Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your San Jose ADU cost →Building an ADU in San Jose costs between $200,000-$450,000 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-$150,000, while prefab/modular ADUs fall in between at $150,000-$300,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | FY 2026-27 Building Fee Schedule (effective Aug 10, 2026): ADU 0-750 sq ft $422 issuance + $1,137 plan review + $1,732 inspection = $3,291; 751-1,200 sq ft $633 + $1,950 + $2,520 = $5,103. Excludes construction taxes, school and parkland fees and any planner meeting ($398/hour). |
| Impact Fees | School and parkland impact fees do not apply to an ADU of 750 sq ft or less; at 751 sq ft and larger both apply (Bulletin #210 rev. Sept 16, 2026, item 17, matching Gov. Code 66311.5(c)). Parkland fees vary by location (city Park Impact Fee map); school fees are set and collected by the school district(s) and the city issues a school-fee referral form at submittal. The permit is not issued until both are paid. The fee schedule also lists city development taxes collected at issuance (residential 2.42% plus 1.54% of building valuation, SJMC Chapters 4.46 and 4.47); confirm with the Building Division whether they apply to your ADU. |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving San Jose, where we have them — free, no obligation.
Get San Jose builder quotes →Permit fees in San Jose are FY 2026-27 Building Fee Schedule (effective Aug 10, 2026): ADU 0-750 sq ft $422 issuance + $1,137 plan review + $1,732 inspection = $3,291; 751-1,200 sq ft $633 + $1,950 + $2,520 = $5,103. Excludes construction taxes, school and parkland fees and any planner meeting ($398/hour).. The review timeline is City-published: the first round of building review typically takes 20 business days and complete plans stay within one or two cycles (ADU FAQs); preapproved plans can be issued the same day as the review meeting. Gov. Code 66317 (SB 543) deems the application approved after 60 days., with plan check: Electronic review in SJePlans in three phases: Prescreen (a permit specialist confirms the package is complete and invoices the initial plan review fee), Plan Review (comment and resubmittal cycles, all through SJePlans), and Issuance Review (residual plan review and inspection fees, taxes, school and parkland fees paid, then the permit card and stamped plans are released). Fire Prevention checks a 150 ft hose path along a 4 ft clear route, a hydrant within 600 ft and a 1,000 gpm at 20 psi flow letter from the water company; the missing letter is the city's most-cited cause of delay.. Impact fees are School and parkland impact fees do not apply to an ADU of 750 sq ft or less; at 751 sq ft and larger both apply (Bulletin #210 rev. Sept 16, 2026, item 17, matching Gov. Code 66311.5(c)). Parkland fees vary by location (city Park Impact Fee map); school fees are set and collected by the school district(s) and the city issues a school-fee referral form at submittal. The permit is not issued until both are paid. The fee schedule also lists city development taxes collected at issuance (residential 2.42% plus 1.54% of building valuation, SJMC Chapters 4.46 and 4.47); confirm with the Building Division whether they apply to your ADU.. Pre-approved plans: Yes. The Preapproved ADU program currently lists 7 city-reviewed standard plans from 5 vendors, 476-799 sq ft (1 bed/1 bath to 2 bed/2 bath); about 15 further plans from 7 vendors, 440-1,000 sq ft, are under review and not yet eligible. Applicants still submit a site-specific plan (siting, setbacks, utilities); a dedicated review team can issue the permit the same day as the plan review meeting when the site documents are complete (deferred structural submittals, clearances or variances take longer). Eligibility: a residential lot with an existing single-family home or duplex, outside geohazard, landslide, flood and Wildland-Urban Interface zones. Gov. Code 65852.27 governs pre-approved plan programs..
| 1-Bedroom Rent | $2,500-$3,000/month |
| 2-Bedroom Rent | $3,100-$3,600/month |
| Annual Rental Income (est.) | $33,000/year |
| Payback Period (est.) | 9.8 years |
| Short-Term Rental | No for stays under 30 days: the city's ADU FAQs set a 30-day minimum rental term for an ADU (including Airbnb-type rentals) and Gov. Code 66333 bars short-term rental of a JADU. Longer rentals to anyone are allowed. |
| Overall ROI Estimate | 8-12% gross annual yield on a new build ($3,300/mo on a $350,000 detached unit is about 11% before vacancy, tax and financing); a $120,000 garage conversion at $2,600/mo is nearer 25% gross. |
A typical ADU in San Jose generates approximately $33,000 per year in rental income based on average 1-bedroom rents. At an average construction cost of $325,000, the estimated payback period is 9.8 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in San Jose and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in San Jose: $90,000-$150,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $150,000-$300,000.
3. Pre-approved plans — available in San Jose, which can save $3,000-$10,000 in design costs and 2-3 months in review time. See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
Tell us about your project and we'll pass it to ADU builders serving San Jose. Free, no obligation — you choose who to work with. We don't have builders in every area yet; if nobody covers yours, we'll email you to say so.
🔒 Your info is secure. We share it only with contractors quoting your project. No spam, no obligation.
Just browsing? Search ADU builders near you by ZIP code.