Accessory Building, Structure, and Dwelling Unit Regulations

Definitions

• Accessory Building: A detached structure in the rear yard, such as a shed or garage.
• Attached Accessory Dwelling Unit (or Accessory Apartment): A secondary living unit enclosed within or attached to a single-unit detached house. Examples include a basement conversion or home addition that contains an independent dwelling unit.
• Detached Accessory Dwelling Unit: A secondary living unit on the same property as a single-unit detached house. Examples include an apartment over a detached garage or a smaller structure (on a foundation) in the backyard.

Applications

• Attached ADU Conditional Use Application
• Detached ADU Conditional Use Application
• Building ADU Permit Application
• Rental ADU License Application

Regulations for Accessory Buildings and Structures

Review the full regulations for accessory buildings and structures in the Zoning Ordinance.

Accessory Building Height

• The maximum height at the minimum setback is 12 feet. Accessory buildings taller than 12 feet must be set back an additional 3 feet for each additional foot of height, up to 15 feet. Accessory buildings may exceed 15 feet in height, up to a maximum of 20 feet, with no additional setback required.
• Height is measured to the peak of the roof of an accessory building. In addition, accessory building heights are measured from the lowest point of the finished grade rather than at the front of the building.
• The height of any accessory building may not exceed the height of the main dwelling.

Accessory Building Area

• The maximum footprint (area on the ground) for any one accessory building is 750 square feet and cannot exceed the footprint of the main building. The maximum footprint of all accessory buildings on a single lot is 1,000 square feet.
• The maximum rear yard building coverage is 15% in R-150, R-200, and R-400 zones and 25% in all other residential zones.

Accessory Building Setbacks

• A minimum requirement of 3 feet of building setback is required from any lot line, with additional setbacks required for accessory buildings taller than 12 feet.

Regulations for Attached Accessory Dwelling Units

The Mayor and Council passed a zoning text amendment on Oct. 9, 2023, to allow attached ADUs as a conditional use in residential zones. This legislation went into effect on April 9, 2024. Homeowners who wish to either build an attached ADU under the new regulations or bring an existing attached ADU into compliance may begin the application process, which requires approval.

Review the full regulations for attached ADUs in the approved zoning text amendment (TXT2023-00263).

Attached ADUs

• Design requirements: The attached ADU must have a separate entrance. Any external modifications to the single-unit detached home must be compatible with the existing dwelling and any neighborhood design guidelines.
• Owner occupancy: The property owner must occupy either the main building or the attached ADU for at least six months of the year.
• Size: The gross floor area of the attached ADU must be equal to or less than 50% of the total floor area of the primary dwelling, unless the attached ADU is located in the basement or cellar, in which case it may equal the square footage of the basement or cellar.
• Parking: Lots with attached ADUs that require modifications to the exterior of the existing building (such as a home addition) must provide two off-street parking spaces. However, lots within a 7/10-mile walking distance of a Metro station are required to provide only one off-street parking space. Applicants may request a waiver from this requirement from the chief of zoning. Lots with attached ADUs that do not require exterior modifications to the existing building (such as a basement conversion) are not required to provide off-street parking spaces.