Can I build a casita in Tempe? ADU rules by district
Updated October 9, 2026
Short answer: yes. On most single-family lots in Tempe 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). A detached casita needs 5 ft from the side and rear property lines, or more where a utility easement is wider. In most Tempe neighborhoods the 45% lot coverage limit is what decides the final size.
What Tempe's planning staff confirmed
- Lot coverage limits the ADU. The house, garage, existing structures and the ADU together must stay under your district's coverage limit.
- Open structures don't count. Open patio covers, carports and awnings are left out of lot coverage.
- The 75% rule uses living area only, not the garage.
- Setbacks: 5 ft from side and rear lines, or the width of a utility easement if that's wider.
- More coverage is possible with a Use Permit Standard (up to 10% more, for example 45% becomes 49.5%), after a public hearing. Converting a garage adds no coverage at all.
Tempe single-family (R1) districts
| District | Max lot coverage | Front setback |
|---|---|---|
| R1-4 | No limit | 15 ft |
| R1-5 | No limit | 20 ft |
| R1-6 | 45% | 20 ft |
| R1-7 | 45% | 20 ft |
| R1-8 | 45% | 20 ft |
| R1-10 | 45% | 30 ft |
| R1-15 | 45% | 35 ft |
R1-4 and R1-5 have no coverage limit, so the ADU is limited by the state size rule and the space in your yard. Footnotes in the code can change side setbacks for small and shared-wall lots.
Tempe multi-family districts
| District | Max lot coverage |
|---|---|
| R-2 | 45% |
| R-3R | 45% |
| R-3 | 50% |
| R-4 | 60% |
| R-5 | 70% |
These districts have a 20 ft front setback. The state ADU law applies where a single-family home is allowed, so confirm with the city that an ADU is allowed on your lot.
A quick example
An R1-6 lot of 7,000 sq ft allows 3,150 sq ft of coverage (45%). If the house and garage cover 2,500 sq ft, there's 650 sq ft left, so the largest new detached ADU is 650 sq ft, even if the home is big enough for 1,000. An open patio cover wouldn't count against you.
Before you build
- Check your HOA's CC&Rs. State law limits the city, not your HOA.
- Find any utility easement along the rear lot line. Tempe measures the setback from its edge if it's wider than 5 ft.
- Talk to Tempe Community Development about permits.
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 Tempe?
Yes, on most single-family lots. Tempe must 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 Tempe?
Up to 75% of your home's living area (not counting the garage) or 1,000 sq ft, whichever is smaller. In most R1 districts the 45% lot coverage limit is what decides the final size.
Do patio covers count toward lot coverage in Tempe?
Tempe counts enclosed buildings. Open patio covers, carports and awnings don't count toward lot coverage.
What if I'm over the lot coverage limit?
Tempe suggests converting existing space, like a garage, into an ADU, which adds no coverage. A Use Permit Standard can also allow up to 10% more coverage after a public hearing.
Sources: Tempe Zoning and Development Code Tables 4-202A and 4-202B; City of Tempe Planning (October 2026); A.R.S. § 9-461.18.