Garage conversion · checked Oct 18, 2026
Garage conversion ADU fees in San José: $6,338–$8,135 for a 400 sq ft garage
That’s $780 less than building the same 400 sq ft as a new detached ADU in San José. Both sizes are under 750 sq ft, so there are no impact fees either way.
What changes
Why a conversion costs less in San José
- Sewage treatment plant connection: $780 for a new detached unit at 550 sq ft, $0 for a conversion. State law bars a new utility connection fee or capacity charge for an ADU inside an existing structure (Gov. Code §66311.5(d)).
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 | ||||
| Planning review of the building permit | May apply$449 | May apply$449 | May apply$449 | May apply$449 |
| Building permit & plan check | ||||
| ADU permit issuance (incl. address) | $422 | $422 | $422 | $422 |
| ADU plan review | $1,137 | $1,137 | $1,137 | $1,137 |
| ADU inspection (incl. meter release) | $1,732 | $1,732 | $1,732 | $1,732 |
| Fire plan check + inspection | May apply$1,269 | May apply$1,269 | May apply$1,269 | May apply$1,269 |
| Construction taxes | ||||
| Building & Structure Construction Tax (1.54% of valuation) | Est.$1,084 | Est.$1,084 | Est.$1,490 | Est.$1,490 |
| Commercial-Residential-Mobilehome Park Construction Tax (2.42%) | Est.$1,703 | Est.$1,703 | Est.$2,342 | Est.$2,342 |
| Construction Tax + Residential Construction Tax (per unit) | $251–$330 | $251–$330 | $251–$330 | $251–$330 |
| State SMIP + building standards fees | Est.$10 | Est.$10 | Est.$14 | Est.$14 |
| Impact fees | ||||
| Parkland impact fee (ADUs over 750 sq ft) | Exempt | Exempt | Exempt | Exempt |
| School district fee | ||||
| School impact fee (your district) | Exempt | Exempt | Up to$2,959 | Up to$2,959 |
| Utility connections | ||||
| Sewage treatment plant connection | Exempt | May apply$780 | Exempt | May apply$780 |
| Modeled total | $6,338–$8,135 | $6,338–$8,915 | $7,387–$12,143 | $7,387–$12,923 |
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 José
How much are the fees to convert a garage into an ADU in San José?
Our model of San José’s official fee schedules comes to $6,338–$8,135 for a 400 sq ft garage conversion and $7,387–$12,143 at 550 sq ft, with a 2,000 sq ft main home. A new detached ADU of the same size would be $6,338–$8,915 and $7,387–$12,923.
Is a garage conversion cheaper than a new ADU in San José?
In fees, yes: $780 less at 400 sq ft and $780 less at 550 sq ft. Sewage treatment plant connection 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
- Which planning and fire review an ADU gets (counted in the high total only).
- Your parcel's parkland fee zone ($1,700–$8,900 range shown).
- School district rates (statewide Level 1 maximum shown instead).
- Water meter and connection charges from your water company.
- Public Works storm and sanitary sewer fees, which the schedule lists per lot and doesn't address for ADUs.
More
Keep going
Sources
Official sources
Every figure comes from these documents; each line’s quoted text is on the San José page.
- City of San José, Planning, Building & Code EnforcementFY 2026-27 Building and Structure Permits Fee Schedule (effective August 10, 2026) (opens in new tab)
- City of San José, Parks, Recreation & Neighborhood ServicesParkland Impact Fees for ADUs (map) (opens in new tab)
- City of San JoséADU Universal Checklist (opens in new tab)
- City of San JoséADU FAQs (opens in new tab)
- City of San JoséDevelopment Construction Taxes (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)