What Is a Granny Flat?

Pink front door of beach cottage

Joseph Shields / Photolibrary / Getty Images

Designed for one or two persons, a granny flat is a self-contained living area usually located on the grounds of a single-family home. A granny flat can be detached, or it can be attached to the other dwelling. It is sometimes called a granny flat because it is a popular way for families to accommodate aging parents.

In the building industry, the granny flat is most often known as an accessory apartment or accessory dwelling unit (ADU). Other terms include granny pod, mother-in-law unit, in-law apartment, bonus unit, casita, carriage unit, and ohana unit (primarily in Hawaii).

Many granny flats fall into the tiny house category, and the surge in interest in tiny house living has been a boon to grandparents who are interested in this type of housing.

Fun Fact

The average tiny home measures just 100 to 400 square feet on average, though they can be as small as 80 square feet or as big as 700 square feet.

Granny flats/tiny houses may be used for nannies or for young adult members of the family. They are sometimes used as rental units, but zoning laws and deed restrictions sometimes ban renting.

As multigenerational housing becomes more accepted, granny flats are likely to become more prevalent. Realtors and builders report that they are already a good selling point.

Amenities in a Granny Flat

Some granny flats are miniature versions of full-sized housing units, with complete kitchens. In others, kitchen facilities are limited, perhaps to a mini-fridge and microwave, which involve fewer safety issues than full kitchens.

The Granny Pod 

The newest wrinkle in the granny flat business is popularly called a granny pod. It offers high-tech monitoring capabilities so that the inhabitant can be checked on via remote access. Other devices include a timed medication dispenser. The amenities that can be installed include a toilet that checks temperature and does simple urinalysis.

Difficulty of Adding a Granny Flat

Barriers to the growth of granny flats include municipal statutes, zoning laws, building restrictions, neighborhood covenants, and other regulations. In many cases, homeowners simply ignore or circumvent such regulations, which is relatively easy to do when converting a garage or other existing structure but is less easy when building a new structure.

New construction is more expensive as well, and homeowners may find it difficult to get financing. Connecting utilities can also be expensive. Some municipalities require that driveways and/or off-street parking be provided for the granny flat occupant, which can add to expenses or be completely unfeasible for certain properties.

The growth of the prefabricated or modular building industry has made it easier for some homeowners to add a granny flat, but this type of structure may be prohibited in some localities.

Advantages of Adding a Granny Flat

Besides providing living space, the granny flat offers other advantages. There is greater security with another tenant on the property, especially if the apartment is oriented toward the side or back of the lot. Tenants can sometimes share transportation and other amenities with the occupants of the main house. Sometimes they may be able to share childcare, lawn care, and other maintenance tasks.