Can I build a casita in Mesa? ADU rules by district
Updated October 9, 2026
Short answer: yes. On most single-family lots in Mesa you can build one attached and one detached casita, each up to 75% of your home's living area or 1,000 sq ft (whichever is smaller), as close as 5 ft to the side and rear property lines. What usually decides the final size is your lot: how much building coverage your zoning district allows and how much space is left in the yard.
The rules that come from state law
- Size: up to 75% of the home's living area or 1,000 sq ft, whichever is smaller.
- Side and rear setbacks: no more than 5 ft.
- Parking: no extra parking required.
- Renting: long-term renting is allowed, and you don't have to live on the property.
See Arizona's ADU law, explained for the full list.
The rules that come from your Mesa zoning district
Your district sets the front setback and how much of the lot buildings may cover. Everything with a roof counts together: the house, garage, any existing casita or shed, and the new ADU. Mesa's single-residence (RS) districts have two limits, building coverage and a looser lot coverage; the stricter one, building coverage, is usually the one that matters.
Single residence (RS) districts
| District | Max building coverage | Max lot coverage | Front setback (living area) |
|---|---|---|---|
| RS-6 | 50% | 60% | 10 ft |
| RS-7 | 45% | 60% | 10 ft |
| RS-9 | 45% | 60% | 15 ft |
| RS-15 | 40% | 50% | 22 ft |
| RS-35 | 35% | 50% | 22 ft |
| RS-43 | 25% | 40% | 22 ft |
| RS-90 | 25% | 40% | 22 ft |
Small-lot (RSL) districts
| District | Max lot coverage | Front setback (building wall) |
|---|---|---|
| RSL-4.5 | 70% | 15 ft |
| RSL-4.0 | 75% | 15 ft |
| RSL-3.0 | 80% | 15 ft |
| RSL-2.5 | 80% | 14 ft |
RSL lots also have an open-space requirement.
Multiple residence (RM) and Downtown (DR) districts
- RM-2, RM-3, RM-4: building coverage of 45%, 50% and 55%, a 20 ft front setback on a local street (more on busier streets), and spacing rules between buildings. These are multi-family districts, so confirm with the city that an ADU is allowed on your lot.
- DR-1, DR-2, DR-3: no coverage limit; front setback 15 ft (10 ft in DR-3); 400 sq ft of open space per home.
A quick example
An RS-6 lot of 7,000 sq ft allows 3,500 sq ft of building coverage (50%). If the house and garage cover 2,600 sq ft, there's 900 sq ft left, so the largest ADU is 900 sq ft even if the home is big enough for 1,000. Then it has to fit in the yard: 5 ft from the side and rear lines, and clear of the house.
Before you build
- Check your HOA's CC&Rs. State law limits the city, not your HOA.
- Look for utility easements along the rear lot line. You can't build over one without the utilities' consent.
- Talk to Mesa Development Services about permits and fees.
Type your Mesa or Tempe address. CasitaFlow pulls your parcel and zoning and shows the largest casita allowed, the setbacks, and a drawing of where it fits. Free, no account needed.
Common questions
Can I build a casita in Mesa?
Yes, on most single-family lots. Mesa has more than 75,000 people, so state law requires it to allow one attached and one detached ADU wherever a single-family home is allowed, without a public hearing.
How big can a casita be in Mesa?
Up to 75% of your home's living area or 1,000 sq ft, whichever is smaller, as long as it fits inside the setbacks and your lot stays under its coverage limit.
How close to the property line can a casita be in Mesa?
State law caps side and rear setbacks for an ADU at 5 ft. The front setback is the same as for the house in your zoning district.
Do I need a permit for a casita in Mesa?
Yes. It's a permitted use, so there's no hearing, but you still need building permits from Mesa Development Services.
Sources: Mesa Zoning Ordinance Tables 11-5-3.A.1, 11-5-3.A.2, 11-5-5 and 11-8-3.A (amended through Ord. 5996, March 2026); A.R.S. § 9-461.18.