DADU vs ADU
DADU vs ADU: the same thing, with a regional accent.
A DADU is a Detached Accessory Dwelling Unit — a standalone secondary dwelling separated from the primary home. Seattle and Portland use 'DADU' specifically; California typically uses 'detached ADU' for the same thing. The relationship: every DADU is an ADU, but not every ADU is a DADU (attached ADUs, JADUs, and garage conversions are also ADUs, but they're not detached).
Option
DADU
Detached Accessory Dwelling Unit
Typical cost
$350–$700/sf in Seattle (New Image 2025); $350K–$650K+ in Bay Area (Barcci 2026)
Option
ADU (general)
Any Accessory Dwelling Unit type
Typical cost
$50K–$400K+ depending on ADU type (CA 2026)
Side-by-side comparison
| Attribute | DADU | ADU (general) |
|---|---|---|
| What it is | Standalone secondary structure, separate from main home | Umbrella term — detached, attached, garage conversion, JADU, prefab all qualify |
| Where the term is used | Seattle, Portland, and parts of WA/OR planning code | California, federal lending guidance, most national publications |
| Cost benchmark (per sq ft, 2025-2026) | $350–$700 Seattle (New Image); $400–$500 CA midpoint | $200–$500 across all ADU types (DQB 2026) |
| Permits (Seattle, 2025) | $8K–$15K typical; impact fees add several thousand more | Varies by ADU type and jurisdiction |
| Privacy / independence | Highest — no shared walls, no shared entry | Highest for detached ADUs; less for attached/JADU types |
Pick DADU when
- You're in Seattle, Portland, or another DADU-specific jurisdiction — use the local terminology.
- Privacy and independence are top priorities.
- Your lot supports a detached structure with required setbacks.
Pick ADU (general) when
- You're searching broadly and don't know which ADU type fits — start with the umbrella term and narrow down by type, size, and location.
- You're in California, where 'detached ADU' is the more common term.
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FAQ
- Are DADU and ADU the same thing?
- Functionally yes, with one caveat: 'DADU' specifically means detached. An attached ADU or a JADU is an ADU but is not a DADU. Seattle and Portland use 'DADU' for detached units; California typically uses 'detached ADU' or 'backyard ADU.'
- Is a DADU more expensive than other ADU types?
- Usually yes — detached units run highest because they need full foundation, framing, roof, and utility connections built from scratch. Seattle DADU costs run $350–$700 per sq ft in 2025; California detached ADUs run $350–$500+ per sq ft (New Image 2025; DQB 2026).
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