ADU cost guide
How much does an ADU really cost in 2026?
Across the most recent California-focused cost surveys — Dynamic Quality Builders, Kellow Construction, Angi, Barcci Builders, and the Terner Center research cited in California HCD's March 2026 handbook — the answer lands consistently. The breakdown below covers every variant homeowners actually search for: by city, by size, and by ADU type. Every number is sourced.
By state and metro
By state and metro
California-focused for launch; expansion markets added in Phase 3.
California overview
$150K–$400K+Statewide ranges by type. Use this as your starting point if you're in California.
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Los Angeles
$130K–$450K+LA County and major LA-area cities. 15–25% above CA state average.
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San Diego
$100K–$400KIncluding Coastal Overlay Zone considerations under AB 462.
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Bay Area
$180K–$650K+San Jose, SF Peninsula, Silicon Valley. Highest in California.
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By size
By size
Per-sqft costs are non-linear: smaller ADUs cost more per square foot because fixed costs (kitchen, bath, permits, utilities) don't scale.
By ADU type
By ADU type
Type is the single biggest cost lever — garage conversions and detached units of the same size can differ 30–40%.
ADU cost FAQ
- What's the average cost to build an ADU in 2026?
- Nationally, $60,000 for the smallest JADU conversions to $400,000+ for premium detached units. In California specifically, $150,000–$400,000+ is the all-in range, with the midpoint around $250,000–$300,000 for a typical 700–900 sq ft mid-finish detached ADU. Kellow Construction (Feb 2026) puts the state average at $150,000–$350,000 at $200–$450 per sq ft.
- Why do ADU costs vary so widely?
- Four factors account for most of the variance: ADU type (garage conversion vs detached can differ 30–40% for the same size), state (California is 30–50% above the national average), city or metro (within California, Bay Area runs 20–35% above LA, which itself is 15–25% above the state average), and site complexity (a sloped lot vs a flat lot can swing $60,000–$120,000).
- What's the cheapest type of ADU?
- A Junior ADU (JADU), $50,000–$100,000 — but it's capped at 500 sq ft and carved out of existing home space. The cheapest standalone unit is a garage conversion at $60,000–$150,000 nationally, $80,000–$175,000 in California.
- How much do impact fees add?
- California state law waives impact fees for ADUs under 750 sq ft. Above 750 sq ft, proportional impact fees apply — typically $10,000–$25,000 in major California metros. For some homeowners, designing to 749 sq ft to capture the waiver is the right move.
Get sourced ADU cost updates
We re-validate every cost range against the publishers above each quarter. Subscribe to get our updates as soon as we publish them.