An ADU builder in Santa Monica 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 Santa Monica'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 Santa Monica [11]
Based on our Santa Monica 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-$500,000 |
| Cost per Sq Ft | $325-$550 |
| Garage Conversion | $140,000-$245,000 |
| Prefab / Modular ADU (installed) | $200,000-$350,000 |
| City Permit & Plan Review | Plan check and building permit fees are valuation-based under the City's adopted fee schedule (finance.smgov.net); Planning charges $985.11 for a deed-restriction application and $833.46 for a Coastal Zone Approval in Concept (fees effective July 1, 2026) |
| Impact Fees | ADUs and JADUs are exempt from the city's Transportation (Ch. 9.66), Parks (Ch. 9.67), Affordable Housing (Ch. 9.64) and Childcare (Ch. 9.65) impact fees (SMMC 9.31.025(O)). Statewide, ADUs 750 sq ft or less and JADUs 500 sq ft or less owe no impact fees (Gov. Code 66311.5); the city warns that ADUs larger than 750 sq ft may owe Public Works (water/wastewater) capital facility fees, and school fees apply above 500 sq ft |
For a full line-item breakdown, see our Santa Monica ADU cost guide. To confirm what you're allowed to build before you hire, review the Santa Monica ADU rules (max detached size: 850 sq ft (studio/1-bedroom) or 1,200 sq ft (2+ bedrooms) under the local standards, 150 sq ft minimum; a garage with an internal connection to the ADU does not count toward the cap (SMMC 9.31.025(I)(1)(c)). The state-mandated alternative under 9.31.025(J) is 800 sq ft; owner-occupancy: ADUs: not required (SMMC 9.31.025; Guide pp.4, 9). JADUs: SMMC 9.31.025(K)(2) and the Nov 2025 Guide require the owner to live in the main house or the JADU; since Jan 1, 2026 state law (Gov. Code 66333(b), AB 1154) allows that only for JADUs that share a bathroom with the main house, so ask Planning how the city applies it).
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How to Vet an ADU Builder in Santa Monica
- 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 Santa Monica 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 (Plan check and building permit fees are valuation-based under the City's adopted fee schedule (finance.smgov.net); Planning charges $985.11 for a deed-restriction application and $833.46 for a Coastal Zone Approval in Concept (fees effective July 1, 2026)), plan check (Electronic Plan Review: a prescreen for completeness, then routed plan check with corrections issued by email; initial plan review fees are paid at submittal and final fees before issuance. Every ADU needs its own address via an Address Application), and impact fees (ADUs and JADUs are exempt from the city's Transportation (Ch. 9.66), Parks (Ch. 9.67), Affordable Housing (Ch. 9.64) and Childcare (Ch. 9.65) impact fees (SMMC 9.31.025(O)). Statewide, ADUs 750 sq ft or less and JADUs 500 sq ft or less owe no impact fees (Gov. Code 66311.5); the city warns that ADUs larger than 750 sq ft may owe Public Works (water/wastewater) capital facility fees, and school fees apply above 500 sq ft) are included.
- Permit handling: Confirm they manage Santa Monica's permit process ("Ministerial building permit only — no design review or hearing (SMMC 9.31.025(D), (G)) — filed through the city's Electronic Plan Review system; JADUs and R1 bonus ADUs also file a Planning deed-restriction application. Coastal Zone parcels need a Coastal Development Permit or waiver from the California Coastal Commission, processed concurrently under Gov. Code 66329", typically 60 days from a complete application, or the ADU is deemed approved (SMMC 9.31.025(G)); since Jan 1, 2026 the city must also issue a completeness notice within 15 business days (Gov. Code 66317, SB 543). A Coastal Zone CDP runs on its own 60-day clock (Gov. Code 66329)) 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 Santa Monica 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 days from a complete application, or the ADU is deemed approved (SMMC 9.31.025(G)); since Jan 1, 2026 the city must also issue a completeness notice within 15 business days (Gov. Code 66317, SB 543). A Coastal Zone CDP runs on its own 60-day clock (Gov. Code 66329)) 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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