What Is a Granny Flat?

A granny flat is a small self-contained living space located on the same lot as a primary residence. It is commonly designed to host aging relatives, long-stay friends, or as an income-producing rental unit.

In addition to the British term “granny flat,” these residential structures are also known by names such as a secondary suite, in-law apartment, casita, tiny house, or by their formal designation, Accessory Dwelling Unit (ADU). These buildings can be anything from a backyard tiny house to an apartment over the garage or a finished basement guest suite with a separate entrance.

Granny Flat Amenities

A granny flat contains essential elements needed for independent living.

• Private living space: An ADU is equipped with private living space such as a living room and bedroom, or may be set up like an open-plan studio apartment.
• Kitchen facilities: ADU kitchens range from small kitchenettes equipped with a microwave and a mini-fridge to full kitchens. 
• Bathroom facilities: A private bathroom that includes a shower, sink, and toilet.
• Laundry facilities: ADUs may or may not include in-unit laundry.
• Senior Care Features: Some ADUs are designed specifically for older people, with everything from wider hallways to non-slip floors, bathroom grab bars, and smart technology such as voice-activated lights and heating, remote health monitoring devices, and automated assistance.
  

Types of Granny Flats

There are a variety of ADU types to suit a range of settings, home styles, and budgets.

Converted Structures

Converted ADU structures repurpose existing spaces or outbuildings to create independent living quarters. This includes everything from finished basements to rooms over the garage, converted attics, and detached backyard buildings such as converted sheds or garage conversions.

These structures are generally more budget-friendly and sustainable since they rely on existing architecture rather than building from scratch. They generally take less time to renovate than a new build.

New Structures

New build ADUs range from tiny houses to guest cottages that are equipped with kitchens and bathrooms. They are either fully detached from the home or in some cases may be an addition to an existing home with a private entrance.

Benefits of Granny Flats

• Create opportunities for multigenerational housing that allows older relatives to live independently and grown kids a place to live before moving out on their own.
• Enhance property values and make homes with ADUs more attractive to buyers.
• Provide rental income from short- or long-term renters depending on local laws. 
• Can help address affordable housing shortages in some areas by providing small and budget-friendly accommodations. 
• Offer flexible spaces that can be used as home offices, art studios, home schooling classrooms, or to house nannies or other long-term guests.
  

Disadvantages of Granny Flats

• Building a new ADU can get expensive and pre-fab options are not permitted in some areas.
• Time-consuming applying for permits, navigating local zoning regulations, connecting utilities, and securing off-street parking.
• May increase property taxes as a result of raising home values with more square footage and amenities.
• Can reduce outdoor space in a backyard.
• Require ongoing maintenance and the associated time and cost.
• May cause conflict with neighbors in regard to additional noise or parking issues in areas that are zoned for single-family housing.
  

Common Granny Flat Sizes

ADUs range in size depending on many factors, including the building type as well as local building regulations that vary from state to state. While they are always smaller than the main residence, they can vary in size starting from as little as 150 square feet to as much as 800 to 1200 square feet depending on where you live.

Cost to Add a Granny Flat

According to HomeAdvisor, it costs between $40,000 and $125,000 or more to build an ADU on your property, with an average cost of about $82,500. The final price will depend on the size of the unit, whether it’s a converted or a new structure, materials used, and local labor costs.