Everything homeowners ask about building an ADU in Alexandria — answered with 2026 data.
Yes, ADUs are allowed in Citywide: an accessory dwelling is a permitted accessory use on any recorded lot developed with a single-unit, two-unit or townhouse dwelling (Sec. 7-101(N), 7-203(B)(1)); no zoning district is excluded. Exterior work in the Old and Historic Alexandria or Parker-Gray districts also needs a Board of Architectural Review approval under Article X (BAR fees in the FY2027 P&Z schedule). 96 ADUs approved from 2021 to Feb 20, 2026 (city Zoning for Housing implementation page). in Alexandria, VA. The maximum size for a detached ADU is First floor of the detached accessory building may not exceed the greater of (a) one-third of the floor area of the principal dwelling's first floor or (b) 350 sq ft on lots of 2,500 sq ft or less / 500 sq ft on lots larger than 2,500 sq ft (Sec. 7-203(C)(1)). Only the first floor is capped; an upper floor is allowed within the 20 ft height limit. For this test, floor area includes space otherwise excluded by Sec. 2-145(A)(12)/(B)(14). Attached ADUs can be up to An accessory dwelling within the principal dwelling may not exceed one-third of the principal dwelling's gross floor area. Alexandria has an ADU-friendliness score of 7/10. Check our full Alexandria ADU rules page for complete zoning details.
ADU construction in Alexandria typically costs $150,000-$350,000. The cost per square foot averages $200-$400. Garage conversions are more affordable at $80,000-$150,000, while prefab ADUs cost $150,000-$300,000. Permit fees add No separate ADU permit since June 2025 (a $135 ADU zoning-permit line remains in the FY2027 P&Z schedule; confirm). Building permit: new construction $0.75/sq ft plus $194 each electrical, plumbing, mechanical; alterations $0.30/sq ft ($95 min); plus 5% tech fee and state levy (FY26 schedule). to your budget. See our detailed Alexandria ADU cost guide.
Detached ADUs in Alexandria can be up to First floor of the detached accessory building may not exceed the greater of. Attached ADUs are limited to An accessory dwelling within the principal dwelling may not exceed one-third of the principal dwelling's gross floor area. Junior ADUs (JADUs) have a cap of Not a category in Alexandria; a small interior unit is simply an accessory dwelling under Sec. 7-203 (one-third of the house's gross floor area cap). Guest houses without a kitchen are a separate accessory use (Sec. 7-101). Maximum height is Detached accessory building: the lesser of the principal dwelling's height or 20 ft, measured to include rooftop appurtenances listed in Sec. 6-403(B) (Sec. 7-203(C)(2)). You are allowed up to One accessory dwelling per recorded lot, including lots subject to Sec. 7-103 on a qualifying lot.
Rear setback: Detached ADU building allowed in the required rear yard: at least 1 ft from the rear lot line including architectural features (unless the zone requires less); 3 ft if a wall with windows or doors faces that line; 2.5 ft for portions taller than 13.5 ft and under 16 ft; 5 ft for portions over 16 ft; and, outside the historic districts, 5 ft including overhang where a neighbor's window or door sill under 20 ft high sits within 3 ft of the shared line (Sec. 7-203(C)(3)). Side setback: Same rule as the rear yard (Sec. 7-203(C)(3)): 1 ft minimum including architectural features; 3 ft where windows or doorways face the nearest side lot line; 2.5 ft for portions 13.5-16 ft tall; 5 ft for portions over 16 ft; 5 ft including overhang opposite a neighbor's low window or door within 3 ft of the shared line (outside the Old and Historic Alexandria and Parker-Gray districts). Front setback: A detached ADU building is a permitted obstruction in any yard except a front yard (Sec. 7-202(C)) and no accessory structure may sit forward of the front building wall facing a primary front yard (Sec. 7-103); the zone's front-yard setback applies. Building an ADU forward of the house needs a BZA variance (BZA #2025-00012 was such a request). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None. An accessory dwelling is exempt from providing off-street parking (Sec. 7-203(C)(4)). A short-term-rental permit for the ADU carries its own parking test under Sec. 7-1403(C). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required. The 2021 rule that the owner live on the property when the ADU permit was issued (former Sec. 7-203(B)(6)) was deleted by Ord. No. 5593, final passage June 14, 2025. The ADU and principal dwelling must stay under common ownership (Sec. 7-203(B)(5)); the ADU cannot be sold separately. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Alexandria is typically Not published. The city posts no residential plan-review time; only a 20-minute walk-thru review is listed for minor work such as finishing a basement (Plan Review Services Division page). Historic-district projects add a BAR hearing cycle. Plan check: Included in the building permit fee (initial review plus one corrected resubmission); optional Accelerated Plan Review at $0.045/sq ft for new residential construction or $0.075/sq ft for alterations (FY26 Code Administration schedule, sec. C). Pre-approved plans availability: Not available. No pre-approved or stock ADU plan program appears on the city's ADU page, the APEX document library or the FY2027 fee schedule.
Average ADU rental income in Alexandria: 1-bedroom units rent for $2,100-$3,150/month, 2-bedroom units for $2,300-$3,500/month. Short-term rentals: Allowed with a city short-term rental permit (Sec. Expected ROI: 7-14% gross annual return.
The minimum lot size for an ADU in Alexandria is None ADU-specific. The 2,500 sq ft figure is only the tier line for the 350 vs 500 sq ft detached footprint cap (Sec. 7-203(C)(1)). The lot must meet its zone's own standards for the principal dwelling; Sec. 2-141 says the ADU does not count toward the zone's density, open-space or lot requirements. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Alexandria, a garage conversion typically costs $80,000-$150,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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