Everything homeowners ask about building an ADU in Tempe — answered with 2026 data.
Yes, ADUs are allowed in Any lot in a zoning district that allows residential use and that already contains a single-family dwelling (ZDC Section 3-402; ADU Development Guide Step 1). Lots with an existing duplex, triplex or apartment building are not eligible. HOA CC&Rs may still restrict ADUs (ARS 9-461.18(C)); most Tempe subdivisions have none. in Tempe, AZ. The maximum size for a detached ADU is Lots under 1 acre: 75% of the main house's gross floor area or 1,000 sq ft, whichever is less. Lots of 1 acre (43,560 sq ft) or more: 75% or 2,000 sq ft, whichever is less. Gross floor area is interior habitable area, excluding garages, carports and exterior storage (ZDC 3-402; ADU Development Guide Step 2). District lot coverage still applies, e.g. 45% in R1-6. Attached ADUs can be up to Same 75% / 1,000 sq ft rule. Tempe has an ADU-friendliness score of 8/10. Check our full Tempe ADU rules page for complete zoning details.
ADU construction in Tempe typically costs $150,000-$280,000. The cost per square foot averages $175-$350. Garage conversions are more affordable at $80,000-$150,000, while prefab ADUs cost $150,000-$300,000. Permit fees add Building permit fee is valuation-based per City Code Fee Schedule Table 1-A, plus a plan review fee of 65% of the permit fee (Community Development Service Fees sheet); the Residential Rebate Program refunds 100% of both after final inspection. to your budget. See our detailed Tempe ADU cost guide.
Detached ADUs in Tempe can be up to Lots under 1 acre: 75% of the main house's gross floor area or 1,000 sq ft, whichever is less. Lots of 1 acre. Attached ADUs are limited to Same 75% / 1,000 sq ft rule. Junior ADUs (JADUs) have a cap of No JADU category in Arizona or Tempe; a converted portion of the house is simply an attached ADU under Section 3-402. ADUs on lots under 1 acre are limited to 3 bedrooms; there is no bedroom limit on lots of 1 acre or more (ADU Development Guide Step 2). Maximum height is Same as the single-family height limit of the underlying district in ZDC Section 4-202 (typically 30 ft); ARS 9-461.18(B)(5) bars a stricter ADU-only cap. Since a December 17, 2025 Board of Adjustment decision the city requires a Use Permit for any two-story ADU design (city ADU page, September 2026). You are allowed up to 2 per lot under 1 acre on a qualifying lot.
Rear setback: 5 ft minimum in all districts unless the district or overlay allows less (ZDC 3-402; ARS 9-461.18(B)(6)). Where the lot backs onto a dedicated public alley the rear setback is measured from the midpoint of the alley (city ADU page). Side setback: 5 ft minimum for interior side and street-side yards in all districts unless the district or overlay allows less (ZDC 3-402; ADU Development Guide Step 2); measured from the alley midpoint where a side yard abuts a dedicated public alley. Front setback: An ADU may not be placed in the front building setback; the front setback is the district standard for buildings in ZDC Section 4-202 (ADU Development Guide Step 2). Look up your district on the Tempe Zoning + Overlays Map. Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
No additional parking may be required for an ADU (ARS 9-461.18(B)(3)). If the ADU removes or alters an existing required space, replace it elsewhere on site or obtain a Use Permit to park in the front or street-side setback; alley-loaded spaces need a 23-ft backing distance (ADU Development Guide Step 2; City Code 21-3(4)). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required for long-term rentals, and the city may not demand a family or employment relationship (ARS 9-461.18(B)(1)-(2)). One exception: an ADU built on or after December 20, 2024 that is licensed as a short-term rental requires the owner to live on the property (Tempe City Code 16A-213(k), authorized by ARS 9-500.39(B)(9)). Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Tempe is typically Target first residential plan review of 5-10 working days for projects under $500,000 and 4-6 working days per resubmittal (Building Safety Target Turn-Around Times, revised Aug 26, 2025); residential engineering review 5-15 working days. Plan check: Plan review fee is 65% of the building permit fee, paid at submittal; it covers the first review plus two resubmittals (a fourth review costs extra). Submit through E-Plan Review; first-review target 5-10 working days. Pre-approved plans availability: Yes, partly: the ADU and Single-Family Standard Plan Library (opened for ARS 9-461.20 submittals on July 1, 2026) held one pre-reviewed detached ADU plan as of Sept 20, 2026, a 600 sq ft studio/1-bath from the 2025 AARP ADU Design Challenge; the other nine challenge winners are not yet licensed. Plans are licensed from the designer, then submitted for a building permit.
Average ADU rental income in Tempe: 1-bedroom units rent for $1,400-$1,750/month, 2-bedroom units for $1,700-$2,100/month. Short-term rentals: Yes, with a Tempe Short-Term Rental License (Ord. Expected ROI: 6-11% gross rental yield.
The minimum lot size for an ADU in Tempe is No minimum lot size; any lot with a permitted single-family dwelling qualifies (ZDC 3-402). Lot size only changes the numbers: under 1 acre = 2 ADUs and a 1,000 sq ft cap; 1 acre (43,560 sq ft) or more = 3 ADUs and a 2,000 sq ft cap. Existing guest quarters count toward the ADU total. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Tempe, a garage conversion typically costs $80,000-$150,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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