How many ADUs can you build on a lot in Arizona?
Arizona cities and towns of more than 75,000 people, and counties, must allow at least one attached and one detached ADU wherever a single-family home is allowed, plus a second detached ADU on lots of an acre or more, with an affordable-rent condition that differs between the two laws.
These are minimums. A city or county can allow more.12
The third unit on an acre or more
The two statutes attach the affordability condition differently:
- Cities and towns of more than 75,000 people must allow the additional
detached ADU only "if at least one accessory dwelling unit on the lot or parcel is a restricted-affordable dwelling unit".1
- Counties must allow the additional detached ADU, and "may require" one
unit on the lot to be restricted-affordable.2
A restricted-affordable unit is one that, through a deed restriction or a development agreement with the city or county, is rented to households earning up to 80% of the area median income.12
What "permitted use" means
Both statutes require the units as a "permitted use". That means approval without a public hearing, variance, conditional use permit, special permit or special exception. The only step left is the routine check that the site plan conforms to the zoning rules.12
If the local rules were never adopted
Cities had until January 1, 2025, and counties until January 1, 2026, to adopt regulations. Where they did not, the statutes allow ADUs on all residentially zoned lots "without limits".12
Who publishes this
Kyrax Developments is a BC Housing-licensed builder based in British Columbia. It publishes this page as a reference to Arizona state law. The page is not legal advice and not an offer of construction services in Arizona. The city or county planning department has the final word on any specific lot.
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