Phoenix ADU Laws and the Arizona Casita Bill: What Investors Need to Know

Arizona passed House Bill 2720 in 2024 — widely known as the "Casita Bill" — making it one of the most permissive states in the country for accessory dwelling unit construction. The law allows ADUs on single-family lots statewide, removing the local zoning restrictions that previously prevented them in many Arizona municipalities. For investors, this created a new tool: a path to adding a second rentable unit to an existing single-family property without rezoning, subdivision, or a commercial-use classification.

The catch is that Phoenix subsequently layered its own rules on top of the state law for short-term rental purposes, and those rules matter significantly for investors whose strategy involves operating the ADU as a short-term rental rather than a long-term lease.

What the Arizona Casita Bill Actually Changed

Before HB 2720, Arizona cities could set their own ADU rules, and many were restrictive. Some municipalities required owner-occupancy of the primary structure, limited ADU size to a small fraction of the primary home, or banned ADUs outright in certain zones.

The Casita Bill effectively overrides local exclusions. Key provisions:

• ADUs are now permitted by right on single-family residential lots statewide
• Cities cannot require owner-occupancy of the primary dwelling as a condition of ADU construction
• Local municipalities retain authority over design standards, setbacks, height limits, and utility connections — but cannot categorically prohibit ADUs in single-family zones
• ADUs must meet applicable building codes and receive permits through the standard process

For investors targeting Phoenix's West Valley, this creates a meaningful yield-enhancement opportunity: acquire a single-family home in the $300,000–$420,000 range on a lot that can accommodate a detached ADU (a "casita"), construct the ADU, and rent both units as separate long-term rentals.

Phoenix-Specific ADU Rules for Short-Term Rentals

This is where investors need to pay close attention. Phoenix's STR ordinance, updated through the SHAPE PHX permitting process, contains a specific provision targeting ADU short-term rental operations:

If the certificate of occupancy for an ADU was issued on or after September 14, 2024, the property owner must submit a notarized attestation confirming they reside on-site full-time while the ADU is operated as a short-term rental. This requirement took effect April 4, 2026.

The practical implication: if you are a non-resident investor who purchased a Phoenix property, added a new ADU after September 14, 2024, and intended to operate both the primary house and the ADU as separate unhosted short-term rentals, the Phoenix ordinance prevents this. You can rent the new ADU as a long-term rental (30 days or more) without the owner-occupancy requirement. The restriction applies specifically to short-term rental operations of new ADUs.

Older ADUs are not subject to this restriction. If the ADU's certificate of occupancy predates September 14, 2024, the owner-occupancy attestation requirement does not apply under Phoenix's current rules. Many investors are specifically targeting properties with existing pre-2024 casitas or guest houses for this reason.

The restriction is Phoenix-specific. Other Arizona municipalities may have different rules for ADU STR operations. Scottsdale, Sedona, and Flagstaff each have their own STR ordinances and may or may not impose owner-occupancy requirements on ADUs.

ADU Permit Process in Phoenix

Phoenix's residential permit system applies to ADU construction. Permitting requirements depend on what is being built:

New detached ADU construction: Full building permits required. This is not exempt work. The permit covers the structure and all associated trade work (electrical, plumbing, HVAC) under Phoenix's unified permit system — you do not need separate trade permits for a unified new construction project.

Garage or accessory structure conversion to livable space: Building permit required. The conversion must bring the structure into compliance with residential building code standards, including insulation, egress windows, ceiling height, and smoke/CO detector requirements.

Permit fees for ADU construction: Phoenix's fee schedule applies. A new detached ADU with a construction valuation of $80,000 would fall into the $50,001–$200,000 tier: $551 base plus $7 per $1,000 over $50,000, yielding approximately $761 in permit fees. Plan review takes 28 days for initial review.

Arizona Residential Building Code requirements for ADUs: The structure must meet the current residential code for insulation, fire separation from the primary dwelling (for attached ADUs), egress, and utility connections. Connection to utilities — water, sewer, electric — requires coordination with the city and utility providers and may require infrastructure upgrades depending on the existing service capacity.

ADU Investment Strategy: The Long-Term Rental Use Case

The most straightforward ADU investment strategy in Phoenix involves:

1. Acquiring a single-family property with a lot capable of supporting a detached casita (typically a lot of 7,000 square feet or more, depending on setback and coverage requirements)
2. Constructing a 400–600 square foot detached ADU with its own entrance, kitchen, and bathroom
3. Renting the ADU as a separate long-term rental unit while retaining or also renting the primary dwelling

In Phoenix's West Valley submarkets (Avondale, Tolleson, Glendale), a detached ADU in good condition can generate $900–$1,400 per month as a long-term rental, depending on finish quality and location. At a construction cost of $80,000–$120,000 for a detached casita, the additional rental income adds materially to the property's total yield and appraised value.

For the BRRRR (Buy, Rehab, Rent, Refinance, Repeat) strategy, adding an ADU increases the after-repair value of the primary property, which can support a larger refinance and the extraction of capital for the next acquisition. Lenders underwriting properties with existing or newly permitted ADUs will typically count 75% of the ADU's market rent as qualifying income.

HOA Restrictions on ADUs

The Casita Bill creates a right to build ADUs statewide, but HOA restrictions can complicate this. If an HOA's recorded CC&Rs contain provisions restricting detached structures, accessory buildings, or the appearance of additions, those restrictions may create grounds for the HOA to challenge ADU construction.

The Kalway v. Calabria Ranch HOA ruling (Arizona Supreme Court, 2022) requires HOA restrictions to be clearly expressed and foreseeable from the original declaration. Restrictions on detached structures are common in CC&Rs and may be enforceable even for ADUs that would otherwise qualify under the Casita Bill.

Before planning an ADU addition on any HOA-governed property, obtain the full recorded CC&Rs and analyze them for restrictions on accessory structures, building footprint, lot coverage ratios, and approval requirements for any new construction. Some HOAs have architectural review committees that must approve exterior modifications — an ADU addition would typically trigger this process.

The Bottom Line

The Arizona Casita Bill represents a genuine expansion of the income-generating options available to Phoenix residential investors, particularly in the long-term rental strategy. The short-term rental restriction for new ADUs in Phoenix is a meaningful limitation for investors who planned to run dual-unit STR operations, but it does not affect the long-term rental use case, and it does not apply to ADUs with pre-2024 certificates of occupancy.

Investors who want to build or buy properties with ADU potential should get the permit history of any existing accessory structures, understand the HOA CC&Rs on the target property, and model the ADU income specifically as long-term rental revenue unless they are either owner-occupying or targeting a pre-2024 ADU.

The Arizona Investment Property Guide covers the ADU framework alongside the full Phoenix renovation permit system, HOA due diligence, property tax classification for multi-unit residential properties, and the STR compliance requirements across Scottsdale, Phoenix, Sedona, and Flagstaff.

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