What are ADUs?
Accessory dwelling units (ADU’s), commonly referred to as “in-law apartments” or “granny flats”, are secondary, independent living units that typically have a separate kitchen, sleeping area and bathroom.
ADU’s can assume different forms including basement apartments, converted garages or new structures detached from a primary residence.
ADU’s can:
Bring in rental income that helps cover housing costs for both first-time homebuyers and long-time Alexandrians at risk of being priced out of the city;
Provide on-site housing options for multi-generational families, caregivers for seniors and persons with disabilities, live-in childcare providers and other caretakers;
Enhance housing affordability for the City’s workforce, including recent graduates and young professionals.
City of Alexandria Accessory Dwelling Unit (ADU) Policy:
Permit ADUs City-Wide:
• Allow one ADU on any property developed with a house (single, two-family or townhouse)
• ADU may be either within an existing home, e.g., an “English basement” style apartment,
or
• Within a detached structure, e.g., a “tiny house” or above a detached garage
General ADU Regulations:
• Only one ADU shall be permitted on any lot developed with a single, two-family or
townhouse dwelling
• No more than three persons shall occupy the ADU.
• Owner occupancy: the property owner shall reside in either the ADU or the main house*
• Ownership: the ADU and main house shall be in common ownership*
Require Administrative Permit for ADUs:
• An applicant wishing to construct an ADU must submit an administrative permit
to the Department of Planning & Zoning
Follow Current City Policies Related to Short-term Rentals:
• Short-term rentals of ADUs is permitted.
Off-street Parking:
• Off-street parking shall not be required for ADU, but
• No required parking spaces shall be removed to accommodate ADU construction
ADU Height and Size Limits:
• ADU height shall not exceed the height of the main house or 20 feet, whichever is less
• ADU size shall be limited by its first floor “footprint.” The ADU footprint shall not
exceed the greater of:
• One-third of the floor area of the main house or
• 350 square feet on lots >2,500 square feet; 500 square feet on lots >2,500 square feet.
ADUs and Floor Area Ratio (FAR):
Floor area devoted to a detached ADU can be excluded as follows:
• 100 square feet for lots less than 2,500 square feet; • 350 square feet for lots
2,500 square feet or greater or
• 600 square feet for lots 8,000 square feet or greater.
• Also, 65 square feet for all lots developed with townhouse dwellings or within the
Alexandria Old and Historic and Parker-Gray Historic Districts.
The total amount eligible for exclusion shall be subject to these limits and existing detached garages
or sheds on a property. For example, a property that is 2,500 square feet which is already
developed with a 100 square-foot shed could not exclude any portions of a new, detached ADU. If
that same property had a 50 square foot shed, 50 square feet of a new, detached ADU would be
eligible for floor area exclusion.
ADU Setbacks:
Consistent with building code and existing Zoning Ordinance regulations related to detached
garages, ADUs shall be setback at least one foot from side and rear lot lines. If the ADU has
windows that face the nearest lot lines, the ADU shall be setback at least three feet from these
lot lines. Dormers shall be required to meet standard zone setbacks.
Special Exception Process for the Conversion of an Existing Detached Accessory Structure:
A property with an existing detached accessory structure (garage, shed, other) that exceeds the
height, size or setback limits may be used as an accessory dwelling with special exception
approval by the Board of Zoning Appeals (BZA).
Some examples of ADU’s. As you can see, they come in all shapes and sizes.
