Types of ADUs
The five types of ADUs (and how to pick).
Every ADU in California falls into one of five categories. Picking the right type is the single most consequential decision in your project — it sets your cost, your timeline, your permitting path, and your design options. Each guide below covers sourced 2026 cost ranges, rules, pros, cons, and when it's the right choice.
Detached ADU
$200K–$400K+ (CA 2026, DQB/Kellow)
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Attached ADU
$150K–$300K (CA 2026, DQB/Kellow)
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Garage Conversion ADU
$60K–$200K nationally (Angi 2026 avg $110K)
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Junior ADU (JADU)
$30K–$100K (San Jose, Redshed 2026)
Read the guide
Prefab ADU
Unit $80K–$300K (LADU 2026)
Read the guide
FAQ
- What are the main types of ADUs?
- Five primary types: detached (standalone backyard ADU), attached (extension off the main home), garage conversion (existing garage converted to a dwelling), junior ADU or JADU (≤500 sq ft inside the primary home or attached garage), and prefab/modular (factory-built and delivered). Each has distinct cost, code, and design implications.
- Which ADU type is cheapest?
- JADUs at $30,000–$100,000 are the cheapest legal ADU in California (Redshed 2026). Among standalone units, garage conversions are cheapest at $60,000–$200,000 (Angi/DQB 2026). Detached new builds are most expensive at $200,000–$650,000+ depending on California metro.
- Can I have more than one ADU on my property?
- Yes — California state law allows one standard ADU plus one JADU on most single-family lots. Multifamily lots can have up to 8 detached ADUs under SB 1211 (2025). The HCD ADU Handbook (March 2026) is the authoritative reference.
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