Building Permits Central: I Want to Build a Detached Accessory Dwelling Unit (DADU)

A Detached Accessory Dwelling Unit (DADU) involves building a small, single-family residence on a property with an existing residence. This is not to be confused with a duplex that can be sold separately and has different site requirements. Whether or not a DADU is allowed depends on the zoning regulations for the property. 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 a parcel's zoning.

DADU Eligibility

1. The lot area of parcel must comply with the minimum lot area for a parcel's zoning.
2. See Table 17.12.020 A
3. The parcel must be within the Detached Accessory Dwelling Unit overlay if the property is zoned RS, Residential-Single Family Only
4. If the parcel is zoned R or RM then it must meet one of the following (See 17.04.060):
   1. Be within a Historic Overlay
   2. Be located on an alley.
   3. Be a lot of at least 15,000 square feet
   4. Be within the Urban Design Overlay (UDO) with development standards for a DADU.

By definition, a DADU is only permitted on a parcel that has one single-family dwelling. Parcels with two single-family dwellings would not be permitted to have a DADU even if the eligibility requirements are met.

Zoning Site Restrictions

If the property meets the eligibility requirements to allow for a DADU then it must also meet the zoning requirements found in sections 17.12.050, 17.12.040 E(1) and 17.16.030 G.

17.12.050 Accessory Building Floor Area Controls

On all lots with a size of less than forty thousand square feet, the building coverage of an accessory structure located to the rear of the principal dwelling and complying with the district setbacks shall be limited to seven hundred square feet or fifty percent of the building coverage (footprint) of the principal dwelling, whichever is greater, but in no case shall exceed two-thousand five-hundred square feet.

17.12.040 E (1) Accessory Building Setbacks

Accessory buildings with a footprint of seven hundred 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 seven hundred square feet shall provide the full setbacks of the zoning district.

A DADU cannot be constructed over a platted setback or easements.

17.16.030G DADU Conditions

Accessory Dwelling, Detached. A detached self-sufficient dwelling unit shall be allowed accessory to a principal structure subject to the following standards:

1. Applicability.
   1. While the following conditions listed below apply to a detached accessory dwelling they do not counter-act or over-ride the applicable life safety standards found in the code editions adopted by the Metropolitan Government of Nashville.
   2. No accessory structure shall exceed two hundred square feet when there is a detached accessory dwelling on the lot.
2. Lot Area. The lot area on which the detached accessory dwelling is to be placed shall comply with Table 17.12.020A.
3. Ownership.
   1. No more than one detached accessory dwelling shall be permitted on a single lot in conjunction with the principal structure.
   2. The detached accessory dwelling cannot be divided from the property ownership of the principal dwelling.
   3. 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.
4. Setbacks. The setbacks for a detached accessory dwelling shall meet the setbacks found in Section 17.12.040.E. for accessory buildings.
5. Site Requirements. A detached accessory dwelling may only be located behind the principal structure.
6. Driveway Access.
   1. On lots with no alley access, the lot shall have no more than one curb-cut from any public street for driveway access to the principal structure as well as the detached accessory dwelling.
   2. On lots with alley access, any additional access shall be from the alley and no new curb cuts shall be provided from public streets.
   3. Parking accessed from any public street shall be limited to one driveway for the lot with a maximum width of twelve feet.
7. Bulk and Massing.
   1. The living space of a detached accessory dwelling shall not exceed seven hundred square feet.
   2. On lots less than ten thousand square feet, the footprint of a detached accessory dwelling shall not exceed seven hundred fifty square feet.
   3. On lots ten thousand square feet or greater, the footprint of a detached accessory dwelling shall not exceed one thousand square feet.
   4. The detached accessory dwelling shall maintain a proportional mass, size, and height to ensure it is not taller than the principal structure on the lot. The detached accessory dwelling height shall not exceed the height of the principal structure as measured to the eave line, with a maximum eave height of ten feet for single-story and seventeen feet for two-story detached accessory dwellings.
   5. The roof ridge line of the detached accessory dwelling must be less than the primary structure and shall not exceed twenty-seven feet in height.
8. Design Standards.
   1. The detached accessory dwelling 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.
   2. The detached accessory dwelling may have dormers that relate to the style and proportion of windows on the detached accessory dwelling and shall be subordinate to the roof slope by covering no more than fifty percent of the roof.
   3. Detached accessory dwellings may have dormers that are setback a minimum of two feet from the exterior wall.
9. Historic Properties.
   1. Metro Historic Zoning Commission Action. Any existing or proposed detached accessory dwelling in a historic overlay district shall comply with the adopted regulations and guidelines of the applicable historic overlay.
   2. Detached accessory dwellings with a second story dwelling unit shall enclose the stairs interior to the structure and properly fire rate them per the applicable life safety standards found in the code editions adopted by the Metropolitan Government of Nashville.
10. Restrictive Covenant. Prior to the issuance of a permit, an instrument shall be prepared and recorded with the register's office covenanting that the detached accessory dwelling is being established accessory to a principal structure and may only be used under the conditions listed above.

Parcels located within a Historic Overlay

• Setbacks and size limitations will be enforced by the Historical Commission. Disregard Zoning Code sections 17.12.040 E(1) and 17.12.050.
• The conditions found in section 17.16.030 G will still be applicable.
• A Historic permit will be required in addition to the Codes building permit.

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
  • Building Code
• 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:

1. Residential Permit Application
2. Site Plan showing the proposed location of project with distances to property lines, existing structures and easements labeled.
3. Renderings showing:
   1. Elevations (height) from each of the four corners.
   2. Elevations showing the conditions listed in 17.16.030 G(7)(d) and (e).
4. 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.