The ADU vocabulary, term by term.

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).

Example: An accessory dwelling unit — also called a granny flat, casita or backyard cottage — is a self-contained home on your existing lot: detached, attached, a Junior ADU (JADU), or a garage conversion.

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 tightest-scope path in Orange County, typically $135K–$220K+ over 4–6+ months, because no new foundation or exterior structure is involved.

Typical size

300 – 500 sqft

Typical cost

$135K – $220K+

Build window

4–6+ mo

Example: Junior ADU (JADU) within the primary footprint: bedroom + kitchenette, with its own exterior entrance.

Standalone unit on your property. Most rental upside, longest schedule, biggest ROI when the property has the room.

Typical size

500 – 1,200 sqft

Typical cost

$245K – $440K+

Build window

5–8+ mo

Example: New foundation, full kitchen + bath, independent utilities.

Addition off the primary residence. Shares a wall, often shares a service line.

Typical size

450 – 1,000 sqft

Typical cost

$200K – $350K+

Build window

5–8+ mo

Example: Extension connected to your home with its own private entrance. Shares a wall for cost savings while maintaining complete independence.

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.

Typical size

350 – 600 sqft

Typical cost

$85K – $170K+

Build window

4–6+ mo

A guesthouse under Sec. 7-9-91 cannot be rented at all and cannot contain a kitchen, which is the distinction owners most often get wrong.

Example: 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.

Government Code section 66314(d)(7) provides that no setback is required for an existing living area or accessory structure being converted. A new detached ADU, by contrast, can be required to sit no more than four feet from the side and rear lot lines. Converting what is already there is the way around a tight lot.

Example: Setbacks, easements, utility lines, neighbor friction reviewed together. We tell you what your vision can carry before drawings.

16 ft for a detached ADU (18 ft within a half-mile walk of major transit or on a lot with a multistory multifamily building). An attached ADU may reach 25 ft or the zone's height limit, whichever is lower.

Example: Units of 750 square feet or less skip the city's development impact fees, heights run 16 feet detached and up to 25 attached, and the standard state protections apply.

California state ADU law preempts most city setbacks (4-ft minimum side + rear) and starts a 60-day ministerial clock on a complete application (Gov. Code §66317), so each correction round delays when that clock begins.

Example: An ADU over the 16-ft height cap, or one that deviates from Chapter 25.17's objective standards, loses ministerial status and goes to design review — staying inside the standards is the schedule.

The city reviews your plans against current building codes, zoning, and setbacks, and usually returns several rounds of corrections. We carry that correspondence with the engineer and keep you posted.

Typical turnaround

4–6+ weeks

Example: A 4–6+ week plan-check turnaround is typical when the package is complete at intake. The state's 60-day ministerial clock starts once the application is complete, so correction rounds are what actually set the calendar.

Title 24 is California's Building Energy Efficiency Standards (Title 24, Part 6 of the California Code of Regulations): every ADU permit set carries an energy compliance report showing the design meets them.

The city runs a Pre-approved ADU Standard Plan program — a city-vetted design that trims drawing costs and review time for lots that fit it — alongside the standard ministerial path.

Example: ADU Express: eligible single-family lots using a city pre-approved detached plan can clear review in about 1–3 days versus the ~60-day standard.

A junior ADU is the exception, and a narrower one than most sites state — §66333(b) requires owner-occupancy only “If the junior accessory dwelling unit has shared sanitation facilities with the existing structure,” and even then the owner may live in either portion; a junior ADU with its own sanitation carries no such requirement.

Before the building permit issues, the city records a deed restriction prohibiting short-term rental of the unit (and its separate sale).

Example: Before the ADU permit issues, Mission Viejo records a city-prepared deed restriction (no short-term rental, no separate sale, JADU owner-occupancy) — a step and a signing homeowners don't anticipate.

For larger lots, build multiple ADUs or convert existing structures into multi-unit properties. SB 9 lot splits and AB 68 multi-ADU provisions create new possibilities.

Example: Avorino runs SB-9 urban-lot-split applications through OC city planning departments, then builds the dual residences as a single coordinated schedule. We've executed this pattern in Anaheim, Costa Mesa, and Garden Grove.

The CalHFA ADU Grant Program reimbursed up to $40,000 of pre-development and non-recurring closing costs, but its funding was fully allocated in December 2023 and it is not accepting new applications.

Example: Many ADU websites still list it as though it were open. Check CalHFA directly for any future round rather than budgeting around it.

Design-build is a project-delivery method where one company handles both the design (architecture and engineering) and the construction under a single contract. Instead of hiring an architect and a contractor separately and managing the handoff yourself, you work with one point of accountability from the first concept through the final walkthrough.

Design-bid-build is the traditional, sequential path — you design a project fully, put it out to bid, then build it. Design-build overlaps those phases under one roof and one contract. The payoff is a budget that's known before you break ground, faster timelines, fewer change orders, and a single point of responsibility instead of an architect and a builder pointing at each other.

The fixed price comes from a site walk and engineered drawings, and Avorino contracts fixed-price so the number you sign is the number you build at.

Example: Avorino works on fixed-price design-build contracts that include architectural plans, structural engineering, Title 24 energy calculations, city permits and plan-check, and construction — so the range reflects a turnkey project, not just the build.