ADU glossary: terms and acronyms

Definitions from state laws and agency guidance · Last reviewed October 10, 2026

A

Accessory dwelling unit (ADU)

Also called: granny flat, in-law unit, backyard cottage, secondary unit

An extra home on the same lot as a main home. California law defines an ADU as an attached or detached unit that "provides complete, independent living facilities for one or more persons," with permanent provisions for living, sleeping, eating, cooking and sanitation; it also counts an efficiency unit and a manufactured home. Washington defines it as a dwelling unit on the same lot as a house, duplex, triplex, townhome or other housing unit, and Arizona says an ADU has its own sleeping and sanitation facilities and "may include" its own kitchen. California's housing agency says ADUs "have been known by many names: granny flats, in-law units, backyard cottages, secondary units and more." See what is an ADU. [1][2][3][4]

Amnesty (legalizing an unpermitted ADU)

Also called: unpermitted ADU, legalization

A program or rule that lets you legalize a unit built without permits. In California, a city may not deny a permit for an unpermitted ADU built before January 1, 2020, just because it breaks building standards or ADU rules, unless the city finds that fixing the problem is needed to protect health and safety or the building is substandard. Cities must tell homeowners they may get a confidential third-party inspection from a licensed contractor before applying. Berkeley, for example, runs a pilot amnesty program to inspect and legalize units such as a converted garage or in-law unit built without proper permits. [1][5]

Area median income (AMI)

The median income for a region. Affordable housing rules state income limits as a percentage of it: Arizona's ADU law, for example, counts a unit as "restricted-affordable" when, through a deed restriction or an agreement with the city, it is rented to households earning up to 80% of area median income. HUD sets income limits for its housing programs from median family income estimates for each metropolitan area and each non-metropolitan county. [3][6]

Attached ADU (AADU)

An ADU that is part of, or attached to, the main home. Washington law defines it as an ADU "located within or attached to" a house, duplex, triplex, townhome or other housing unit. Under California law, an ADU can be attached to or inside the main home, including an attached garage or storage area. Seattle calls a permitted unit in the house an attached accessory dwelling unit (AADU). [1][2][7]

B

By right

Also called: as of right, permitted use

Approval without a discretionary zoning decision. Montana defines "by right" as the ability to be approved without a public hearing; a variance, conditional use permit, special permit or special exception; or other discretionary zoning action beyond checking that a site plan meets the zoning rules. Massachusetts uses "as of right" for development that can go ahead without a special permit, variance, zoning amendment, waiver or other discretionary zoning approval. Arizona's ADU law calls the same idea a "permitted use." [3][8][9]

C

California Environmental Quality Act (CEQA)

California's environmental review law. ADUs and junior ADUs approved ministerially are exempt from CEQA, and because SB 9 approvals are ministerial, CEQA does not apply to them either. A discretionary coastal development permit for an ADU may still be subject to CEQA. [1][10]

Certificate of occupancy

In California, the document a local building department issues certifying that a newly built home has been inspected for compliance with the state building code and local ordinances. California requires you to get a certificate of occupancy from the city or county before anyone lives in an ADU or junior ADU. In Los Angeles, other departments' clearances must be approved before the permit and certificate of occupancy are issued. [1][11]

Coastal development permit (CDP)

A permit that development in California's coastal zone may need, processed at the same time as the ADU application. Where the local coastal program covers ADUs, the city must approve or deny a coastal development permit for an ADU within 60 days of a complete application when there is an existing main home, and it doesn't have to hold a public hearing. Where the city has no certified local coastal program, the California Coastal Commission decides within 60 days. See the ADU permit process. [1]

Coastal zone

In California, the coastal area where the California Coastal Act applies. State ADU law applies in the coastal zone too, but it does not "alter or lessen the effect or application of Coastal Act resource protection policies." An ADU there may also need a [coastal development permit](#coastal-development-permit). [1]

Completeness review

Also called: completeness notice, completeness determination

The first check of your permit application: is everything there? In California, the permitting agency must tell you in writing within 15 business days whether your ADU application is complete. If it is not, the notice must list the missing items and say how to fix them, and you can appeal. If the agency misses the 15-day deadline, the application is "deemed complete." In Minnesota, the 60-day decision clock restarts for missing information only if the agency tells you within 15 business days what is missing. [1][12]

Conditional use permit

Also called: CUP

Approval for a use the zoning code lists as "conditional," granted when the applicant shows it meets the standards in the ordinance. Minnesota law, for example, lets a city designate certain developments as conditional uses, approved by the governing body or another designated authority when the applicant shows the standards and criteria will be satisfied. Arizona and Montana define by-right ADU approval as approval without a conditional use permit. [3][8][13]

Connection fee and capacity charge

Also called: capacity charge, utility connection fee

Charges from a city, special district or water company for utility service such as water and sewer. California law treats them separately from impact fees. ADUs made from existing space and junior ADUs can't be treated as a new residential use for these charges unless they are built along with a new home, and for other ADUs the charge must be proportionate to the ADU's burden, based on its square footage or drainage fixture units compared with the main home. See ADU costs. [1]

Converted ADU

An ADU made from existing space instead of new construction, such as part of the house, a garage or another accessory structure. In California, one converted ADU per single-family lot must be allowed; it needs exterior access and setbacks for fire and safety but not the four-foot side and rear setbacks, and one made from an accessory structure may add up to 150 square feet for an entry or stairs. See garage conversions. [1]

Covenants, conditions and restrictions (CC&Rs)

Rules that govern the use of property in a community, such as one run by a homeowners association. In California, CC&Rs that effectively prohibit or unreasonably restrict building or using an ADU or junior ADU on a lot zoned for single-family homes are void and unenforceable. "Reasonable restrictions" may not include fees or other financial requirements. See also [homeowners association](#hoa). [1]

D

Deed restriction

A restriction recorded against a property. In California, a city cannot put an affordable housing deed restriction on an ADU, but a city's junior ADU ordinance must require a recorded deed restriction that bars selling the junior ADU separately from the house and limits its size and features to what state law allows. Some programs use them to keep rents affordable: Arizona counts a unit as "restricted-affordable" when, through a deed restriction or an agreement with the city, it is rented to households earning up to 80% of area median income. [1][3]

Deemed approved

Approved automatically because the agency missed its deadline. In California, a complete ADU or junior ADU application is deemed approved if the city has not approved or denied it within 60 days. In Minnesota, an agency's failure to deny a zoning request within 60 days "is approval of the request." See how fast cities must decide. [1][12]

Department of Housing and Community Development (HCD)

California's state housing department. HCD writes the state's ADU Handbook, and its Housing Accountability Unit holds cities accountable for complying with state housing laws, including state ADU law; violations can lead to referral to the California Attorney General. See California. [1]

Department of Housing and Urban Development (HUD)

The federal housing department. The [Federal Housing Administration](#fha) is part of HUD, and HUD sets the income limits used by its housing assistance programs. [6][14]

Department of Land Conservation and Development (DLCD)

An Oregon state department. Its policy board, the Land Conservation and Development Commission, oversees statewide land-use goals, local compliance and coastal planning, and DLCD publishes statewide housing planning guidance for local communities. Senate Bill 1537 (2024), which set up Oregon's [Housing Accountability and Production Office](#hapo), tasked DLCD and the state Building Codes Division with addressing Oregon's housing needs. See Oregon. [15][16][17]

Department of Local Affairs (DOLA)

The Colorado state department that carries out parts of Colorado's ADU law, HB24-1152. The law names it as the department that certifies local governments as "Accessory Dwelling Unit Supportive Jurisdictions," and a 2025 executive order directs it to summarize the law's framework, criteria and benchmarks. See Colorado. [18][19]

Detached ADU (DADU)

Also called: backyard ADU, backyard cottage

An ADU in its own building, separate from the main home but on the same lot. Washington law defines it as an ADU that consists partly or entirely of a building that is "separate and detached" from the main home "and is on the same property." California counts detached garages, and on a single-family lot a city must allow one new detached ADU of up to 800 square feet with four-foot side and rear setbacks. Seattle calls a permitted unit outside the house a detached accessory dwelling unit (DADU). [1][2][7]

Discretionary review

A permit decision in which officials use their own judgment, not just a checklist, often with a public hearing. Variances, conditional use permits, special permits and special exceptions are the kinds of approvals that Montana's definition of "by right" leaves out. In California, the ADU approval process may not include discretionary processes, and subjective standards such as "compatibility with neighboring properties" may not be applied to ADUs. [1][8][9][10]

Duplex

Two homes on one lot. Oregon law defines a duplex as "two attached or detached dwellings in any configuration on a lot or parcel." California's SB 9 requires ministerial approval of up to two primary units on a lot in a single-family zone. See SB 9 lot splits and [middle housing](#middle-housing). [10][17]

E

Efficiency kitchen

California's term for the kitchen in a junior ADU: a cooking facility with appliances, a food preparation counter and storage cabinets of reasonable size for the unit. A city cannot be stricter than that definition, for example by requiring set counter or cabinet sizes, gas or electric connections, or appliance types, and 220V circuits are not required. See junior ADUs. [1]

Egress window

Also called: emergency escape and rescue opening

A window or opening for emergency escape and rescue. Los Angeles's bulletin for ADUs made by converting an existing building, or legalizing an unpermitted one, requires one from every sleeping room, opening directly to a yard or public way, with a clear opening at least 24 inches high and 20 inches wide, at least 5.7 square feet of openable area, and a sill no more than 44 inches above the floor. See garage conversions. [11]

Executive Office of Housing and Livable Communities (EOHLC)

Massachusetts' state housing office. Under the state zoning law, EOHLC may issue guidelines or regulations to carry out the rule that zoning can't prohibit, unreasonably restrict or require a special permit for a single ADU in a single-family zoning district. See Massachusetts. [20]

F

Factory-built housing

Also called: prefabricated structure

A home built in a factory and then moved to its site. California's housing agency describes factory-built housing as "a factory-constructed version of a site-built residential building that is manufactured and then transported to its permanent installation location," and regulates its manufacture for sale in California. Oregon's term is "prefabricated structure": a building or subassembly made largely off-site using closed construction and assembled on-site, which is not a manufactured dwelling. See prefab ADUs. [21][22]

Federal Housing Administration (FHA)

Part of HUD that provides mortgage insurance on loans made by FHA-approved lenders, which protects lenders against losses. Its 203(k) program lets homebuyers and homeowners finance repairs or major rehabilitation into their mortgage. See ADU financing. [14][23]

Fire separation

Fire-rated walls and floors between homes, or between a home and the property line. Los Angeles's bulletin for converted and legalized ADUs calls for a 1-hour fire-resistance rated wall between the main home and an attached ADU or junior ADU, and 1-hour rated exterior walls on a converted unit less than 5 feet from the property line (less than 3 feet if sprinklered). Portland's ADU code guide says that, except as the guide allows otherwise, dwellings must be separated by wall and floor assemblies with at least a one-hour fire-resistance rating. [11][24]

Floor area ratio (FAR)

Building floor area compared with lot area. Portland's zoning code defines it as "the amount of floor area in relation to the amount of site area"; a ratio of 2 to 1 means two square feet of floor area for every square foot of site. In California, FAR and lot coverage limits can't stop an ADU of at least 800 square feet with four-foot side and rear setbacks. [1][25]

H

Historic district

An area designated for its historic, architectural or cultural merit. Portland defines one as "a geographic area that has been designated for its archaeological, architectural, cultural, or historical merit." In California, ADUs are allowed in historic districts, and cities may impose standards that prevent adverse impacts on properties listed in the California Register of Historical Resources. [1][25]

Home equity line of credit (HELOC)

A line of credit, like a credit card, that borrows against the equity in your home. If you already have a mortgage, a HELOC or home equity loan is a second mortgage you pay in addition to your first. A home equity loan, by contrast, pays out a set amount in a lump sum. See ADU financing. [26]

Home rule

Broad local self-government power under a state constitution. In Illinois, any municipality with more than 25,000 people is a home rule unit, smaller ones can opt in by referendum, and a home rule unit can opt out by referendum. A home rule unit may exercise any power pertaining to its government and affairs, including regulating for public health, safety and welfare, except as limited. See Illinois. [27]

Homeowners association (HOA)

The association that runs a common interest development, such as a condominium project or planned development, and enforces its governing documents. In California, an HOA may set limited, reasonable objective standards for an ADU, such as materials or architectural style, but it can't effectively prohibit or unreasonably restrict an ADU on a lot zoned for single-family homes, and it may not review or influence the city's or county's approval of an ADU. See also [CC&Rs](#ccrs). [1]

Housing Accountability and Production Office (HAPO)

An Oregon state initiative set up by Senate Bill 1537 (2024), the governor's housing production package, which tasked DLCD and the state Building Codes Division with addressing Oregon's housing needs. HAPO works with local governments and housing developers on state housing laws about land use and permitting, and takes inquiries and complaints. See Oregon. [16]

I

Impact fee

A charge on new development to help pay for public facilities. California's ADU law defines it as any charge, other than a tax or special assessment, that a local agency collects when it approves an ADU or junior ADU, to pay for public facilities related to it. In California, an ADU with 750 square feet or less of interior livable space is exempt from impact fees; for a larger ADU, fees must be proportional to its size compared with the main home. Washington's ADU law bars the cities and counties it covers from charging an ADU more than 50% of the impact fees for the main home. See ADU costs. [1][28]

Interior livable space

California's measure for ADU size limits and fee exemptions: space in a home intended for human habitation, including living, sleeping, eating, cooking or sanitation. It includes bedrooms, bathrooms, kitchens, laundry rooms, closets and interior stairs. [1]

J

Junior accessory dwelling unit (JADU)

Also called: junior ADU

A California type of small unit: no more than 500 square feet of interior livable space, entirely within a single-family home (an attached garage counts). It may have its own bathroom or share one with the house. If it shares a bathroom, the owner must live in the house or the junior ADU (unless the owner is a government agency, land trust or housing organization), and a junior ADU can't be a short-term rental. See junior ADUs. [1]

L

Lot coverage

Also called: building coverage

The share of a lot covered by buildings. Portland calls it building coverage: "the area that is covered by buildings or other roofed structures," including decks more than 6 feet above grade. In California, lot coverage limits can't stop an ADU of at least 800 square feet with four-foot side and rear setbacks. [1][25]

Lot split

Dividing one lot into two or more. California's SB 9 requires ministerial approval of splitting a parcel in a single-family zone into two, and the city must allow up to two units on each new lot. A city need not approve an SB 9 split if the same owner has already split an adjacent lot. Oregon law also provides for a "middle housing land division." See SB 9 lot splits. [10][17]

M

Manufactured home

A factory-built home on a permanent chassis, built to the federal HUD code. Federal rules define it as a structure transportable in one or more sections, at least 8 feet wide or 40 feet long when moved, or at least 320 square feet when set up, built on a permanent chassis and designed as a dwelling. California law counts a manufactured home as an ADU. See prefab ADUs. [1][29][30]

Middle housing

Homes with two or more units, built at a scale that fits among single-family houses. Oregon law defines it as duplexes, triplexes, quadplexes, cottage clusters or townhouses. Arizona defines it as buildings "compatible in scale, form and character with single-family houses" that contain two or more homes, including duplexes, triplexes, fourplexes and townhouses. See Oregon and Arizona. [17][31]

Ministerial approval

Also called: administrative approval, staff-level review

Approval by staff checking the application against fixed rules, without discretionary review or a hearing. California's SB 9 guidance says ministerial review involves "no personal judgment by the public official as to the wisdom of carrying out the project" and is nearly always a staff-level review. California requires ministerial approval of ADUs. Colorado's similar "administrative approval process" has staff decide based solely on objective standards, with no public hearing. [1][10][18]

O

Objective standards

Also called: clear and objective standards

Rules you can check against a fixed measure, such as a height in feet. California defines them as standards that "involve no personal or subjective judgment by a public official" and can be verified against a benchmark known to both the applicant and the official before you apply; cities may apply only objective standards to ADUs. Colorado's ADU law uses a similar definition, and Oregon generally allows only "clear and objective" standards for housing. [1][17][18]

Overlay zone

Also called: overlay district

A mapped area with extra zoning rules layered on top of the base zone, such as historic, design or environmental overlays. In Portland, land in an overlay zone is subject to both the base zone and overlay rules, and where they conflict the overlay rules generally win. Portland's official zoning maps show the base zones, overlay zones and plan districts. [32][33]

Owner occupancy

A rule that the owner must live on the property. California bars cities from requiring it for ADUs (with a narrow exception for some ADUs sold to qualified buyers), but requires it for a junior ADU that shares a bathroom with the house. Oregon (in cities over 2,500 people and counties over 15,000, inside urban growth boundaries) and Massachusetts (for one ADU in a single-family zone) also bar owner-occupancy requirements, and Washington's ADU law bars the cities and counties it covers from requiring the owner to live on the lot. [1][17][20][28]

P

Permit expediter

Also called: permit consultant

A paid helper who deals with the city to get your permit. San Francisco calls this a permit consultant: someone paid to provide "permit consulting services," meaning contact with city departments such as building inspection or planning to help an applicant obtain a permit, and requires those who qualify under city law to register with the Ethics Commission. See hiring ADU help. [34]

Plan check

The building department's review of your drawings before it issues a permit. Los Angeles requires "a complete set of plans" for plan check, and plan check generates the clearances other departments must approve before the permit is issued. See the ADU permit process. [11]

Pre-approved plans

Also called: preapproved ADU plans, standard plans

ADU designs a city has already reviewed. California cities had to set up a program by January 1, 2025, to preapprove ADU plans submitted by anyone and post them online. A city must approve or deny a detached ADU that uses a preapproved plan, or a plan identical to one it already approved, within 30 days. [1]

S

SB 9

California's Senate Bill 9 (2021). It requires ministerial approval of up to two primary units on a lot in a single-family zone, a split of that lot into two, or both, so up to four homes can go on land typically used for one house. Don't confuse it with a 2025 bill also numbered SB 9 (Chapter 510, Statutes of 2025), which made changes to California's ADU law. See SB 9 lot splits. [1][10]

School impact fee

Also called: school fee

A fee a school district may charge on new housing. In California, school districts may, but don't have to, charge impact fees on ADUs larger than 500 square feet of interior livable space; ADUs and junior ADUs under 500 square feet are not subject to them. [1]

Setback

The minimum distance required between a building and another point, usually a property line. Portland's code says setbacks "are usually measured from lot lines." In California, a city may require no more than four feet from the side and rear lot lines for an attached or detached ADU, and no setback for an ADU or junior ADU made within existing space or rebuilt in the same place and size as an existing structure. [1][25]

Short-term rental (STR)

Also called: vacation rental

Renting a home for short stays; many laws draw the line at 30 days. Colorado's ADU law defines it as renting a lodging unit for less than 30 days, but lets local governments use their own definition; Idaho's short-term rental law covers stays of 30 days or less. California junior ADUs can't be short-term rentals and, if rented, must be rented for longer than 30 days, and Massachusetts lets cities and towns restrict or ban short-term rental of ADUs. [1][9][18][35]

Special exception

A zoning approval, expressly provided for in the zoning code, that a board grants case by case. In Dallas, the Board of Adjustment hears requests for variances and special exceptions, and an owner may ask it for a special exception to build or rent an additional dwelling unit; the board may grant one when it won't adversely affect neighboring property. [36][37]

System development charge (SDC)

Oregon's term for a charge on new development for water, sewer, drainage, transportation or parks facilities. Oregon law defines it as a reimbursement fee, an improvement fee or both, collected when you get a permit, connect to the system or increase its use. See Oregon. [38]

T

Tiny house

Also called: tiny home

A very small home. Seattle's residential code defines it as a dwelling of 400 square feet or less, not counting lofts. California HCD's 2016 bulletin on tiny homes says one is legal to occupy if it fits the definition of a recreational vehicle, manufactured home, factory-built housing or a home built to the California building code. See tiny houses in the backyard. [30][39]

Tiny house on wheels

Also called: THOW, movable tiny house

A tiny house built on a chassis with wheels. Washington's law on tiny house communities defines a "tiny house with wheels" as permanent housing with permanent provisions for living, sleeping, eating, cooking and sanitation, built to the state building code. California HCD's tiny home bulletin says a tiny home may qualify as a recreational vehicle, but RVs are "not intended for occupancy as a permanent dwelling." See tiny houses in the backyard. [30][40]

U

Unified development ordinance (UDO)

The name some cities give their land development code. Charlotte's UDO, in effect since June 1, 2023, describes itself as "your guide to land development regulations for Charlotte, NC." [41]

V

Variance

Permission to depart from a zoning rule because of a hardship particular to your property. Minnesota law allows a variance when the owner shows "practical difficulties": a reasonable use the code doesn't permit, caused by circumstances unique to the property and not created by the owner, that won't alter the locality's essential character. In Dallas, the Board of Adjustment decides variance requests. [36][42]

Z

Zoning

Local rules that say what uses and buildings are allowed on each piece of land. In Portland, for example, the official zoning maps show the zones, and all land divisions, uses and development must comply with the zoning code. In Massachusetts, a city's or town's zoning may apply reasonable rules on setbacks, bulk and height to a single ADU in a single-family district, but may not prohibit it, unreasonably restrict it or require a special permit for it. [20][33]

Definitions differ from state to state and city to city. When it matters, the definition in your city's code is the one that counts.