How much does an ADU cost?
Answered by Netanel Presman, General Contractor (CSLB #1105249) · Updated
Short answer
Detached ADUs in California typically run $275,000-$500,000 turnkey as of 2026 (300-800 sqft, including design, permits, utilities, finish). Attached or garage-conversion ADUs run $150,000-$300,000. Costs outside California are generally lower because California's Title 24 energy code and labor rates compound. Prefab or panelized ADUs can land at $200,000-$350,000 installed.
In detail
ADU cost varies by three main levers:
- Detached vs attached vs conversion — A detached new structure includes foundation, framing, roof, and full utility run, which can add $75,000-$150,000 versus converting an existing garage.
- Jurisdiction — California's Title 24 Part 6 (2025 revision) requires electrification in new ADUs, meaning heat pump HVAC and heat pump water heating, which adds $8,000-$15,000 versus gas. Coastal California additionally requires solar PV sized to the ADU load.
- Finish level — A "developer finish" ADU (LVP floors, mid-range cabinets, quartz counters) runs 40-60% of the cost of a "primary home finish" ADU with hardwood, stone counters, custom millwork.
Typical 2026 California ADU cost ranges (turnkey, all-in):
- Garage conversion, 300-500 sqft, basic finish: $120,000-$200,000
- Garage conversion, 300-500 sqft, mid-range finish: $200,000-$280,000
- Detached, 500 sqft, basic finish: $275,000-$375,000
- Detached, 800 sqft, mid-range finish: $425,000-$525,000
- Detached, 1,200 sqft, high-end finish: $600,000-$800,000+
Costs that often surprise homeowners:
- Utility separation (separate electrical meter, sewer lateral): $15,000-$40,000
- Site work on sloped lots: $20,000-$75,000
- Impact fees and school fees in some cities: $5,000-$20,000
- Soft costs (architectural, structural, T24, survey): 10-15% of hard cost
AskBaily's LA ADU scoping accounts for lot conditions, utility separation, and whether SB 9 lot-split financing is on the table.
Sources
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