Quick Answer: In California, an ADU (Accessory Dwelling Unit) and a JADU (Junior ADU) are both allowed on single-family lots but have key differences. A JADU is smaller (maximum 500 sq ft), must be created from existing space within the primary dwelling (not built new as a detached structure), can share a bathroom with the main house instead of having a separate bathroom, and requires the owner to live on the property (in either the main house or the JADU). An ADU has no ownership requirement, can be built as a new detached structure, can be any size up to 1,200 sq ft (or 50% of main house size, whichever is less), and must have its own kitchen and bathroom. A homeowner can have both a JADU and an ADU on the same single-family lot in California.
ADU vs JADU Comparison — California 2025
Helpful Resources:
| Factor | ADU | JADU |
|---|---|---|
| Maximum size | 1,200 sq ft (or 50% of main house, whichever is less) | 500 sq ft |
| Can be detached? | Yes — new detached construction allowed | No — must be from existing space within the primary dwelling |
| Separate bathroom required? | Yes | No — can share bath with main house |
| Separate kitchen required? | Yes — full kitchen with stove | Efficiency kitchen (no stove required; wetbar OK) |
| Owner-occupancy required? | No (as of AB 3182) | Yes — owner must live on property |
| Can be rented? | Yes — market rate or affordable | Yes — but owner must occupy main house or JADU |
| Typical conversion source | Garage, new construction, or home addition | Master suite, family room, or attached garage |
| Typical cost | $80,000 – $200,000+ | $40,000 – $100,000 |
Quartz Construction builds ADUs and converts existing space to JADUs throughout San Jose. Free consultation on which type makes most financial sense for your property. Learn about ADU services. CSLB #1003436 | Call (650) 749-7436.
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"Quartz Construction did an amazing job on our kitchen remodel. The team was professional, on time, and the results exceeded our expectations. Highly recommend to any Bay Area homeowner!"
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"We hired them for a bathroom remodel in our San Jose home. From permitting to final walkthrough, everything was handled perfectly. The tile work is stunning. 5 stars without hesitation."
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"Just finished our ADU garage conversion. The project came in on budget and on schedule — rare in the Bay Area! The rental income already started. Could not be happier with Quartz Construction."
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