A granny flat is a small, self-contained home on the same property as a main house. It may sit inside the main home, connect to it as an extension, or stand separately in the backyard. Most granny flats include a living or sleeping area, kitchen, bathroom and private entrance.
The name describes the type of accommodation, not the person who lives there. An older relative, adult child, guest, carer or tenant may use the space.
Rules vary by location.
Granny Flat at a Glance
| Feature | Typical description |
|---|---|
| Location | On the same lot as a primary home |
| Design | Attached, internal or detached |
| Facilities | Kitchen, bathroom and living or sleeping space |
| Common US term | Accessory dwelling unit, or ADU |
| Common Australian planning term | Secondary dwelling |
| Typical uses | Family accommodation, rental income, ageing in place or guest accommodation |
| Legal status | Subject to local zoning, building and planning rules |
What Makes a Granny Flat Different From a Guest Room?
A granny flat is designed to operate as an independent dwelling. A guest room usually shares the main home's kitchen, bathroom or entrance.
A self-contained granny flat generally has:
- A private or separate entrance
- A kitchen or kitchenette
- A bathroom
- Sleeping and living space
- Its own utilities or service connections in some designs
- A layout that supports independent living
A bedroom with an ensuite is not automatically a granny flat. It may also need kitchen facilities and approval as an independent dwelling.
Where Can a Granny Flat Be Built?
A granny flat can be built in several parts of a property, depending on local rules:
- Detached: A separate building in the backyard
- Attached: An extension connected to the main house
- Internal: A converted basement, garage or upper floor
- Above a garage: An additional dwelling over a garage, where permitted
In the United States, a granny flat is usually called an accessory dwelling unit, or ADU. In New South Wales, Australia, the formal planning term is generally secondary dwelling.
Why Do People Build Granny Flats?
People build granny flats for several reasons:
- Multigenerational living: Family members can live close to one another while keeping separate living spaces.
- Ageing in place: An older person can remain near relatives without moving into the main house.
- Rental income: The owner may rent out the unit, subject to local laws and approval conditions.
- Accommodation for adult children: A granny flat can provide independent space without the cost of a separate property.
- Caregiving: A carer or support worker may live on the same property.
- Guest accommodation: Visitors can stay in a separate unit.
An ADU may also help an older resident remain in their community or give a homeowner an additional source of income.
Is a Granny Flat the Same as a Second House?
No. A granny flat is usually an additional dwelling linked to a primary home on the same lot. It is often smaller and may be subject to restrictions that do not apply to a separately titled house.
Some planning systems do not allow a granny flat to be subdivided or sold separately from the main home. In New South Wales, planning guidance describes a secondary dwelling as remaining on the same site as the principal dwelling.
Do You Need Permission to Build a Granny Flat?
Usually, yes. The approval process depends on the location, the property and the proposed design.
Local authorities may regulate:
- Maximum floor area
- Building height
- Setbacks from property boundaries
- Site coverage
- Parking
- Fire safety
- Plumbing and electrical work
- Separate entrances
- Rental or occupancy arrangements
- Whether the unit can be subdivided or sold
Some areas offer a faster approval process when a design meets preset standards. Other projects require a full planning or development application. Check with the relevant city, county, council or planning authority before designing or building a granny flat.
The Simple Definition
A granny flat is a self-contained secondary home on the same property as a primary residence. Depending on the region, it may also be called an ADU, in-law suite, secondary dwelling, backyard cottage or accessory apartment.