The ADU glossary

An accessory dwelling unit (ADU) is a second, independent home on a single-family or multifamily lot, with its own kitchen, bathroom, and entrance. In California it can be detached, attached, or converted from existing space, and can be rented separately from the main house.

A Junior ADU (JADU) is an ADU of up to 500 square feet created within the existing walls of a single-family home, often a converted bedroom. It may share a bathroom with the main house but needs its own entrance and a small kitchen. JADUs are the lowest-cost ADU type.

A detached ADU is a standalone backyard home built separate from the main house, with its own foundation, walls, and roof. In Sacramento it can reach up to 1,200 square feet and commands the highest rent and resale value of any ADU type, at roughly $250–$360 per square foot turnkey.

A garage conversion ADU turns an existing attached or detached garage into a legal dwelling. It is usually the cheapest path to a full ADU — from about $95,000 in Sacramento — because it reuses the existing slab, walls, and roof, and no replacement parking is required under California law.

A setback is the minimum required distance between a structure and the property line. Under California ADU law, detached ADUs need only a 4-foot side and rear setback — cities cannot require more — and a garage conversion staying inside the existing footprint generally needs no added setback.

Ministerial approval means an ADU permit is reviewed against objective standards only — no public hearing, no discretionary design review, no neighbor appeal. California requires jurisdictions to approve or deny a complete ADU application within 60 days, which is why ADUs have a more predictable permit path than a conventional addition.

Owner-occupancy rules require the property owner to live on site. California suspended this requirement for standard ADUs permitted on or after January 1, 2020 — so you can rent both the main house and the ADU. Junior ADUs are the exception: a JADU still requires the owner to occupy either the main house or the JADU.

Floor area ratio (FAR) is the ratio of a building's total floor area to the lot size, used to cap how much you can build. California ADU law overrides FAR and lot-coverage limits that would block at least an 800-square-foot ADU — so a tight FAR can't be used to deny a reasonably sized unit.

Lot coverage is the percentage of a lot's area covered by buildings. Like floor area ratio, California ADU law bars a jurisdiction from using lot-coverage limits to block an ADU of at least 800 square feet — so even a Sacramento lot already near its coverage cap with the main house can still add a unit.

SB 1211, effective January 1, 2025, raised the cap on detached ADUs allowed on a multifamily lot from two to as many as eight, and barred cities from requiring replacement of demolished uncovered parking. It is the most significant recent ADU law change for owners of small apartment parcels.

AB 1033 is a California law that lets cities opt in to allow ADUs to be sold separately from the main house as condominiums. Where a jurisdiction has adopted it, an ADU becomes a sellable asset rather than only a rental — but it only applies in cities that have passed the local ordinance.

Impact fees are one-time charges local governments levy on new construction to fund infrastructure. Under California law, ADUs under 750 square feet are fully exempt from impact fees — which is why many Sacramento owners deliberately size a unit just under that threshold to save thousands to over $20,000.

Mello-Roos is a special property tax levied within a Community Facilities District (CFD) to fund local infrastructure like schools and roads. It is common in newer Sacramento-region master-planned tracts — Folsom Ranch, parts of Elk Grove, Roseville, and Lincoln — and pushes the effective property-tax rate above the standard ~1–1.25%.

California law caps a contractor's down payment at $1,000 or 10% of the contract, whichever is less — so on an ADU it is $1,000. The remaining cost is paid in milestone draws released only after each phase (design, permit, foundation, framing, MEP, drywall, completion) passes inspection.

Title 24 is California's building energy-efficiency standard, part of the state building code. Every new ADU must include Title 24 compliance documentation — covering insulation, windows, HVAC, and often electrification — in its permit submittal. New detached units face the strictest requirements; garage conversions and JADUs that reuse existing structure have lighter ones.

Pre-approved or shelf-ready plans are ADU designs a jurisdiction has already vetted for code compliance. Building from a pre-approved set can shorten plan check from the 60-day state maximum to roughly 30 days, and lowers design cost. The City of Sacramento and Sacramento County both publish pre-approved ADU plan programs.

Egress is a code-required emergency escape route — typically a compliant exit door plus an emergency escape-and-rescue window in every sleeping room. It is a frequent trigger in garage and interior conversions, where existing openings often must be enlarged to meet the California building code before a room can be a legal, permitted bedroom.