People use these terms loosely, and they overlap. A garage conversion is a way of building an ADU or a JADU. A detached ADU is a new building. A JADU is a small unit carved out of the house. Getting the vocabulary right helps you read your city's rules.
LA ADU Guide is an information site. We do not design, build or finance projects. Confirm details with your building department.
The four common types
Detached ADU
A new, separate building in the yard. Under Gov. Code section 66323(a), a city "shall ministerially approve" one detached, new-construction ADU with side and rear setbacks of no more than four feet. CAL FIRE's 2025 bulletin lists the state size cap for detached ADUs as 1,200 square feet. Section 66321(b)(3) also requires cities to allow at least 800 square feet.
Attached ADU
An addition that shares a wall with the house. Where a city has no ADU ordinance, the state size guide is 50 percent of the main home's size. A city with an ordinance must allow at least 850 or 1,000 square feet, depending on bedrooms. Local rules may allow more.
Conversion ADU
An ADU made from space that already exists, such as a spare room, basement or an accessory structure. Section 66323(a)(1) allows an ADU "within the proposed space of a single-family dwelling or existing space of a single-family dwelling or accessory structure." CAL FIRE notes these conversions "have no size limitations." An existing structure converted in the same location and to the same dimensions needs no setback.
JADU
Section 66313(d) defines a junior ADU as "no more than 500 square feet in size and contained entirely within a single-family residence." It can have its own bathroom or share one with the main home. If it has no separate bathroom, section 66333(e)(2) says it "shall include a separate entrance from the main entrance to the structure, with an interior entry to the main living area." The 2025 legislative summary also notes AB 1154, effective January 1, 2026, covers JADUs that share sanitation with the main home. Read the current text before relying on that detail.
Where the garage fits
A garage conversion is simply a conversion ADU (or a JADU, if the garage is attached and inside the home). Two points come up often:
- Section 66323(a)(1) lets a city approve a conversion of existing accessory structure space with no size limit.
- State law bars cities from requiring replacement parking when a garage is converted for ADUs. The HCD Handbook explains this under the ADU parking rules.
Garage conversions are often called the simplest path because the walls and slab already exist. That does not make them free of work. The garage still has to meet residential building code for insulation, egress, electrical, plumbing and, in some cases, fire sprinklers. Habitability rules apply to anything people sleep in.
An older or unpermitted garage is a different story. HCD says a city may not deny an ADU because of "the correction of unpermitted accessory structures that do not present a threat to public health and safety" (section 66322(b)). AB 2533 (effective January 1, 2025) added an amnesty process for some unpermitted ADUs and JADUs built before 2020.
Side-by-side
| Detached ADU | Attached ADU | Conversion ADU | JADU | |
|---|---|---|---|---|
| New footprint | Yes | Yes | No | No |
| State size guide | Local cap not below 850 sq ft (1 bedroom) or 1,000 sq ft (2+); 1,200 only with no local ordinance | Same floor; 50% of main home only with no local ordinance | No limit | 500 sq ft max |
| Setbacks | 4 ft side and rear max | 4 ft side and rear max | None if same footprint | None |
| Owner occupancy | Not required (AB 976) | Not required | Not required | Required (66333) |
Where each type is defined
| Type | Key section | What it says |
|---|---|---|
| Detached ADU | Gov. Code 66323(a) | One new detached ADU with setbacks of no more than four feet |
| Conversion ADU | Section 66323(a)(1) | Space within or existing in a home or accessory structure, no size limit |
| JADU | Section 66313(d) | No more than 500 sq ft, entirely within a single-family residence |
| JADU without its own bathroom | Section 66333(e)(2) | Separate entrance plus an interior entry to the main living area |
| Unpermitted space | Section 66322(b) | A city may not deny an ADU over unpermitted-structure corrections that pose no threat to public health and safety |
Can you build more than one?
Yes, in many cases. HCD told the City of Los Angeles that state law lets an owner create "one (1) converted ADU, one (1) detached, new construction ADU, and one (1) JADU, in any order without prejudice, totaling three units." That makes a garage conversion plus a detached ADU plus a JADU possible on one single-family lot, if each unit meets its own rules. Rules for multifamily lots differ: converted ADUs inside non-livable space, plus up to eight detached ADUs under SB 1211, capped by the number of existing units.
Fire sprinklers matter here. CAL FIRE says "All ADUs, attached or detached, require fire sprinklers if the primary dwelling is equipped with a fire sprinkler system," and adding an ADU cannot trigger sprinklers in the main home. See ADUs in fire hazard zones.
Things that don't change by type
- Review time: 60 days for a complete application (section 66317).
- Short-term rentals: many local rules limit rentals to more than 30 days. Check your agency.
- Sale: an ADU generally cannot be sold apart from the main home, with narrow exceptions.
- Fees: no impact fees for ADUs of 750 square feet or less (section 66311.5(c), formerly 66324).
Questions to ask before you pick
- Do I have a garage or other structure worth converting, and is it in sound shape?
- Is the yard big enough for a detached unit after setbacks?
- Do I plan to live on the property? A JADU requires it.
- Is the lot in a fire, flood or hillside area that adds requirements?
- What does my city say it will approve, and under which section?
For cost ranges, see ADU costs in Los Angeles. For prefab options, see prefab and preapproved plans. Unfamiliar terms are in the ADU glossary. The overall state framework is in California ADU rules, and more guides are in the ADU types hub.
This page is general information, not legal advice.