Side by side
| Junior ADU | Full ADU | |
|---|---|---|
| Max size | 500 sq ft | 850–1,200 sq ft typical |
| Location | Within existing home walls | Detached, attached or converted |
| Kitchen | Efficiency kitchen allowed | Full kitchen |
| Bathroom | May share with main house | Must be private |
| Owner-occupancy | Usually required in CA | Not required in CA |
| Relative budget | Lowest — no foundation | Higher — new construction |
| Typical rent | $950 – $1,500 | $1,600 – $2,800 |
Where the JADU wins
If you have an unused wing, a converted bedroom with exterior access, or a floor plan that already splits cleanly, a JADU is the cheapest legal dwelling you can create. Permits are lighter, there is no foundation, no new utility service in most cases, and construction runs 8–12 weeks rather than half a year.
It is also the right answer when the goal is family housing rather than maximum yield. Housing a parent inside existing walls beats new construction on both budget and timeline every time.
- Lowest capital outlay and fastest occupancy
- No lost yard and minimal site disturbance
- Often no new sewer or electrical service required
Where the full ADU wins
Rent scales with privacy and bedroom count far more than with square footage. A detached one-bedroom typically rents for roughly double a JADU in the same neighborhood, and it appraises better because it functions as a genuine separate residence. Over a ten-year hold, the larger unit usually returns more in absolute dollars even though its payback period is longer.
The full ADU also avoids the owner-occupancy condition that most California jurisdictions attach to JADUs — which matters if you might move out and rent the whole property.
Can you build both?
On most single-family lots in California, yes: state law generally permits one detached ADU plus one JADU on the same parcel. That combination — a converted 400 sq ft JADU inside the home and an 800 sq ft detached unit in the yard — is the highest-density legal outcome for a typical suburban lot, and it is the play we run most often for investor clients.