A secondary suite (also known as an accessory dwelling unit (ADU), in-law apartment, granny flat, granny annex or garden suite) is a self-contained apartment, cottage, or small residential unit that is located on a property that has a separate main single-family home, duplex, or other residential unit. It may be attached to the principal dwelling or an entirely separate unit, located above a garage, across a carport, or in the backyard on the same property. Reasons for wanting to add a secondary suite to a property may be to receive additional income, provide social and personal support to a family member, or obtain greater security.

Description

Background Naming conventions vary by time period and location, but secondary suites may also be referred to as accessory dwelling units (ADUs), mother-in-law suites, granny flats, coach houses, laneway houses, Ohana dwelling units, granny annexes, granny suites, in-law suites, and accessory apartments. The prevalence of secondary suites is also dependent on time and location with varying rates depending on the country, state, or city. Furthermore, regulations on secondary suites vary widely across jurisdictions. Some allow them with limited regulation, while others prohibit them entirely through zoning, restrict occupancy to certain household members, or regulate whether the units may be rented.

Spatial relationship to main residence

A secondary suite is considered "secondary" or "accessory" to the primary residence on the parcel. It normally has its own entrance, kitchen, bathroom and living area. There are three main types of accessory units: interior, interior with modification, and detached. Examples include:

A suite above a rear detached garage (a "garage apartment, garage suite, coachhouse, or Fonzie flat"), A suite above the main floor of a single-detached dwelling, (an "up-and-down duplex") A suite below the main floor of a single-detached dwelling (a "basement suite"). A suite attached to a single-detached dwelling at grade (similar to a "duplex", but that word implies two distinct legal parcel of land with houses that simply share a wall) A suite detached from the principal dwelling (a "garden suite" or "guesthouse" (called a "laneway house" if it faces the back lane)). A granny flat, granny annex, mother-in-law cottage and the like are generic familial names for an ADU.

Benefits and drawbacks

Benefits Higher density residential areas have many advantages. They require less resources for transport, heating and cooling, infrastructure and maintenance. They allow for closer-knit communities by facilitating interaction between neighbors, especially children and teenagers. Creating affordable housing options as secondary suites are typically small, easy to construct, and require no land acquisition. Enabling seniors to "age-in-place" by creating small and affordable units where seniors can downsize in their own neighborhood. Some of the recent popularity of secondary suites in the United States can be attributed to the activities of the American Association of Retired Persons (AARP) and other organizations that support seniors. Supporting diverse and multi-generational households as seniors, young-adults, or other relatives can live on the same property as their families while maintaining independence and privacy. For seniors, this arrangement can improve social life, allow to easily provide care, and possibly live in more walkable neighborhoods when they can no longer drive. Facilitating homeownership by providing a reliable extra income that can support mortgage payments and home maintenance. Creating sustainable and energy-efficient housing as smaller or attached units require fewer resources. ADUs can be integrated into the scale and character of single-family neighborhoods while also promoting workforce housing in these neighborhoods. Municipal budgets may benefit from new taxable housing that does not require new infrastructure or significant utility upgrades.

Drawbacks Linked properties cannot easily be sold separately. In case of shared ownership each party may require permission from the other party to make changes to the building.

By country

Australia In Australia, the term 'granny flat' is often used for a secondary dwelling on a property. The land is not subdivided with construction requiring approval from the council or relevant authority. The approval processes vary between States and Territories, and between councils. This is different from a dual occupancy, where two primary dwellings are developed on one allotment of land, being either attached, semi-detached or detached. In 2018, New South Wales led the construction of new granny flats while Victoria had the fewest number of new granny flats constructed. In 2019, the federal government launched a study concerning prefabricated buildings and smaller homes citing affordable housing, extra space for family members, and support for the construction industry as reasons for the study. The government set aside $2 million for the initial study and then planned to set up an innovation lab to help manufacturers design prefabricated buildings.

New Zealand Similar to Australia, a secondary dwelling on a property is also known as a 'granny flat', but more commonly as a 'sleepout'. A sleepout, or 'cabin',:

Is separate from the main house Can be used as an extra accommodation, a hobby room, home office or storage Does not contain cooking, sanitary facilities or drinking water supply.

According to an official New Zealand government website property owners can begin building a sleepout, or secondary dwelling, without building consent if they meet the following requirements:

Not exceed 30m2 in floor area Be one storey in height, with a maximum height of 3.5 metres above floor level Have a floor level not exceeding 1 metre above the supporting ground, including any mezzanine floor Not contain plumbing or facilities for the storage of drinking water Be used for sleeping accommodation only if it is associated with a dwelling and does not contain cooking facilities Have a smoke alarm installed if used for sleeping accommodation Be sited at least 1 metre from any residential building or boundary, if it measures more than 10 square metres in floor area.

However, even if the project does not require a building consent, property owners must still ensure that a project complies with the national Building Code.

In September 2025, a select committee report called for minor amendments to the government's legislation allowing small homes like granny flats (sleepouts, backyard studios, home offices, man-caves, she-sheds, teenage retreats) to be built without a consent. The Amendment Bill would allow for standalone dwellings of up to 70 square metres (increased from the current 30 square metres) to be built without a consent, so long as certain conditions are met.

The proposed changes, championed by Housing Minister Chris Bishop, were backed unanimously by all parties and the bill is expected to pass by the end of the year.

Canada

Secondary suites have existed in Canada since the 19th century where they took the form of coach houses, servant houses, stables converted to permanent apartments, and small apartments for young people within large houses. Secondary suites became increasingly popular during the economic crisis of 1929 and the housing shortage following WWII. During this period the Canadian government actively supported the creation of secondary suites. However, suburbanization and zoning changes in the 1950s and 60s led to a decrease in secondary suites in Canada. More recently, secondary suites are increasing in popularity and many municipalities are reexamining their regulations to support secondary suites.

CMHC (government program) The Canada Mortgage and Housing Corporation provides a financial assistance program to help Canadians create affordable housing for low-income seniors and adults with a disability within a secondary suite. The program is called the Residential Rehabilitation Assistance Program (RRAP) -- Secondary/Garden Suite. The maximum fully forgivable loan depends on the location of the property: Southern areas of Canada: $24,000/unit Northern areas of Canada: $28,000/unit Far northern areas: $36,000/unit A 25% supplement in assistance is available in remote areas.Residential Rehabilitation Assistance Program (RRAP) -- Secondary/Garden Suite

British Columbia After adopting legislation in 2009 to support secondary suites, Vancouver, British Columbia became one of the leading North American cities for their construction. In the city, approximately a third of single-family houses have legally permitted secondary suites, many of which are laneway houses. The Housing Policy Branch of British Columbia's Ministry of Community, Aboriginal and Women's Services published a guide for local governments to implement secondary suite programs called 'Secondary Suites: A Guide For Local Governments'. The current issue is dated September 2005. The intent of the guide is to "help local governments develop and implement secondary suite programs". It also highlights good secondary suite practices as well as providing practical information to "elected officials, planners, community groups, homeowners, developers, and others interested in secondary suites".

Europe In German speaking countries an interior secondary suite is known as an Einliegerwohnung.

In the United Kingdom, "granny flats" are increasing in popularity with one in twenty UK households (5%) having such a space. 7% of householders say they have plans to develop this type of space in the future. 27% of those surveyed were making plans for older relatives, 25% were planning for grown-up children, 24% were planning to rent as holiday lets, and 16% were planning to take in lodgers.

In Norway, particularly in the bigger cities, it is quite common to build separate adjoined smaller flats that the owner of the main flat will rent out.

In Sweden, a friggebod is a small house or room which can be built without any planning permission on a land lot with a single-family or a duplex house.

United States

In the United States, secondary suites are generally referred to as accessory dwelling units or "ADUs". Zoning permissions and laws concerning accessory dwelling units can vary widely by state and municipality. Accessory dwelling units were popular in the early 20th century in the United States, but became less common after WWII when a shift to suburban development occurred and many municipalities banned ADUs through zoning regulations. With increases in the price of housing in many cities and suburbs, increased awareness of the disadvantages of low-density car-oriented development patterns, and an increased need to care for aging Americans, many government entities and advocacy groups have supported ADUs. Some critics perceive ADUs to be a threat to the character of single-family residential neighborhoods. Several states have enacted legislation to promote accessory dwelling units.

California

In California, Government Code Sections 65852.150, 65852.2 & 65852.22 pertain to local regulation of ADUs. SB 1069 and AB 2299 are California bills approved in 2016 and effective 1 January 2017, that limit local government authority to prohibit ADUs in certain cases (and also reduce cost and bureaucracy hurdles to construction). On 1 January 2020, the state of California passed the most lenient ADU laws in the country allowing not one but two types of accessory units, the accessory dwelling unit (ADU) and the junior accessory dwelling unit (JADU or JDU). State-exempt ADUs can now be at least , while JADUs are limited to .

Statewide Reforms