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What Are The Additional Dwelling Units (ADU)?

Additional dwelling units are also known as backyard cottages, accessory dwelling units, secondary units, or in-law units. They add much-needed housing that is innovative, effective, and affordable. This type of housing is attached to or located on the same grounds as a larger primary house. The establishment of an ADU falls under different regulations and zoning rules depending on where you live. It has its own living area, kitchen, and a separate entrance but uses energy and water connections of the primary house.

Zoning changes in most states allow for additional dwelling units. However, they limit the size and style of these secondary units and require the owner to live on the property. This article gives an in-depth view of additional dwelling units including the types and benefits of constructing this type of housing.


All ADU additions are perceived as major residential construction projects. This means that you need to acquire a permit from planning to final construction. First, you need to make sure that your ADU addition plans have been approved by your city. Besides the basic building permits, you will need electrical permits, encroachment permits, and other permits required by the authorities. Construction of an ADU can only begin once you have all the necessary permits. The finished construction needs to be checked off to ensure it complies with the building codes and regulations. Different laws regarding ADU govern different states or municipalities within states. Therefore, the regulation set in the area you live in becomes the minimum baseline.

Types of Additional Dwelling Units

  • Detached ADU

This independent structure is entirely separate from the primary house. Detached ADUs are often located in the backyard and may vary in size depending on the jurisdiction in your area. It can be either a cottage or tiny house, constructed as a stand-alone unit. However, detached ADUs tend to be more expensive than other types of secondary units because it is very involving.

  • Attached ADUs

Attached ADUs are living spaces connected to the primary structure. They can be basement or attic conversions, garage conversions, or additions to your main house. This additional unit can be located to the side of the primary house or the backyard. It is also possible to construct an attached ADU on top of a garage that was initially attached to the main structure.

  • Interior ADUs

Interior ADUs are built through the conversion of an existing space such as the basement or the attic. Unlike attached or detached ADUs, these secondary units are located within the primary dwelling and are referred to as junior ADUs. Units smaller than 500 square feet may be exempted from certain fees in other states.

Benefits of ADUs

Additional dwelling units offer an affordable housing option for both low and moderate-income residents. ADUs are convenient for disabled or elderly persons who want to live close to caregivers and family members. Young adults who are just getting started in the workforce also find ADUs affordable and suitable for their current needs. Besides affordable housing, ADUs provide extra income to homeowners who rent out this living space to people who need it most. This extra income from ADUs can help homeowners mitigate the costs of living besides what they earn from their primary sources of income.

ADUs can also maintain compatibility with established neighborhoods by integrating the existing design with the surrounding architecture. This helps to preserve community character so that it does not deviate from the initial plans. There is no need for developing new infrastructure whether you have an attached or detached ADU. These secondary units are connected to the existing utilities of the main house thus makes use of existing house stock to meet the demand for housing. It offers better alternative to major zoning changes that interfere with the existing plans of neighborhoods.

The growing demand for affordable housing together with limited land available for development has led to flexible rules and regulations regarding the use and development of additional dwelling units. Many communities within low-density areas across the nation have adopted flexible zoning codes to increase affordable housing supply. ADUs do not require additional infrastructure and since they are smaller in size, there is no need for purchasing land. States that have limited available land can benefit significantly from allowing the development of additional dwelling units. For an ADU program to succeed, it needs to be flexible, uncomplicated and supported by a public education campaign that generates community support and increases awareness.

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