For California Homeowners
Thinking About An ADU In California?
An accessory dwelling unit is a second, smaller home on your lot: a garage conversion, a backyard cottage, or a unit built into the house. Start with the costs, the state rules, and the permit steps. Share your project only if you want builders to reach out.
What Counts As An ADU
California law defines an accessory dwelling unit as an attached or detached residential unit with complete independent living facilities for one or more people, on the same lot as a primary home. A junior ADU, or JADU, is a smaller unit of no more than 500 square feet built inside a single-family home. The state housing department explains the definitions in its ADU Handbook (March 2026).
Where To Start
Costs
Published ranges and what moves them. See ADU Cost In California.
State Rules
What your city must allow, in plain words. See California ADU Rules.
Money
The main ways homeowners pay for an ADU. See ADU Financing.
Before You Talk To Anyone
- Find your lot size, zoning, and whether you are in a hillside, fire, or coastal area.
- Decide what the unit is for: family, rental, or both.
- Check whether your city publishes ready-made ADU plans.
- Set a budget that includes design, permits, utility work, and a cushion.
Guides
ADU Cost In California
Published cost figures for California ADUs: a statewide owner survey, regional medians, and ranges for garage conversions and detached units, with what changes the number.
California ADU Rules
A plain language summary of California ADU law: unit combinations, size and height limits, setbacks, fees, parking, and owner occupancy, with links to the statutes and HCD guidance.
Garage Conversion To ADU
How a garage becomes an ADU in California: what state law says about setbacks, parking, utility connections, and fees, a sourced cost range, and what to check first.
Detached ADU
What California allows for a detached backyard ADU: the 800 square foot minimum, height limits, setbacks, utility connections, parking, and a sourced cost range.
Junior ADUs (JADUs)
California junior ADU rules in plain words: the 500 square foot limit, shared bathrooms, owner occupancy, rental terms, parking, fire sprinklers, and fees.
ADU Financing
The main ways California homeowners pay for an ADU: cash, home equity loans, renovation and construction loans, and agency programs. No rates quoted.
ADU Permits And Timeline
The permit steps for a California ADU and the review deadlines set by state law, plus how pre-approved plans and appeals work. Build time depends on your project.
Rental Rules And Income
What California law says about renting an ADU: minimum rental terms, owner occupancy, JADU limits, and how lenders may treat rental income. No income promises.
Prefab Versus Site-Built ADUs
How factory-built and site-built ADUs differ in process, site work, permits, and the questions to ask. No prices claimed for either, with links to state guidance.
Questions To Ask An ADU Builder
A checklist of questions for any California ADU builder: license, insurance, scope, price structure, schedule, payments, and permits. We do not rank or endorse builders.
Your ADU Company Closed. What Now?
What to do if your ADU builder or prefab company closed, was sold, or stopped answering: check the license and bond, file a claim, secure your plans and permit, and find a builder to finish.
Garage Conversions In Oakland
How a garage conversion works in Oakland: the Category One limits, the two-step permit process, what state law says about replacement parking, and what to check in fire zones.
ADUs In Los Angeles
What to know about building an ADU in Los Angeles: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
ADUs In San Diego
What to know about building an ADU in San Diego: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
ADUs In San Jose
What to know about building an ADU in San Jose: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
ADUs In Sacramento
What to know about building an ADU in Sacramento: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
ADUs In Oakland
What to know about building an ADU in Oakland: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
ADUs In Orange County
What to know about building an ADU in Orange County: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
ADUs In Fresno
What to know about building an ADU in Fresno: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
ADUs In Roseville
What to know about building an ADU in Roseville: the local pre-approved plan program, a regional cost reference, and what to check at your planning counter.
Tell Us About Your Project
Three short steps, about a minute. Only the first step is required before your contact details.
Only one builder sees your details, and we tell you who it is before they contact you.
Step 1 Of 3
Common Questions
What is the difference between an ADU and a JADU?
An ADU can be attached, detached, or converted from existing space. A JADU is limited to 500 square feet and sits inside a single-family home. See Junior ADUs.
Does my city have to approve my ADU?
State law requires cities and counties to approve or deny a complete application within set time limits, and limits what they can require. See California ADU Rules and Permits And Timeline.
Do I have to live on the property?
For most ADUs, a city cannot require the owner to live on site. JADUs with shared bathrooms are different. See Rental Rules And Income.
How much does an ADU cost?
A statewide owner survey found a median of about $150,000, with wide variation by region and type. See ADU Cost In California.
Do you build or recommend builders?
No. We publish guides. We do not rank or endorse builders. See Questions To Ask An ADU Builder.
What happens if I fill out the form?
Your details are kept by BTTRYZN LLC and shared only with the one builder you are matched with, and we tell you who it is first. See the consent details.