Garage conversion · checked Oct 18, 2026
Garage conversion ADU fees in San Diego: $6,117–$6,282 for a 400 sq ft garage
At 400 sq ft that’s the same as a new detached ADU in San Diego, but at 550 sq ft, the size you reach with the 150 sq ft expansion state law allows, a conversion costs $9,486 less. Both sizes are under 750 sq ft, so there are no impact fees either way.
What changes
Why a conversion costs less in San Diego
- Building plan check (Table 501A): $7,539 new vs $3,601 converted at 550 sq ft. Detached ADU up to 500 sq ft: the Add/Remodel row ($3,275.45). Detached ADU over 500 sq ft: the single-dwelling row ($7,538.70). Attached ADUs and conversions up to 1,100 sq ft: $3,275.45 plus $6.51 per sq ft over 500. A converted detached accessory structure over 500 sq ft may be charged the single-dwelling row instead.
- Building inspection (Table 501A): $7,834 new vs $2,286 converted at 550 sq ft. Collected at permit issuance, from the same rows as plan check.
Line by line: converted garage vs new detached ADU
2,000 sq ft main home (example assumption), law in force today. Garage sizes are examples: 400 sq ft is a typical two-car garage; 550 sq ft adds the 150 sq ft expansion.
| Fee | Garage, 400 sq ft | New detached, 400 sq ft | Garage + 150, 550 sq ft | New detached, 550 sq ft |
|---|---|---|---|---|
| Planning & zoning | ||||
| General Plan Maintenance Fee | $737 | $737 | $737 | $737 |
| Building permit & plan check | ||||
| Mapping Fee | $11 | $11 | $11 | $11 |
| Building plan check (Table 501A) | $3,275 | $3,275 | $3,601 | $7,539 |
| Building inspection (Table 501A) | $2,078 | $2,078 | $2,286 | $7,834 |
| Water/sewer plan check (no meter change) | May apply$165 | May apply$165 | May apply$165 | May apply$165 |
| Fee collection (other agencies) | $16 | $16 | $16 | $16 |
| Impact fees | ||||
| Development Impact Fees (DIF) | $0 | $0 | $0 | $0 |
| School district fee | ||||
| School fee (district; statewide cap shown) | Exempt | Exempt | Up to$2,959 | Up to$2,959 |
| Modeled total | $6,117–$6,282 | $6,117–$6,282 | $6,651–$9,775 | $16,137–$19,261 |
State law
What California guarantees for a garage conversion
A city must approve one ADU inside an existing accessory structure such as a garage, can’t require a setback for it, and can’t make you replace the parking you lose.
Gov. Code §66323(a)(1)
One accessory dwelling unit and one junior accessory dwelling unit per lot with a proposed or existing single-family dwelling if all of the following apply:
Gov. Code §66323(a)(1)(A)
may include an expansion of not more than 150 square feet beyond the same physical dimensions as the existing accessory structure
Gov. Code §66314(d)(7)
No setback shall be required for an existing living area or accessory structure or a structure constructed in the same location and to the same dimensions as an existing structure that is converted to an accessory dwelling unit or to a portion of an accessory dwelling unit
Gov. Code §66314(d)(11)
When a garage, carport, covered parking structure, or uncovered parking space is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit, the local agency shall not require that those offstreet parking spaces be replaced.
Quoted from Government Code, Title 7, Division 1, Chapter 13 (Accessory Dwelling Units), incl. §66311.5 (opens in new tab), checked Oct 18, 2026.
FAQ
Questions about garage conversion in San Diego
How much are the fees to convert a garage into an ADU in San Diego?
Our model of San Diego’s official fee schedules comes to $6,117–$6,282 for a 400 sq ft garage conversion and $6,651–$9,775 at 550 sq ft, with a 2,000 sq ft main home. A new detached ADU of the same size would be $6,117–$6,282 and $16,137–$19,261.
Is a garage conversion cheaper than a new ADU in San Diego?
At 400 sq ft the fees are the same; at 550 sq ft a conversion is $9,486 less. Building plan check (Table 501A) is lower for a conversion. Building inspection (Table 501A) is lower for a conversion.
Do I have to replace the garage parking?
No. When a garage is converted to an ADU, state law bars the city from requiring replacement off-street parking (Gov. Code §66314(d)(11)).
Does a garage conversion pay impact or school fees?
No impact fees: the unit is under 750 sq ft. School fees apply only above 500 sq ft; at 550 sq ft the statewide cap would be up to $2,959, and the district may charge less.
Not modeled yet
What these totals leave out
- Water and sewer capacity fees (per EDU, Public Utilities) and County Water Authority meter fees aren’t modeled.
- State strong-motion (SMIP) and building standards fees are small valuation-based state fees and aren’t shown.
- The 2.5-hour DIF assessment review, lead hazard fee (pre-1978 homes only), storm water and express fees aren’t included.
- Projects with more than one ADU also pay the Regional Transportation Congestion Improvement Program fee.
More
Keep going
Sources
Official sources
Every figure comes from these documents; each line’s quoted text is on the San Diego page.
- City of San Diego Development ServicesInformation Bulletin 501: Fee Schedule for Construction Permits – Structures (opens in new tab)
- City of San Diego Development ServicesInformation Bulletin 400: Accessory Dwelling Unit / Junior Accessory Dwelling Unit (opens in new tab)
- City of San Diego City PlanningPublic Spaces: Development Impact Fee FAQ (opens in new tab)
- California State Allocation Board (Department of General Services, OPSC)State Allocation Board item: 2026 adjustment to the Level I developer fee (meeting of January 28, 2026) (opens in new tab)
- California Legislative Information (leginfo.legislature.ca.gov)Government Code, Title 7, Division 1, Chapter 13 (Accessory Dwelling Units), incl. §66311.5 (opens in new tab)
- HCD via data.ca.govHousing Element Annual Progress Report (APR) data, Table A2: ADU building permits by year (opens in new tab)