Everything you need to know about building an ADU in San José — lot eligibility, size limits, permit process, and costs. All sourced from official city records.
Data verified 2026-07-08 · City of San José official sources · CA HCD
Lot Eligibility
ADUs are allowed on most residential lots in San José. Enter your lot details below — the calculator uses verified San José zoning rules to show your max size, setbacks, and impact fee status instantly.
Instant eligibility check — San José rules as of 2026-07-08
ADUs are allowed in R-1, R-2, R-M, PD zones. State law also requires ADUs anywhere single- or multi-family housing is permitted.
California removed the owner-occupancy requirement in January 2020 (SB 13). You can build an ADU on a rental property or investment lot.
Lot coverage, access, fire-flow availability, and utility stub conditions. Our feasibility review covers all of these before you commit.
ADU Types & Sizes
San José allows four ADU types. Size limits are set by local zoning (SJMC Title 20) with a state-law floor of 800 sqft that the city cannot go below.
| Rule | San José | Source |
|---|---|---|
| Min. detached ADU size (state floor) | 800 sqft | CA Gov. Code §66321 |
| Side & rear setback (detached) | 4 ft minimum | CA Gov. Code §66332 |
| Parking required | None | CA Gov. Code §66333 |
| Impact fee exemption threshold | Under 750 sqft | SB 13 (Jan 2020) |
| Ministerial approval clock | 60 days | CA Gov. Code §66333 |
| Short-term rental (Airbnb) | 30+ day min. only | CA AB 976 (2023) |
Permit Process
State law caps ministerial approval at 60 days from a complete application. Realistically, plan review runs 8–16 weeks. A code-compliant, complete first submission is the fastest path through.
#1: Missing fire-flow letter
A letter from San José Water or San José Municipal Water confirming adequate fire flow to the site. This is the #1 cause of plan-check holds. Order it before you submit — it can take weeks.
#2: SJePlans file naming
SJePlans requires specific file naming conventions for every uploaded document. Non-compliant filenames are rejected before plan review even begins — the application goes on hold.
Feasibility & Zoning Check
Confirm your zoning (R-1, R-2, R-M, PD), setbacks, and lot coverage. Free ADU Ally consultation available through the City of San José.
Design & Engineering
Full permit-ready plan set: architectural drawings, structural engineering, and Title 24 CF1R energy compliance — prepared to Bulletin 211 standards.
Order Fire-Flow Letter
Contact San José Water or San José Municipal Water for a fire-flow confirmation letter. This takes weeks and is the #1 cause of plan-check holds — order it early.
Do this before submitting plans, not after.
Submit via SJPermits + SJePlans
Open your permit on SJPermits.org and upload plans to SJePlans. Files must follow the city's exact naming convention — non-compliant files are rejected on intake.
Plan Review & Corrections
City reviews your submission (8–16 weeks typical). Correction letters are issued in SJePlans. Pre-approved plans can cut this to 4–8 weeks.
Permit Issued — Build
Pay permit fees online, receive your building permit, and schedule required inspections (foundation, framing, rough MEP, insulation, final) through SJPermits.
Cost Guide
ADU costs in San José break into three buckets. Ranges below are market estimates — your actual costs depend on lot conditions, ADU type, and design scope.
$7,000 – $16,000+
Architectural drawings, structural, Title 24 CF1R. Complex sites (geohazard, boundary survey) are at the higher end.
$5,000 – $15,000+
Calculated hourly on ICC project valuation by the Building Division. Rates update annually — confirm against the current fee schedule.
$300 – $500+ / sqft
Detached ADUs: $200K–$500K+ total. Garage conversions often less, but utility upgrades add cost. Get contractor bids early.
The 749 sqft Strategy — How to Save Thousands
Sized 1 sqft below the 750 sqft impact-fee exemption threshold — eliminates school and parkland fees entirely. This is intentional, not coincidental. Under California SB 13 (effective Jan 2020), ADUs under 750 sqft are completely exempt from school and park/recreation impact fees — a meaningful cost savings. ADUs at or above 750 sqft owe these fees proportionally. One square foot of intentional design eliminates the fee line entirely.
Want a cost estimate specific to your lot and ADU type?
Get a Project EstimateFAQ
Common questions about ADU eligibility, zoning, setbacks, permits, and costs in San José.
Have a question not answered here?
Our San José ADU experts typically respond within one business day.
Our Services
From a kitchen remodel to a full ADU build, zHeight handles the design, planning, and permitting for every project type. We work alongside your contractor — we are not the builder.
Design & permitting only. zHeight provides architectural drawings, structural engineering, Title 24 compliance, and permit processing. We do not provide construction or contracting services. We coordinate with your chosen builder throughout the process.
Detached ADU, attached ADU, JADU, and garage conversion plans — permit-ready and SJePlans-compliant.
Layout changes, kitchen and bath redesigns, wall removals, and structural updates. We draw the plans — you hire the contractor.
New rooms, bedroom additions, second stories, and square footage expansions — fully permitted and code-compliant.
Ground-up home builds and whole-home designs. We handle the full plan set from concept to permit approval.
zHeight San José
We handle the complete plan set — architectural drawings, structural, Title 24 CF1R, SJePlans-compliant file prep, and correction response — so your project moves from submission to permit.
All regulatory data verified 2026-07-08 against City of San José, SJMC Title 20, CA HCD, and CA Gov. Code §66310–66342.