ADU paperwork is full of short terms. This page explains the ones you will meet. Where a term has a legal definition, we point to the source. Statute definitions are in Government Code section 66313, part of the ADU law (sections 66310 to 66342, renumbered in 2024 from the former section 65852.2). Definitions can change, so check the current text.
LA ADU Guide is an information site, not a design, building or lending business.
The units
ADU (accessory dwelling unit). CSLB describes it as "a small house or apartment located on the same residential lot as an existing home." It can be detached, attached to the house, or converted from a space such as a garage or basement. See ADU vs JADU vs garage conversion.
Detached ADU. A separate building on the lot, such as a backyard cottage.
Attached ADU. An ADU that shares a wall with the main house, such as an addition.
Conversion ADU. An ADU made from existing space, such as a garage, basement or storage room, rather than new floor area.
JADU (junior accessory dwelling unit). A small unit inside an existing or proposed single-family home. Summaries of state law describe it as no more than 500 square feet and requiring an efficiency kitchen. Recent legislation has changed parts of the JADU definition, so check HCD and the current text of section 66313 for the exact wording.
Efficiency kitchen. A compact kitchen. Local codes generally describe it as a cooking facility with appliances plus a food preparation counter and storage. The exact statutory wording is in section 66313.
Efficiency unit. A small dwelling unit. State law points to Health and Safety Code section 17958.1 for its meaning.
Primary dwelling. The main house on the lot.
Multifamily ADU. An ADU on a lot that already has multifamily housing. State law allows these in certain circumstances. See ADU rules in California.
Construction types
Site-built. Constructed on your lot from start to finish.
Prefab or factory-built. Built mostly off site, then delivered.
Modular. Factory-built in sections and assembled on a foundation. Usually permitted by the local building department.
Manufactured home. Built to a federal HUD standard. CSLB notes that permits for a manufactured ADU may come from the state Department of Housing and Community Development.
Pre-approved plan (standard plan). A design already reviewed by a building department. LADBS calls these "privately owned, pre-approved" designs. See prefab and pre-approved plans.
Zoning and site terms
Zoning. The city or county rules about what can be built where.
Setback. The required distance between a building and a lot line. State law limits how much setback a city can require for certain ADUs. See ADU rules in California.
Lot coverage. The share of the lot that buildings may cover.
Floor area ratio (FAR). Building floor area divided by lot area. Cities use it to limit size.
Height limit. The maximum building height allowed.
Easement. A legal right for someone else, such as a utility, to use part of your lot. It can block building in that strip.
Overlay zone. An extra layer of rules on top of base zoning, such as hillside, coastal or historic overlays.
Objective standards. Measurable rules, like a height in feet, as opposed to subjective ones, like "compatible character." State law requires ADU standards to be objective.
Passageway. A path from the street to an entrance of the unit. Local codes often describe it as unobstructed and open to the sky.
Tandem parking. Two or more cars parked on a driveway lined up one behind another.
Fire Hazard Severity Zone (FHSZ). A map area with higher wildfire risk, drawn by CAL FIRE. Extra building requirements apply. See ADUs in fire hazard zones.
Permit and review terms
Ministerial review. A check of an application against fixed standards, with no public hearing and no discretion to deny a compliant project.
Plan check. The building department's review of your drawings for code compliance.
Corrections. The list of changes the reviewer asks for. It is common to get one. See the permit process.
Deemed complete or deemed approved. Status that applies if the city misses a state deadline. SB 543 (effective 2026) changed these deadlines. Check Government Code section 66317 for the current rule.
Tolling. Pausing a review clock, for example while an applicant requests a delay.
ePlanLA. The LADBS online portal for submitting plans and tracking applications.
LADBS. The Los Angeles Department of Building and Safety.
HCD. The California Department of Housing and Community Development, which publishes the ADU handbook and reviews city ADU ordinances.
Certificate of Occupancy. The document confirming the finished building passed final inspection and may be lived in.
Unpermitted ADU. A unit built without permits. State law includes a process for legalizing some of them. Ask your building department.
Costs and money terms
Impact fee. A charge to offset the effect of new development on public services. See impact fees and utility connections.
Utility connection fee. A charge by a water, sewer or power provider to connect the unit.
Valuation. The estimated construction cost LADBS uses to compute permit fees.
Property tax reassessment. A change in assessed value after new construction. See rental income and property tax.
Home improvement contract. A written contract for work on a residence. CSLB says ADU construction falls under it. See hiring an ADU builder.
Down payment. An up-front payment. California law caps it at $1,000 or 10 percent of the contract price, whichever is less.
Progress payment. A payment tied to finished work or delivered materials.
Mobilization. The start-up phase when the builder sets up the site. CSLB's sample schedule uses it as the first payment stage.
Change order. A written change to the scope or price of the contract.
Trades and licenses
CSLB. The Contractors State License Board, which licenses California contractors.
B license. General Building Contractor, which can build or install an ADU.
C-47 license. General Manufactured Housing Contractor, which can install a manufactured ADU.
MEP. Mechanical, electrical and plumbing, the three main systems trades.
Subcontractor. A specialist hired by the main builder for one trade.
Punch list. The final list of small items to fix before the job is complete.
Key numbers
| Term | Number | Where it is covered |
|---|---|---|
| JADU size | No more than 500 sq ft | ADU vs JADU vs garage conversion |
| Impact fee exemption | ADUs of 750 sq ft or less | Impact fees |
| Review clock | 60 days (section 66317) | Permit process |
| Down payment cap | $1,000 or 10 percent of the contract price, whichever is less | Hiring a builder |
Where to go next
Start with ADU rules in California for what you can build, then see the permit process.