ADU Learning Center.

AB 2533

California Assembly Bill 2533 (effective 2025). Establishes a voluntary amnesty pathway allowing homeowners to legalize unpermitted ADUs by bringing them up to current safety standards. Limits the scope of inspections to life-safety items rather than full code compliance, making legalization more practical and affordable.

Accessory Dwelling Unit (ADU)

A secondary housing unit on the same parcel as a primary single-family or multi-family home. ADUs can be detached (a separate structure), attached (connected to the main home), or a conversion of an existing space such as a garage or basement. California state law (AB 2221, AB 976, CA Gov Code §65852.2) sets minimum rights for ADU construction statewide.

ADU Standard Plan Program

A City of Los Angeles program that offers pre-approved ADU design plans. Using a standard plan can shorten the permit review period by 60–90 days because the structural and architectural drawings have already passed city review. Applicable plans are available through LADBS.

Attached ADU

An ADU that shares at least one wall with the primary dwelling. California law allows attached ADUs up to 50% of the primary dwelling's square footage or 1,200 sq ft, whichever is less. Height limits typically match those of the primary structure.

Certificate of Occupancy (CO)

A document issued by the local building authority confirming that a building meets all applicable codes and is safe to occupy. For ADUs, the CO is the final step in the permit process — issued after all inspections pass. An ADU cannot be legally rented or occupied without a CO.

Coastal Development Permit (CDP)

A permit required by the California Coastal Commission for development within the coastal zone. Properties west of the Commission's jurisdiction line — including parts of Santa Monica, Venice, Malibu, and Pacific Palisades — require a CDP in addition to a standard building permit. CDPs add 3–9 months to the timeline.

Detached ADU

A freestanding accessory dwelling unit that does not share walls with the primary home. California state law allows detached ADUs up to 1,200 sq ft. Detached ADUs must maintain a 4 ft side and rear setback under state minimums, though some cities impose additional requirements.

FAR (Floor Area Ratio)

A zoning measurement that expresses the total floor area of all buildings on a lot as a ratio to the lot's land area. For example, an FAR of 0.5 on a 5,000 sq ft lot allows up to 2,500 sq ft of total building area. ADU construction that exceeds the FAR may trigger a variance or be subject to additional review in some jurisdictions.

Fire Hazard Severity Zone (FHSZ)

A CAL FIRE–designated zone indicating elevated wildfire risk. Properties in High or Very High FHSZ areas — common in LA hillsides — require fire-resistant construction materials, ember-resistant vents, and in some cases, automatic sprinklers for new ADUs. This adds cost and may require engineering review.

Garage Conversion ADU

An ADU created by converting an attached or detached garage into livable space. Under California law, garage conversions are not required to replace the eliminated parking. They often qualify for streamlined permitting because they use an existing structure.

HCOZ (Hillside Construction Ordinance Zone)

A Los Angeles Municipal Code overlay that imposes additional design and structural requirements on properties in hillside areas. HCOZ regulations address grading, slope stability, drainage, and access. ADUs on HCOZ-designated parcels typically require a geotechnical report and more extensive plan review.

JADU (Junior Accessory Dwelling Unit)

A unit of no more than 500 sq ft created entirely within the walls of an existing primary home, including its attached garage. JADUs must include a separate entrance and an efficiency kitchen. They are exempt from most parking and setback requirements. Only one JADU is allowed per single-family parcel, though one JADU and one ADU may coexist on the same lot.

Ministerial Approval

A permit approval that does not require discretionary review or a public hearing — the jurisdiction must approve it if the application meets objective standards. California ADU law mandates ministerial approval for most ADUs, preventing cities from using design review, neighborhood input, or CEQA processes to block compliant applications.

Owner-Occupancy Requirement

A historical requirement that the property owner live on-site to build or rent an ADU. California AB 976 (effective January 1, 2023) removed owner-occupancy requirements for ADUs permitted before January 1, 2025. As of 2025, no California jurisdiction may require owner-occupancy as a condition of ADU approval.

Permit Valuation

The estimated construction cost used by a jurisdiction to calculate permit fees. Permit valuation is set by the applicant or estimated by the building department based on square footage and construction type. It does not reflect the total project cost — design, soft costs, and site work are usually excluded.

R1 Zoning

Single-Family Residential zoning, the most common zone type for ADU projects. R1 parcels are eligible for one ADU and one JADU under California state law regardless of any local restrictions that would otherwise prohibit them. R1 lots still must comply with setback, height, and lot coverage rules.

Rent Stabilization Ordinance (RSO)

A Los Angeles city ordinance that limits rent increases and protects tenants from eviction on older rental units. Newly constructed ADUs are generally exempt from RSO, meaning owners can set market-rate rents. However, if an ADU is created through conversion of an existing unit that was RSO-covered, the converted unit may retain RSO status.

SB 9

California Senate Bill 9 (effective January 1, 2022). Allows homeowners in single-family zones to split their lot into two parcels or build up to two housing units per lot, or both. SB 9 creates a pathway to four units on a single-family lot (two per parcel after a lot split) in most California cities.

SB 1211

California Senate Bill 1211 (effective January 1, 2025). Requires that multifamily properties be allowed to build one detached ADU per existing unit, up to a maximum of eight ADUs per lot. Significantly expands ADU capacity for apartment owners and investors.

Setback

The minimum required distance between a structure and a property line (or another structure). California state law sets a 4 ft minimum side and rear setback for detached ADUs. Some cities impose larger setbacks, and properties in fire hazard zones or hillside ordinance areas may have additional requirements. Front setbacks are generally not enforced for ADU conversions.

ADU rules and California state law change frequently. This glossary reflects rules current as of May 2026. Always verify with your local building department before submitting.