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 [4][5]
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) | $220,000-$420,000 |
| Cost per Sq Ft | $300-$500 |
| Garage Conversion | $110,000-$190,000 |
| Prefab / Modular ADU (installed) | $150,000-$300,000 |
| City Permit & Plan Review | Design review/building permit and inspection fees apply — confirm current amounts with Fremont Planning & Building Permit Services |
| Impact Fees | Waived for ADUs under 750 sq ft (state law); proportional above 750 sq ft |
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; owner-occupancy: Not required for ADUs (codified in FMC 18.190.005). JADUs: required only if the JADU shares sanitation facilities with the main home (AB 1154)).
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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 (Design review/building permit and inspection fees apply — confirm current amounts with Fremont Planning & Building Permit Services), plan check (Expedited plan review and lower permitting costs for preapproved plans; standard review otherwise), and impact fees (Waived for ADUs under 750 sq ft (state law); proportional above 750 sq ft) are included.
- Permit handling: Confirm they manage Fremont's permit process ("Ministerial building permit review — no hearings or discretionary review; preapproved plans get expedited processing", typically 60-day state-mandated review; deemed approved if the city misses the deadline (SB 543, Jan 2026)) 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 (60-day state-mandated review; deemed approved if the city misses the deadline (SB 543, Jan 2026)) 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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