JADU vs ADU in California: which one your house can actually take

Law verified as of 10 September 2026 against the text published by the California Legislature.

The comparison that matters

Most comparisons lead with square footage. Size is the least consequential difference. What decides whether a JADU suits you is the set of conditions attached to it.

	Accessory dwelling unit	Junior accessory dwelling unit
Maximum size	Local maximum, which cannot be set below 850 sq ft (1,000 sq ft with more than one bedroom) — § 66321(b)(2)	500 sq ft of interior livable space — § 66313(d)
Where it can go	Attached or detached, on a lot with a proposed or existing primary residence — § 66313(a)	Entirely within the walls of the single-family residence; an attached garage counts as part of the residence — §§ 66313(d), 66333(d)
Owner must live on site	Cannot be required — § 66315	Required where sanitation is shared; not required if it has its own sanitation, or the owner is a government agency, land trust or housing organisation — § 66333(b)
Recorded deed restriction	Not required	Required — bars separate sale, binds future purchasers — § 66333(c)
Number per lot	Depends on the category and lot type	One — § 66333(a)
Kitchen	Full kitchen, as a complete independent dwelling	Efficiency kitchen — § 66333(f)
Bathroom	Its own	May share with the house — § 66313(d)
Separate entrance	Not separately specified	Required — § 66333(e)
Additional parking	Barred in the circumstances listed in § 66322(a)	Cannot be required at all — § 66334(a)
Impact fees	None at 750 sq ft or less — § 66311.5(c)(1)	None, since every JADU is at or under 500 sq ft — § 66311.5(c)(1)
Decision deadlines	15 business days to completeness, 60 days to decide — § 66317	Same — § 66335

The bathroom decision is the occupancy decision

This is the single most useful thing to understand before you draw anything.

Section 66313(d) allows a JADU to share sanitation facilities with the house. Section 66333(b) then requires owner-occupancy where those facilities are shared, and expressly removes that requirement where the JADU has its own.

So the plumbing choice determines whether you are free to move out and rent both units. If you intend to keep living on the property, sharing a bathroom is a legitimate way to save cost and space. If you might not, giving the JADU its own sanitation is what preserves that option — and the decision is far cheaper to make on paper than after the walls are closed.

What the deed restriction actually does

A JADU carries a recorded restriction that runs with the land. Under § 66333(c) it must prohibit selling the JADU separately from the house, state that it is enforceable against future purchasers, and restrict the unit’s size and attributes to what the article permits.

That is not a formality. It is a permanent encumbrance on title that a future buyer’s lender and title company will see. It does not make the property harder to sell as a whole, but it forecloses the separate-conveyance routes that exist for ADUs, and it should be a conscious choice rather than a surprise at recordation.

When a JADU is the right answer

A JADU suits a specific situation well: a house with genuinely surplus internal volume — an oversized primary suite, a rarely used formal dining room, an attached garage — where the owner intends to stay on the property, and where the goal is a self-contained space for a family member or a modest rental rather than a second household of full size.

It is cheap relative to new construction because it uses existing structure, foundation and roof. It attracts no impact fees and no additional parking requirement. It is contained, so it does not consume garden.

When it is not

If you want a full second dwelling, a JADU will disappoint you at 500 square feet with an efficiency kitchen. If you may want to rent both units without living on site, the shared-sanitation route removes that option. If you want the flexibility to convey the unit separately later, the deed restriction closes that door.

In those cases the detached ADU — or a conversion of a detached garage, which is a different protected category under § 66323(a)(1)(A) — is the better instrument. And because § 66323(a)(1) requires ministerial approval of one of each on a single-family lot, treating them as competing options is often the mistake. On the right house they are complementary.

A caution about local ordinances

Section 66333 is written permissively: a local agency “may, by ordinance, provide for the creation of junior accessory dwelling units,” and the list of requirements applies to an ordinance that is adopted. Separately, § 66323(a)(1) requires ministerial approval of one ADU and one JADU per single-family lot notwithstanding §§ 66314 to 66322, where the conditions there are satisfied.

The practical consequence is that what your city’s own ADU handout says about JADUs may be narrower than what state law requires of it — and the two need to be read together for your specific address before you rely on either.