As of October 2026, Phoenix allows two ADUs on a lot with one single-family home, and a third on an acre or more if one is income-restricted. On lots up to 10,000 sq ft an ADU can reach 1,000 sq ft, never over 75% of the main home. No added parking is required, though a converted garage's parking must be replaced.
What does the state law require?
HB 2720, signed May 21, 2024, added A.R.S. § 9-461.18. For any city or town over 75,000 people, it requires:
- At least one attached and one detached ADU as a permitted use where a single-family home is allowed.
- One more detached ADU on a lot of an acre or more, if at least one unit is restricted-affordable, meaning rented or sold to households at or below 80% of area median income.
- An allowed size of at least 75% of the main home's gross floor area or 1,000 sq ft, whichever is less.
- No side or rear setback over 5 feet, and no height or coverage rules stricter than for a house in the same zone.
- No added parking, no design-matching requirement, no fire sprinkler mandate.
- No ban on renting the house or ADU as separate long-term rentals of 90 days or more.
The ASU Morrison Institute counts 16 covered cities, including Phoenix, Scottsdale, Tempe and Glendale. Cities that missed the January 1, 2025 deadline would have had to allow ADUs on all residential lots without limits.
What changed in 2025 and 2026?
HB 2928, approved May 23, 2025, amended the law. Among other changes, it narrowed the areas near airports where the ADU rules do not apply, which opened more of Scottsdale to ADUs. In February 2026, the House Appropriations Committee rejected HB 4028, which would have removed the 1,000 sq ft cap and the 5-foot setback limit. As of October 2026, the caps stand.
What are Phoenix's own numbers?
| Rule | City of Phoenix, as of October 2026 |
|---|---|
| Number | Two ADUs per single-family detached lot; a third on one acre or more with an affordable unit |
| Size, lots up to 10,000 sq ft | 1,000 sq ft, and no more than 75% of the main home |
| Size, larger lots | Lesser of 3,000 sq ft or 10% of net lot area, and no more than 75% of the main home |
| Height | 15 ft in a required yard unless a use permit allows more; outside required yards, the main home's height limit |
| Detached setbacks | 3 ft from interior side or rear lines, 5 ft from a street side line, none at a dedicated alley |
| Attached setbacks | 3 ft from the rear line, 5 ft from a side line |
| Parking | None added; a converted garage or carport's parking must be replaced on the lot |
| Short-term rental | Allowed with a city STR permit; owner must live on site for newer ADUs |
Where does it depend?
The table is the starting point, not the answer. Lot coverage limits in your zoning district, public utility easements, airport areas and your HOA's covenants can all shrink what fits. The size cap based on 75% of the main home means a small house limits its own ADU. And older guidance documents may predate the 2024 amendment, so we work from the ordinance text.
Can I sell the ADU separately?
The state law does not create a right to sell an ADU apart from the house, and Scottsdale's rules expressly prohibit it. Plan on the house and the ADU selling together.
Sources, as of October 2026:
- A.R.S. § 9-461.18, added by HB 2720 (Laws 2024, Ch. 196, approved May 21, 2024) and amended by HB 2928 (Laws 2025, Ch. 217, approved May 23, 2025).
- City of Phoenix ADU web page, Beginner's Guide to ADUs and staff report Z-TA-2-24 (September 30, 2024).
- City of Phoenix short-term rental page.
- ASU Morrison Institute, ARCHES fact sheet on ADUs and HB 2720 (September 2025).
- Scottsdale Area Association of Realtors, report on HB 4028 (February 26, 2026).