What's Required in San Jose
- One attached or detached ADU plus one junior ADU per single-family lot, two units total (SJMC 20.80.175.B.1)
- Floor area 1,000 sq ft on lots up to 9,000 sq ft, 1,200 sq ft on larger lots; attached ADU up to 50 percent of the home; no cap for conversions
- Height 18 ft for a detached one-story ADU, 25 ft for two stories; side and rear setbacks 0 ft (4 ft for a second story); 6 ft from the main house
- Rear-yard coverage of ADU plus accessory structures 40 percent, but an 800 sq ft ADU with 4 ft setbacks is always allowed
- Full kitchen and full bathroom required; no parking required
- Completeness decision within 15 business days and approval or denial within 60 days of a complete application (Gov. Code 66317)
- No fire sprinklers if the main house has none; rentals longer than 30 days (Gov. Code 66323)
- No impact fees on ADUs of 750 sq ft or less; ADU processing fee $422 up to 750 sq ft, $633 for 751-1,200 sq ft
- Ordinance-sized tree removal is processed with the ADU approval at 1:1 replacement (SJMC 20.80.177)
How Much Does an ADU Permit Cost in San Jose?
San Jose publishes its own answer. The Building Division's online Fee Estimator averages recent permits by ADU type and size band, and in September 2026 it reported a detached ADU of 0 to 750 square feet at $12,628 total (permit issuance $3,912, plan check $2,508, trade permits $2,078, taxes $4,129), a detached ADU of 751 to 1,200 square feet at $21,446, an attached ADU of 0 to 750 square feet at $10,298, and an attached 751 to 1,200 square foot unit at $18,697. Those are averages of actual city permits, taxes included, not quotes. The processing component alone is fixed in the Schedule of Fees and Charges effective July 1, 2026: $422 for an ADU up to 750 square feet and $633 for 751 to 1,200 square feet. Size matters for a second reason: state law bars impact fees on an ADU of 750 square feet of livable space or less, and above that they are charged in proportion to the primary home. Get an itemized estimate from the estimator for your own size before you budget.
San Jose ADU Rules by Scenario
| What you are doing | City filing | Rule |
|---|---|---|
| Detached ADU up to 750 sq ft on a single-family lot | Building permit, ministerial; no impact fees | Fee estimator average $12,628; HCD handbook 750 sq ft rule |
| Detached ADU 751 to 1,200 sq ft | Building permit; impact fees charged proportionately | Fee estimator average $21,446; SJMC 20.80.175 size cap |
| Attached ADU (up to 50 percent of the existing home) | Building permit; ministerial | Fee estimator average $10,298; SJMC 20.80.175.D.1.a |
| Garage or accessory structure conversion | Building permit; no size maximum for conversion; existing setbacks kept | SJMC 20.80.175.D.1.d and D.3.d |
| State-exempt 800 sq ft detached ADU with 4 ft side and rear setbacks | Ministerial approval under SJMC 20.80.176 and Gov. Code 66323 | SJMC 20.80.176; Gov. Code 66323(a)(2) |
| ADU plus a junior ADU on one single-family lot | Allowed; two units total in any order | SJMC 20.80.175.B.1 |
| Removing an ordinance-sized tree for the ADU | Processed with the ADU approval; 1:1 replacement | SJMC 20.80.177 |
What Can You Build?
Municipal Code 20.80.175 allows one attached or detached ADU plus one junior ADU on a lot with a single-family home, two units in total. The floor-area cap is 1,000 square feet on a lot up to 9,000 square feet and 1,200 square feet on a larger lot; an attached ADU may not exceed 50 percent of the existing home, and a conversion of an existing detached structure has no maximum. Height is 18 feet for a detached one-story unit and 25 feet for a two-story unit, attached or detached. Side and rear setbacks are 0 feet for a single story and 4 feet for any second story, a detached unit must sit 6 feet from the main house, and a new detached unit with a 4-foot side setback may be placed 45 feet from the front property line. The ADU, accessory buildings and other structures may cover 40 percent of the rear yard, but that ratio cannot block an 800-square-foot ADU with 4-foot setbacks. The unit must have a kitchen with a sink, counter, cabinets and a range or cooktop, and a full bathroom. No parking is required, and removed covered parking need not be replaced.
How the Review Works
State law makes ADU review ministerial: the city must tell you within 15 business days whether the application is complete, and must approve or deny a complete application within 60 days when a home already exists on the lot. Fire sprinklers are not required in the ADU if the main house does not have them, and a rental must be for longer than 30 days. Owner occupancy cannot be required. The city's estimator data includes site-specific pre-approved ADU records, so a pre-approved plan is a route worth asking the Permit Center about. Applications start at SJPermits.org with plans uploaded to SJePlans, and inspections run through foundation, rough trades, framing and final.
Who Builds It
An owner may act as owner-builder and hire licensed subcontractors; any contractor needs a state license for a job of $1,000 or more. Plans are required and the building official can require an engineer or architect. Expect the fee to be paid in stages: plan check at intake, the building and trade permits plus construction taxes at issuance.
How to Get a ADU Permit in San Jose
Pick the type and size band
Detached or attached, under or over 750 sq ft; the size band drives both the city fee and whether impact fees apply.
Run the city fee estimator
permits.sanjoseca.gov/fee-estimator gives the average total for your type and size, itemized by permit, plan check, trades and taxes.
Prepare plans to the zoning standards
Site plan with setbacks, separation and rear-yard coverage, floor plans with kitchen and bath, elevations at 18 ft or 25 ft; consider a pre-approved plan.
Apply on SJPermits.org and upload to SJePlans
The city has 15 business days to check completeness and 60 days to approve or deny; pay plan check at intake and the permits and taxes at issuance.
Build and inspect
Foundation, rough trades, framing and final inspections; cancel by 2 pm two business days ahead.