ADU basics · Orange County
An ADU is a second home on a lot that already has a house.
An ADU, or accessory dwelling unit, is a permitted, self-contained second home on a lot that already has a house: its own kitchen, its own full bath, and its own entrance. California state ADU law recognizes four typologies — detached, attached, Junior ADU, and garage conversion. In Orange County, Avorino builds all four, from a garage conversion at typically $85K – $170K+ to a detached ADU at typically $245K – $440K+.
The ranges on this page are Avorino’s published Orange County figures, across the 37 cities we build in, under California General-B License #1107538.
The four kinds of ADU.
Every ADU is one of four typologies under California state ADU law. They differ in where the unit sits, how big it gets, what it costs, and how long it takes to build. Here are all four side by side.
| ADU type | What it is | Typical size | Typical cost | Build window |
|---|---|---|---|---|
| Detached ADU | Standalone unit on your property. Most rental upside, longest schedule, biggest ROI when the property has the room. | 500 – 1,200 sqft | $245K – $440K+ | 5–8+ mo |
| Attached ADU | Addition off the primary residence. Shares a wall, often shares a service line. | 450 – 1,000 sqft | $200K – $350K+ | 5–8+ mo |
| Junior ADU (JADU) | Conversion within the existing footprint. Tightest scope, kitchenette + bedroom only. | 300 – 500 sqft | $135K – $220K+ | 4–6+ mo |
| Garage conversion | Existing garage rebuilt as living space. Fastest move when the garage frame is sound. | 350 – 600 sqft | $85K – $170K+ | 4–6+ mo |
What makes a unit an ADU.
An ADU is defined by what it contains, not by how it is built: its own kitchen, its own full bath, and its own entrance. That is what separates one from a bedroom addition or a finished garage, and it is why an ADU is permitted, inspected, and recorded as a second dwelling rather than as extra square footage. California state ADU law recognizes four ways to get there — detached, attached, Junior ADU, and garage conversion — and the Junior ADU, smallest of the four at 300 – 500 sqft, does it with a kitchenette and full bath inside the existing footprint.
Which one your lot can take.
The type is usually settled by the lot rather than by preference: the setbacks, the room behind the house, and whether the garage is worth giving up. The ADU cost estimator prices a build for your city, square footage, and finish level in about a minute. The Orange County ADU permit index names how each of the 37 cities takes an ADU application. The ADU hub carries the rest: process, financing, and the cities we build in.
ADU questions, answered
- What is an ADU?
- An ADU (accessory dwelling unit) is a permitted, self-contained second home on a lot that already has a house: its own kitchen, its own full bath, and its own entrance. California state ADU law recognizes four typologies: detached (standalone, 500–1,200 sqft), attached (built off the primary residence), Junior ADU (converted inside the existing footprint), and garage conversion (an existing garage rebuilt as living space).
- What is an ADU home?
- ADU home and ADU describe the same thing: an accessory dwelling unit. People say home because the unit really is one — full-time living space with its own kitchen or kitchenette, its own full bath, and its own entrance, rather than a converted room, an office, or a shed. Avorino builds all four typologies that way.
- What is a Junior ADU (JADU)?
- A Junior ADU is a conversion inside the existing footprint of the primary house: typically an unused interior wing or bedroom, 300–500 sqft, one bedroom, with a kitchenette and full bath. It's the cheapest and tightest-scope path in Orange County, typically $135K–$220K+ over 4–6+ months, because no new foundation or exterior structure is involved.
- What is a garage conversion ADU?
- A garage conversion turns an existing garage into permitted living space: insulation, a conditioned envelope, and a full kitchen and bath, usually 350–600 sqft as a studio or one bedroom. In Orange County it typically runs $85K–$170K+ over 4–6+ months, and it's the fastest move when the existing garage frame is sound and you're ready to give up the parking.
- What is the difference between a detached ADU and an attached ADU?
- A detached ADU is a standalone unit on your property, typically 500 – 1,200 sqft at $245K – $440K+ over 5–8+ mo. It carries the most rental upside and the longest schedule, and it needs the room on the lot. An attached ADU is an addition off the primary residence: it shares a structural wall, and often a utility service line, at typically 450 – 1,000 sqft and $200K – $350K+ over 5–8+ mo. Attached is the answer when the lot is tight on setbacks but the house has a wall to extend off.
- What do ADUs typically cost in Orange County?
- Detached ADUs typically run $245K–$440K+. Attached ADUs $200K–$350K+. Junior ADUs $135K–$220K+. Garage conversions $85K–$170K+. Use the Avorino cost estimator for a calibrated range on your specific project.
- What are typical ADU build windows in Orange County?
- Detached: 5–8+ months. Attached: 5–8+ months. Junior ADU: 4–6+ months. Garage conversion: 4–6+ months. Windows vary with city, plan-check timing, and finish-level decisions.
- What types of ADUs do you build in Orange County?
- Detached ADUs, attached ADUs, Junior ADUs, and garage conversions, every permitted typology under California state ADU law.
See what your lot can take.
Send us the address and the ADU you have in mind. Avorino handles design, structural engineering, Title 24 calculations, and permitting in-house, on one fixed-price contract, across 37 Orange County cities.