What Is an ADU? Meaning, Types & Rules in LA

An ADU is a second, self-contained home on a property that already has a house. Here's the plain-English meaning, the main types, rough Los Angeles costs, and the 2026 California rules — without the jargon.

We match you with vetted, California-licensed ADU builders in your area — no guesswork, no cold-calling contractors.

If you've heard the term "ADU" thrown around and quietly wondered what it actually means, you're in good company. A Freddie Mac survey found that 71% of Americans are unfamiliar with the term "ADU" — yet most of them already know the concept by another name. Granny flat. Casita. In-law suite. Backyard cottage. They're all describing the same thing.

The 30-second answer

ADU stands for accessory dwelling unit — a smaller, completely independent home built on the same lot as a primary house. It has its own kitchen, bathroom, sleeping area, and entrance. In Los Angeles you can build one on almost any residential lot: there's no minimum lot size, California guarantees you at least an 800 sq ft / 16 ft unit, and the City of LA lets detached ADUs run up to 1,200 sq ft. People build them to house family, earn rent ($2,000–$4,500/mo in LA), or add value — CA homes with an ADU appraise about $349,000 higher on average.

What's on this page

1. ADU meaning, spelled out
2. Granny flat, casita & other names
3. The types of ADUs
4. Basic LA & California rules
5. Why people build an ADU
6. How to find out if you qualify
7. Frequently asked questions

ADU meaning, spelled out

ADU is short for "accessory dwelling unit." Break that phrase apart and it explains itself: it's accessory (secondary to the main house), it's a dwelling (a place someone can actually live), and it's a unit (a single, self-contained home). The legal test that separates an ADU from a den, a converted office, or a "bonus room" is independence: to count as an ADU it must have its own kitchen, its own bathroom, a place to sleep, and its own entrance. If you could rent it to a stranger and they'd never need to walk through your house, it's an ADU.

That's the whole idea. An ADU is a complete, smaller home that shares a lot with a bigger one. It can sit in the backyard, attach to the side of the house, or be carved out of a garage or basement. California specifically created the category so homeowners could add housing without subdividing their land or going through a rezoning fight.

One distinction worth flagging early: a JADU (junior accessory dwelling unit) is a special, smaller sub-type — up to 500 sq ft, carved out of the existing house, with looser kitchen rules but an owner-occupancy requirement. We cover it below, and in more depth in ADU vs JADU.

Granny flat, casita & the other names you already know

Here's the thing about that 71% unfamiliarity stat: most people aren't actually clueless about the concept — they just search a different word for it. Before "ADU" became the legal term, Californians had a dozen folksy names for the same backyard home, and many still type those into Google first.

• Granny flat — the classic name, from the original purpose of housing an aging parent close by.
• Casita — "little house" in Spanish; common in Southern California and the Southwest.
• In-law suite — emphasizes the family-housing use; sometimes attached to the main home.
• Backyard cottage — descriptive name for a freestanding detached ADU.
• Guest house — informal term; note a true ADU is more than a guest room because it has a full kitchen.
• Garage apartment — usually a garage conversion or a unit built above a garage.

All of these are ADUs in the eyes of California law. The names differ; the permits, rules, and value don't. If you want the full breakdown of which term fits your situation, we wrote a dedicated guide on granny flats, casitas & in-law suites.

Why the name matters less than you think

Whatever you call it, LADBS reviews it under the same state ADU law. So don't get hung up on terminology — focus on the type (detached, attached, conversion, or JADU), because that's what drives your cost, timeline, and what's allowed on your specific lot.

The types of ADUs

There are four main types of ADUs, and the type you build is the single biggest driver of cost. A garage conversion reuses an existing structure, so it's the cheapest path; a ground-up detached unit gives you the most freedom but costs the most. Here's how they compare in the Los Angeles market.

Ranges are LA-area estimates, not quotes; ADU construction runs roughly $250–$400 per square foot in LA, with garage conversions closer to $100K–$225K. The statewide median ADU costs about $150K, and 71% come in under $200K.

Detached ADU

The freestanding backyard home most people picture. It's the most popular type because you get full control over layout and privacy, and it doesn't disrupt the main house during construction. It's also the priciest because you're building everything from scratch — foundation, walls, roof, and new utility runs.

Attached ADU

A new unit bolted onto the existing house, sharing at least one wall. It can be slightly cheaper than detached because it borrows structure and sometimes utility lines, but it ties the build to your existing home and footprint.

Garage or basement conversion

Converting a garage (or, less commonly in LA, a basement) is the budget-friendly route since the shell already exists. You're mainly adding insulation, plumbing, a kitchen, and bringing it up to code. The trade-off is you usually lose your garage parking — though LA's transit-area parking waivers often mean you don't have to replace it.

Junior ADU (JADU)

A JADU is the smallest, cheapest option: up to 500 sq ft carved out of your existing home (often a converted primary bedroom). It can share a bathroom and have just an efficiency kitchen, but it comes with an owner-occupancy requirement — you have to live on the property. See our full guide to the types of ADUs in California for how to choose between them.

Not sure which type fits your lot?

The cheapest way to find out is a free property check. We'll look at your zoning, lot size, and setbacks and tell you straight what you can build — before you spend a dollar on plans.

The basic LA & California rules

California has spent the last several years rewriting its laws to make ADUs easy to approve. The result is a set of statewide protections that override most restrictive local rules. Here are the basics every LA homeowner should know.

• No minimum lot size. ADUs are allowed on essentially any single-family or multifamily lot in California (source). Your yard doesn't need to be big.
• State-guaranteed size. The state guarantees you can build at least an 800 sq ft, 16 ft tall ADU regardless of local limits. In the City of LA, detached ADUs can go up to 1,200 sq ft (LA ADU rules).
• Small setbacks. Detached ADUs need just 4 feet from the side and rear property lines.
• Parking often waived. If your property is within 1/2 mile of public transit, the city can't require you to add parking for the ADU (2026 housing laws). Much of LA qualifies.
• No impact fees under 750 sq ft. Under SB 13, ADUs smaller than 750 sq ft are exempt from development impact fees — often saving thousands.

The "60-day approval" reality check

You'll see headlines about a 60-day ADU approval law. That's a statute (SB 13), not what happens on a custom build. In the real world, custom LA ADU permits take roughly 3–6 months, and the full project — design, permitting, and construction — usually runs 8–14 months end to end. Pre-approved standard plans move faster. We break the timeline down honestly in our 2026 California ADU laws guide.

For the deeper dives, see our pillar guides on the ADU permit process in LA and whether you can build an ADU on your lot.

Why people build an ADU

ADUs have gone mainstream in California for a simple reason: they solve real problems. A 2024 study found that 66% of California homeowners have considered building one. Here's what's driving them.

Housing family

This is the number-one reason. A survey found 61% of ADUs are built for multigenerational housing — aging parents who want to stay close but independent, or adult kids priced out of the LA market. The granny flat lives up to its name.

Rental income

An ADU is a built-in income stream. In Los Angeles, ADUs rent for roughly $2,000–$4,500 per month depending on size and neighborhood. Note that LA effectively restricts short-term rentals, so plan around a long-term (30+ day) tenant rather than nightly stays.

Property value

Adding a legal, permitted ADU meaningfully raises what your property is worth. The FHFA found that California homes with an ADU appraised at a median of $1,064,000 versus $715,000 for homes without one — a gap of roughly $349,000. (Important: only the new ADU gets reassessed for property taxes, at about 1%/yr of its value; your home keeps its existing Prop 13 basis. The "taxes will explode" fear is a myth — more in do ADUs increase property taxes.)

The honest caveat

An ADU is a six-figure project, and the biggest risk in LA isn't the permit — it's hiring the wrong builder. SoCal has been a documented hotspot for ADU contractor scams. That's exactly why we verify every builder's CSLB license before we'll match you with them. Learn how to vet an ADU builder or browse our vetted LA ADU builders.

How to find out if you qualify

Now you know what an ADU is, the types, and the rules. The next question is the practical one: can you build one on your lot, and what would it cost? You don't need to guess, and you don't need to pay an architect to find out.

Our free property qualification check looks at your address — zoning, lot size, setbacks, transit overlays — and tells you straight whether an ADU is viable. If it looks good, we connect you with a vetted, California-licensed LA builder for a free on-site feasibility assessment. We're a directory and pre-qualification service, not a contractor — our job is to point you to the right licensed pro, with their CSLB number on file, so you can build with confidence.

From there, the usual next steps are understanding what an ADU costs in LA and your builder options. Or just start with the free property check and we'll take it from there.

Frequently asked questions

What does ADU stand for?

ADU stands for "accessory dwelling unit." It's a smaller, fully independent home built on the same lot as a primary house, with its own kitchen, bathroom, sleeping area, and entrance.

What's the difference between an ADU and a granny flat?

There's no legal difference. "Granny flat," "casita," "in-law suite," "backyard cottage," and "guest house" are all everyday names for an ADU. California law reviews them all under the same accessory dwelling unit rules.

What are the main types of ADUs?

The four main types are detached (a standalone backyard home), attached (an addition sharing a wall with the house), a garage or basement conversion (existing space converted to a living unit), and a JADU or junior ADU (up to 500 sq ft carved from inside the existing home).

Do I need a big lot to build an ADU in Los Angeles?

No. California law sets no minimum lot size for an ADU, and the state guarantees you can build at least an 800 square foot, 16 foot tall unit on essentially any residential lot. Detached ADUs need just 4 feet from the side and rear property lines.

How much does an ADU cost in LA?

In Los Angeles, ADUs run roughly $250 to $400 per square foot, or about $150,000 to $400,000-plus all in for a detached unit. A garage conversion is cheaper, around $100,000 to $225,000. A junior ADU can cost less still. These are estimates, not quotes, and vary by property.

Will building an ADU spike my property taxes?

No. Only the new ADU is added to your assessment, taxed at roughly 1 percent per year of its value. Your existing home keeps its Proposition 13 tax basis. The fear that an ADU re-assesses your whole property is a myth.