What you can build

Mother-in-law suites: what's allowed and how to permit one

Checked against state laws and official agency sources · Last reviewed October 10, 2026

What the term means in law

California's housing department says ADUs "have been known by many names: granny flats, in-law units, backyard cottages, secondary units and more." Phoenix says ADUs are "often referred to as guest houses," casitas or granny flats. What counts is which legal category the space fits in your city's code. Common categories, with examples:

• An ADU. California defines an ADU as a unit with "complete, independent living facilities for one or more persons," including "permanent provisions for living, sleeping, eating, cooking, and sanitation." It can be attached, detached or inside the main home. See what an ADU is.
• A junior ADU (California). A unit of no more than 500 square feet of interior livable space, entirely inside a single-family home. It may share the house's bathroom. See junior ADUs.
• Guest quarters. San Diego allows "guest quarters or habitable accessory buildings": attached or detached living quarters that "do not provide complete, independent living facilities" and are only for the people in the main home, their guests or employees. Fort Worth uses the name "accessory dwelling unit" for something closer to guest quarters: "non-rented or leased living facilities within a detached building" for temporary guests or a family member, "which does not contain cooking equipment."
• Part of the main house. A bedroom suite can also stay part of your home. In Seattle, Director's Rule 7-83, a 1983 code-enforcement rule still linked from the city's ADU page, allows privacy locks on bathrooms and bedrooms but lists other features as evidence of a second unit (see the kitchen section below).
• A second home on the lot. In some cities an accessory building can't be a separate home, so a true second home needs zoning that allows two. Fort Worth's code, for example, says a habitable accessory building in a one-family district "may not be used as a separate independent residence." The city's "B" Two-Family district allows one-family and two-family homes, with a minimum lot of 7,500 sq ft for two detached homes.

[1][2][3][4][5][6][7][8][9]

Can an in-law suite have a kitchen?

In the codes below, a kitchen is what separates guest space from a separate home:

• San Diego: guest quarters "shall not contain a kitchen or facilities for the storage and preparation of food. A bar sink and miniature refrigerator may be permitted."
• Fort Worth: the city's accessory dwelling unit, in a detached building, is one "which does not contain cooking equipment."
• Seattle: Director's Rule 7-83, issued in 1983 and still listed on the city's ADU page, says a food preparation area is evidence of a dwelling unit. Under that rule a wet bar is allowed, but it "will not contain permanently installed appliances other than a refrigerator, and will not have a 208 or 220-volt appliance outlet or gas appliance outlets." The rule lists other evidence of a second unit, including separate meters, separate addresses, lockable interior doors that close off part of the home, a separate water heater, and rental agreements for part of the house. "Second range permits in single family dwellings will not be approved without field inspection by a Zoning inspector." Because the rule is old, ask the Seattle Department of Construction and Inspections how it applies today.
• Las Vegas: an ADU "provides an independent living space, including full kitchen facilities." The code's definition of kitchen facilities includes "a sink, refrigerator and a significant cooking appliance such as a range, stove or oven."
• California: an ADU must have permanent provisions for cooking. A junior ADU needs an efficiency kitchen: a cooking facility with appliances, a food preparation counter and storage cabinets of reasonable size. HCD says cities can't be stricter than that, and 220V circuits are not required.

In these examples, a full kitchen fits the ADU category, not guest quarters. Ask your city's zoning office what it counts as a kitchen and which category your plan falls in. [2][3][4][7][9][10]

Do you need a permit?

Permit rules vary by city and project, so check with your city's building department. Some examples:

• Garage conversions in Federal Way, Washington: "Converting a residential garage into living space requires a building permit, and may require electrical, mechanical, and plumbing permits as well," and the space must meet current building and energy codes.
• ADUs in Seattle: the city says ADUs "are not legal unless they have been established through a permit process," and must meet current residential, building, mechanical, electrical, energy and land use codes.
• Guest quarters in San Diego: the city allows them in some zones as a limited use under its Process One. Before a building permit is issued, the owner must sign an agreement with the city that the main home and the guest quarters won't be sold separately; the city sends it to the County Recorder to be recorded.
• Habitable accessory buildings in Fort Worth: they must meet the city's building code for habitable structures and may not be taller than the main home.

For the steps from plans to final inspection, see the ADU permit process. If you're converting a garage, see garage conversions. [3][5][9][11]

Can you rent it out?

It depends on the category.

• ADUs in California: a city can't require you to live on the property, but it may require that rentals be for terms of 30 days or longer. Rentals of ADUs approved under Government Code 66323 and of junior ADUs must be for terms longer than 30 days.
• ADUs in Las Vegas: the code's ADU definition covers living space for the occupants of the main home "or their tenants, domestic employees or temporary guests."
• Guest quarters in San Diego: they "shall not be rented, leased, or sold as a separate dwelling unit" and are used only by the people in the main home, their guests or their employees.
• Fort Worth: the accessory dwelling unit is "non-rented." A "temporary guest" is a nonpaying guest who doesn't use the unit as an address and stays no more than 14 days in any 30-day period. Our Fort Worth page covers zoning that allows a rentable second home.

If you might rent the suite later, ask your city which category allows that before you apply. [2][3][4][10]

Family-only options

Some rules are built around family members:

• Minnesota: under Minn. Stat. 462.3593, a caregiver or relative can get a local permit for a temporary family health care dwelling. It is a small mobile unit, assembled off site, of no more than 300 gross square feet, not on a permanent foundation, for one mentally or physically impaired person who needs help with two or more instrumental activities of daily living. "Relative" includes in-law relationships. Only one is allowed per lot, it must be on property where the caregiver or relative lives, and the permit lasts six months, renewable once for six more. The local government has 15 days to decide (30 for a city that holds regular meetings only once a month), and may charge up to $100 for the permit and $50 for the renewal unless its ordinance says otherwise. A local government may opt out of the law by ordinance. See the Minnesota Statutes, section 462.3593.
• Illinois: state zoning law lets cities "classify, to regulate and restrict the use of property on the basis of family relationship," which it may define as people related by blood, marriage or adoption "and maintaining a common household." Check your city's code for any rule on who may live in a second unit.
• Fort Worth: the accessory dwelling unit is for temporary guests or "a member of the family of the main dwelling unit."

[4][12][13]

Attached or detached

An in-law suite can be inside the house, attached to it, or in a separate building, and codes treat these differently.

• Washington law defines an attached ADU as one "located within or attached to" a house or other housing unit, and a detached ADU as one in a building "separate and detached" from it on the same property. Seattle calls them AADUs and DADUs.
• California: an ADU can be attached, detached or inside the home, including an attached garage. A junior ADU must be inside the single-family home.
• Fort Worth: an accessory dwelling unit is in a detached building. A building joined to the house only by a breezeway or covered walkway, whose roofline isn't part of the house, "shall not be considered to be an extension of the primary structure."
• San Diego: guest quarters may be attached or detached, but they don't have direct access to the main home.

[2][3][4][5][9][14]

Cost, financing and property tax

For budgets and loan options, see our guides to ADU cost and ADU financing.

In California, an in-law suite can raise your property tax. New construction is generally assessable and may increase your property's taxable value. The State Board of Equalization lists "Additions to existing improvements," "Increasing the square footage of a residence" and "Conversion of a garage, unfinished basement, or attic into a living area" as new construction. The assessor reassesses only the newly built part; the existing home and land keep their assessed value. See ADU property tax for other states. [15]

Legalizing an existing unpermitted in-law suite

In California, AB 2533 (in effect since January 1, 2025) bars a city from denying a permit for an unpermitted ADU or junior ADU built before January 1, 2020, because of building code violations, unless the city finds that fixing the violation is needed to keep the building from being substandard. The city can't penalize you for having had the unpermitted unit, and generally can't charge impact fees or connection or capacity charges. You may get a confidential code inspection from a licensed contractor before you apply.

Some cities run their own programs:

• Berkeley: a pilot amnesty program for units "such as a converted garage or in-law unit," limited to single-family lots with an unpermitted ADU or junior ADU built before January 1, 2020. It runs from January 1, 2025 to December 31, 2028. Before applying, you can set up a free, confidential consultation (email UDUamnesty@berkeleyca.gov).
• Oakland: the city's legalization page offers amnesty from Planning Code violations for units built before January 1, 2021, a delay in enforcement for units built before January 1, 2020, and the AB 2533 permit path for units built before 2020. You choose one option.

Outside California, ask your city's building department how to permit work that was done without permits. [2][16][17]

Questions people ask