What is an ADU?

Updated on
May 11, 2025

An Accessory Dwelling Unit, or ADU, is a smaller, self-contained living space built on the same property as a main home. Think of it as a mini-house that can be attached to or separate from the primary residence. ADUs are gaining popularity as a flexible, affordable way to add living space, whether for family, friends, or even as a rental to generate extra income.

Key Features of an ADU

Independent Living: ADUs typically include a kitchen, bathroom, and sleeping area, making them fully functional for day-to-day living.

Size: They’re smaller than the main home, often ranging from 300 to 1,200 square feet, depending on local regulations.

Location: ADUs can be built as a backyard cottage, a garage conversion, an addition to the main house, or even a basement apartment.

Versatility: They can serve many purposes, like housing aging parents, giving young adults their own space, or acting as a rental unit.

Why Consider an ADU?

ADUs offer a practical solution for homeowners looking to maximize their property. They’re often more affordable than buying a separate home or moving to a larger one. Plus, they can increase property value and provide a steady rental income. For communities, ADUs help address housing shortages by adding more homes without changing a neighborhood’s character.

Common Types of ADUs

  • Detached ADU: A standalone structure, like a backyard cottage or tiny house.
  • Attached ADU: Connected to the main home, such as an addition or converted attic.
  • Garage Conversion: Turning an existing garage into a livable space.
  • Basement ADU: A finished basement with its own entrance and amenities.

Things to Know Before Building an ADU

Local zoning laws and building codes vary, so check with your city or county before starting. Some areas have restrictions on ADU size, placement, or whether you can rent them out. You’ll also need to consider costs, which can range from $50,000 to $200,000 or more, depending on the design, materials, and labor.

Is an ADU Right for You?

If you need extra space, want to house loved ones, or are looking for a way to earn rental income, an ADU could be a great fit. It’s a smart way to make the most of your property while adding value and flexibility to your home.

Have questions about ADUs or ready to explore building one? Contact your local planning department or a contractor to get started!