Accessory Dwelling Unit (ADU) Regulations in Mesa, Arizona
In the City of Mesa, property owners in residential, agricultural, and commercial districts are generally permitted to build one attached and one detached Accessory Dwelling Unit (ADU) per lot. These units are limited to a maximum size of 1,000 square feet or 75% of the primary residence’s habitable area, whichever is less, and the City of Mesa does not require any additional on-site parking for these units [Section 11-31-3].
Permitted Zoning Districts in Mesa
The City of Mesa allows the development of Accessory Dwelling Units in a wide variety of base zones. According to the City of Mesa Land Use Tables, ADUs are classified as a permitted accessory use ("P") in the following areas:
| District Group | Specific City of Mesa Districts |
|---|---|
| Agricultural | AG [Table 11-4-2] |
| Residential | RS, RSL, RM [Table 11-5-2] |
| Commercial | NC, LC, GC, OC, MX [Table 11-6-2] |
| Downtown | DR-1, DR-2, DR-3, DB-1, DB-2, DC [Table 11-8-3] |
| Public | PS [Table 11-10-2] |
| Transect (FBC) | T3N, T4N, T4NF, T4MS, T5N, T5MSF, T5MS, T6MS [Section 11-58-3] |
General Requirements and Unit Allowances
The City of Mesa Zoning Ordinance establishes specific limits on the number of units allowed per parcel. In standard districts, a property owner is permitted one attached ADU and one detached ADU [Section 11-31-3(A)].
A third ADU may be permitted in the City of Mesa if the following criteria are met:
- The lot or parcel is one acre or larger in size.
- At least one of the ADUs is restricted as an "affordable" dwelling unit, rented to households earning up to 80% of the area median income [Section 11-31-3(A)].
Prohibited Unit Types
The City of Mesa strictly prohibits the use of Manufactured Homes, Recreational Vehicles (RVs), and trailers as Accessory Dwelling Units [Section 11-31-3(B)]. Furthermore, an ADU must have a separate and independent entrance from the primary residence and is limited to one kitchen per unit [Section 11-31-3(B)].
Development and Building Standards
All ADUs in the City of Mesa must conform to the following technical specifications regarding size, height, and parking.
| Standard | Requirement |
|---|---|
| Maximum Unit Size | 75% of primary residence habitable area or 1,000 sq. ft. (whichever is less) |
| Minimum Lot Size | No minimum requirement to establish an ADU |
| Maximum Height | Must comply with primary residence height requirements for the district |
| Required Parking | Zero (0) additional spaces required |
| Kitchen Limit | Maximum of one (1) kitchen per ADU |
[Section 11-31-3 and Table 11-32-3.A]
Setbacks and Placement
The City of Mesa provides different setback requirements depending on whether the ADU is a new structure or a conversion of an existing building.
New Construction
For newly constructed attached or detached units, the City of Mesa requires a minimum side and rear setback of five (5) feet. Front and secondary front (street side) setbacks must comply with the primary residence setback requirements of the underlying Mesa zoning district [Section 11-31-3(D)].
Conversions of Existing Structures
The City of Mesa allows for the conversion of existing legal non-conforming detached accessory buildings into ADUs without requiring additional setbacks, provided the conversion does not increase the non-conformity [Section 11-31-3(D)]. If a second story is added to an existing structure for an ADU, the setbacks for that new story must comply with the primary residence setbacks for the underlying district [Section 11-31-3(D)].
Utilities and Infrastructure
The City of Mesa requires all ADUs to be provided with water, sewer, and electric utilities. Crucially, these units must be served by the same utility providers and meters as the primary residence [Section 11-31-3(H)]. Building an ADU on top of a current or planned public utility easement is prohibited unless the property owner obtains written consent from the applicable utility provider [Section 11-31-3(H)].
Special Provisions for Transect Zones
In the City of Mesa’s Form-Based Code (Transect) zones, the "Carriage House" is the only recognized detached ADU type allowed [Section 11-59-4]. In these zones, if a garage or carport is converted into an ADU, the property owner is not required to replace the covered parking for the primary residence elsewhere on the lot [Section 11-34-1].
Sections Cited
- Section 11-4-2 (Agricultural District Land Use)
- Section 11-5-2 (Residential District Land Use)
- Section 11-6-2 (Commercial District Land Use)
- Section 11-8-3 (Downtown District Land Use)
- Section 11-10-2 (Public and Semi-Public Land Use)
- Section 11-31-3 (Accessory Dwelling Unit)
- Section 11-32-3 (Parking Spaces Required)
- Section 11-58-3 (Transect Land Use Regulations)
- Section 11-59-4 (Single-Unit House, Village)
- Section 11-86-2 (Residential Use Classifications)