In most other states, they can. Review your CC&Rs before spending money on plans.

Contact your city's planning department

A 10-minute call with your parcel number can confirm or flag issues faster than hours of online research. Most planning departments are helpful — they want permitted projects.

Want to skip the manual legwork? Get your property-specific ADU report in 60 seconds.

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Detailed reports available in CA, UT, TX, CO, and NY.

What If Your State Looks Restrictive?

A “restricted” or “city-by-city” rating does not mean “no ADU.” It means the answer lives at the local level.

→

Look at your city, not just your state. Texas has no statewide ADU law, but Austin is one of the most ADU-friendly cities in America. Illinois has no statewide framework, but Chicago's ADU program is expanding.

→

Garage and basement conversions are often easier. In restrictive areas, converting existing space may face fewer barriers than building a new detached structure.

→

The momentum is on your side. More states passed ADU legislation in the last four years than in the previous four decades. AARP, housing advocacy groups, and both political parties are increasingly supportive. If your state has not acted yet, it may be a matter of time.

What Changed in 2025–2026

ADU legislation is a fast-moving target. Here are the most significant recent changes:

🟢 Arkansas(Effective January 1, 2026)

Act 313 created the state's first comprehensive ADU framework, requiring every municipality to allow ADUs by right with no parking or owner-occupancy mandates.

🟢 Iowa(Effective July 1, 2025)

SF 592 made Iowa one of the strongest statewide ADU frameworks in the country — by-right approval, no parking, no owner-occupancy, no discretionary review.

🟢 California(Effective January 1, 2026)

SB 543 tightened permitting timelines. AB 1154 changed JADU owner-occupancy rules. AB 462 addressed coastal and disaster-zone ADU permits.

🟡 Maryland(Effective Oct. 1, 2025; local adoption by Oct. 1, 2026)

HB 1466 created a statewide ADU policy framework with mandatory local implementation — the first comprehensive ADU law in Maryland history.

🟡 Nevada(Local adoption by July 1, 2026)

AB 396 requires major cities and counties to adopt ADU ordinances. Non-compliant jurisdictions face automatic ADU authorization.

🟢 Colorado(Effective June 30, 2025)

HB24-1152 went live, creating the state's first comprehensive ADU framework. HOA restrictions on ADUs overridden statewide.

ADU Grants and Incentive Programs by State

Several states offer financial assistance for ADU construction. Always verify current status directly with the program — many have limited funding or eligibility requirements.

State	Program	Amount	Status (April 2026)
California	CalHFA ADU Grant	Up to $40,000	Fully allocated as of Dec 2023; not currently accepting applications. Confirm with CalHFA for future rounds.
New York	Plus One ADU Program	Up to $125,000	Active — verify eligibility with NY HCR.
Vermont	VHIP 2.0	0% interest forgivable loans	Active — verify with VHFA.
Colorado	CHFA ADU Financing	Varies by lender	Active through local lenders.
Massachusetts	MassHousing ADU Loan	Varies	Active — verify with MassHousing.

Confirm program status directly with the administering agency before making plans that depend on grant or loan funding. Some city and county governments also offer local ADU incentive programs not listed here.

While state-level funding can significantly reduce costs, most homeowners finance their ADU through home equity, construction loans, or cash-out refinance. If grant funding is unavailable or your project does not qualify, these remain proven paths. Explore ADU financing options →

Free Resource

Free 2026 ADU Starter Kit

State law summaries, cost worksheets, permitting checklists, and financing comparison guides — before you talk to a single contractor. Over 14,000 homeowners have downloaded it this year.

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Types of ADUs: Quick Reference

The type of ADU your state's law covers — and the type your lot can support — shapes everything. Here's the essential reference:

Detached ADU (Backyard Cottage / DADU)

A standalone structure with its own entrance, kitchen, bathroom, and living space. Highest rental value and property-value impact. Requires the most lot space.

Attached ADU

An addition to your main house with its own entrance and facilities. Often less expensive because you share one wall. Requires structural connection to the primary dwelling.

Garage Conversion

Converting an existing garage into a living unit. Often the lowest-cost path because the structure already exists. Strong states ban parking replacement requirements for garage conversions.

Basement or Attic Conversion (Internal ADU)

Finishing existing interior space into a separate unit. This is the type allowed by-right under Utah's statewide law. Often the fastest path in restrictive areas.

Junior ADU (JADU)

A California-specific designation for a unit of 500 sq ft or less within an existing single-family home. Different rules apply — including potential owner-occupancy requirements (if the JADU shares a bathroom) and a ban on short-term rentals.

All seven “strong statewide” framework states require cities to allow both attached and detached ADUs.

Frequently Asked Questions About ADU Laws by State

Are ADUs legal in every state?

ADUs are possible in all 50 states, but the ease of building varies enormously. More than 20 states have enacted statewide ADU legislation. In states without statewide laws, whether you can build depends on your local zoning code.

Which state is the most ADU-friendly?

California has the most comprehensive and well-established ADU framework, followed closely by Oregon and Washington. Arkansas and Iowa are recent standouts — both passed strong statewide laws in 2025.

Can my city override state ADU law?

In "strong statewide" framework states (CA, OR, WA, CO, ME, AR, IA), no — your city cannot reimpose the barriers that state law removes. In "partial" states, your city may retain control over certain regulations. In "city-by-city" states, your city has full control.

Can my HOA stop me from building an ADU?

In California, Colorado, Arkansas, and Iowa, HOAs cannot prohibit or impose more restrictive rules on ADU construction than state law. Maryland prohibits unreasonable HOA restrictions on ADUs. In most other states, HOA CC&Rs can still restrict or prohibit ADUs.

How big can an ADU be?

Size limits vary by state and city. Common maximums range from 750 to 1,200 square feet. California allows up to 1,200 sq ft for detached ADUs. Vermont caps at 900 sq ft or 30% of the primary home. Iowa caps at 1,000 sq ft or 50% of primary residence, whichever is larger.

Do I need extra parking for an ADU?

In strong statewide framework states, parking mandates are banned or severely limited. In other states, you may need additional spaces. Exemptions commonly apply near transit stops and for garage conversions.

Can I rent out my ADU?

In all states with statewide ADU laws, ADUs can be used as rental housing. Short-term rental rules are set separately and vary by city — always check local ordinances.

Can I sell my ADU separately?

In California (AB 1033) and parts of Washington, ADUs can be sold as separate condominiums. In most places, the ADU must remain part of the same property as the primary dwelling.

How long does ADU permitting take?

In California, cities must act within 60 days (with a 15-day completeness review). Vermont requires action within 30 days. In states without mandated timelines, permitting can vary significantly.

What is a JADU?

A Junior Accessory Dwelling Unit (JADU) is a California-specific designation for a unit of 500 square feet or less within an existing single-family home. JADUs have different rules including a ban on short-term rentals.

What states allow two ADUs on one lot?

Washington requires urban municipalities to allow at least two ADUs per residential lot. Hawaii will require at least two per urban residential lot by the end of 2026.

What should I check before paying for plans?

Follow the seven-step workflow above: state baseline, city zoning, lot dimensions, overlays, utilities, HOA, and a planning department call. Do not pay for drawings until you have confirmed the project is feasible.

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Editorial Methodology and Sources

Every state entry in this directory is verified against an official state statute, agency handbook, legislative record, or municipal ordinance. We use the framework developed by Emily Hamilton and Kol Peterson at the Mercatus Center at George Mason University — specifically their Taxonomy of State Accessory Dwelling Unit Laws (August 2025) — as the foundation for our tier classifications.

How we classify states:

Strong Statewide: State law eliminates all three “poison pill” barriers (owner-occupancy, parking mandates, discretionary approval) and requires both attached and detached ADUs.
Partial Statewide: State law exists but leaves one or more poison pills in local hands, retains an opt-out mechanism, is newly enacted with implementation still rolling out, or provides a funding program without full zoning preemption.
City-by-City: No broad statewide ADU preemption identified. Policies set by local governments.
Restricted: No statewide law and most local governments restrict or functionally ban ADUs.

How often we verify: Full review twice per year (January and July). Individual state entries updated within 30 days of significant legislative changes. Each entry includes a verification date.

Why local confirmation is still required: State-level classifications cannot capture lot-specific factors like setbacks, utility capacity, overlay districts, or HOA restrictions. Always confirm with your local planning department before making financial commitments.

Key sources:

Mercatus Center: A Taxonomy of State Accessory Dwelling Unit Laws 2025 (Hamilton & Peterson, August 2025)
California HCD: ADU Handbook with 2026 Addendum
Washington Dept. of Commerce: ADU Guidance
AARP: ADU Model State Act and Local Ordinance (2021)
Virginia Housing Commission: Exploring ADU Regulation Discussion Points and State Practices
Individual state statutes as cited per entry

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Related Guides

The Dwelling Index is an independent educational resource. We are not a law firm, lender, or builder. Our content is not legal, financial, or construction advice. State ADU laws change frequently — consult qualified professionals and your local planning department before making financial commitments specific to your property and situation.

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