Accessory Dwelling Tips

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Are you converting an existing space in your home to an accessory dwelling (AD) or constructing an addition for this purpose? Creating an AD will most likely require multiple permits and construction work. Use the following tips to ensure you follow all of the correct procedures and codes.

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 Building Code. Taking this step 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 so you don’t end up with any unpleasant surprises. You may also set up a pre-submission meeting with the Zoning Division to discuss requirements.

Do your homework before investing time and money

You will need a Residential Building Permit if you are converting an existing space to an accessory dwelling or constructing an addition. For more information, consult the following:

Building Code Implications

Within Main Dwelling

The Building Code 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 time-consuming and expensive.

The most common Building Code implications of changing a single-dwelling-unit building into a two-dwelling-unit building are outlined below. Be aware that all of the Building Code requirements must be met.

  • 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 areaways 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. The addition of another story to the building may cause the building to fall out of compliance with height and area requirements, may cause the building to be subject to the Building Code 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 a not-less-than-one-(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 seven (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. 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 eight (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 four (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: Contact the Inspection Services Division to determine if a separate address is required. If it is required for the second dwelling unit, it must meet County address standards. The application procedure for new addresses can take up to three (3) weeks.
Detached Accessory Dwelling

The most common Building Code implications for constructing a new accessory building as a detached accessory dwelling are outlined below. Be aware that all of the Building Code requirements must be met.

  • A New, Separate Structure Is Treated as a New Residential House: For the Inspection Services Division, a new accessory structure that serves as a detached accessory dwelling must comply with all of the requirements of a new residential house. Learn more about the construction documents and supporting information typically required for plan review of residential projects.
  • Addresses: Contact the Inspection Services Division to determine if a separate address is required. If it is required for the second dwelling unit, it must meet County address standards. The application procedure for new addresses can take up to three (3) weeks.