Accessory Structures in Mesa, AZ

If you live in Mesa or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Mesa has 3 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Shed & Carport Rules

Mesa exempts small detached accessory structures, tool sheds, storage sheds, playhouses, from the building permit requirement when they serve a single-family, duplex, or similar residential occupancy and stay at or under 200 square feet, under Title 4, Chapter 1. The exemption doesn't apply on Desert Uplands land, in Historic Preservation Overlay Districts, or on landmark sites.

Key details: Exempt floor area: 200 sq ft or less. Eligible occupancies: R-3, R-4, R-5 (residential). Excluded land: Desert Uplands standards areas. Excluded districts: Historic Preservation Overlay/landmarks. Governing section: Title 4, Ch. 1, § 4-1-4(B)(1)(a).

A shed built over the 200-square-foot threshold, or on a Desert Uplands, Historic Preservation Overlay, or landmark-designated lot, without a permit is unpermitted construction: the Building Safety Director can require a stop-work order, retroactive permitting, or removal, since 4-1-4(B) never authorizes work that violates the technical codes or other city ordinances.

Garage Conversions

Mesa lets homeowners convert an existing detached garage, carport, or accessory structure into an ADU without adding new setbacks, and doesn't require replacing the covered parking a converted garage or carport used to provide. Section 11-31-3(D)(2) and (G)(2) of the Zoning Ordinance govern the conversion.

Key details: Governing section: § 11-31-3(D)(2) & (G)(2). Extra setback for conforming conversion: None required. Replacement parking after conversion: Not required. Applies to: Garage or carport converted to ADU. Interior connection to house: Not permitted.

A garage conversion that adds interior habitable floor area without securing a building permit, or that fails to provide the ADU's required independent entrance and single-kitchen limit, does not qualify for the setback and parking exceptions in § 11-31-3(D)(2) and (G)(2) and is treated as a code violation subject to the City's standard zoning and building enforcement process, including stop-work orders on unpermitted construction.

ADU Rules

Mesa allows one attached ADU and one detached ADU per lot in any Agricultural, Residential, Commercial and Mixed Use, or Downtown district where a Single Residence is permitted. There's no minimum lot size, but an ADU's interior habitable area can't exceed 75% of the primary residence's footprint or 1,000 square feet, whichever is smaller, under Mesa City Code § 11-31-3.

Key details: ADUs allowed per lot: 1 attached + 1 detached. Minimum lot size: None required. Max ADU size: 75% of primary home or 1,000 sq ft. New-structure side/rear setback: 5 feet minimum. Additional parking required: None.

An ADU built with an internal connecting doorway to the primary residence, with more than one kitchen, or using a manufactured home, RV, or trailer as the structure does not meet § 11-31-3 and is not a lawful ADU under the Zoning Ordinance. An ADU exceeding the 75%/1,000-square-foot size cap, encroaching into the required 5-foot side or rear setback for new structures, or exceeding the primary residence's height limit is likewise noncompliant and subject to the City's zoning enforcement process for unpermitted or nonconforming structures.

The Bottom Line

Mesa's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Mesa is broadly strict or permissive.

All of the above reflects Mesa's municipal code as of our last review. If you need specifics on fines, exemptions, or filing requirements, the detailed ordinance pages linked above have the full breakdown.