What are the ADU and casita rules in Mesa, Arizona?

One attached and one detached accessory dwelling unit per single-family lot is the standard Zoning Ordinance Section 11-31-3 sets, adopted by the city through Ordinance 5883 on October 7, 2024. An ADU, commonly called a casita in Arizona, is a self-contained second home with its own entrance, bathroom, and kitchen. The interior of an ADU "shall not exceed 75% of the primary residence's interior habitable area, or 1,000 square feet, whichever is less." A new unit needs a five-foot side and rear setback. Mesa requires no extra parking and, unlike Scottsdale, sets no owner-occupancy rule. That makes Mesa one of the most flexible Valley cities for adding a rentable casita.

Mesa wrote these standards to meet a state ADU mandate. It then made several owner-friendly choices, especially around converting an existing garage or building. Below is what each Mesa rule means for a real project.

How many ADUs Mesa allows and how big

A Mesa single-family lot can hold one attached and one detached ADU, with a third unit possible on large lots. Section 11-31-3 permits one attached and one detached ADU "per lot or parcel in any of the following zoning districts where a single residence is allowed." Any lot with an existing single residence gets the same two units regardless of district. A lot of one acre or more can add one more detached ADU if at least one unit is a restricted-affordable home, defined as one rented to households earning up to 80% of area median income.

Size is capped by floor area. The interior of an ADU "shall not exceed 75% of the primary residence's interior habitable area, or 1,000 square feet, whichever is less." So if your main home is 2,400 square feet, 75% is 1,800. But the 1,000-square-foot cap controls because it is smaller. If your home is 1,100 square feet, 75% is 825, and that lower number applies. Mesa measures interior habitable area, not the gross footprint. So a garage or patio attached to the unit does not eat into the cap the same way a wall-to-wall measure would.

Mesa also keeps the unit a real, single household. There is no minimum lot size to build an ADU. The unit must have its own separate entrance. It may have a partial or full kitchen, but "no more than one (1) kitchen per ADU is allowed." Manufactured homes, RVs, and trailers cannot be used as an ADU. So a parked RV in the yard does not count as your casita.

Mesa setbacks, height, and converting existing buildings

A new Mesa ADU needs a five-foot side and rear setback, but converting an existing structure usually needs no added setbacks. A setback is the minimum distance a building must keep from a lot line. For new construction, Section 11-31-3 requires "a minimum side and rear setback of five (5) feet," with front and street-side setbacks matching the main home's district rules. That five-foot floor matches state law and lets a detached casita sit close to the back fence.

The conversion rules are where Mesa is generous. The code says "existing structures converted to an ADU shall require no additional setbacks." Say a legal building already sits closer than five feet to the line. It can often still become an ADU. The side and rear must stay at a five-foot minimum, and the work cannot increase the nonconformity. Even an existing second story can be converted with no added setbacks. This makes garage and casita conversions much easier than ground-up builds on tight older lots.

Height is simple in Mesa. An attached or detached ADU "shall comply with the primary residence height requirements for the underlying zoning district." There is no separate low height cap for an ADU in a required yard the way Phoenix sets 15 feet. The ADU also has to meet the district's lot-coverage and building-coverage limits. Confirm your zoning district's height and coverage numbers before you design. Those numbers vary across Mesa's residential, downtown, and mixed-use districts.

Parking and garage conversions in Mesa

Mesa requires no extra parking for an ADU, and converting a garage to a casita does not force you to replace the covered parking. State law bars the city from requiring additional parking to accommodate an ADU, and Mesa follows that floor: "No additional parking spaces are required for an ADU." That removes a barrier that used to block projects on lots with no room for another parking pad.

The garage-conversion rule is the standout. Mesa states that "if a garage or carport is converted to an ADU, covered parking for the primary residence is not required to be replaced elsewhere on the lot or parcel." Many cities make you rebuild covered parking somewhere else if you convert the garage, which can kill the math on a project. Mesa drops that requirement, which makes turning an attached garage into a rentable unit one of the cheapest ways to add an ADU in the city. You keep the existing slab, walls, and roof, and you skip the cost of building a new carport.

Utilities still have to be real. An ADU "shall be provided with water, sewer, and electric utilities." It must use the same providers and meters as the primary home. The unit also cannot be built on top of a current or planned public utility easement. The one exception is written consent from the utilities involved. Plan utility capacity early. A panel upgrade or a new sewer branch can move the budget more than the framing does, and it is far cheaper to plan for than to find mid-build.

Renting a Mesa ADU and the owner-occupancy difference

Mesa lets you rent an ADU and does not require you to live on the property, which sets it apart from Scottsdale. Mesa's ordinance carries no owner-occupancy condition for renting an ADU. It simply has to meet the building code and the development standards above. That means a Mesa casita can be a long-term rental whether or not the owner lives in the main home, giving investors and owner-occupants the same path.

This flexibility traces back to the state law Mesa was implementing. Ordinance 5883 says it "is intended to comply with the requirements of A.R.S. 9-461.18." That statute forced cities over 75,000 people to allow ADUs. It also bars a city from requiring "a familial, marital, employment or other preexisting relationship" between the home's owner and the ADU's occupant. And it protects the right to rent the unit as long-term housing. Mesa chose not to layer an owner-occupancy rule on top. So the unit stands on its own as rentable housing, which is a real edge for an investor weighing Mesa against Scottsdale.

Short-term rental rules are a separate question and can change. Confirm the current ADU and short-term-rental terms with the City of Mesa before you count on rental income. For the statewide rules these city standards build on, see our pages on Arizona's ADU requirements and which Arizona cities are required to allow ADUs.

How Jematell Homes helps

We design to your lot's zoning envelope from the first sketch. If you are planning a custom home in Scottsdale, Rio Verde, or the greater Phoenix metro, we are happy to walk through your project.

Sources

• City of Mesa Ordinance 5883 (Accessory Dwelling Units; Zoning Ordinance Section 11-31-3)
• A.R.S. 9-461.18 (Accessory dwelling units; municipalities)
• City of Mesa: Development Codes, Ordinances, Regulations and Standards