Types of ADUs in California: Detached, Attached, Garage & JADU

Four ways to add an accessory dwelling unit to your LA property — each with its own footprint, rules, and price tag. Here's what separates them, and which one fits your lot.

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If you've started looking into building a backyard unit, you've probably run into a wall of acronyms — ADU, JADU, detached, attached, conversion. They're not interchangeable. The type you choose decides how big you can build, how much it costs, what the permit looks like, and whether you can rent it out long-term. In California, there are four practical paths, and picking the right one for your lot is the single most important decision you'll make before you ever talk to a builder.

This guide breaks down all four — detached, attached, garage or basement conversion, and the junior ADU (JADU) — with the honest pros, cons, and rough Los Angeles cost ranges for each. (If you're brand new to the concept, start with what is an ADU, then come back here.)

The 30-second answer

California recognizes four ADU types. A detached ADU is a standalone backyard unit (most freedom, highest cost — roughly $200K–$400K+ in LA). An attached ADU shares a wall with your house (~$150K–$300K). A garage or basement conversion reuses existing space (cheapest, $100K–$225K in LA). A JADU is a unit of 500 sq ft or less carved from inside the house ($50K–$150K, owner-occupancy required). State law lets you build both one ADU and one JADU on the same single-family lot.

On this page

1. Detached ADU
2. Attached ADU
3. Garage / basement conversion
4. Junior ADU (JADU)
5. Side-by-side comparison
6. Which type fits your lot
7. FAQ

1. Detached ADU — the standalone backyard unit

A detached ADU is a fully separate structure built in your yard, with its own walls, roof, entrance, kitchen, and bathroom. It's the classic "backyard cottage" most people picture, and it's the most flexible type: you can design the layout from scratch, give your tenant or family member real privacy, and add the most rentable square footage.

California guarantees you can build a detached ADU of up to 800 sq ft and 16 feet tall on virtually any residential lot, regardless of local zoning. The City of LA goes further and allows detached units up to 1,200 sq ft, with just 4-foot side and rear setbacks, and parking is waived if your property is within a half-mile of transit (aduzoning.org LA rules, 2026 housing laws).

Detached at a glance

Pros: Maximum size and privacy; highest rental value; no disruption to your main house during construction; you design it however you want. Cons: Highest cost; needs its own foundation and full utility runs; a separate sewer lateral or pump and meter are common — and sitework/utilities are the most under-budgeted line item, often 10–15% of the job (sitework cost drivers). Rough LA cost: ~$200K–$400K+, anchored to the LA average of $250–$400/sq ft (LA ADU cost).

2. Attached ADU — shares a wall with the main house

An attached ADU is a brand-new addition that bolts onto your existing home, sharing at least one wall. Think of a bump-out off the back or side of the house that has its own entrance, kitchen, and bath. It's a middle path: you still get new, purpose-built space, but you save on one wall and often on utility runs because you're tying into the main house's systems nearby.

Attached units are a smart choice on narrower lots where a standalone building won't fit, or when you want the new unit close to the main house for an aging parent. They follow the same core state rules — no minimum lot size, ministerial approval — though an attached unit is capped relative to the existing home's size in some local rules, so size depends more on your house than a detached unit does.

Attached at a glance

Pros: Cheaper than detached (shared wall + shorter utility runs); efficient use of a tight lot; keeps family close. Cons: Construction touches your existing home (some disruption); less privacy than a freestanding unit; layout is constrained by the house it attaches to. Rough LA cost: ~$150K–$300K, against the LA $250–$400/sq ft figure and the median California ADU of ~$150K (LA ADU cost, Terner Center ADU survey).

3. Garage or basement conversion — reuse existing space

A conversion ADU turns space you already have — most often a detached or attached garage, sometimes a basement — into a legal dwelling. Because the shell, foundation, and roof already exist, this is usually the most affordable route into an ADU. State law even lets you add up to 150 sq ft to a conversion for ingress and egress.

The catch is that "existing" rarely means "ready." Old garages routinely need a new or upgraded foundation, drainage and waterproofing work, ceiling-height fixes to hit code, and full insulation, plumbing, and electrical. Those upgrades are exactly where conversion budgets blow up, so a real on-site look matters more here than with any other type.

Conversion at a glance

Pros: Lowest cost of the four "full ADU" types; reuses existing footprint so you keep more yard; often faster since the structure stands. Cons: Hidden costs — foundation, drainage, ceiling height, moisture; you lose your garage/parking; basements add waterproofing and egress complexity. Rough LA cost: ~$100K–$225K in LA (LA ADU cost, garage conversion cost).

Want the full breakdown? See our deep dive on what an ADU costs in Los Angeles.

4. Junior ADU (JADU) — carved from inside the house

A junior ADU is a small unit — 500 sq ft or less — created entirely within the walls of your existing single-family home, typically by converting a bedroom or a portion of the house. It needs an efficiency kitchen and its own exterior entrance, but it can share a bathroom with the main house. Because no new structure goes up, a JADU is the cheapest path of all and is exempt from any extra parking requirement.

There are two strings attached. First, a JADU requires owner-occupancy — you (or the JADU's occupant) must live on the property, which makes it ideal for a relative or a long-term tenant but not for a fully hands-off rental. Second, it's small by design. The big upside: state law lets you build both a JADU and a separate ADU on the same single-family lot, so a JADU can be one piece of a two-unit plan (California HCD ADU guidance).

JADU at a glance

Pros: Cheapest type; no extra parking; fast to permit; pairs with a full ADU for two extra units on one lot. Cons: 500 sq ft cap; owner-occupancy required; efficiency kitchen and possible shared bath limit who it suits. Rough LA cost: ~$50K–$150K, depending on how much plumbing and structural work the conversion needs.

Confused about where the line falls between a JADU and a full ADU? We compare them head-to-head in ADU vs JADU.

The four ADU types, side by side

Here's the quick comparison. Cost ranges are LA-specific and anchored to the area's $250–$400/sq ft figure and the ~$150K median California ADU — treat them as planning ranges, not quotes (cost source, Terner median).

Two state perks apply across the board: there's no minimum lot size for an ADU (CA zoning rules), and any ADU under 750 sq ft is exempt from impact fees under SB 13 (HCD ADU handbook). For the full rulebook, see California ADU laws for 2026.

Not sure which type your lot can support?

Start with a free, no-obligation property check. We review your address — zoning, lot size, setbacks, transit overlays — and tell you straight which ADU types are realistic before you spend a cent.

Which ADU type fits your lot?

The "right" type is mostly decided by your lot, your budget, and what you want the unit to do. A few honest rules of thumb:

• You have backyard room and want maximum rent or resale value → detached ADU. It's the biggest spend but the biggest upside, especially on a deep LA lot.
• Your lot is narrow or you want a parent close by → attached ADU. You trade some privacy for a lower cost and a tighter footprint.
• You have an underused garage and a tight budget → conversion. Just budget honestly for the foundation, drainage, and ceiling-height surprises — have a pro look before you commit.
• You want the cheapest, fastest unit and you'll live on-site → JADU. And remember you can pair a JADU with a detached ADU for two extra units on one single-family lot.

Before any of this is real, two things have to check out: whether your zoning and setbacks allow the type you want, and whether your existing utilities and panel can carry a second unit. That's exactly what a feasibility check answers. See can I build an ADU in Los Angeles for the eligibility basics, and when you're ready to actually build, work with a vetted, CSLB-licensed LA ADU builder — we'll match you with one.

A note on timelines

Whatever type you pick, plan realistically. The "60-day approval" you'll read about is a statute, not the lived reality for custom builds — custom LA permits typically run about 3–6 months, and the full project (design through construction) usually takes the better part of a year. Conversions and JADUs tend to be on the faster end.

Common questions about ADU types

What are the four types of ADUs in California?

California recognizes four practical types: a detached ADU (a standalone backyard unit), an attached ADU (a new addition that shares a wall with the main house), a garage or basement conversion (an ADU created from existing space), and a JADU or junior ADU (a unit of 500 square feet or less carved from inside the existing house).

What is the difference between a detached and an attached ADU?

A detached ADU is a fully separate structure in your yard with its own foundation, roof, and utilities, offering the most size and privacy but the highest cost. An attached ADU is a new addition that shares at least one wall with your existing home, which lowers the cost and fits narrower lots but ties the new unit's layout to the main house.

Which type of ADU is the cheapest to build?

A junior ADU is typically the cheapest because it is carved from existing interior space and requires no new structure, often running about $50,000 to $150,000 in Los Angeles. A garage or basement conversion is the next most affordable at roughly $100,000 to $225,000, though hidden foundation, drainage, and ceiling-height upgrades can drive that higher.

How much does each type of ADU cost in Los Angeles?

Rough LA planning ranges are: detached ADU about $200,000 to $400,000 or more, attached ADU about $150,000 to $300,000, garage or basement conversion about $100,000 to $225,000, and JADU about $50,000 to $150,000. These are anchored to the LA average of roughly $250 to $400 per square foot and the median California ADU of about $150,000. They are estimates, not quotes.

What is a JADU and how is it different from a regular ADU?

A JADU, or junior ADU, is a unit of 500 square feet or less created within the walls of an existing single-family home. It needs an efficiency kitchen and its own entrance but can share a bathroom with the main house, requires owner-occupancy, and needs no extra parking. A regular ADU can be larger, freestanding, and does not require the owner to live on the property.

Can I build more than one ADU on my property?

On a single-family lot, California law lets you build one ADU and one JADU on the same property, so you can add two extra units. The exact mix depends on lot size, setbacks, and local rules, so a free property check is the fastest way to learn what your specific lot can support.