California ADU questions, answered

An accessory dwelling unit (ADU) is a small, self-contained home on the same lot as your main house — a backyard cottage, a converted garage, or an addition with its own kitchen, bathroom and entrance. California treats ADUs as a special category with fast-tracked permitting under state law.

No. Since 2017, state law has stripped cities of most discretionary review for ADUs. A compliant ADU must be approved ministerially — by right — if your lot is in a residential zone. Cities can't require owner-occupancy for most ADUs, can't impose minimum lot sizes, and can't charge impact fees on units under 750 sq ft.

State law guarantees you can build at least 800 sq ft with 4-foot side and rear setbacks on any residential lot. Many cities allow up to 1,200 sq ft for detached ADUs. Junior ADUs (inside your existing home) can be up to 500 sq ft.

Owner-occupancy is banned for most ADUs built after January 2020. Exceptions apply to junior ADUs in some cases and to newly built homes. Your city's planning department confirms the current rule for your address.

Yes. Once the ADU has its certificate of occupancy, you can rent out either the main house, the ADU, or both — no owner-occupancy requirement for most new ADUs.

On single-family lots, you can typically add one detached ADU plus one junior ADU inside the existing home. Multi-family lots can qualify for multiple units — up to 8 detached ADUs on large properties under recent state rules.

Statewide, most ADUs land between $150k and $420k all-in. Garage conversions start near $150k, standard detached 1-bedroom units run $220k–$320k, and custom detached 2-bedroom units with site work can exceed $400k. Junior ADUs are the most affordable at roughly $90k–$160k.

Site access, soil, slope, utility distance and finish level move the number more than square footage does. A flat lot with utilities at the property line and straightforward design sits at the low end; hillside lots, long trenching runs and custom kitchens sit at the high end.

Plan check and building permit fees typically run $3k–$8k depending on the city. Impact fees are waived for ADUs under 750 sq ft; larger units pay a proportionate share. Utility connection fees vary widely by provider — we estimate them for you during the feasibility check.

Common routes include cash-out refinance, home equity line of credit (HELOC), construction loans, and FHA 203(k) renovation loans. California also offers ADU grant programs through CalHFA for income-qualified homeowners. Your lender confirms which products fit your situation.

It depends on your market's rents and your all-in cost. In most California metros we see payback windows of 8–14 years from rental income alone, faster when the ADU replaces a need you'd otherwise pay for — like housing for family or eliminating a commute.

Plan-only projects take 6–12 weeks to permit. A full garage conversion typically takes 4–7 months from first call to move-in; a detached ADU runs 9–14 months including design and permitting. Small cities often permit faster than large ones.

State law requires cities to act on complete ADU applications within 60 days. In practice, most California plan checks complete in 4–14 weeks depending on the city and how complete the plan set is — which is why our in-house drafting team focuses on first-pass completeness.

A plan reviewer checks your drawings against building, fire, zoning and energy codes. They issue correction notices if anything's missing. We respond to every notice — usually in one or two review cycles — until your permit is issued.

Typical sequence: foundation, framing, rough electrical, rough plumbing, rough mechanical, insulation, then final inspections for a certificate of occupancy. Our project manager schedules each one so the build never waits on an inspector.

No. ADU construction happens outside or within the converted space; most clients stay in their home the entire time. We coordinate deliveries, dust control and utility shutoffs to minimize disruption.

California reassesses only the new construction's value as an addition — typically 1.1–1.5% of the ADU's build cost per year. Your existing home's assessment is untouched.

Usually yes, modestly — most carriers treat an ADU as added dwelling coverage. Some require a rental rider if you lease it out. We recommend quoting your carrier before construction starts.

New detached ADUs generally need solar under California's energy code; garage conversions and JADUs usually don't because they reuse existing building space. Your plan set will spell out exactly what's required for your project.

Yes — after final inspection we can connect you with local property managers and provide a rent recommendation based on current comparable units in your city.

No. We're California ADU specialists — design, permitting and construction across the state's cities, with deep experience in LA, San Diego, Orange, Riverside, San Bernardino, Santa Clara, Alameda and Sacramento counties, plus the Central Coast, Central Valley and beyond.