ADU vs JADU vs Garage Conversion: Which One Can You Build?

A junior ADU is up to 500 square feet inside the existing house at $60,000 to $120,000. A garage conversion reuses an existing structure at $120,000 to $150,000. A detached ADU is new construction at $150,000 to $400,000. You can build a junior ADU and a full ADU on the same single-family lot, which is how many owners end up with two rentals.

Side by side

	Junior ADU	Garage conversion	Detached ADU
Cost	$60,000 to $120,000	$120,000 to $150,000	$150,000 to $400,000
Maximum size	500 sq ft	Whatever the garage is	Commonly up to 1,200 sq ft
Where it goes	Inside the existing house	In the existing garage	Anywhere the setbacks allow
Own bathroom	Optional, may share	Required	Required
Kitchen	Efficiency kitchen	Full kitchen	Full kitchen
Owner must live on site	Only if it shares a bathroom	No	No
Replacement parking	Not applicable	Not required	Not required
Setbacks	Existing walls	Keeps what the garage has	4 ft side and rear
Typical rent	Lowest	Middle	Highest
Build time	2 to 4 months	3 to 5 months	5 to 8 months

You can usually build more than one

On a single-family lot, California law requires cities to allow one ADU plus one junior ADU. That means a junior unit carved out of the house and a detached unit in the back yard, on the same property, at the same time.

On a lot with an existing apartment building the numbers get larger: conversions of non-livable space up to 25 percent of the existing unit count, plus up to eight detached units capped at the number of units already there.

The junior ADU trade-off

A junior ADU is the cheapest legal unit you can create, because you are reusing a bedroom and part of a hallway. You are adding an efficiency kitchen, a separate exterior entrance, a fire-rated door to the main house and some electrical work.

What you give up is a bedroom from the main house, and the unit is small enough that it rents for noticeably less than a detached unit. The owner-occupancy rule also still applies if it shares a bathroom with the house, which a full ADU no longer carries at all.

When the garage is the answer

When you have a garage you do not need, the slab is sound, and it sits somewhere that makes a decent rental, usually detached at the rear. It is the best cost-per-rent-dollar unit on the list.

When it is not: if the garage is falling apart, you are paying conversion prices for new-build work. If you genuinely need covered parking, the trade is not worth it. And if the garage is attached and awkwardly positioned, the resulting unit can feel like a converted garage, which affects what it rents for.

When to just build new

When the rear yard has room, access is workable, and you want the unit to rent at the top of the local range. A purpose-built unit has the layout, the ceiling height, the light and the privacy that a conversion cannot match, and it appraises accordingly.

It is the most expensive option and usually the best long-term asset.

Los Angeles County figures, reviewed 2026-10-29 by America General Contractors, California contractor licence CSLB 1083262. Planning ranges, not a quote, and not legal advice. We confirm the current rules for your parcel before anything is drawn.

Questions

Can I build a JADU and an ADU at the same time?

Yes, on a single-family lot state law requires cities to allow both. Doing them together saves money because the permit, the drawings and the mobilisation are shared.

Is a converted garage worth less than a built ADU?

It generally rents for a bit less and appraises for a bit less, but it also costs far less to build. On return rather than absolute value, the garage conversion frequently wins.

Do I have to live on the property?

Not for a full ADU. That requirement was removed permanently. For a junior ADU it can still be required where the junior unit shares a bathroom with the main house.

Can I rent any of them short term?

Not in the City of Los Angeles and most surrounding cities. ADU short-term rental is restricted, and junior ADU rentals must run longer than 30 days by state law.

Which one should I build?

The one that matches your lot and your goal. If you have a sound detached garage, convert it. If you have a good rear yard and want maximum rent, build new. If you have neither but have a spare bedroom and a side entrance, build a junior ADU.