Contractors, planning departments, and permit paperwork all use ADU-specific vocabulary that most homeowners have never needed before. Misunderstanding one of these terms early on — confusing a JADU with a full ADU, for example, or not knowing what a setback requirement means for your lot — can lead to real confusion later in the process. This glossary covers the terms that come up most often.
ADU (Accessory Dwelling Unit)
A secondary, independent living space on a residential property, with its own entrance, kitchen, and bathroom.
JADU (Junior Accessory Dwelling Unit)
A smaller secondary unit, generally created within the existing walls of the primary home, that may share certain systems (such as a bathroom) with the main house, following distinct size and permit rules from a full ADU.
Setback
The required minimum distance between a structure and a property line, set by local zoning code.
FAR (Floor Area Ratio)
A zoning measurement comparing a structure's total floor area to the size of the lot it sits on, used by some jurisdictions to limit overall building bulk.
Ministerial review
A staff-level permit approval process based on objective standards, without a discretionary public hearing — the review path California's ADU law generally requires for qualifying projects.
Detached ADU
A standalone secondary structure, separate from the primary residence.
Attached ADU
A secondary unit built as an addition that shares at least one wall with the primary residence.
Conversion ADU
An ADU created by converting existing space, most commonly a garage, into livable square footage.
Site plan
A drawing showing a property's lot lines, existing structures, and the proposed new structure's location, used during permit review.
Certificate of occupancy
Official confirmation from the local building department that a structure has passed final inspection and may be legally occupied.
Terms not covered here
This glossary focuses on the terms most homeowners actually run into during planning and permitting. If a contractor or your local planning department uses a term you do not recognize, it is always reasonable to ask them to explain it in plain language — a good contractor will not mind the question.
For deeper explanations of several of these terms — particularly the ADU vs. JADU distinction and the permit process — see our full ADU basics guide and permit process guide.
Knowing this vocabulary will not build your ADU for you, but it will help you follow a plan set, a permit comment letter, or a contractor's proposal without needing everything translated line by line.
Have a question about your specific project?
Call (877) 300-2747 or request a match, and mention you have questions related to “ADU Glossary” — we will route you to a licensed contractor who can speak to it directly.