An ADU builder in San Jose is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through San Jose's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in California.
What ADU Builders Cost in San Jose [13][14][15]
Based on our San Jose cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $200,000-$450,000 |
| Cost per Sq Ft | $300-$500 |
| Garage Conversion | $90,000-$150,000 |
| Prefab / Modular ADU (installed) | $150,000-$300,000 |
| City Permit & Plan Review | 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. |
For a full line-item breakdown, see our San Jose ADU cost guide. To confirm what you're allowed to build before you hire, review the San Jose ADU rules (max detached size: Two tracks that cannot be mixed. City standards (SJMC 20.80.175 D.1, Table 20-55): 1,000 sq ft on lots up to 9,000 sq ft, 1,200 sq ft on larger lots, and no cap when converting an existing detached accessory structure. State standards (SJMC 20.80.176 / Gov. Code 66323): 800 sq ft. Minimum 150 sq ft on either track. Square footage is livable floor space measured to the exterior finish; a covered porch or balcony more than 50% enclosed counts (20.80.175 E.3).; owner-occupancy: Not required for an ADU: the owner signs Form 312 (a declaration, not an occupancy covenant) and SJMC 20.80.175 F says a later sale or rental does not affect the unit's legal status. For a JADU, owner-occupancy of the main home is required only if the JADU shares sanitation facilities with it (Gov. Code 66333(b), as amended by AB 1154 and applied by SJMC 20.80.178 since July 2026); a JADU with its own bathroom has none. A Form 313 deed restriction is recorded for every JADU.).
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How to Vet an ADU Builder in San Jose
- License: Confirm a current contractor's license in California and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near San Jose and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (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).), 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.), and 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.) are included.
- Permit handling: Confirm they manage San Jose's permit process ("Ministerial building permit, no planning hearing. Step 1: complete the ADU Universal Checklist (Bulletin #210) and, optionally, book a preliminary virtual meeting with a planner ($398/hour, 30-minute minimum). Step 2: prepare plans to Bulletin #211. Step 3: open the application on SJPermits.org (folder '1 & 2 Family Detached Dwellings (including ADU)', sub-type 'ADU') and name an ePlan Applicant. Step 4: upload to SJePlans the plans, Bulletin #213 inspection checklist, Title 24 energy and CALGreen documents, Form 302 address request, Form 312 owner declaration (Form 313 deed restriction for a JADU), and the water company's hydrant flow letter. Step 5: Prescreen, Plan Review and Issuance Review in SJePlans. Step 6: construction, inspections and final. Multifamily lots and AB 2533 legalizations go through the ADU Ally team (adu.ally@sanjoseca.gov); preapproved plans use a separate expedited path.", typically 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.) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in San Jose in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (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.) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent California ADU client references?
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