Convert an existing space
You are considering converting an existing space in your home to an Accessory Dwelling (AD) unit or constructing an addition for this purpose. We would like to see you succeed in your endeavor. Creating an Accessory Dwelling (AD) unit will most likely require some construction work and building permits. Construction work takes time and requires that you follow all the correct procedures and codes.
PRINT/DOWNLOAD: Accessory Dwellings (AD) – General Guidelines
Hire a professional architect or an experienced contractor
We strongly recommend that you hire a professional architect or an experienced contractor who is familiar with the Virginia Uniform Statewide Building Code (VUSBC). It will save you time and money in the long run. Once you’ve hired an architect or a contractor and have a conceptual design, you may want to request a code consultation meeting with the technical staff in the County’s Inspection Services Division (ISD) – so you don’t end up with any unpleasant surprises. We recommend that you also email the Zoning Division to set up a pre-submission meeting to discuss the Zoning Division and Inspection Services Division (ISD) requirements.
Do your homework before you invest time and money
You will need a building permit if you are converting an existing space to an accessory dwelling unit or constructing an addition.
- Zoning Ordinance: Make sure that your proposal is allowed under the County’s Zoning Ordinance. Review this guidance from Zoning on the new application for the approval of an Accessory Dwelling (AD). Contact Zoning Administration at 703-228-3883 or email.
- Historic Preservation: Any exterior work to be performed in a historical district must be accompanied by a Certificate of Appropriateness (CoA) obtained prior to applying for permit. Contact Historic Preservation at 703-228-3549 or email.
- Environmental Services: The addition of any plumbing fixtures may incur an impact fee from the Department of Environmental Services (DES) at 703-228-3629 or email.
Building Code Implications
The Virginia Uniform Statewide Building Code (VUSBC) contain several requirements for buildings containing two dwelling units: units must be separated by fire-rated construction; units require separate mechanical, electrical and plumbing systems; units require separate means of egress; etc… Meeting these requirements can be very time consuming and expensive.
Most common building code implications of changing a single dwelling unit building into a two dwelling unit building:
- Means Of Egress: A second dwelling unit would require a code compliant means of egress. Providing such a means of egress could entail significant alteration to existing basement area ways or adding an exterior exit stair from an attic level.
- Height & Area Limitations: The alteration of an unoccupied attic space into a second dwelling unit may cause the attic space to be classified as another story. This addition of another story to the building may cause the building to fall out of compliance with height & area requirements, may cause the building to be subject to the VUSBC rather than the Virginia Residential Code, and may require the installation of a sprinkler system.
- Sleeping Rooms: All sleeping rooms created in the new second dwelling unit would require emergency egress windows and any required corresponding window wells. All sleeping rooms also require smoke detectors.
- Dwelling Unit Separation: Dwelling units in two-family dwellings shall be separated from each other by fire rated wall and floor assemblies having not less than 1-hour fire-resistance rating. Major alterations and/or a sprinkler system may be required to fully separate the two dwelling units.
- Ceiling Height: Habitable rooms, hallways, corridors, bathrooms, toilet rooms, laundry rooms and basements shall have a ceiling height of not less than 7 feet. The required height shall be measured from the finish floor to the lowest projection from the ceiling. Many existing basements and attics do not meet the required minimum ceiling height and significant alteration to the structure could be required to meet this requirement.
- Light, Ventilation & Heating: All habitable rooms shall be provided with aggregate glazing area of not less than 8 percent of the floor area of such rooms. Natural ventilation shall be through windows, doors, louvers or other approved openings to the outdoor air. Such openings shall be provided with ready access or shall otherwise be readily controllable by the building occupants. The minimum open able area to the outdoors shall be 4 percent of the floor area being ventilated. Meeting the minimum light and ventilation requirements may require significant alteration to an in-ground basement level.
- Mechanical, Electrical & Plumbing Systems: Significant alteration to the structure may be required to provide separate mechanical, plumbing and electrical systems to each dwelling unit.
- Addresses: Approved numbers or addresses shall be provided for all buildings in such a position as to be plainly visible and legible from the street or road fronting the property. A separate address for the second dwelling unit must meet County address standards and the application procedure for new addresses can take up to three weeks.