Mostly, yes. Granny flat, casita, in-law suite, backyard cottage, guest house — they're all everyday names for what California law calls an ADU. Here's where the terms line up, where they don't, and what actually makes it legal in Los Angeles.
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If you've searched "build a house for my mom in my backyard" or "how much is a granny flat in LA," you've already pictured the thing you want. You just may not know it has a clear legal name — and a defined permit pathway in California. That gap is bigger than most people think: a Freddie Mac survey found that 71% of Americans are unfamiliar with the term "ADU", yet once it's explained, 32% of non-owners say they'd be interested. Most homeowners reach for a synonym first.
Yes — in everyday use, granny flat, casita, in-law suite, mother-in-law suite, backyard cottage, guest house, and garage apartment all describe the same thing California law calls an Accessory Dwelling Unit (ADU). They're informal nicknames; "ADU" is the legal term that unlocks the streamlined state permit rules. There's one real catch: an in-law or mother-in-law "suite" with no kitchen that just shares the main house isn't a legal ADU at all — it's a bedroom. The kitchen plus independent living is what turns a spare room into an ADU.
So the names aren't wrong — they're just imprecise. Below, we map each common term to what it usually means and whether it counts as a legal ADU in Los Angeles, then explain the one feature that decides it.
Here's the quick translation table. The deciding question in the right column is always the same: does it have its own kitchen, bathroom, sleeping area, and entrance?
| Common name | What people usually mean | Is it a legal ADU? |
|---|---|---|
| Granny flat | A small standalone or attached unit, often for an aging parent | Yes — if it has a kitchen + entrance |
| Casita | A small detached "little house" in the yard | Yes — if it has full independent living |
| Backyard cottage | A detached unit in the rear yard | Yes — this is a classic detached ADU |
| In-law / mother-in-law suite | A room or wing for a relative, often sharing the main home | Only if it has its own kitchen + entrance |
| Guest house | A detached space for visitors | Sometimes — many older ones are unpermitted |
| Garage apartment | Living space converted from or built over a garage | Yes — a permitted garage conversion ADU |
| Junior ADU (JADU) | A unit carved out of the existing house | Yes — a JADU, with its own rules (below) |
The names overlap on purpose — people describe what they can picture. The legal status comes down to one thing, which we get into next. If you're starting from zero, our plain-English guide to what an ADU is covers the basics.
California's housing department (HCD) is clear on the definition. An ADU is a self-contained residence with its own:
That's the dividing line. A "mother-in-law suite" that's really a bedroom and bath off the hallway — no kitchen, shared front door — is a great setup for a relative, but it is not a legal ADU. It can't be rented as a separate unit, doesn't get its own address, and won't show up on title as a second dwelling. Add a kitchen and a private entrance and the same space becomes an ADU.
A Junior ADU (JADU) is the in-between option: up to 500 sq ft carved out of the existing house (often a converted bedroom or attached garage) with an efficiency kitchen. It can share a bathroom with the main home, but owner-occupancy is required — you have to live in the house or the JADU. It's the cheapest way to add a legal unit because you're working inside the existing footprint. See our breakdown of ADU vs. JADU for which one fits your lot and budget.
A lot of LA properties have an existing "guest house" that was built decades ago without permits, or permitted as something else (a "rec room," a "studio"). On paper it might not be a legal dwelling at all. If that's your situation, you don't necessarily have to tear it down — California has a path to legalize an unpermitted ADU, and bringing it up to code is often cheaper than building new.
The most common name — "granny flat" — tells you why this category exists. ADUs are overwhelmingly a family-housing solution: 61% of ADUs are built for multigenerational housing. And AARP found that 77% of older adults want to age in their own home, and 62% of adults 50+ would build an ADU for a loved one who needs care.
The math is part of it. Assisted living in the LA area runs roughly $4,000–$10,000 a month, every month, with nothing to show for it at the end. A granny flat is a one-time build that keeps a parent close, gives everyone privacy, and stays an asset on your property afterward — rentable later, or a place for an adult kid, an office, or a future buyer's bonus. It's not a small decision, but it's a different kind of spend than a monthly facility bill.
You're also not alone in considering it: 66% of California homeowners have considered adding an ADU.
Whatever you call it, the build is the same. In Los Angeles, ADUs run roughly $250–$400 per square foot, or $150K–$400K+ all-in depending on size and finishes. A garage-conversion granny flat is the budget end, around $100K–$225K in LA. The median California ADU comes in near $150K. We break the line items down in our LA ADU cost guide.
On size and feasibility, the rules are friendlier than most people expect. There's no minimum lot size — the state guarantees you can build at least an 800 sq ft / 16 ft unit on a qualifying lot regardless of local limits, and the City of LA allows detached ADUs up to 1,200 sq ft. So whether you wanted a tiny casita or a full two-bedroom granny flat, there's usually room. The real question is what your specific address allows — that's what the free check below answers. (For the full picture, see can I build an ADU in Los Angeles, and our overview of the types of ADUs in California.)
Skip the guesswork. We'll check your actual address — zoning, lot size, setbacks — and tell you straight whether an ADU works, for free. No cost, no commitment.
Request an intro to a verified builderDon't let the vocabulary slow you down. If you want a small living space on your property for a parent, a kid, a renter, or yourself, you want an ADU — whatever word you used to describe it. The one thing to get right is the kitchen-plus-entrance test: that's what separates a real, legal, valuable second unit from a glorified spare room.
Once you know that, the next move is checking what your lot can actually support, then matching with a vetted, CSLB-licensed builder. We can do both. Start with the free property check, or browse our directory of the best ADU builders in Los Angeles.
Before you spend a dollar on permits, let us check your address — zoning, lot size, setbacks, overlays — and tell 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. No cost, no commitment.
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