What's considered an Accessory Dwelling Unit (ADU)?

What's considered an Accessory Dwelling Unit (ADU)?

As housing costs continue to rise across many cities, the demand for alternative housing options is growing. One solution that is gaining popularity is the accessory dwelling unit (ADU), also known as a granny flat, in-law suite, or backyard cottage. An ADU is a secondary living unit on a single-family residential lot, either attached or detached from the primary residence.

In recent years, many cities and states have relaxed zoning regulations to encourage the development of ADUs as a way to increase housing supply and provide affordable housing options. However, regulations and definitions of what constitutes an ADU vary widely from place to place. In this article, we will explore what is considered an ADU, the different types of ADUs, and the benefits and challenges of building an ADU.

What is considered an ADU?

As mentioned, an ADU is a secondary living unit on a single-family residential lot. It can be either attached or detached from the primary residence. An ADU typically contains a kitchen, bathroom, and sleeping area. It can also have separate entrances, utilities, and parking. The primary residence must remain the owner's primary residence, and the ADU cannot be sold separately.

Different types of ADUs

There are different types of ADUs, and they can be created in various ways. The most common types of ADUs are:

  1. Attached ADUs: An attached ADU is attached to the primary residence, typically as an addition or a conversion of an existing space, such as a garage or basement.

  2. Detached ADUs: A detached ADU is a separate structure from the primary residence, typically located in the backyard. It can be a new construction or a conversion of an existing structure, such as a shed or a garage. Get started with one of our detached ADU garage designs here

  3. Junior ADUs: A junior ADU is a smaller, self-contained unit within the primary residence. It can be created by converting an existing bedroom or by adding a new one. A junior ADU typically has a kitchenette, bathroom, and separate entrance.

Benefits of building an ADU

Building an ADU can have many immediate benefits, including:

  1. Increased housing supply: ADUs can help increase housing supply in areas with high demand by adding more units to existing residential lots.

  2. Rental income: Homeowners can rent out their ADUs to generate extra income, which can help offset the cost of building the unit.

  3. Multigenerational living: ADUs can provide a separate living space for family members, such as elderly parents or adult children, who want to live close to each other.

  4. Affordable housing: ADUs can provide affordable housing options in areas where housing costs are high, such as in urban areas.

Challenges of building an ADU

While building an ADU can have many benefits, there are also some challenges to consider:

  1. Cost: Building an ADU can be expensive, especially if it requires new construction or major renovations to an existing structure.

  2. Zoning regulations: Zoning regulations vary widely from place to place, and not all areas allow ADUs. Homeowners need to check with their local government to determine if they are allowed to build an ADU on their property and what the zoning regulations are.

  3. Design and construction: Designing and building an ADU requires careful planning and coordination with architects, contractors, and city officials. Homeowners need to ensure that the design and construction of their ADU comply with all local building codes and regulations.

  4. Financing: Financing an ADU can be challenging, as it may not qualify for traditional home loans. Homeowners may need to explore alternative financing options, such as home equity loans or personal loans.


ADUs are typically smaller than the main dwelling and can range in size from a studio apartment to a small house. They can be attached to the primary residence, located within the same building, or detached, such as a standalone cottage in the backyard. ADUs may also have their own separate entrance, kitchen, bathroom, and living area.

Back to blog