What Is An ADU? (ADU Meaning & Examples)

An illustration of an ADU in a garden next to a house

An Accessory Dwelling Unit (ADU) is a secondary housing unit located on the same property as a primary residence. 

These units are designed to provide additional living space and can serve various purposes, such as rental income, housing for family members, or guest accommodations. 

ADUs are increasingly popular in urban and suburban areas where housing affordability and availability are major concerns.

Types of ADUs

There are several types of Accessory Dwelling Units, including detached ADUs, Attached ADUs, and converted spaces, and each sub-category includes different variations.

For example, a converted space ADU could be a basement space that has been converted or an attic/garage.

Detached ADUs

These are standalone structures separate from the main house. Detached ADUs – also known as DADUs – are often referred to as backyard cottages, granny flats, or carriage houses. 

They offer the most privacy for both the occupants of the main house and the ADU.

Attached ADUs

These units are connected to the main house but have a separate entrance and living facilities. 

This type of ADU can include additions to the home, such as a new wing or extension, providing an independent living space while maintaining proximity to the main residence.

Converted Space ADUs

These involve transforming existing spaces into livable units, such as basements, garages, or attics. 

This type is often the most cost-effective option since it utilizes existing structures, reducing the need for extensive new construction.

Benefits of ADUs

ADUs offer several benefits, not only for homeowners but for the community as well.

Increased Housing Options

ADUs provide additional housing in areas with high demand, helping to alleviate housing shortages. This can be particularly beneficial in urban areas with limited space and high housing costs.

Rental Income

Homeowners can generate extra income by renting out ADUs. 

According to a study by the Terner Center for Housing Innovation at UC Berkeley, ADUs can significantly enhance a homeowner’s financial stability by providing a steady stream of rental income.

This is especially helpful in today’s economic situation, where the price of home ownership has skyrocketed, and finding a place to rent is more difficult than ever.

Family Accommodation

ADUs are ideal for housing elderly parents, adult children, or extended family members. This promotes multigenerational living, allowing families to stay close while maintaining independent living spaces.

Property Value

Adding an ADU can increase the overall value of the property. 

Real estate experts from the National Association of Realtors report that properties with ADUs tend to have higher resale values (up to 35%) due to their added flexibility and potential for rental income.

Sustainable Living

ADUs often require fewer resources to build and maintain than traditional housing, contributing to more sustainable living practices. 

A study by the American Council for an Energy-Efficient Economy found that due to their size and efficient use of space, ADUs allow people to live in areas closer to work, reducing their overall carbon footprint.

Local Benefits Of ADUs

According to research by Portland State University’s Urban Studies and Planning Department, ADUs have become increasingly popular in Portland due to the city’s progressive zoning laws and incentives. 

The study found that ADUs in Portland provide affordable housing options and contribute positively to the local economy. The city offers financial incentives and streamlined permitting processes, making it easier for homeowners to add ADUs to their properties.

Regulations and Permit Considerations

Building an ADU typically requires compliance with local zoning laws and building codes. 

These regulations can vary widely by location. Homeowners should consult with local planning departments to understand the specific requirements, including:

  • Minimum Lot Size: Regulations often specify the minimum lot size required to add an ADU.
  • Maximum Unit Size: There are typically limits on the size of the ADU relative to the main house.
  • Parking Requirements: Some jurisdictions require additional parking spaces for ADUs.
  • Setback and Height Restrictions: Regulations may dictate how far the ADU must be from property lines and the maximum allowable height.


Q: What are the main types of ADUs?
A: The main types of ADUs are detached units, attached units, and converted space units.

Q: How do ADUs benefit homeowners?
A: ADUs increase housing options, generate rental income, accommodate family members, enhance property value, and promote sustainable living.

Q: What are the common regulations for building an ADU?
A: Common regulations include minimum lot size, maximum unit size, parking requirements, and setback and height restrictions.

Q: Can ADUs be rented out?
A: Yes, ADUs can be rented out, providing homeowners with additional income. However, rental regulations may vary by locality.

Q: Are there financial incentives for building ADUs?
A: In some areas, there are financial incentives such as tax breaks or grants to encourage the construction of ADUs.


An Accessory Dwelling Unit (ADU) is a versatile and beneficial addition to any property. By offering additional living space, rental income, and housing options for family members, ADUs play a crucial role in addressing housing shortages and promoting sustainable living. 

Homeowners interested in building an ADU should research local regulations and consider the various types of ADUs to find the best fit for their needs. You can also use Presite to experiment with different ADU layouts and floor plans.

The popularity of ADUs in cities like Portland, Oregon, demonstrates their potential to enhance housing options and support community growth.

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