A Detached Accessory Dwelling Unit (DADU) involves building a small, single-unit residence on a property with an existing single-family residence. This is not to be confused with a duplex that can be sold separately and has different development requirements. Applicants wanting to add a DADU to a property must complete the permitting process with the Metro Codes and Building Safety. Zoning examiners will review your application and plans for use, setback, footprint, and height restrictions based on the criteria below.
DADU Eligibility
- The Land Use Table must show the parcel’s zoning district permits DADU’s with conditions (PC).
- The lot area of parcel must comply with the minimum lot area for a parcel’s zoning. See bulk regulation tables located in 17.12.
- The parcel must meet one of the following:
- Be in the Urban Services District.
- Be within a DADU overlay within the General Services District.
- Be within a Urban Design Overlay (UDO) with development standards for a DADU.
- Be within a Specific Plan (SP) with development standards for a DADU.
- Only one DADU shall be permitted on a parcel and only when one single-family principal structure is present. When two or more principal structures are present, a DADU is not permitted.
If the property meets the eligibility requirements to allow for a DADU then it must also meet all zoning conditions found in 17.16.030G. The information below highlights those conditions related to use and size requirements.
Zoning Use Restrictions
- By definition (17.04.060) a DADU shall be clearly subordinate in size, height, and purpose to the principal structure, it shall be located on the same lot as the principal structure and is detached from the principal structure. A detached accessory dwelling unit can be an independent structure, it can be a dwelling unit above a garage, or it can be attached to a workshop or other accessory structure on the same lot as the principal structure.
- The detached accessory dwelling shall be owned by the same person as the principal structure and one of the two dwellings shall be owner-occupied.
- Short Term Rental Property (STRP). Upon enactment of this section, on any single-family-zoned, Residential Neighborhood-zoned, or Residential Limited-zoned lot where a new detached accessory dwelling unit is built, or on any single-family-zoned, Residential Neighborhood-zoned, or Residential Limited-zoned lot where a new detached accessory dwelling unit is established via conversion of an existing accessory structure, short term rental property—owner occupied, is not a permitted use in the accessory dwelling unit.
Zoning Site Restrictions
DADU Footprint Controls
The footprint of a DADU must not exceed the footprint of the primary structure. Additionally, no other accessory structure shall exceed two hundred square feet when there is a detached accessory dwelling on the lot. These footprint controls are meant to encourage the living space of a DADU, and additional accessory structure uses to fall under one roof.
DADU Height Controls
(17.16.060G.7.b) The detached accessory dwelling unit shall maintain a proportional mass, size, and height to ensure it is not taller and/or larger than the principal structure on the lot. The detached accessory dwelling unit height shall not exceed the height of the principal structure measured to the eave line, with a maximum eave height of ten feet for single-story and seventeen feet for two-story detached accessory dwelling units as measured from average finished grade.
(17.16.060G.7.c) The roof ridge line of the detached accessory dwelling unit must be less than the primary structure and shall not exceed twenty-seven feet in height as measured from average finished grade.
DADU Living Space Controls
(17.16.030G.7.a) The living space of a detached accessory dwelling unit shall not exceed seven hundred (700) square feet for lots less than ten thousand square feet, or eight hundred and fifty (850) square feet for lots ten thousand square feet or greater and shall not exceed the size of the principal structure.
DADU Building Setbacks
(17.12.040E.1.a) Accessory buildings (DADU) with a footprint of eight hundred fifty (850) square feet or less and located to the rear of a principal structure shall provide a minimum side setback equal to one-half of that required for the zoning district, but not less than three feet, and a minimum rear setback of at least three feet, except when garage doors or carport openings face or open directly to an alley, in which case the minimum rear setback shall be ten feet. Accessory buildings with a footprint of more than eight hundred fifty (850) square feet shall provide the full setbacks of the zoning district.
In addition, a DADU cannot be constructed over an easement or a platted setback. A DADU cannot be constructed over a side street setback requirement for a corner lot.
DADU Design Standards
(17.16.030G.8.a) The detached accessory dwelling unit shall be of similar style, design and material color as used for the principal structure and shall use similar architectural characteristics, including roof form and pitch, to the existing principal structure.
b. The detached accessory dwelling unit may have dormers that relate to the style and proportion of windows on the detached accessory dwelling unit and shall be subordinate to the roof slope by covering no more than fifty percent of the roof.
c. Detached accessory dwelling units may have dormers that are setback a minimum of two feet from the exterior wall.
Parcels Located Within a Historic Overlay, SP or UDO
Historic Overlay
- Setbacks, size limitations and design requirements will be enforced by Historic.
- Conditions listed in 17.16.030G, restricting use and living space will be enforced by Zoning.
- A Historic permit will be required in addition to the Codes building permit.
Parcels located within an SP or UDO with DADU development standards
- The Planning Department will determine requirements for DADU.
- A building permit will be required with Metro Codes and require Planning approval.
Resources
- Use Parcel Viewer to view your zoning, and to determine if there are any overlays on the parcel. The base zoning and additional overlays will be listed under the zoning tab.
Contact the Planning Department to inquire about further requirements for properties within a Residential PUD overlay, Specific Plan (SP) or the Urban Design Overlay (UDO).
If the property is located within the Neighborhood Conservation Overlay or the Historic Preservation Overlay contact the Historic Commission to inquire about any relevant regulations. - The full setbacks can be found in Table 17.12.020 A and section 17.12.030 C(3) of the Zoning Code. The side street setback requirement for corner lots can be found in table 17.12.030 A. Contact the Zoning Help Desk to see if the side street setback can be reduced.
- The Metropolitan Department of Codes and Building Safety does not maintain easement records. If available, a recorded plat may depict easements created at the time of a subdivision but is not conclusive. A Title Abstract conducted for your subject property often will note any recorded easements discovered, a land survey when requested may note visible or observed evidence of unrecorded easements. Direct requests to utility companies and agencies (NES, Piedmont, Metro Water Services etc.) may be conducted to determine if they retain any easements over the subject property.
- Metro Codes does not determine where property lines are located. If you are unsure of where your property lines are you will need to get a copy of your deed. The deed will provide you with a description of your property and where property lines end and begin. If you are unable to determine where the property lines are you will need to hire a surveyor to come and identify your property lines.
- The Register of Deeds can provide a copy of the plat or any recorded private easements.
- Anytime the footprint is increased on a parcel it is recommended that you contact Metro Stormwater to inquire about any further restrictions they may have.
- Contact Tennessee 811 at least three (3) working days before starting a project. Tennessee 811 processes the notification of proposed digging and notifies member utilities, or their contract locators, to mark their underground facilities prior to the digging.
- See Chapter 16 of Metro Code of Laws for the Residential Building Code. Questions about the residential building code should be directed to the building division.
Phone: 615-862-6550 - A property owner is not permitted to pull a self-permit to construct a DADU or to renovate an existing garage into a DADU. A contractor must pull the permit. If the DADU was already permitted as a DADU and renovations are needed, then the homeowner can pull the permit for work up to $25,000.
- For questions about the zoning code, resources, or the permitting process contact the Zoning Help Desk for assistance.
How to Apply for a Permit
To apply for a permit, a registered contractor must submit the following documents to the Zoning Help Desk.
- Residential Permit Application
- Site Plan showing the proposed location of project with distances to property lines, existing structures and easements labeled.
- Renderings showing:
- Elevations (height) from each of the four corners.
- Elevations showing the conditions listed in 17.16.030 G(7)(d) and (e).
- Floor plan showing the proposed layout of the interior and include any proposed fixtures and appliances. The floor plan must also show the conditions of 17.16.030 G(7)(a).
The permit application will be assigned to a zoning examiner. Should the Zoning Examiner have any questions or need additional information they will reach out to you by e-mail or by phone or registered contractors can apply for residential building permits by visiting ePermits. You will need to email Permit Issuance to obtain your username and password for the e-permits website.
Once your application is processed, the Zoning Examiner will provide a checklist showing other Codes divisions and Metro agencies to contact for approvals before the permit can be issued. It is your responsibility to follow the requirements of the checklist on the building permit application and to make sure all necessary signoffs are received.
Do not seek to determine what reviews and approvals are required on your own. If you fail to complete the steps identified in your permit application your process will be delayed. Allow plenty of time. You can track the progress of the application by address or by using the permit application number on ePermits.
Once you have all the required signoffs you can pay for the permit and begin construction. It is also the applicant's responsibility to schedule the necessary inspections with Metro Nashville at the proper time in the building process.
