Accessory dwelling units in Mesa, Arizona
Mesa is the third-largest city in Arizona and, at a little over half a million residents, comfortably inside the group of cities that A.R.S. § 9-461.18 applies to. Since Ordinance No. 5883 took effect in October 2024, Mesa has allowed one attached and one detached accessory dwelling unit on any lot where a single residence is permitted — and, unusually, on any lot that already contains a single residence regardless of how it is zoned.
In practice that covers most of the city. Mesa is a city of post-war tract subdivisions on generous lots: an RS-6 lot runs 6,000 square feet with a 55-foot frontage, an RS-9 lot 9,000 with 75 feet, and the older neighborhoods north of Main Street and around Lehi have deeper lots still. The rear yards that came with that pattern are exactly what the statute was written to unlock.
What follows is Mesa’s implementation, district by district, with the state statute it sits on top of. Every figure is taken from the adopted ordinance text or from the city’s own published GIS layers.
The numbers, in short
A.R.S. § 9-461.18Maximum size
1,000 sq ft
Or 75% of your house’s interior habitable area, whichever is less.
Side and rear setback
5 ft or less
Five feet is the most a city may require — and where a district lets a house sit closer, your unit gets the narrower figure too.
Parking
None
No additional spaces, and no fee charged in place of them.
Units permitted
1 attached + 1 detached
A second detached unit becomes available on a lot of an acre or more if one unit is deed-restricted as affordable.
Setbacks by Mesa zoning district
Mesa Zoning Ordinance § 11-5-3, Tables 11-5-3.A.1 and 11-5-3.A.2The left-hand columns are what Mesa requires of a house. The right-hand columns are what an accessory unit is entitled to once A.R.S. § 9-461.18(B)(5) and (B)(6) are applied. Where the two differ at the side or rear, the statutory cap is doing the work.
| District | Min lot | House front | House side | House rear | Unit side | Unit rear | Height | Coverage |
|---|---|---|---|---|---|---|---|---|
| AG | 435,600 sq ft | 30 ft | 60 ft | 60 ft | 5 ft | 5 ft | 30 ft | 15% |
| RS-90 | 90,000 sq ft | 22 ft | 20 ft | 30 ft | 5 ft | 5 ft | 30 ft | 25% |
| RS-43 | 43,560 sq ft | 22 ft | 10 ft | 30 ft | 5 ft | 5 ft | 30 ft | 25% |
| RS-35 | 35,000 sq ft | 22 ft | 10 ft | 30 ft | 5 ft | 5 ft | 30 ft | 35% |
| RS-15 | 15,000 sq ft | 22 ft | 7 ft | 30 ft | 5 ft | 5 ft | 30 ft | 40% |
| RS-9 | 9,000 sq ft | 15 ft | 7 ft | 25 ft | 5 ft | 5 ft | 30 ft | 45% |
| RM-2 | 7,200 sq ft | — | 5 ft | 15 ft | 5 ft | 5 ft | 30 ft | 45% |
| RS-7 | 7,000 sq ft | 10 ft | 5 ft | 20 ft | 5 ft | 5 ft | 30 ft | 45% |
| RS-6 | 6,000 sq ft | 10 ft | 5 ft | 20 ft | 5 ft | 5 ft | 30 ft | 50% |
| RM-3 | 6,000 sq ft | — | 5 ft | 15 ft | 5 ft | 5 ft | 40 ft | 50% |
| RM-4 | 6,000 sq ft | — | 5 ft | 15 ft | 5 ft | 5 ft | 40 ft | 55% |
| RSL-4.5 | 4,000 sq ft | 15 ft | 4.5 ft | 15 ft | 4.5 ft | 5 ft | 30 ft | 70% |
| RSL-4.0 | 3,600 sq ft | 15 ft | 4 ft | 12 ft | 4 ft | 5 ft | 30 ft | 75% |
| RSL-3.0 | 2,925 sq ft | 15 ft | 4 ft | 10 ft | 4 ft | 5 ft | 30 ft | 80% |
| RSL-2.5 | 2,400 sq ft | 14 ft | 3 ft | 10 ft | 3 ft | 5 ft | 30 ft | 80% |
- City ordinanceMesa Zoning Ordinance § 11-5-3, Tables 11-5-3.A.1 and 11-5-3.A.2 (read 2026-10-10)
- City ordinanceMesa Zoning Ordinance Table 11-4-3 — Development standards for the AG district. (read 2026-10-10)
- City ordinanceMesa Zoning Ordinance Table 11-5-3.A.1 — Development standards for the RS single-residence districts. (read 2026-10-10)
- City ordinanceMesa Zoning Ordinance Table 11-5-3.A.1 — Development standards for the RS single-residence districts. (read 2026-10-10)
Gaps in this table
- RSL-4.5: Table 11-5-3.A.2 sets a maximum lot coverage for the RSL districts but no separate building coverage figure, so the coverage budget below uses lot coverage.
- RSL-4.0: Table 11-5-3.A.2 sets a maximum lot coverage for the RSL districts but no separate building coverage figure, so the coverage budget below uses lot coverage.
- RSL-3.0: Table 11-5-3.A.2 sets a maximum lot coverage for the RSL districts but no separate building coverage figure, so the coverage budget below uses lot coverage.
- RSL-2.5: Table 11-5-3.A.2 sets a maximum lot coverage for the RSL districts but no separate building coverage figure, so the coverage budget below uses lot coverage.
What is distinctive about Mesa
Mesa Zoning Ordinance § 11-31-3- No minimum lot size
- Mesa states outright that there is no minimum lot size to establish an accessory unit. A small lot is not, by itself, a reason you cannot build.
- An existing house qualifies the lot
- One attached and one detached unit are permitted on any lot that already contains a single residence, whatever the zoning district. A house on a commercially zoned lot still gets the entitlement.
- Converting a shed keeps its setbacks
- An existing detached accessory building may be converted into a dwelling without having to meet the five-foot setbacks, even if it is already non-conforming. A solid structure close to a lot line is worth more than it looks.
- Garage conversion costs you no parking
- Convert a garage and you do not have to replace the covered parking elsewhere on the lot — though the city still expects two spaces for the house.
- No manufactured homes, RVs or trailers
- Mesa does not allow any of the three to serve as an accessory unit. Tempe does allow converted trailers and tiny homes, so a product that works in one city may not work in the other.
- Airport overflight areas matter here
- Mesa maps overflight areas around Falcon Field and Phoenix-Mesa Gateway, and residential use is restricted in the two closest. We check those for you.
Mesa Zoning Ordinance § 11-31-3 — Accessory Dwelling Unit. Brought into line with state law by Ord. No. 5883, § 2, adopted 7 October 2024. Read the ordinance.
Questions Mesa homeowners ask
Can I build a casita in Mesa?
Yes, on almost any lot. Mesa permits one attached and one detached accessory dwelling unit on any lot where a single residence is allowed, and on any lot that already contains a single residence regardless of zoning. It is a permitted use, which means no public hearing, no variance and no conditional use permit — though you do need a building permit.
How big can a casita be in Mesa?
The interior habitable area may not exceed 75% of your house’s interior habitable area, or 1,000 square feet, whichever is less. A 1,673 square foot house gives you the full 1,000 square feet; a 1,100 square foot house gives you 825.
How close to the property line can I build a casita in Mesa?
Mesa requires a minimum of five feet from the side and rear property lines. The front and street-facing side setbacks follow whatever the underlying district requires of the house — 10 feet in RS-6 and RS-7, 15 feet in RS-9, 22 feet in the larger RS districts.
Do I need a permit to build a casita in Mesa?
You need a building permit, but not a zoning approval that involves a hearing. The state statute defines an accessory dwelling unit as a permitted use, which it in turn defines as approval without a public hearing, variance, conditional use permit, special permit or special exception. If your property is in a Historic District you will also need a Certificate of Appropriateness from Mesa’s Historic Preservation Office.
Can I rent out a casita in Mesa?
Yes. State law bars a city from prohibiting either the house or the accessory unit from being leased as separate long-term rental housing, and bars requiring any pre-existing relationship between the occupants. Short-term rental is governed separately and needs a Mesa short-term rental license. You cannot sell the unit separately from the lot.
Do I have to live in the house to rent out my Mesa casita?
No. There is no owner-occupancy requirement in Mesa’s ADU section, and the state statute would not permit one. Your HOA’s covenants are a separate question and may restrict you.
How much parking do I need for a Mesa casita?
None for the unit itself. A city may not require additional parking for an accessory dwelling unit or charge a fee instead. If you convert a garage, Mesa does not require you to replace the covered parking — but the city still expects the house to keep two parking spaces.
Can I convert my garage into a casita in Mesa?
Yes, and it is often the cheapest route. An existing detached accessory building that meets Mesa’s detached-accessory setbacks may be converted without having to meet the five-foot ADU setbacks, and even a legally non-conforming building may be converted as it stands. Any expansion has to meet current setbacks.
Does my Mesa casita have to match my house?
No. State law forbids a city from requiring an accessory unit to match the exterior design, roof pitch or finishing materials of the house. Mesa’s ADU section contains no design standards at all. An HOA may still require a match.
What zoning districts allow casitas in Mesa?
Agricultural, all residential districts (RS, RSL and RM), and the commercial, mixed-use and downtown districts where a single residence is allowed. Separately, any lot containing an existing single residence is permitted a unit regardless of district.
The full Mesa rules
Every provision, subsection by subsection: size, setbacks, height, coverage, parking, permits, rental, easements and covenants.
Read the explainer →
Compare with Tempe
The state floor is the same in both cities, but the implementations differ — on size, on construction type, and on what counts against your allowance.
Tempe rules →
Statute text read from A.R.S. § 9-461.18 on azleg.gov. Mesa population 517,142, per the U.S. Census Bureau — comfortably over the 75,000 threshold at A.R.S. § 9-461.18(H).