Phoenix calls them accessory dwelling units (also guest houses or casitas). California state ADU law does not apply here. When a lot has no more than one single-family detached primary dwelling, the zoning ordinance allows ADUs as set out in Section 706.[1]
What is an ADU? An accessory dwelling unit is a small second home on the same lot as the main house: a backyard unit, garage conversion, attached addition or guest house with its own kitchen and bath.
| Size limits | Any ADU may not exceed 75% of the gross floor area of the primary dwelling, and also: up to 1,000 sq ft on lots up to 10,000 sq ft net, or the lesser of 3,000 sq ft or 10% of net lot area on lots over 10,000 sq ft. A garage, attached shade structure or carport built with a detached ADU does not count toward that floor area. City FAQ materials also say two ADUs are permitted on a typical single-family lot, with a third possible under limited circumstances.[2][1] |
|---|---|
| Height | Detached ADU inside a required rear or side yard: max 15 ft unless a use permit allows more. Outside required yards: same height as the primary dwelling. Attached ADUs follow the primary dwelling height rules.[2] |
| Setbacks | Detached: min 5 ft from a street-side property line; min 3 ft from an interior side or rear line; no setback next to a fully dedicated alley. Front setbacks follow the zoning district. Attached ADUs use the same setbacks as the primary dwelling. Detached ADUs may sit in rear or side yards; between the house and the front property line needs a use permit.[2] |
| Parking | Not verified. We did not find this on the official pages we checked. Ask the city before you design. |
| Owner occupancy | Not verified. We did not find this on the official pages we checked. Ask the city before you design. |
| Permit steps and timeline | The city is building a free ADU Standard Plan Library from a 2024 design competition; as of our check, listed plans were still marked in review. A plot/site plan is still required for permitting. Confirm eligibility with Planning and Development before you alter the property.[1] |
| Fees | Not verified. We did not find this on the official pages we checked. Ask the city before you design. |
Also worth knowing: Check HOA rules separately. Use My Community Map to confirm your zoning district and lot coverage.[1]
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Sources
Every fact above links to an official city or state page. Rules change; check the source before you build.
- [1] City of Phoenix: Accessory Dwelling Units (ADU) checked Oct 2026
- [2] Phoenix Zoning Ordinance 706 (Accessory Uses and Structures) checked Oct 2026