How Much Does an ADU Cost in Santa Ana, CA?

Construction Cost Breakdown

Building an ADU in Santa Ana costs between $180,000-$400,000 for new construction, with per-square-foot costs averaging $300-$500. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $90,000-$180,000, while prefab/modular ADUs fall in between at $150,000-$280,000.

Permit Costs & Timeline

Permit fees in Santa Ana are Planning Division FY2026-27 fee schedule (effective July 1, 2026): Accessory Dwelling Unit Review $1,940; ADU Over-the-Counter Review $594; ADU Pre-Approved Plan Review $524; Minor Exception (appeal of a denial) $3,579. A 7% technology fee is added to all Planning, Building and Public Works applications, plan checks and permits, and card payments carry a 2.5% processing fee. Building Safety has no ADU-specific line: the FY2026-27 fee schedule (Section X) charges structural plan check and inspection per sq ft by project type, for example $1.42/sq ft plan check for a single-story residential single-family structure ($3.14 two-story) plus $0.81/sq ft inspection, or $1.78 plus $1.42 per sq ft for a first-floor residential addition up to 500 sq ft, with electrical, plumbing and mechanical items priced separately; ask Building Safety at (714) 647-5800 which lines apply to your unit. Public Works: sewer connection fee $53 per plumbing fixture unit and a water capacity fee of $930 for a new 5/8-inch meter (FY2026-27 Public Works summary). The review timeline is 60 days from a complete application for the city to approve or deny, or the ADU is deemed approved (Gov. Code 66317(a)(3), SB 543, in force since January 1, 2026); the clock is tolled if you request a delay. The city publishes no shorter target for standard review. For a pre-approved plan the city says an over-the-counter submittal 'may be approved in as little as one day' when complete and code-compliant (wording that predates the July 2026 move to online filing); confirm the current turnaround with Planning, with plan check: Electronic plan check through the Accela Citizen Access portal for Planning, Building Safety and Public Works together; detached ADUs on single-family lots and ADU conversions are on the city's E-Plan eligible list. The city's ADU code-compliance form asks for a transit proximity map if you claim the half-mile parking exemption, the water heater inside the ADU footprint, no exterior washer or dryer, underground utilities (SAMC 41-626), a landscaped front yard (SAMC 41-240), and windows, roof and finishes compatible with the main house (Citywide Design Guidelines). Fire sprinklers are required only if the main house is sprinklered (Gov. Code 66314(d)(12)); OCFA reviews sprinkler plans. A new detached ADU needs a grading permit or the signed grading waiver (form PCC-20), and a separate address. Impact fees are No city impact fees for an ADU of 750 sq ft or less; over 750 sq ft fees are charged in proportion to the ADU's share of the main house's floor area (Gov. Code 66311.5, as renumbered by SB 543). Capacity charges are separate: Orange County Sanitation District charges every ADU the Capital Facilities Capacity Charge at the average-demand rate of $1,710 per 1,000 sq ft or portion thereof, and its $6,588 minimum does not apply to ADUs (OCSD Table A, effective July 1, 2026), so a 400 sq ft or an 800 sq ft unit each owe about $1,710. The city's Transportation System Improvement Area fee applies only to projects of 5 or more units. The same Public Works summary lists a Transportation Corridor fee of $4,912 (Foothill/Eastern) or $5,348 (San Joaquin Hills) per single-family unit and a per-acre drainage assessment in mapped areas; under Gov. Code 66311.5 (as renumbered by SB 543) neither can be charged on an ADU of 750 sq ft or less, and Public Works ((714) 647-5037) will confirm which apply to a larger unit. School district developer fees are set and collected by the district (Santa Ana, Tustin, Orange or Garden Grove Unified) and do not apply under 500 sq ft. Pre-approved plans: Yes. The city offers 10 free downloadable pre-approved plan sets for detached ADUs: three 399 sq ft studios (Ranch, Spanish, Traditional), three 499 sq ft one-bedrooms (Ranch, Spanish, Traditional), a 625 sq ft one-bedroom Contemporary, a 677 sq ft one-bedroom Craftsman and a 677 sq ft one-bedroom Spanish, and a 749 sq ft two-bedroom Contemporary; every set stays within the 750 sq ft impact-fee exemption. Planning review drops to $524. Eligibility: a lot with an existing or proposed single-family home, outside FEMA flood zones A and AE, outside the French Park (SD-19), Downtown and Floral Park historic districts and Heninger Park (SD-40), and able to meet the grading-permit exemption. Submit the site plan, completed cover sheet, application and affidavit, hold-harmless agreement, grading waiver and a six-month title report; the city asks for a pre-submittal consultation via planning@santa-ana.org.

Rental Income & ROI

A typical ADU in Santa Ana generates approximately $29,100 per year in rental income based on average 1-bedroom rents. At an average construction cost of $290,000, the estimated payback period is 10.0 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Santa Ana and varies by market (often less than build cost).

Ways to Reduce ADU Costs in Santa Ana