Can you build an ADU in Loudoun County?
Loudoun already allows a second dwelling on a residential lot, detached or inside the house, and the size limits are the most generous in Northern Virginia — up to 2,500 sq ft on rural land. You do not have to wait for July 2027. How big yours can be depends on which zoning district your lot sits in.
What’s true today
Can you build one?
Allowed, with conditions. Loudoun calls these accessory dwellings — locally "ADU" means an Affordable Dwelling Unit under a separate program, the same naming collision Fairfax has. One accessory dwelling is allowed on a lot under 20 acres, and it may sit inside the main house or in a detached accessory building. Larger parcels may have more: one extra at 20 acres or more, and in the AR-1 and AR-2 districts one more for every 25 acres above 20. Beyond that it takes a special exception.
§ 4.02.01.A, D, FRead the sectionRead at source Sep 6, 2026How big can it be — Rural, Transition and Joint Land Management Area districts?
Up to 2,500 sq ft, or 70% of your house’s floor area — whichever is smaller. Applies depends on your zoning district — the county GIS map shows yours. The footprint is separately capped at 70% of the house’s footprint.
§ 4.02.01.B(1)Read the sectionHow big can it be — Urban districts?
Up to 1,200 sq ft, or 70% of your house’s floor area — whichever is smaller. Applies depends on your zoning district.
§ 4.02.01.B(2)Read the sectionHow big can it be — Suburban districts?
Up to 1,200 sq ft, or 50% of your house’s floor area — whichever is smaller. Applies depends on your zoning district. The footprint is separately capped at 50% of the house’s footprint.
§ 4.02.01.B(3)Read the sectionHow far from the property line?
An accessory dwelling inside an existing building follows that building’s yard requirements. A detached one in an accessory building follows the district’s front yard and setback rules, but may sit as close as 5 ft to side and rear lot lines provided the part that encroaches has no windows or doors.
§ 4.02.01.GRead the sectionRead at source Sep 6, 2026Do you have to live there?
Section 4.02.01 imposes no owner-occupancy requirement — notably unlike Fairfax and Arlington. Check the general use limitations in § 3.03, which 4.02.01.H incorporates, before stating this either way.
§ 4.02.01 (silent); see § 3.03Read the sectionRead at source Sep 6, 2026Do you need more parking?
Section 4.02.01 sets no parking requirement for accessory dwellings. District-wide parking standards may still apply and need reading at source before this is stated on the page.
§ 4.02.01 (silent)Read the sectionRead at source Sep 6, 2026Which kinds are allowed?
An accessory dwelling may be located within an accessory building or in the principal structure, so detached builds and conversions are both available.
§ 4.02.01.FRead the sectionRead at source Sep 6, 2026The rules are being rewritten right now
These standards come from the county’s zoning ordinance rewrite. The section carries the history ZOAM-2020-0002, adopted 12 June 2024 and effective 12 March 2025. Because that predates 1 January 2026, Va. Code § 15.2-2292.4(I) may exclude Loudoun from the 2027 statewide ADU law — see docs/research/sb-531-subsection-i.md. Do not assert the by-right 2027 change here until that is resolved.
ZOAM-2020-0002Read the sectionRead at source Sep 6, 2026If you’re in an HOA
The state law does not override your HOA. Check your deed and closing paperwork for a recorded declaration of covenants, or look the property up in the Loudoun County land records. Much of eastern Loudoun was built as covenanted subdivisions, so this is worth checking before anything else.
Va. Code § 15.2-2292.4(F)Read the sectionRead at source Sep 6, 2026What the process looks like
On a lot with a septic system, the Health Department has to approve the accessory dwelling. On a lot served by a community wastewater system, Loudoun Water has to approve it. Accessory dwellings do not count towards density, so adding one does not use up development capacity on the parcel.
§ 4.02.01.C, ERead the sectionRead at source Sep 6, 2026Every rule on this page links to the section of the Loudoun County ordinance it comes from, so you can read it yourself. Localities are amending these rules ahead of July 1, 2027 — worth confirming the section before you commit money to a design. This is general information about Loudoun County, not a determination about your particular lot.
What does this mean for your lot?
Three questions. We’ll check the Loudoun County rules against your situation and tell you what you’re actually looking at — including if the answer is no.