Phoenix’s "Two Casita" Rule: How to Unlock Double-ADU Lots in Arcadia, Biltmore & Beyond

Backyard Casita in Phoenix, Arizona built by AzADU

If you own a single-family home in Phoenix, your property’s development potential expanded substantially. Under enacted Arizona legislation and corresponding City of Phoenix zoning ordinances, single-family residential lots are no longer limited to a single secondary structure: homeowners are now legally permitted to build two accessory dwelling units (ADUs) on a qualifying single-family parcel.

For property owners in prime Phoenix enclaves—including Arcadia (85018), Biltmore/Uptown (85016), Paradise Valley Village (85028), Central Phoenix (85012), and Desert Ridge (85050)—this regulatory change opens the door to transforming underutilized residential land into high-yield, permanent real estate equity.

Here is what the enacted law authorizes, how it impacts your property rights, and how building two turnkey casitas converts a standard residential lot into an executive multi-door asset.

The Legal Framework: Arizona HB 2720 and Phoenix Ordinance G-7317

This is settled, enacted law and not a municipal proposal.

In 2024, the Arizona Legislature passed House Bill 2720, codified as Arizona Revised Statutes (A.R.S.) § 9-461.18 (and expanded by HB 2928). The statute mandates that Arizona municipalities with populations exceeding 75,000 must allow accessory dwelling units as a permitted use on any lot where a single-family dwelling is established. A "permitted use" means designs that meet standard zoning criteria require only administrative plan checks, completely eliminating public hearings, neighborhood variance votes, and subjective conditional use permit hurdles.

To align with this state mandate, the Phoenix City Council formally enacted Ordinance G-7317 (Zoning Ordinance Text Amendment Z-TA-2-24). This action updated Phoenix Zoning Ordinance Chapter 6 and Section 706, removing the historical single-guesthouse cap and establishing standard development rules for multi-ADU parcels.

What the Updated Laws Authorize by Right

The statutes outline clear parameters regarding what single-family homeowners can construct by right:

• Two Permitted ADUs per Single-Family Lot: Municipalities must allow at least one attached ADU and one detached ADU on qualifying single-family parcels. Under Phoenix Section 706, two ADUs attached to one another (forming a detached "duplex casita" separate from the main residence) are legally classified as two detached ADUs.

  
  

• A Third ADU on Acreage Parcels: Homeowners with parcels of one net acre or larger (43,560 sq. ft.) may build a third ADU, provided at least one unit qualifies as deed-restricted affordable housing under statutory median income definitions (A.R.S. § 9-461.18(A)(2)).

  
  

• Generous Size Ceilings: Each ADU can measure up to 75% of the primary dwelling’s interior habitable area or up to 1,000 square feet, whichever is smaller (lots exceeding 10,000 net sq. ft. qualify for expanded square footage under Section 706).

  
  

• Relaxed Rear and Side Setbacks: State law restricts municipalities from imposing side or rear setbacks greater than 5 feet. Phoenix’s adopted standards allow interior setbacks as close as 3 to 5 feet depending on specific yard placement and wall height configurations.

  
  

• No Added Parking Mandates: Cities cannot require additional paved off-street parking spots or in-lieu fees as a prerequisite for permitting either ADU.

  
  

• Architectural Freedom: Municipalities can no longer mandate that an ADU mirror the primary residence’s roof pitch, exterior architecture, or exact finishing materials.

  
  

Quick Lot Test: Calculating Your Maximum Allowable Casita Footprint

To determine your lot's baseline allowable footprint, run this simple three-step formula:

1. Find your primary residence interior square footage (e.g., 2,800 sq. ft. in Arcadia). The statute measures gross floor area as interior habitable space, excluding garages and covered patios.

   
   

2. Multiply by 0.75 (2,800 × 0.75 = 2,100 sq. ft.).

   
   

3. Apply the statutory ceiling: Because 2,100 exceeds 1,000, your maximum ADU size is 1,000 sq. ft. (If your main home is 1,200 sq. ft., your ceiling is 900 sq. ft.).

   
   

AzADU’s pre-approved, permit-ready floor plans fit cleanly within these statutory boundaries:

Model Plan	Layout	Footprint	Starting Base Price	Ideal Property Application
The Chameleon	1 Bed / 1 Bath	Compact Studio	$169,500	Executive Office / Independent Rental Suite
The Bisbee	1 Bed / 1 Bath	400+ Sq. Ft.	$179,500	Independent Living / Private Guest Retreat
The Camelback	1 Bed / 1 Bath	Expanded Luxury	$204,500	High-End Estate Casita / Multi-Gen Suite
The Saguaro	2 Bed / 1 Bath	784 Sq. Ft.	$214,500	Full In-Law Residence / Two-Tenant Layout
The Cholla	2 Bed / 2 Bath	784 Sq. Ft.	$229,500	Dual Primary Suite Executive Rental

The Bisbee floor plan by AzADU

The Double-ADU Investment Model: Turning Single-Family Lots into Multi-Door Assets

While early casita conversations focused on simple guest rooms, forward-looking Phoenix homeowners are leveraging A.R.S. § 9-461.18 to execute a long-term rental wealth strategy.

• Traditional Single-Family Setup

  • Configuration: Primary Residence (1 Door)

  • Revenue Potential: Single income stream from a standard residential parcel

• The Double-ADU Compound Strategy

  • Door 1: Primary Residence (Owner-occupied or primary lease)

  • Door 2: 1,000 Sq. Ft. Attached/Detached Suite (Executive lease)

  • Door 3: 1,000 Sq. Ft. Detached Luxury Casita (Executive lease)

    
    

• Total Asset Value: 3 independent doors generating cash flow from one underlying land parcel

Statutory Protection for Long-Term Rentals

Under A.R.S. § 9-461.18(B)(1), municipalities are barred from prohibiting the separate leasing or advertising of an ADU as a long-term rental (defined as a lease term of 90 days or longer, or month-to-month). Phoenix allows long-term ADU leasing without requiring the owner to live on-site, providing broad operational freedom for property investors and estate owners.

Executive Rental Yields

In high-demand submarkets such as Arcadia (85018), Central Phoenix (85012), and the Biltmore corridor (85016), demand for high-end, private living spaces remains strong. Traveling medical specialists, relocating corporate executives, and seasonal residents actively seek quiet residential settings over dense commercial apartment complexes.

A detached luxury casita commanding local executive rental rates generates recurring cash flow while operating under one primary land title, one tax parcel number, and shared underlying utility infrastructure. Building two units effectively creates a private multi-family compound within a prime single-family zip code.

Navigating the Critical Details: HOAs, Lot Coverage, and PBCC Building Code

While state and city laws have broadened development rights, building two accessory dwellings requires navigating specific regulatory and engineering constraints:

1. Private HOA Covenants Remain Legally Enforceable

A.R.S. § 9-461.18(C) explicitly states that state law does not override private restrictive covenants or deed restrictions entered into between private parties. If your property is located in an HOA-governed community or a subdivision with active CC&Rs—common in master-planned pockets of Desert Ridge or gated communities in the Biltmore area—your Architectural Review Committee (ARC) still holds authority over secondary structures. AzADU prepares and coordinates full architectural review submissions to guide projects through HOA boards.

2. Zoning District Lot Coverage Limits Still Apply

Although setbacks are relaxed to 5 feet, builds must respect the maximum lot coverage percentages of your underlying zoning classification. Phoenix Ordinance G-7317 increased single-story lot coverage in low-density single-family districts (such as RE-43, RE-24, R1-14, and RE-35) by 10%—permitting up to 40% maximum lot coverage when all structures remain single-story (under 15–20 feet depending on yard placement). Confirming remaining lot coverage is the essential first step before drafting two units.

3. Compliance with the 2024 Phoenix Building Construction Code (PBCC)

ADUs must comply with 2024 PBCC life-safety and energy guidelines. Key provisions include:

• EV-Ready Conduit: Installing dedicated 240V/50-amp electrical conduit pathways to accommodate EV charging infrastructure.

  
  

• EPA WaterSense Compliance: Installing compliant plumbing fixtures engineered for Arizona conservation targets.

  
  

• Utility Infrastructure Capacity: Verifying sewer tie-ins, grade fall, water meter sizing, and main electrical panel capacity (200A to 400A service upgrades) to safely power three independent dwellings on one parcel.

Order a Double-ADU Lot & Rental Feasibility Audit

Capitalizing on Arizona’s "Two Casita" rule requires careful spatial planning, electrical calculation, and zoning analysis.

AzADU handles the full construction lifecycle, from architectural layout, civil utility routing, and city permitting to turn-key, move-in delivery. Owned and operated locally, AzADU builds every casita to verified residential standards backed by an A+ Better Business Bureau accreditation and Arizona ROC licensure.

Interested in building on your Phoenix property?

Contact AzADU directly to schedule a Site Feasibility & Zoning Audit. We review your property's setback lines, net lot coverage, utility pathways, and floor plan options to determine your build parameters.

• Builder Credentials: Arizona ROC License #351233 | BBB A+ Accredited

  
  

• Service Areas: Arcadia, Biltmore, Paradise Valley Village, Central Phoenix, Desert Ridge, and surrounding metro communities

  
  

• Project Baseline: Turnkey site-built luxury ADUs from $169,500+