Herndon, VA Accessory Structures: Garage Conversions (2026)

Garage conversions in the Town of Herndon are treated as a change of use from storage to habitable space and are regulated by both the Virginia Uniform Statewide Building Code (USBC) and the Herndon Zoning Ordinance. A building permit is required regardless of whether the conversion is a full ADU or simply additional family living area. Plans must demonstrate compliance with IRC habitable space standards including: minimum ceiling height of 7 feet, minimum room dimensions, at least one emergency escape and rescue opening (egress window) per sleeping room, proper ventilation, insulation meeting the Virginia Energy Conservation Code, functioning heating system, and smoke and CO alarms.

Electrical, plumbing, and mechanical work triggered by the conversion requires separate trade permits and inspections. If the conversion results in a second full kitchen and the space functions as an independent dwelling unit, it becomes an ADU and must also satisfy ADU requirements including owner-occupancy and special exception if applicable.

On the zoning side, Herndon requires a minimum number of off-street parking spaces per dwelling unit (typically 2 spaces for single-family homes). Eliminating garage parking through conversion often requires providing replacement off-street parking elsewhere on the lot, such as an extended driveway, to meet the parking standard. Lots without room to replace parking may be denied conversion approval. Lot coverage and setback rules still apply since the garage footprint remains. Homeowners associations commonly require architectural review and approval for garage conversions because they change the visible facade of the home and can affect the neighborhood aesthetic. Unpermitted conversions are a significant issue at time of sale, since they do not appear on county records and can trigger forced restoration or retroactive permitting.