ADUs in Arizona: Rules, Costs, What to Know
How state law changed the game, what each city allows, and what it actually costs to build
A detached ADU (casita) in the Phoenix metro costs $120,000 to $350,000+ depending on size, site conditions, and finish level. Arizona's HB 2720, effective January 2025, requires cities with populations over 75,000 to permit at least one attached and one detached ADU on any single-family lot. Most cities now allow ADUs by right, no public hearings, no special use permits.
What is an ADU, and what types exist in Arizona
An accessory dwelling unit is a second, self-contained living space on a single-family residential lot. Arizona homeowners use them to house aging parents, generate rental income, create multigenerational living arrangements, or add a dedicated home office with a full bath.
The term "casita" is used interchangeably with ADU across Phoenix metro real estate listings. They are the same thing: a separate dwelling with a kitchen (or kitchenette), bathroom, and sleeping area. The four main types in Arizona are:
Detached Casita
Built from the ground up. Most expensive option but gives complete separation between primary home and ADU. Common in Scottsdale, Paradise Valley, and Gilbert custom lots. Requires independent foundation, exterior walls, and often separate utility connections.
Garage Conversion
Converts an existing 2-car or 3-car garage into livable space. Lower construction cost because the structure is already there, but you lose the garage. Works well on lots where a new detached structure would be too tight on setbacks. Plumbing and electrical are the biggest cost drivers.
Attached Addition
A room addition with its own exterior door, kitchen, and bath. Shares a wall with the primary home but functions independently. Typically less expensive than a detached structure because it shares the existing foundation perimeter. Framing and utility tie-ins are simpler.
Basement Apartment
Rare in Arizona due to soil conditions and the cost of excavation in our desert climate. Some custom homes in the Scottsdale foothills and Paradise Valley have basements, and these can be converted to ADUs. Waterproofing and egress windows add significant cost in this market.
For most Arizona homeowners, the detached casita or garage conversion is the most practical path. Which one makes sense depends on your lot size, setbacks, how much privacy you want to provide, and whether you can tolerate losing garage space.
Arizona's ADU law: what changed and what it means for you
Governor Katie Hobbs signed House Bill 2720 in May 2024. It went into effect January 1, 2025 and rewrote the rules for ADU construction across the state.
What HB 2720 requires
Every Arizona city with a population over 75,000 must permit at least one attached ADU and one detached ADU on any single-family residential lot. Cities can no longer require special use permits, variances, or public hearings for ADUs that meet the minimum standards. That means if your lot qualifies, the city must approve your ADU, it is no longer discretionary.
Key statewide minimums cities cannot restrict below:
| Standard | State Minimum | Notes |
|---|---|---|
| Rear & side setbacks | 5 feet | Cities cannot require more than 5 ft from rear/side property lines |
| Max ADU size | Lesser of 75% of main home or 1,000 sq ft (lots under 10,000 sq ft) | On lots over 10,000 sq ft: lesser of 3,000 sq ft or 10% of lot area |
| Parking | No additional parking required | Cities cannot mandate ADU-specific parking spaces |
| Design matching | Not required | Cities cannot require ADU to match primary home architecture |
| Owner occupancy | Not required for long-term rentals | Required only for short-term rentals (under 90 days) built after Sept. 2024 |
| ADUs allowed per lot | 1 attached + 1 detached minimum | Phoenix allows a 3rd ADU on lots 1 acre or larger (affordable housing condition) |
What HB 2928 added in 2025
A follow-on bill, HB 2928, signed in May 2025, extended these same ADU rights to unincorporated county areas statewide. If your property sits in unincorporated Maricopa County rather than inside city limits, you now have the same ADU rights as homeowners in Phoenix or Mesa.
Short-term rental rules
ADUs built on or after September 14, 2024 and used for short-term or vacation rentals (under 90 days) may require the property owner to reside on-site. This does not affect long-term leases of 90 days or longer. If you plan to rent your ADU on Airbnb or VRBO, confirm the current short-term rental rules with your city before breaking ground.
The legal changes are a genuine shift. Before 2024, many cities used discretionary approvals, setback requirements, and design standards to effectively block most ADU applications. Those barriers are largely gone for properties inside city limits. The remaining variables are lot size, your HOA's CC&Rs, and site-specific conditions.
ADU rules by city
Every city sets rules within the state framework. Some cities are more permissive than the state minimum. A few have added requirements on top of HB 2720. Always verify current ordinances with your city's planning department before finalizing a design.
| City | Max Size | Min Setbacks | Parking | Notable Rules |
|---|---|---|---|---|
| Phoenix | 75% of main home or 1,000 sq ft (lots under 10K sq ft); up to 3,000 sq ft on larger lots | 5 ft rear & side | None required | Up to 2 ADUs per lot (1 attached, 1 detached). 3rd ADU allowed on 1-acre+ lots if at least one qualifies as affordable housing. No short-term rentals of ADUs. |
| Scottsdale | 1st ADU: 75% of main home. 2nd & 3rd ADUs: capped at 500 sq ft | 5 ft rear & side | None required | Second and third ADUs are significantly smaller than other cities allow. Separate electrical and gas metering required, adds $5,000–$10,000 to project cost. Updated ordinance adopted September 2025 under HB 2928. |
| Paradise Valley | Per state minimums (typically 1,000 sq ft on standard lots) | 5 ft rear & side | None required | Large lot sizes typical in PV (1+ acre) allow for substantial detached casitas. Luxury finish expectations drive costs higher. Confirm current PV ordinance, town has historically had restrictive ADU rules. |
| Mesa | 75% of main home or 1,000 sq ft | 5 ft rear & side | None required | Follows state minimums closely. ADU by right in all single-family zones. Strong permitting department with online portal. |
| Gilbert | 75% of main home or 1,000 sq ft | 5 ft rear & side | None required | Follows state minimums. Many Gilbert lots are HOA-governed, verify CC&Rs. Production home lots can be small, limiting feasible ADU footprints. |
| Chandler | 75% of main home or 1,000 sq ft | 5 ft rear & side | None required | ADU by right in single-family zones. Standard plan review process. HOA restrictions remain common in master-planned communities like Fulton Ranch. |
| Tempe | 800 sq ft of livable area maximum; max 2 bedrooms | 5 ft rear & side | None required | Tempe caps ADUs at 800 sq ft, slightly below the state standard. Pre-approved standard plan program available, selecting a pre-approved design can save $2,000–$6,000 in design and plan review costs. |
City ordinances are subject to change. Verify current requirements with your local planning department before design begins. This table reflects 2025–2026 rules to the best of our knowledge.
How much does an ADU cost in Arizona
Three tiers of ADU construction, from a basic garage conversion to a fully custom detached casita. The gap between tiers is real, a garage conversion and a custom detached structure are not interchangeable options. They serve different purposes.
What drives ADU cost up or down
Site conditions matter more for ADUs than most homeowners expect. A flat lot with easy access from the back alley or side gate is straightforward. A sloped lot in the Scottsdale foothills requires grading, retaining walls, or stepped foundation work that can add $20,000 to $40,000. Soil conditions in some parts of the Valley require deeper footings or engineered slabs, which adds cost.
Utility connections are the second major variable. Scottsdale requires separately metered electrical and gas for ADUs. That means a new meter, a new service panel in the ADU, and separate trenching from the street or utility junction. Budget $8,000 to $15,000 for utility connections on a new detached structure in cities with this requirement.
Per-square-foot cost ranges in the Phoenix metro: new detached ADU construction runs $200 to $400+ per square foot depending on finish level and site conditions. A 600 sq ft mid-range casita at $250/sq ft equals $150,000 before permits and site work. Garage conversions cost less per square foot, roughly $100 to $175/sq ft, because the structure exists.
Where the money goes: cost breakdown
For a typical mid-range detached ADU in the Phoenix metro, here is how the budget splits across major cost categories.
Labor note: Arizona's construction labor market has tightened since 2020. Skilled tradespeople, framing crews, electricians, plumbers, tile setters, are in high demand. This keeps labor as the largest single budget line regardless of ADU type. Budget-level contractors exist, but quality variance shows up in framing tolerances, waterproofing, and tile work.
Permits and fees: Permit costs vary by city and are tied to the value of construction. Phoenix, Mesa, and Gilbert use fee schedules based on total project valuation. Expect $5,000 to $12,000 in permit fees alone on a new detached ADU. Scottsdale and Paradise Valley can run higher. Tempe's pre-approved plan program can reduce review fees by $2,000 to $6,000 if you use one of their standard designs.
ROI and rental income potential
An ADU rented long-term in the Phoenix metro generates meaningful monthly income. Whether that income justifies the construction cost depends on your total project budget, your financing, and your specific submarket.
Monthly rental income by area
| Area | Studio / 400 sq ft | 1 Bed / 600 sq ft | 2 Bed / 800 sq ft | Notes |
|---|---|---|---|---|
| Scottsdale (North) | $1,600–$2,000 | $2,000–$2,800 | $2,600–$3,400 | High demand, low vacancy. Premium for newer construction. |
| Scottsdale (Central / Old Town) | $1,400–$1,900 | $1,800–$2,500 | $2,400–$3,100 | Walkable area drives demand for smaller units. |
| Paradise Valley | $1,800–$2,400 | $2,400–$3,200 | $3,000–$4,000 | Limited rental stock. High-income tenants. |
| Tempe | $1,300–$1,700 | $1,600–$2,200 | $2,000–$2,600 | ASU proximity keeps occupancy high. Strong demand year-round. |
| Phoenix (Arcadia / Biltmore) | $1,400–$1,800 | $1,800–$2,400 | $2,200–$2,900 | Established neighborhoods with strong renter demand. |
| Mesa / Gilbert | $1,100–$1,500 | $1,400–$1,900 | $1,800–$2,300 | Larger lots, suburban market. Steady but not the highest rents. |
| Chandler | $1,100–$1,500 | $1,400–$1,900 | $1,700–$2,200 | Tech corridor employment base supports occupancy. |
Simple payback math
A mid-range 600 sq ft ADU in Scottsdale costing $200,000 renting at $2,200/month generates $26,400 per year in gross income. After expenses (vacancy, minor repairs, insurance, property management if used), net income of $20,000–$22,000 per year puts simple payback at 9–10 years. If you finance the ADU at current rates, the monthly payment on $200,000 over 20 years at 7% is roughly $1,550, leaving $650–$700/month in positive cash flow before vacancy and maintenance.
The other half of the ROI equation is property value. An ADU in a market where custom homes are selling for $1M+ adds meaningful appraised value. Studies generally show ADUs add 20–35% of their construction cost to property value in strong markets. In practice, a well-built $200,000 casita in Scottsdale can push appraised value up by $150,000 to $180,000, which is a reasonable return even before rental income enters the picture.
Short-term rental income is higher, sometimes $3,000 to $6,000 per month in premium areas, but requires owner occupancy of the primary home on lots with ADUs built after September 2024. Management overhead is also significantly greater for STR operations. Most homeowners building ADUs for income choose long-term rentals to keep it simple.
HOA restrictions: what the state law does and does not override
State ADU law does not override your HOA
This is the most common misunderstanding we encounter. Both HB 2720 and HB 2928 explicitly preserve the enforceability of private restrictive covenants. If your HOA's CC&Rs prohibit ADUs, detached structures, or additional dwelling units, your HOA can deny your request, regardless of what city zoning allows.
Before spending any money on plans or permits, pull your HOA's CC&Rs and design guidelines and read the sections on additional structures, dwelling units, and lot coverage. If the language is ambiguous, submit a written inquiry to the HOA board and get a written response.
Many HOAs in master-planned communities (Fulton Ranch, DC Ranch, Power Ranch, Eastmark) have CC&Rs that restrict or outright prohibit separate dwelling structures. The HOA's authority over this is independent of state zoning law.
HOAs in Arizona can still restrict: exterior design and materials to match community standards, setbacks within the lot that exceed city minimums (in some cases), maximum lot coverage percentages, and use for commercial activity. What they cannot do under recent state law is impose restrictions that are more burdensome than the ones the legislature has preempted, but ADU prohibition as a private covenant is still enforceable.
Custom lots outside HOAs
Single-family custom lots without HOA covenants are the simplest situation. If there is no HOA, you deal only with city zoning and state law. Many of the rural and semi-rural areas in the Valley, Cave Creek, Rio Verde, parts of Queen Creek, and unincorporated Maricopa County, have no HOA governance. Custom lots in these areas are among the most ADU-friendly in the metro.
If you are buying land specifically to build a home with an ADU, verify during due diligence whether the property is subject to any recorded CC&Rs. Older subdivisions and master-planned communities almost always have them. Raw lots and custom home subdivisions often do not.
The ADU building process
From the first conversation to a finished casita, most Arizona ADU projects run 6 to 10 months. Garage conversions can be completed in 4 to 6 months. Custom detached casitas with complex sites can take up to 12 months.
Garage conversions: 4–6 months. Custom detached casitas on complex sites: 10–14 months. HOA approval adds unpredictable time depending on the association's review cycle.
Tips for planning your ADU
Things that experienced builders know but first-time ADU homeowners often learn the hard way.
- Check the HOA before anything else. If you are in an HOA, the first call is to the HOA management company, not the city. State ADU law does not override private CC&Rs. A 15-minute review of your HOA documents saves months of wasted design work if ADUs are prohibited in your community.
- Measure your lot before you size the ADU. A 6,000 sq ft lot sounds reasonable until you account for the primary home footprint, 5-foot setbacks on all sides, and existing structures. Many Phoenix metro production home lots leave 800 to 1,200 sq ft of usable backyard area. Your ADU footprint needs to fit within that, including overhangs.
- Budget for utility connections, not just construction. Homeowners consistently underestimate utility costs. A new detached ADU needs water, sewer, electrical, and possibly gas connections. Trenching, new meters (where required), and service panels can add $10,000 to $20,000 to your total budget. Get utility costs line-itemed in any proposal you evaluate.
- Decide up front whether you will rent or house family. A unit designed for a long-term rental tenant prioritizes durability: LVP flooring, laminate or quartz countertops, no-fuss maintenance materials. A casita for an aging parent or adult child might prioritize accessibility features: wider doorways, a roll-in shower, grab bars, single-floor living. These decisions affect design and cost before the first line is drawn.
- Pull permits. Every time. An unpermitted ADU creates serious problems: insurance liability if someone is injured in the structure, disclosure obligations at resale that can kill deals, and possible code enforcement requiring demolition or costly retrofits. Cities in the Phoenix metro are increasingly proactive about unpermitted structures identified via aerial imagery and neighborhood complaints.
- Get a fixed-price contract for the full scope. Cost-plus contracts shift construction risk to you as the owner. A reputable builder who has built ADUs in Arizona should be able to give you a fixed-price proposal covering all labor, materials, permits, and utility connections, not a range with a disclaimer. If the proposal you receive is a broad estimate with a large contingency built in, ask the contractor to identify what is unresolved and require actual bids from subcontractors before signing.
Frequently asked questions
Can I build an ADU on my Phoenix area property?
How much does an ADU cost to build in Arizona?
Do I need a permit to build an ADU in Arizona?
What is the maximum size for an ADU in Arizona?
Can my HOA block me from building an ADU?
Can I rent out my ADU in Arizona?
How long does it take to build an ADU in Arizona?
Does an ADU add value to my property?
Thinking about building an ADU?
We take on a limited number of projects each year so we can stay personally involved. Tell us about your property and your goals and we will give you an honest assessment of what is feasible and what it will cost.