A homeowner’s starting point · California
ADU Info & Regulations
Understand the possibilities before you choose a plan. A clear introduction to ADUs, California’s framework and the local checks that shape your project.
Reviewed October 6, 2026. General guidance; confirm current requirements with the permitting agency for your property.
01 · The basics
What does ADU mean?
An accessory dwelling unit is a second home on a property with a primary residence. It has its own living, sleeping, cooking and bathroom facilities. People also call it a backyard home, granny flat or in-law unit.
Detached or attached
A detached ADU stands apart from the main home. An attached ADU shares a wall with the residence while providing an independent living space.
Conversion or junior ADU
A conversion repurposes existing space, such as a garage. A JADU is a smaller unit, up to 500 square feet, within a single-family residence; it may share a bathroom.
Read more: Los Angeles ADU introduction · California HCD handbook
02 · The statewide framework
California ADU rules, at a glance
State law creates pathways for ADUs on qualifying residential properties. The applicable pathway and local standards depend on your site and proposed unit.
Size & setbacks
State law protects qualifying 800-square-foot ADUs from certain local development limits. Side and rear setbacks generally cannot exceed four feet; coastal requirements can differ. Larger units follow additional standards.
Height & placement
Height allowances vary by unit type and location. Transit proximity and attachment to the main home can matter. Verify the envelope before assuming a second story fits.
Parking
Many ADUs qualify for parking exemptions, including those within a half-mile walking distance of public transit. Coastal conditions and local programs need separate review.
Permit review
Qualifying complete applications generally have a 60-day approval-or-denial period. That is not a guaranteed total project timeline; completeness, exceptions and other approvals matter.
Source: HCD ADU Handbook, March 2026 — size, setbacks, height, parking and permitting sections.
What still needs a property-specific check?
Property boundaries, easements, existing structures, utility routes, access, drainage and applicable building requirements all affect the design. A satellite placement preview is a starting point; it does not confirm an allowable building area or permit eligibility.
03 · Local context
San Diego & Los Angeles areas
Your mailing address does not always identify your permitting agency. City rules apply within city boundaries; county or another city’s standards may apply elsewhere in the region.
San Diego
The City of San Diego requires a building permit for an ADU or JADU. Its guidance generally lists ADUs up to 1,200 square feet and addresses coastal approvals, parking exceptions and additional-unit programs.
Check the coastal overlay and Beach Impact Area early. Bonus or affordable ADUs have additional conditions; do not assume the same unit count or parking rules for every lot.
Los Angeles
The City of Los Angeles applies state ADU law alongside its local development standards. Start with LADBS’s ADU resources and the current ADU/JADU bulletin.
Its Approved Standard Plans Program can simplify plan review, but an approved design still requires property-specific zoning and foundation review. Our studio’s model packages are design starting points; they are not represented as city-preapproved plans.
These are regional starting points, not a directory of every jurisdiction. Use the agency responsible for the actual parcel.
04 · From information to a plan
Start with your property. Then your design.
1. Establish the basics
Bring your address, available property documents and goals for the space to a consultation.
2. Explore a test fit
Compare a selected model or a bespoke layout against the site information and the applicable requirements.
3. Develop the drawings
Resolve the design, coordinate required consultants and prepare site-specific documents for permit review.