What Is an Accessory Dwelling Unit (ADU)?

An ADU is a self-contained home that includes its own kitchen, bathroom, living, and sleeping areas, and has a separate entrance from the main house.

While ADUs can take many forms, they are always located on the same property as a larger, primary residence and cannot be sold separately from that main home.

Types of ADUs

ADUs vary widely in form and can be created in several ways:

• Detached ADU: A stand-alone structure built separately from the main house, such as a backyard cottage or converted outbuilding.

• Attached ADU: An addition built onto the main home, like a side or rear extension, sometimes sharing a wall with the primary residence.

• Interior Conversion: A portion of the existing home—such as a basement, attic, or large bedroom—converted into a separate living unit.

• Garage Conversion: Transforming an existing garage into a living space.

All ADUs must be fully independent, with their own kitchen and bathroom, and must be accessible without passing through the main residence.

Common Names for ADUs

Depending on the region or context, ADUs may be called:

• Granny flat

• In-law suite

• Carriage house

• Backyard bungalow

• Basement apartment

• Garage apartment

• Guest house

• Laneway house

Why Build an ADU?

ADUs offer several benefits:

• Flexible Living Arrangements: Ideal for multigenerational families, providing privacy while keeping loved ones close.

• Rental Income: Homeowners can rent out the ADU for extra income, making homeownership more affordable.

• Aging in Place: Older adults can downsize or live near family without leaving their community.

• Affordable Housing: ADUs add to the housing supply and are often more affordable than traditional homes.

Key Regulations and Considerations

• Zoning Laws: Local zoning rules determine whether and how ADUs can be built, including size, style, and occupancy limits.

• Owner Occupancy: Many areas require the property owner to live in either the main house or the ADU.

• Utilities: ADUs often share water and energy connections with the primary home, though separate meters may be required in some areas.

• Financing: ADUs can be financed through renovation loans, construction-to-permanent loans, or by including rental income in mortgage qualification.

Bottom Line

An accessory dwelling unit (ADU) is a self-contained, smaller home located on the same lot as a primary single-family residence. ADUs provide flexible living solutions, potential rental income, and can help address affordable housing needs. However, they are subject to local zoning, building codes, and ownership restrictions, so homeowners should research local regulations before planning an ADU project.

The main physical forms an Accessory Dwelling Unit (ADU) can take on a property are:

• Detached ADU: A standalone structure separate from the main house, such as a backyard cottage, carriage house, or laneway house. Detached ADUs offer the highest level of privacy and design flexibility but usually require more space and higher construction costs.

• Attached ADU: An addition physically connected to the primary residence. This could be a side or rear extension, or a unit built above a garage. Attached ADUs share at least one wall with the main home and can creatively add square footage while blending with the existing structure.

• Conversion/Internal ADU: Created by converting existing space within the main house, such as a basement, attic, or a large bedroom. These ADUs leverage the current footprint of the home, often resulting in lower costs and faster construction.

• Garage Conversion ADU: An existing garage is transformed into a fully functional living unit. This is a popular option for homeowners who want to maximize underused space without new construction.

• Junior ADU (JADU): A smaller unit (often under 500 square feet) created within the main home, typically by converting a bedroom or part of the house. JADUs have their own entrance and efficiency kitchen but share some facilities with the main residence.

These forms allow homeowners to choose the best fit for their property, budget, and privacy needs, while complying with local zoning and building regulations.