An ADU builder in Fremont 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 Fremont'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 Fremont [9][10][11][12]
Based on our Fremont 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) | $250,000-$460,000 |
| Cost per Sq Ft | $300-$480 |
| Garage Conversion | $100,000-$170,000 |
| Prefab / Modular ADU (installed) | $150,000-$300,000 |
| City Permit & Plan Review | Limited Design Review for an ADU/JADU: $2,000 deposit billed at cost. Building plan check and inspection are valuation-based (e.g. $967.27 + $5.91 per $1,000 above $100,000) plus 15% Community Planning and 3% technology surcharges (Master Fee Schedule eff. 7/1/2026); preapproved plans $1,000 flat. |
| Impact Fees | None. The City's ADU Informational Handout (updated 1/5/2026) states ADUs are not subject to development impact fees regardless of size, and FMC 18.290.110(b) exempts ADU remodels and additions; that is broader than the state floor, which exempts only ADUs of 750 sq ft or less (Gov. Code 66311.5). Utility connection fees (ACWD water, Union Sanitary District sewer, PG&E's required separate electric meter) and Fremont Unified School District fees may still apply. |
For a full line-item breakdown, see our Fremont ADU cost guide. To confirm what you're allowed to build before you hire, review the Fremont ADU rules (max detached size: 1,200 sq ft of interior livable space for a new detached ADU (FMC 18.190.005(c)(4)(B)(ii)); garages, carports, covered porches, patios and breezeways are not counted. An ADU converted from existing floor area has no size limit (c)(4)(A). Rooftop decks are prohibited (c)(4)(C).; owner-occupancy: Not required for the primary dwelling or the ADU (FMC 18.190.005(c)(9)). JADU: required only if the JADU shares a bathroom with the main house, and the owner may live in either unit; not required if the JADU has its own bathroom or the owner is a government agency, land trust or housing organization (18.190.005(d)(5); Gov. Code 66333 as amended by AB 1154, Jan 2026).).
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How to Vet an ADU Builder in Fremont
- 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 Fremont 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 (Limited Design Review for an ADU/JADU: $2,000 deposit billed at cost. Building plan check and inspection are valuation-based (e.g. $967.27 + $5.91 per $1,000 above $100,000) plus 15% Community Planning and 3% technology surcharges (Master Fee Schedule eff. 7/1/2026); preapproved plans $1,000 flat.), plan check (The building plan-check fee covers up to three review cycles (FMC 15.10.090); further cycles cost $147/hr, and expedited plan check at the applicant's request adds $181/hr. Project valuation is set from the City's Exhibit 1 minimum values (RS Means, San Jose modifier), updated each July 1. A preapproved detached plan is reviewed in 7 business days for a flat $1,000; a standard plan set in 15 business days.), and impact fees (None. The City's ADU Informational Handout (updated 1/5/2026) states ADUs are not subject to development impact fees regardless of size, and FMC 18.290.110(b) exempts ADU remodels and additions; that is broader than the state floor, which exempts only ADUs of 750 sq ft or less (Gov. Code 66311.5). Utility connection fees (ACWD water, Union Sanitary District sewer, PG&E's required separate electric meter) and Fremont Unified School District fees may still apply.) are included.
- Permit handling: Confirm they manage Fremont's permit process ("Two applications through the Accela Citizen Access portal: a Ministerial Design Review Permit (no hearing, no discretionary review) and a separate building permit, which may be filed together with a Request for Concurrent Processing; a new address is assigned. The ADU permit must stand alone: applications that bundle ADU work with a remodel of the main house are rejected. Every ADU and JADU, including conversions, needs a building permit (FMC 18.190.005(b)(4)-(5)).", typically Completeness notice within 15 business days and a decision within 60 days of a complete application (FMC 18.190.005(b)(4)); deemed approved if the City misses the 60 days (SB 543, Jan 2026). Preapproved plans are reviewed in 7 business days, standard plans in 15.) 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 Fremont 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 (Completeness notice within 15 business days and a decision within 60 days of a complete application (FMC 18.190.005(b)(4)); deemed approved if the City misses the 60 days (SB 543, Jan 2026). Preapproved plans are reviewed in 7 business days, standard plans in 15.) 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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