What is an accessory home?

Granny flat, in-law suite, converted garage, backyard cottage, basement apartment – accessory homes, accessory dwelling units or ADUs go by many names, but are always a self-contained home smaller than the main house and legally part of the same property.

Accessory homes can take many forms and vary in size, but always contain everything someone needs to live, including a kitchen, bathroom, and place to sleep. Accessory homes typically range from 220 square-foot studios to nearly 1,200 square foot houses with multiple bedrooms. 

Interested in learning more about accessory homes (including our new pre-reviewed plans)? Watch our recent 2023 Housing Speaker Series webinar recordings below!

Did you know?

Now is a better time than ever to build an accessory home. Recent state legislation has significantly reduced or eliminated fees for many Accessory Homes. Homeowner associations (HOAs and CC&Rs) can no longer restrict the construction of accessory homes. Also to note, Placer County offers pre-reviewed plans, significantly saving you more money if you choose to use one.

When you build an ADU, you will save $20,000 in government fees plus $6,000 to $10,000 in design fees if you choose to use one of Placer's free building plans!

Types of accessory homes:


free-standing structure


shares at least one wall with the primary home


built from existing or converted space (i.e. attic or basement)

Garage Apartment

converted former garage space

Above Garage
Above Garage

unit built above garage

Why build an accessory home?

People build accessory homes for lots of reasons, but the most common are rental income or to house relatives. Having an accessory home is a simple and old idea to convert unused space or create new flexible space. Accessory homes are a relatively affordable type of construction because they do not require purchasing land or major new infrastructure. Here are some of the reasons to build an accessory home:

Rental Income
Rental Income

Many homeowners build accessory homes to help pay the mortgage because accessory homes offer a steady source of income.

Flexible Space
flexible space

A homeowner’s needs may change over time and an ADU allows for flexibility and for the property to adapt to new needs, such as a growing family or live-in nanny.

Housing for Relatives

Accessory homes allow homeowners with adult children, aging relatives, or relatives with special needs to live together but also maintain privacy.

Sound Investment

ADUs are generally a good investment because they have a short payback period and increase a home’s resale value.


Some homeowners build an ADU for themselves, often in retirement, while they rent the primary dwelling.

Community Benefits

Accessory homes can help address the housing challenges in Placer County by adding homes that are generally more affordable, which helps provide workforce housing and preserves diversity and community character.