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 [3][4]
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) | $180,000-$400,000 |
| Cost per Sq Ft | $250-$450 |
| Garage Conversion | $100,000-$220,000 |
| Prefab / Modular ADU (installed) | $130,000-$300,000 |
| City Permit & Plan Review | City building permit fees, FY 2026-27 Building and Structure Permits Fee Schedule, effective August 10, 2026. ADU 0-750 sq ft: permit issuance $422, plan review $1,137, inspection $1,732 (total $3,291). ADU 751-1,200 sq ft: permit issuance $633, plan review $1,950, inspection $2,520 (total $5,103). Permit issuance includes addressing assignment for the unit; inspection includes the meter release inspection. Modular fees are 10% lower for plan review and 20% lower for inspections. Separately, an optional preliminary virtual meeting with a planner is billed at the Planning Division's hourly rate of $398/hour with a 30-minute minimum (i.e. $199). These are city permit fees only and exclude school/parkland impact fees, construction taxes, and construction cost. |
| Impact Fees | Two impact fees apply in San José and both are size-gated: school impact fees and parkland impact fees. The city states neither applies to ADUs under 750 sq ft. At 750 sq ft and above, parkland impact fees apply and vary by location (the city publishes a Park Impact Fee map), and school fees are set and collected by the school district(s) for the location, not by the city - the city issues a school fee referral form at submittal. The building permit will not be issued until these are paid. CAUTION for our copy: the city's checklist gates the charge at '750 sf or greater' while Gov. Code 66311.5(c)(1) exempts an ADU of 750 sq ft or less, so at exactly 750 sq ft the city's published wording appears one square foot stricter than the state exemption. Worth hedging rather than restating either side as settled. |
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: Depends on which standards track the applicant chooses. CITY Development Standards (SJMC 20.80.175): 1,000 sq ft on lots under 9,000 sq ft; 1,200 sq ft on lots over 9,000 sq ft. STATE Development Standards (SJMC 20.80.176): 800 sq ft on any lot. Minimum size 150 sq ft under either track. The tracks cannot be mixed. Same size table applies on duplex/multifamily lots under the City track.; owner-occupancy: Not required for an ADU. For a JADU, owner-occupancy of the main home is required ONLY where the JADU does not have its own sanitation facilities; a JADU with its own bathroom carries no owner-occupancy requirement. Where it applies, it is secured by a recorded deed restriction (Form 313 JADU Deed Restriction Agreement, which the County Recorder requires to be wet-signed). ADU applicants must separately sign Form 312 ADU Property Owner Declaration - a declaration, not an occupancy requirement. Rentals of under 30 days are not permitted for either.).
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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 (City building permit fees, FY 2026-27 Building and Structure Permits Fee Schedule, effective August 10, 2026. ADU 0-750 sq ft: permit issuance $422, plan review $1,137, inspection $1,732 (total $3,291). ADU 751-1,200 sq ft: permit issuance $633, plan review $1,950, inspection $2,520 (total $5,103). Permit issuance includes addressing assignment for the unit; inspection includes the meter release inspection. Modular fees are 10% lower for plan review and 20% lower for inspections. Separately, an optional preliminary virtual meeting with a planner is billed at the Planning Division's hourly rate of $398/hour with a 30-minute minimum (i.e. $199). These are city permit fees only and exclude school/parkland impact fees, construction taxes, and construction cost.), plan check (Standard review process), and impact fees (Two impact fees apply in San José and both are size-gated: school impact fees and parkland impact fees. The city states neither applies to ADUs under 750 sq ft. At 750 sq ft and above, parkland impact fees apply and vary by location (the city publishes a Park Impact Fee map), and school fees are set and collected by the school district(s) for the location, not by the city - the city issues a school fee referral form at submittal. The building permit will not be issued until these are paid. CAUTION for our copy: the city's checklist gates the charge at '750 sf or greater' while Gov. Code 66311.5(c)(1) exempts an ADU of 750 sq ft or less, so at exactly 750 sq ft the city's published wording appears one square foot stricter than the state exemption. Worth hedging rather than restating either side as settled.) are included.
- Permit handling: Confirm they manage San Jose's permit process ("Ministerial, run through a defined six-step city process. 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 per Bulletin #211. Step 3: apply online via SJPermits.org and name an 'ePlan Applicant'. Step 4: upload the submittal package to SJePlans - must include Bulletin #211 plans, Bulletin #213 inspection checklist, Title 24 energy and CalGreen documents, Form 302 address assignment, Form 312 owner declaration (or Form 313 for a JADU), and a water-flow letter from the water company. Step 5: three-phase review - Prescreen (invoice for initial plan review fees), Plan Review (comment/resubmittal cycles), Issuance Review (residual plan review, inspection, school and parkland fees paid, then permit issues). Step 6: construction and inspections. Preapproved-plan projects use a separate expedited path with a dedicated City review team. Multifamily and AB 2533 legalization projects are routed through the ADU Ally team.", typically The city's own published figure is that the first round of building review typically takes 20 business days, with complete and accurate plans staying within one or two review cycles. Preapproved-plan projects may receive same-day permit issuance at the scheduled plan review meeting. The 60-day figure in our record is the state ministerial deadline (Gov. Code Chapter 13 / SB 543), not a San José-published processing time, and should not be presented as a city fact. The city flags the missing water-company flow letter as a main cause of delay.) 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 (The city's own published figure is that the first round of building review typically takes 20 business days, with complete and accurate plans staying within one or two review cycles. Preapproved-plan projects may receive same-day permit issuance at the scheduled plan review meeting. The 60-day figure in our record is the state ministerial deadline (Gov. Code Chapter 13 / SB 543), not a San José-published processing time, and should not be presented as a city fact. The city flags the missing water-company flow letter as a main cause of delay.) 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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How much do ADU builders charge in San Jose?
ADU builders in San Jose typically quote $180,000-$400,000 for a new detached unit, or about $250-$450 per square foot, including design, permitting, and construction. A garage conversion runs $100,000-$220,000 and a prefab/modular ADU averages $130,000-$300,000. Add city permit and plan-review fees (City building permit fees, FY 2026-27 Building and Structure Permits Fee Schedule, effective August 10, 2026. ADU 0-750 sq ft: permit issuance $422, plan review $1,137, inspection $1,732 (total $3,291). ADU 751-1,200 sq ft: permit issuance $633, plan review $1,950, inspection $2,520 (total $5,103). Permit issuance includes addressing assignment for the unit; inspection includes the meter release inspection. Modular fees are 10% lower for plan review and 20% lower for inspections. Separately, an optional preliminary virtual meeting with a planner is billed at the Planning Division's hourly rate of $398/hour with a 30-minute minimum (i.e. $199). These are city permit fees only and exclude school/parkland impact fees, construction taxes, and construction cost.) plus impact fees of Two impact fees apply in San José and both are size-gated: school impact fees and parkland impact fees. The city states neither applies to ADUs under 750 sq ft. At 750 sq ft and above, parkland impact fees apply and vary by location (the city publishes a Park Impact Fee map), and school fees are set and collected by the school district(s) for the location, not by the city - the city issues a school fee referral form at submittal. The building permit will not be issued until these are paid. CAUTION for our copy: the city's checklist gates the charge at '750 sf or greater' while Gov. Code 66311.5(c)(1) exempts an ADU of 750 sq ft or less, so at exactly 750 sq ft the city's published wording appears one square foot stricter than the state exemption. Worth hedging rather than restating either side as settled.. Quotes for the same scope commonly vary 20-40% between builders, so collect at least three bids.
How do I find a good ADU builder in San Jose?
Look for a licensed contractor with completed ADU projects in San Jose specifically — ADUs involve local zoning, setback rules, and utility connections that general remodelers may not have handled. Verify the license, ask for an ADU-specific portfolio and references, confirm they carry liability and workers' comp insurance, and get a written fixed-price or detailed bid. Submit a request below and we'll forward it to local ADU builders serving San Jose for free quotes.
Do ADU builders in San Jose handle permits?
Most full-service ADU builders manage the permit process for you. In San Jose the approval process is "Ministerial, run through a defined six-step city process. 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 per Bulletin #211. Step 3: apply online via SJPermits.org and name an 'ePlan Applicant'. Step 4: upload the submittal package to SJePlans - must include Bulletin #211 plans, Bulletin #213 inspection checklist, Title 24 energy and CalGreen documents, Form 302 address assignment, Form 312 owner declaration (or Form 313 for a JADU), and a water-flow letter from the water company. Step 5: three-phase review - Prescreen (invoice for initial plan review fees), Plan Review (comment/resubmittal cycles), Issuance Review (residual plan review, inspection, school and parkland fees paid, then permit issues). Step 6: construction and inspections. Preapproved-plan projects use a separate expedited path with a dedicated City review team. Multifamily and AB 2533 legalization projects are routed through the ADU Ally team." with a typical review timeline of The city's own published figure is that the first round of building review typically takes 20 business days, with complete and accurate plans staying within one or two review cycles. Preapproved-plan projects may receive same-day permit issuance at the scheduled plan review meeting. The 60-day figure in our record is the state ministerial deadline (Gov. Code Chapter 13 / SB 543), not a San José-published processing time, and should not be presented as a city fact. The city flags the missing water-company flow letter as a main cause of delay.. Confirm in writing whether permit fees, plan check (Standard review process), and impact fees are included in the bid or billed separately.
How long does it take to build an ADU in San Jose?
Plan for the permit review (The city's own published figure is that the first round of building review typically takes 20 business days, with complete and accurate plans staying within one or two review cycles. Preapproved-plan projects may receive same-day permit issuance at the scheduled plan review meeting. The 60-day figure in our record is the state ministerial deadline (Gov. Code Chapter 13 / SB 543), not a San José-published processing time, and should not be presented as a city fact. The city flags the missing water-company flow letter as a main cause of delay. in San Jose) plus construction. Most detached ADUs take 4-8 months of construction after permits are issued; garage conversions and prefab units are often faster. Ask each builder for a realistic schedule and what could delay it.
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